JP7499931B2 - Method for estimating contact stress of rolling parts, program for estimating contact stress of rolling parts, and device for estimating contact stress of rolling parts - Google Patents

Description

This invention relates to a method for estimating the fatigue level of rolling parts, a device for estimating the fatigue level of rolling parts, a program for estimating the fatigue level of rolling parts, and a method for estimating the contact stress of rolling parts.

The lifespan of rolling bearings (hereafter referred to as bearings) is known to depend on operating conditions such as load and lubrication conditions, and material properties such as hardness, structure, and residual stress. Traditionally, bearing lifespans have been estimated using a lifespan formula that can be calculated from operating conditions and material properties. This formula is used to estimate how long a bearing can be used under certain conditions, or under what conditions a bearing should be used so that it will not break during the required period of use. Generally, bearings are used under operating conditions that are set based on the lifespan formula. Therefore, if a bearing is used under the assumed conditions, the lifespan of that bearing should not be an issue.

However, bearing life is often an issue in the market. One of the reasons for this is thought to be that actual bearings are used in unexpected environments and conditions. For this reason, a method has been proposed for estimating the degree of fatigue of rolling bearings based on the results of surveys of bearings that have actually been used.

For example, for internally originating damage that occurs in bearings used under good lubrication conditions, there is a method for estimating the dynamic equivalent load of a bearing using a contact stress estimation method obtained by X-ray analysis disclosed in Non-Patent Document 1, and estimating the fatigue level from the calculated life calculated from the dynamic equivalent load and the usage time up to that point (see Patent Document 1). In the fatigue level estimation method described above, the load on the rolling part is estimated from the residual stress distribution, utilizing the correspondence between the stress repeatedly applied to the rolling surface on which the load acts in the rolling part and the residual stress generated by that stress. The life is then calculated based on the estimated load, and the fatigue level is estimated from the ratio of that life to the rotation speed or usage time of the rolling part.

A method has also been proposed for estimating the degree of fatigue caused by internally originating damage in rolling components, based on the relationship between the analysis value of X-ray stress measurement and the degree of rolling fatigue (see Patent Document 2).

JP 2011-069681 A Japanese Patent Publication No. 63-34423

"Application of X-ray stress measurement to bearing failure analysis", Tsushima, M. et al., Bearing Engineer No. 49, pp. 25-34 (1984)

In general, the progress of rolling fatigue of rolling parts, such as the rolling elements of rolling bearings, can be divided into a first stage in which residual stress is generated up to ¹⁰³ rotations, a second stage in which rolling fatigue occurs after residual stress is generated but the half-width, the amount of residual austenite, and the residual stress do not change, and a third stage in which structural changes occur in areas where relatively high stress acts during rolling fatigue and the residual stress is redistributed accordingly. Therefore, the residual stress generated in the rolling parts before the third stage accurately reflects the load conditions that acted on the rolling parts at the beginning of use. On the other hand, after the third stage, the residual stress is redistributed with each increase in the number of rotations due to the influence of structural changes of the material in the areas where stress acts in the rolling parts. For this reason, in rolling parts in which rolling fatigue has progressed to the third stage or later, the load estimation of the rolling parts due to residual stress becomes inaccurate, and the accuracy of the fatigue degree estimated by the method disclosed in the above-mentioned Patent Document 1 may decrease.

In addition, in the method of estimating the degree of fatigue disclosed in Patent Document 2, X-ray analysis (e.g., measurement of the half-value width and the amount of retained austenite) is performed to detect changes in the structure of the material at a depth inside the rolling part where fatigue is likely to occur. The fatigue degree of the rolling part is then estimated using a database of the relationship between the changes in data obtained by the X-ray analysis and the number of rotations of the rolling part. This method can be applied to estimating the degree of fatigue from the third stage onwards, where the material's structure changes gradually occur depending on the number of rotations of the rolling part. On the other hand, in the second stage, where the structure changes due to rolling fatigue do not progress even if the number of rotations of the rolling part changes, the detection data by X-ray analysis corresponding to the structure changes do not change even if the number of rotations of the rolling part changes. For this reason, it was difficult to accurately estimate the fatigue degree of rolling fatigue that has progressed to the second stage using the method of estimating the degree of fatigue of the rolling part disclosed in Patent Document 2.

Therefore, the object of the present invention is to provide a rolling part fatigue degree estimation method, a rolling part fatigue degree estimation device, and a rolling part fatigue degree estimation program that can estimate the fatigue degree of rolling parts with high accuracy.

Another object of the present invention is to provide a method for estimating the contact stress of rolling parts that can be used to estimate the fatigue degree of rolling parts with high accuracy.

The method for estimating the fatigue degree of a rolling part according to the present disclosure includes a step of acquiring data for estimating the fatigue degree of the rolling part from a rolling part to which a repeated load due to rotation is applied. The acquiring step includes a step of acquiring first data related to the microstructure of the rolling part, and a step of acquiring second data, which is measurement data of X-ray analysis values related to the rolling part by irradiating the fatigue part of the rolling part with X-rays. The method for estimating the fatigue degree of a rolling part further includes a step of judging whether or not a structural change has occurred in the fatigue part of the rolling part based on the data acquired in the acquiring step, and a step of estimating a first fatigue degree related to internal origin type damage of the rolling part based on the judgment result in the judging step and the data acquired in the acquiring step. In the step of estimating the first fatigue degree, if it is judged in the judging step that a structural change has not occurred, a step of estimating the load acting on the rolling part based on the second data, a step of calculating a life based on the load and the use conditions of the rolling part, and a step of calculating the first fatigue degree of the rolling part from the number of rotations and life of the rolling part are performed. Furthermore, in the step of estimating the first fatigue level, if it is determined in the determining step that a tissue change is occurring, a step of estimating the first fatigue level from the second data based on a predetermined relationship between the second data and the first fatigue level is carried out.

A fatigue degree estimation program according to the present disclosure is a fatigue degree estimation program for a rolling component, and causes a computer to execute a step of acquiring data for estimating a fatigue degree from a rolling component to which a repeated load due to rotation is applied. The acquiring step includes a step of acquiring first data related to the microstructure of the rolling component, and a step of acquiring second data, which is measurement data of X-ray analysis values related to the rolling component by irradiating a fatigued portion of the rolling component with X-rays. The fatigue degree estimation program causes a computer to execute a step of determining whether or not a structural change has occurred in the fatigued portion of the rolling component based on the data acquired in the acquiring step, and a step of estimating a first fatigue degree related to internal origin type damage of the rolling component based on the judgment result in the judging step and the data acquired in the acquiring step. In the step of estimating the first fatigue degree, when it is determined in the judging step that no structural change has occurred, a step of estimating a load acting on the rolling component based on the second data, a step of calculating a life based on the load and the use conditions of the rolling component, and a step of calculating a first fatigue degree of the rolling component from the number of rotations and the life of the rolling component are performed. In the step of estimating the first fatigue level, if it is determined in the judging step that a tissue change is occurring, a step of estimating the first fatigue level from the second data based on a predetermined relationship between the second data and the first fatigue level is carried out.

The rolling component fatigue degree estimation device according to the present disclosure includes a judgment unit, a load estimation unit, a life calculation unit, a first fatigue degree calculation unit, and a first fatigue degree estimation unit. The judgment unit judges whether or not a structural change has occurred in the fatigue portion of the rolling component based on at least one of first data related to the microstructure of the rolling component and second data which is measurement data of X-ray analysis values related to the rolling component obtained by irradiating the fatigue portion of the rolling component with X-rays. The load estimation unit estimates the load acting on the rolling component based on the second data when the judgment unit judges that no structural change has occurred. The life calculation unit calculates the life based on the load and the usage conditions of the rolling component. The first fatigue degree calculation unit calculates the first fatigue degree of the rolling component from the number of rotations and the life of the rolling component. When the judgment unit judges that a structural change has occurred, the first fatigue degree estimation unit estimates the first fatigue degree from the second data based on a predetermined relationship between the X-ray analysis value and the first fatigue degree.

The method for estimating fatigue degree of a rolling component according to the present disclosure includes a step of acquiring data for estimating fatigue degree of the rolling component from a rolling component to which a repeated load due to rotation is applied. The acquiring step includes a step of acquiring first data on the microstructure of the rolling component, and a step of acquiring second data, which is measurement data of X-ray analysis values on the rolling component by irradiating X-rays on the fatigued portion of the rolling component. The method for estimating fatigue degree of a rolling component further includes a step of determining whether or not a structural change has occurred in the fatigued portion of the rolling component based on the data acquired in the acquiring step, and a step of estimating a first fatigue degree related to internally originating damage of the rolling component based on the judgment result in the determining step and the data acquired in the acquiring step. The second data includes distribution data in the depth direction of the X-ray analysis values on the rolling component. In the step of estimating the first fatigue degree, if it is determined in the step of determining that no structural change has occurred, the steps of estimating the load acting on the rolling part based on the second data, calculating the life based on the load and the use conditions of the rolling part, and calculating the first fatigue degree of the rolling part from the number of rotations and the life of the rolling part are performed. If it is determined in the step of determining that a structural change has occurred, the steps of estimating the load acting on the rolling part based on the distribution data in the depth direction, calculating the life based on the load and the use conditions of the rolling part, and calculating the first fatigue degree of the rolling part from the number of rotations and the life of the rolling part are performed.

A fatigue degree estimation program according to the present disclosure is a fatigue degree estimation program for a rolling component, and causes a computer to execute a step of acquiring data for estimating a fatigue degree from a rolling component to which a repeated load due to rotation is applied. The acquiring step includes a step of acquiring first data related to a microstructure of the rolling component, and a step of acquiring second data, which is measurement data of X-ray analysis values related to the rolling component by irradiating a fatigued portion of the rolling component with X-rays. The fatigue degree estimation program causes a computer to execute a step of determining whether or not a structural change has occurred in the fatigued portion of the rolling component based on the data acquired in the acquiring step, and a step of estimating a first fatigue degree related to internally originating damage of the rolling component based on the determination result in the determining step and the data acquired in the acquiring step. The second data includes distribution data in the depth direction of the X-ray analysis values related to the rolling component. The step of estimating the first fatigue degree, when it is determined in the step of determining that no structural change has occurred, includes the steps of estimating the load acting on the rolling component based on the second data, calculating a life based on the load and the usage conditions of the rolling component, and calculating a first fatigue degree of the rolling component from the number of rotations and the life of the rolling component. The step of estimating the first fatigue degree, when it is determined in the step of determining that a structural change has occurred, includes the steps of estimating the load acting on the rolling component based on the distribution data in the depth direction, calculating a life based on the load and the usage conditions of the rolling component, and calculating a first fatigue degree of the rolling component from the number of rotations and the life of the rolling component.

A fatigue degree estimation device according to the present disclosure includes a judgment unit, a load estimation unit, a life calculation unit, and a first fatigue degree calculation unit. The judgment unit judges whether or not a structural change has occurred in the fatigue portion of the rolling component based on at least one of first data related to the microstructure of the rolling component and second data, which is measurement data of X-ray analysis values related to the rolling component obtained by irradiating the fatigue portion of the rolling component with X-rays. The load estimation unit estimates the load acting on the rolling component based on the second data. The life calculation unit calculates the life based on the load and the usage conditions of the rolling component. The first fatigue degree calculation unit calculates the first fatigue degree of the rolling component from the number of rotations and life of the rolling component. The second data includes distribution data in the depth direction of the X-ray analysis values related to the rolling component. The load estimation unit estimates the load acting on the rolling component based on the second data when the judgment unit judges that no structural change has occurred. When the judgment unit determines that a structural change has occurred, the load estimation unit estimates the load acting on the rolling part based on the distribution data in the depth direction.

The method for estimating contact stress in a rolling part according to the present disclosure includes the steps of irradiating X-rays from the surface to the inside of a fatigued part of the rolling part to obtain distribution data in the depth direction of the variation in diffraction intensity with respect to the central angle of the ring-shaped diffracted X-rays diffracted at the fatigued part, and estimating the contact stress repeatedly acting on the fatigued part of the rolling part based on the distribution data in the depth direction.

According to the above, a rolling part fatigue degree estimation method, a rolling part fatigue degree estimation device, and a rolling part fatigue degree estimation program are obtained that are capable of estimating the fatigue degree of rolling parts with high accuracy.

In addition, the above provides a method for estimating the contact stress of rolling parts that can be used to estimate the fatigue level of rolling parts with high accuracy.

1 is a schematic diagram illustrating a configuration of a fatigue level estimation system according to a first embodiment. FIG. 2 is a diagram illustrating a hardware configuration of the fatigue level estimation device illustrated in FIG. 1 . 2 is a diagram illustrating a functional configuration of the fatigue level estimation device illustrated in FIG. 1 . 10 is a flowchart showing a procedure for estimating a fatigue level. FIG. 11 is a schematic diagram illustrating a configuration of a fatigue level estimation system according to a second embodiment. 6 is a diagram illustrating a functional configuration of the fatigue level estimation device illustrated in FIG. 5 . 10 is a flowchart showing a procedure for estimating a fatigue level. 13 is a flowchart illustrating a procedure of a fatigue level estimation process according to the third embodiment. 1 is a graph showing a depth distribution of an equivalent stress of a residual stress. 13 is a graph showing the relationship between the variation in diffraction intensity obtained with circumferential incidence and the test time. 1 is a graph showing the relationship between the reduction rate of retained austenite and test time. FIG. 2 is a schematic diagram for explaining a coordinate system for X-ray measurement. FIG. 2 is a schematic diagram of diffracted X-rays. FIG. 2 is a schematic diagram of the measured ring-shaped diffracted X-rays. FIG. 1 is a schematic diagram for explaining the variation in diffraction intensity. 1 is a graph showing the depth direction distribution of circumferential residual stress, which is a result of X-ray measurement of a first test piece. 1 is a graph showing a depth direction distribution of the diffraction intensity variation, which is a result of X-ray measurement of a first test piece. 13 is a graph showing the depth direction distribution of circumferential residual stress, which is a result of X-ray measurement of a second test piece. 13 is a graph showing the depth direction distribution of the diffraction intensity variation, which is the result of X-ray measurement of the second test piece. 13 is a graph showing an estimation result of the contact stress of a first test piece. 13 is a graph showing an estimation result of the contact stress of the second test piece.

The following describes an embodiment of the present invention with reference to the drawings. Note that the same or corresponding parts in the following drawings are given the same reference numbers and their description will not be repeated.

(Embodiment 1)
<Configuration of fatigue level estimation system>
Fig. 1 is a schematic diagram showing a configuration of a fatigue level estimation system according to embodiment 1. Referring to Fig. 1, the fatigue level estimation system includes a fatigue level estimation device 14, an irradiation unit 11, an X-ray detector 12, and a microstructure observation unit 23.

The irradiation unit 11 includes an X-ray tube that is installed so that it can face the rolling component 90, which is the bearing component to be inspected. The irradiation unit 11 irradiates the rolling component 90 with X-rays. The irradiated X-rays are irradiated along the arrow α so that they are incident on the rolling component 90 at a predetermined angle of incidence. The rolling component 90 includes the rolling elements of a rolling bearing and part or all of the raceway of a rolling bearing, which is a bearing component for diagnosis or testing. The X-rays may be irradiated, for example, to part of the raceway of the rolling bearing.

The X-ray detector 12 detects annular X-rays (X-ray diffraction rings) diffracted by the rolling element 90. Specifically, the X-ray detector 12 includes a hole 12B formed in the center through which the X-rays irradiated from the irradiation unit 11 pass, and a planar detection unit 12A that can be placed opposite the rolling element 90. For example, an X-ray CCD (Charge Coupled Device) can be used as the detection unit 12A. The X-rays incident on the rolling element 90 along the arrow α are diffracted to form a conical surface β and reach the detection unit 12A. Then, in the detection unit 12A, the X-ray diffraction rings are detected by signals of an intensity corresponding to the intensity of the X-rays output by each pixel.

The microstructure observation section 23 measures the state of the microstructure of the material that constitutes the rolling component 90. For example, an optical microscope can be used as the microstructure observation section 23. The surface of the rolling component 90 to be measured may be, for example, a cross section of a portion of the raceway of a rolling bearing and a cross section of the rolling element.

The fatigue degree estimation device 14 estimates the fatigue degree of the rolling part 90 based on the X-ray diffraction ring detected by the X-ray detector 12 and the observation results of the microstructure of the rolling part 90 detected by the microstructure observation section 23. The fatigue degree estimation device 14 may be, for example, a small computer device (such as a personal computer).

<Hardware configuration of fatigue level estimation device>
Fig. 2 is a diagram showing a hardware configuration of the fatigue level estimation device shown in Fig. 1. The fatigue level estimation device 14 includes an input unit 17, a CPU (Central Processing Unit) 15, a memory 16, and a display unit 18.

The input unit 17 receives the measurement results of the microstructure observation unit 23 and the detection results of the X-ray detector 12. The memory 16 can store a fatigue degree estimation program and the like. The CPU 15 uses the data input to the input unit 17 to execute the fatigue degree estimation program stored in the memory 16. The display unit 18 displays the fatigue degree estimation results by the CPU 15.

<Functional configuration of the fatigue level estimation device>
Fig. 3 is a diagram showing a functional configuration of the fatigue level estimation device shown in Fig. 1. The fatigue level estimation device 14 shown in Fig. 3 includes an input unit 17, a display unit 18, a storage unit 61, a control unit 60, a data preparation unit 21, a determination unit 31, a load estimation unit 32, a lifespan calculation unit 33, a first fatigue level calculation unit 34, a first fatigue level estimation unit 41, and a diagnosis unit 70. The storage unit 61 is realized by the memory 16. The control unit 60, the data preparation unit 21, the determination unit 31, the load estimation unit 32, the lifespan calculation unit 33, the first fatigue level calculation unit 34, the first fatigue level estimation unit 41, and the diagnosis unit 70 are realized by the CPU 15 executing a fatigue level estimation program stored in the memory 16.

<Procedure for fatigue level estimation method>
4 is a flowchart showing the procedure of the fatigue level estimation process. The fatigue level estimation process in the fatigue level estimation system shown in FIG.

First, a data acquisition step (S110) is performed. In this step (S110), the data preparation unit 21 acquires data for estimating the fatigue level of the rolling part 90 from the rolling part 90 to which a repeated load due to rotation is applied. In this step (S110), data is prepared for use in the fatigue level determination step (S120) described below and each subsequent step for estimating the fatigue level. For example, based on data input from the microstructure observation unit 23 shown in FIG. 1 via the input unit 17, the data preparation unit 21 prepares first data regarding the microstructure in the fatigued part of the rolling part 90.

The data preparation unit 21 also receives measurement data of X-ray analysis values related to the rolling part 90 from the X-ray detector 12 shown in FIG. 1 via the input unit 17. The measurement data of the X-ray analysis values becomes the second data. Examples of the measurement data of the X-ray analysis values include data related to residual stress in the fatigued parts of the rolling part 90, more specifically, measurement data of the depth distribution of residual stress.

Next, a fatigue stage determination step (S120) is performed. In this step (S120), the determination unit 31 determines whether or not a structural change has occurred in the fatigue portion of the rolling part 90 based on the data obtained in the acquisition step (S110).

If it is determined in the above step (S120) that no structural change has occurred, that is, if the determination unit 31 determines that fatigue has not progressed to the third stage in the fatigued portion of the rolling part 90, a contact stress estimation step (S131) is performed. In this step (S131), the load estimation unit 32 estimates the contact stress in the fatigued portion of the rolling part 90 based on the measurement data of the depth distribution of residual stress in the fatigued portion of the rolling part 90 contained in the second data.

Next, a load estimation step (S132) is performed. In this step (S132), the load estimation unit 32 estimates the load in the fatigued portion of the rolling element 90 based on the measurement data of the depth distribution of residual stress in the fatigued portion of the rolling element 90. In the above steps (S131) and (S132), the load estimation unit 32 may estimate the contact stress and the load using, for example, the method disclosed in Patent Document 1.

Here, in step (S120), the judgment unit 31 judges that no structural change has occurred in the fatigued portion of the rolling part 90 (i.e., fatigue of the rolling part 90 has not progressed to the third stage), so the residual stress of the rolling part 90 accurately reflects the load conditions acting on the rolling part 90. Therefore, the contact stress and load can be accurately estimated as described above based on the residual stress data.

Next, a step (S133) of estimating the 10% life (L ₁₀ ) is performed. In this step (S133), the life calculation unit 33 calculates the 10% life (L ₁₀ ) based on the load and the use conditions of the rolling element 90. The use conditions of the rolling element 90 include, for example, the rotation speed of the rolling element 90, the temperature when the rolling element 90 is used, the oil type information of the lubricant oil supplied when the rolling element 90 is used, and the information of the contamination level of the lubricant oil supplied when the rolling element 90 is used. Any method can be used as a method for calculating the 10% life. In addition, the life _Ln for any probability of breakage can be calculated, for example, by multiplying the 10% life (L ₁₀ ) by the reliability coefficient a1. Specifically, the life Ln can be calculated from the 10% life as follows.

Next, a first fatigue degree calculation step (S134) is performed. In this step (S134), the first fatigue degree calculation unit 34 calculates the first fatigue degree (N/ _L10 ) of the rolling element 90 from the number of rotations N of the rolling element 90 and the 10% life ( _L10 ) described above. Note that the usage time of the rolling element 90 may be used instead of the number of rotations N.

On the other hand, if it is determined in step (S120) that a structural change has occurred, that is, if the determination unit 31 determines that fatigue has progressed to the third stage in the fatigued portion of the rolling element 90, a step (S141) of estimating the first fatigue degree using the relationship between the X-ray analysis value and the first fatigue degree is performed. In this step (S141), the first fatigue degree estimation unit 41 estimates the first fatigue degree (N/L ₁₀ ) from the X-ray analysis value based on the relationship between the X-ray analysis value (X-ray stress measurement result) as the second data and the first fatigue degree that has been determined in advance. The above relationship may be, for example, a relationship between the fatigue degree obtained from a rolling fatigue life test performed on the rolling element 90 and the X-ray stress measurement result of a test piece that has been rolled up to the fatigue degree. Data indicating the relationship is stored in the storage unit 61.

Here, since it is determined in step (S120) that a structural change has occurred in the fatigued portion of the rolling part 90 (i.e., fatigue of the rolling part 90 has progressed to the third stage), it is considered that a redistribution of residual stress occurs in the rolling part 90 as the number of rotations increases. Therefore, since there is a correlation between the change in the material structure of the rolling part 90 and the degree of fatigue, a more accurate estimation of the first degree of fatigue is possible by estimating the first degree of fatigue based on the relationship between the X-ray analysis value reflecting the structural change and the degree of fatigue, as shown in step (S141).

Next, a diagnosis step (S161) is performed. In this step (S161), the diagnosis unit 70 judges whether the value of the first fatigue degree obtained as described above exceeds a predetermined reference value. If the obtained value of the first fatigue degree exceeds the reference value, a signal indicating that the value of the first fatigue degree exceeds the reference value is transmitted from the diagnosis unit 70 to the control unit 60. The control unit 60 that receives the signal displays, for example, on the display unit 18, a message indicating that the rolling part 90 needs to be replaced. If the obtained value of the first fatigue degree does not exceed the reference value, a signal indicating that the value of the first fatigue degree does not exceed the reference value is transmitted from the diagnosis unit 70 to the control unit 60. The control unit 60 that receives the signal displays, for example, on the display unit 18, a message indicating that the rolling part 90 does not need to be replaced. Note that, depending on the reference value for the first fatigue degree described above, a message indicating the time to replace the rolling part 90 may be used as the message to be displayed on the display unit 18 when the value of the first fatigue degree exceeds the reference value.

<Action and effect>
The method for estimating fatigue degree of a rolling component according to the present disclosure includes a step (step (S110)) of acquiring data for estimating fatigue degree of the rolling component from a rolling component to which a repeated load due to rotation is applied. The acquiring step (step (S110)) includes a step of acquiring first data related to the microstructure of the rolling component, and a step of acquiring second data, which is measurement data of X-ray analysis values related to the rolling component, by irradiating a fatigued portion of the rolling component with X-rays. The method for estimating fatigue degree of a rolling component further includes a step (step (S120)) of judging whether or not a structural change has occurred in the fatigued portion of the rolling component based on the data acquired in the acquiring step (step (S110)), and a step (steps (S131) to (S134) and (S141)) of estimating a first fatigue degree related to internal origin type damage of the rolling component based on the judgment result in the judging step (step (S120)) and the data acquired in the acquiring step (step (S110)). In the step of estimating the first fatigue degree, if it is determined in the step of determining (step (S120)) that no structural change has occurred, the following steps are performed: estimating the load acting on the rolling part based on the second data (step (S132)), calculating a life based on the load and the usage conditions of the rolling part (step (S133)), and calculating a first fatigue degree of the rolling part from the number of rotations of the rolling part and the above-mentioned life (step (S134)). Also, in the step of estimating the first fatigue degree, if it is determined in the step of determining (step (S120)) that a structural change has occurred, a step of estimating the first fatigue degree from the second data based on a predetermined relationship between the second data and the first fatigue degree (step (S141)) is performed.

As described above, the fatigue degree estimation method for rolling parts includes a step (step (S120)) of determining whether or not a structural change has occurred in the fatigued portion, so that depending on whether or not a structural change has occurred in the fatigued portion of the rolling member, that is, whether or not the progression of rolling fatigue has reached the third stage, different fatigue degree estimation methods corresponding to each state can be used. Therefore, the fatigue degree of the rolling parts can be estimated with high accuracy.

In the above-mentioned method for estimating the fatigue degree of a rolling part, the use conditions of the rolling part may include the rotational speed of the rolling part 90, the temperature when the rolling part 90 is in use, information on the type of lubricant supplied when the rolling part 90 is in use, and information on the degree of contamination of the lubricant supplied when the rolling part 90 is in use.

In this case, if no structural changes have occurred in the fatigued portion of the rolling part 90 (i.e., if the rolling fatigue has not progressed to the third stage), the 10% life can be accurately estimated in the 10% life estimation step (step (S133)), and as a result, the life of the rolling part 90 can be calculated with high accuracy.

In the above method for estimating the fatigue degree of a rolling part, the second data may include at least one data selected from the group consisting of data on six components of residual stress in the fatigued part of the rolling part 90, data on the amount of residual austenite in the fatigued part of the rolling part 90, data showing the variation in diffraction intensity with respect to the central angle of the annular diffracted X-ray diffracted in the fatigued part of the rolling part 90, data on the half-width of the peak of the diffraction intensity, data on the average value of the diffraction intensity, and data on the difference between the minimum and maximum values of the diffraction intensity.

In this case, since the above-mentioned data has a strong correlation with the fatigue state of the rolling part 90, the fatigue degree of the rolling part 90 can be estimated with high accuracy by using the above-mentioned data as the second data.

The rolling part fatigue degree estimation method may further include a step (step (S161)) of notifying whether the rolling part 90 requires replacement or notifying the timing of replacement based on the first fatigue degree. In this case, appropriate maintenance of the rolling part 90 can be performed based on the accurately estimated first fatigue degree.

The fatigue degree estimation program according to the present disclosure is a fatigue degree estimation program for a rolling component, and causes a computer to execute a step (step (S110)) of acquiring data for estimating fatigue degree from a rolling component to which a repeated load due to rotation is applied. The acquiring step (step (S110)) includes a step of acquiring first data regarding the microstructure of the rolling component, and a step of acquiring second data, which is measurement data of X-ray analysis values regarding the rolling component, by irradiating X-rays to the fatigued portion of the rolling component. The fatigue degree estimation program causes a computer to execute a step (step (S120)) of determining whether or not a structural change has occurred in the fatigued portion of the rolling component 90 based on the data acquired in the acquiring step (step (S110)), and a step of estimating a first fatigue degree regarding internal origin type damage of the rolling component 90 based on the judgment result in the judging step (step (S120)) and the data acquired in the acquiring step (step (S110)). In the step of estimating the first fatigue degree, if it is determined in the step of determining (step (S120)) that no structural change has occurred, the following steps are performed: estimating the load acting on the rolling element 90 based on the second data (step (S132)); calculating the life based on the load and the use conditions of the rolling element 90 (step (S133)); and calculating the first fatigue degree of the rolling element 90 from the number of rotations and the life of the rolling element 90 (step (S134)). In the step of estimating the first fatigue degree, if it is determined in the step of determining (step (S120)) that a structural change has occurred, the following step is performed: estimating the first fatigue degree from the second data based on a predetermined relationship between the second data and the first fatigue degree (step (S141)).

In this way, the fatigue degree estimation program for the rolling part 90 described above causes the computer to execute a step (step (S120)) of determining whether or not a structural change has occurred in the fatigued portion, so that the first fatigue degree can be estimated by using an estimation method corresponding to each state depending on whether or not a structural change has occurred in the fatigued portion of the rolling part 90, that is, whether or not the progression of rolling fatigue has reached the third stage. Therefore, the fatigue degree of the rolling part 90 can be estimated with high accuracy.

The fatigue degree estimation program may further cause the computer to execute a step (step (S161)) of notifying the user whether the rolling part requires replacement or notifying the user when to replace the rolling part based on the first fatigue degree. In this case, information to be used for maintenance of the rolling part 90 can be notified based on the accurately estimated first fatigue degree.

The rolling component fatigue degree estimation device 14 according to the present disclosure includes a determination unit 31, a load estimation unit 32, and
The apparatus includes a life calculation unit 33, a first fatigue degree calculation unit 34, and a first fatigue degree estimation unit 41. The judgment unit 31 judges whether or not a structural change has occurred in the fatigued part of the rolling component 90 based on at least one of first data related to the microstructure of the rolling component 90 and second data, which is measurement data of X-ray analysis values related to the rolling component obtained by irradiating the fatigued part of the rolling component 90 with X-rays. The load estimation unit 32 estimates the load acting on the rolling component 90 based on the second data when the judgment unit 31 judges that no structural change has occurred. The life calculation unit 33 calculates the life based on the load and the use conditions of the rolling component 90. The first fatigue degree calculation unit 34 calculates the first fatigue degree of the rolling component 90 from the number of rotations of the rolling component 90 and the above-mentioned life. When the judgment unit 31 judges that a structural change has occurred, the first fatigue degree estimation unit 41 estimates the first fatigue degree from the second data based on a relationship between the X-ray analysis value and the first fatigue degree determined in advance.

As described above, the rolling part fatigue degree estimation device 14 is equipped with a judgment unit 31 that judges whether or not a structural change has occurred in the fatigued portion, and therefore can estimate the first fatigue degree using a fatigue degree estimation method corresponding to each state depending on whether or not a structural change has occurred in the fatigued portion of the rolling part 90, that is, whether or not the progression of rolling fatigue has reached the third stage. Therefore, the first fatigue degree of the rolling part 90 can be estimated with high accuracy.

(Embodiment 2)
<Configuration of fatigue level estimation system>
Fig. 5 is a schematic diagram showing the configuration of a fatigue level estimation system according to embodiment 2. Referring to Fig. 5, the fatigue level estimation system basically has the same configuration as the fatigue level estimation system shown in Fig. 1, but differs from the fatigue level estimation system shown in Fig. 1 in that it includes a surface profile measuring device 13.

The surface shape measuring device 13 measures the surface shape of the rolling part 90. For example, a laser microscope can be used as the surface shape measuring device 13. The surface to be measured may be, for example, a portion of the surface of a raceway of a rolling bearing as the rolling part 90, or the entire surface of a rolling element as the rolling part 90.

The fatigue level estimation device 14 shown in FIG. 5 estimates the fatigue level of the rolling part 90 based on the X-ray diffraction ring detected by the X-ray detector 12, the observation results of the microstructure of the rolling part 90 detected by the microstructure observation section 23, and the data on the surface shape of the rolling part 90 measured by the surface shape measuring instrument 13 described above. Note that the hardware configuration of the fatigue level estimation device 14 shown in FIG. 5 is basically the same as the hardware configuration of the fatigue level estimation device 14 according to embodiment 1 shown in FIG. 2.

<Functional configuration of the fatigue level estimation device>
Fig. 6 is a diagram showing a functional configuration of the fatigue level estimation device shown in Fig. 5. The fatigue level estimation device 14 shown in Fig. 6 basically has the same functional configuration as the fatigue level estimation device 14 shown in Fig. 3, but differs from the fatigue level estimation device 14 shown in Fig. 3 in that it includes a contact stress estimation unit 51, a lifespan estimation unit 53, a second fatigue level estimation unit 54, and a fatigue level determination unit 55 in addition to the configuration of the fatigue level estimation device 14 shown in Fig. 3. The control unit 60, the data preparation unit 21, the determination unit 31, the load estimation unit 32, the lifespan calculation unit 33, the first fatigue level calculation unit 34, the first fatigue level estimation unit 41, the diagnosis unit 70, the contact stress estimation unit 51, the lifespan estimation unit 53, the second fatigue level estimation unit 54, and the fatigue level determination unit 55 are realized by the CPU 15 executing a fatigue level estimation program stored in the memory 16.

<Procedure for fatigue level estimation method>
FIG. 7 is a flowchart showing the procedure of the fatigue level estimation process.
The fatigue level estimation process in the fatigue level estimation system shown in Fig. 5 will be described with reference to Fig. 7. The fatigue level estimation process shown in Fig. 7 basically has the same configuration as the fatigue level estimation process shown in Fig. 4, but differs from the fatigue level estimation process shown in Fig. 4 in that the types of data acquired in the data acquisition step (S110) are increased, that the process includes steps (S151) to (S154) for estimating a second fatigue level for surface-originating damage, and that the process includes a step (S155) for determining the larger of the first fatigue level and the second fatigue level as the fatigue level of the rolling component. The details will be described below.

In the data acquisition step (S110), the data preparation unit 21 prepares third data related to the surface shape of the fatigued part of the rolling part 90 in addition to the first data related to the microstructure in the fatigued part of the rolling part 90 described in FIG. 3 and the second data which is the measurement data of the X-ray analysis value related to the rolling part 90. The third data is, for example, data on the measured shape of the surface of the rolling part 90 measured by the surface shape measuring instrument 13. The surface shape data is input to the data preparation unit 21 via the input unit 17. The second data includes data on the three-axis residual stress on the surface of the fatigued part of the rolling part 90 and depth distribution data of the residual stress by X-rays.

Next, step (S120) is performed in the same manner as in the fatigue level estimation process shown in FIG. 4. Depending on the result of the determination in step (S120), steps (S131) to (S134) or step (S141) are performed in the same manner as in the fatigue level estimation process shown in FIG. 4. As a result, a first fatigue level related to internally originating damage is obtained.

On the other hand, in order to obtain the second fatigue level related to the surface-originating damage, a calculation step (S151) of the contact stress of the real contact part is performed. In step (S151), the contact stress estimation unit 51 calculates the contact stress of the real contact part based on the second data and the third data. The calculation of the contact stress may use data such as the rotation speed of the rolling part 90, the operating temperature, the type of lubricant oil, and the load. Here, when calculating the stress of the real contact part from data on the surface shape (for example, data on the surface roughness), the value of the contact load is required. The contact load may be an estimated load obtained from a depth analysis of X-ray stress measurement, or if the operating load of the rolling part 90 can be estimated in advance, the value of the operating load may be used.

Next, a step (S152) of estimating the repeated stress on the rolling surface is performed. In step (S152), the contact stress estimation unit 51 estimates the contact stress acting repeatedly on the fatigue portion of the rolling part 90 based on the contact stress of the real contact portion calculated in the above step (S151).

Next, a step (S153) of estimating a 10% life from the SN diagram is performed. In this step (S153), the life estimation unit 53 estimates a 10% life (L ₁₀ ) using a previously obtained relationship between contact stress and life, that is, a so-called SN diagram. The SN diagram is stored in the storage unit 61.

Next, a step (S154) of estimating the surface fatigue degree (second fatigue degree) is performed. In this step (S154), the second fatigue degree estimator 54 calculates the second fatigue degree (N/ _L10 ) of the rolling element 90 from the number of rotations N of the rolling element 90 and the above-mentioned 10% life ( _L10 ). Note that the usage time of the rolling element 90 may be used instead of the number of rotations N.

Next, a step (S155) is carried out in which the larger of the first fatigue degree and the second fatigue degree is determined as the fatigue degree of the rolling element 90. In step (S155), the fatigue degree determiner 55 determines the larger of the first fatigue degree related to the internal origin type damage obtained in step (S134) or step (S141) and the second fatigue degree related to the surface origin type damage obtained in step (S154) as the fatigue degree of the rolling element 90.

Next, a diagnosis step (S161) is performed in the same manner as in the fatigue degree estimation process shown in FIG. 4. In this step (S161), the diagnosis unit 70 judges whether the value of the fatigue degree determined as described above exceeds a predetermined reference value. If the determined value of the fatigue degree exceeds the reference value, a signal indicating that the value of the fatigue degree exceeds the reference value is transmitted from the diagnosis unit 70 to the control unit 60. The control unit 60 that receives the signal displays, for example, on the display unit 18, a message indicating that the rolling part 90 needs to be replaced. If the determined value of the fatigue degree does not exceed the reference value, a signal indicating that the value of the fatigue degree does not exceed the reference value is transmitted from the diagnosis unit 70 to the control unit 60. The control unit 60 that receives the signal displays, for example, on the display unit 18, a message indicating that the rolling part 90 does not need to be replaced.

<Action and effect>
In the above-described rolling component fatigue degree estimating method, the acquiring step (step (S110)) may include a step of measuring the fatigued portion of the rolling component 90 to obtain third data relating to the surface shape. The method for estimating a fatigue degree of a rolling part may include a step (step (S151) to step (S154) of estimating a second fatigue degree related to surface-originating damage of the rolling part 90 based on data obtained in the acquiring step (step (S110)). The step of estimating the second fatigue degree may include a step (step (S152)) of estimating a contact stress repeatedly acting on a fatigued portion of the rolling part 90 based on the second data and the third data, a step (step (S153)) of estimating a life from the contact stress based on a predetermined relationship between the contact stress and the life (SN diagram), and a step (step (S154)) of estimating a second fatigue degree of the rolling part 90 from the number of rotations and the life of the rolling part 90. The method for estimating a fatigue degree of a rolling part may include a step (step (S155)) of determining the larger of the first fatigue degree and the second fatigue degree as the fatigue degree of the rolling part 90.

In this case, the fatigue degree of the rolling part 90 can be estimated more accurately by considering both the first fatigue degree related to the internally originating damage and the second fatigue degree related to the surface originating damage.

The above-mentioned rolling part fatigue degree estimation method may further include a step of notifying whether the rolling part 90 requires replacement or notifying the timing of replacement of the rolling part 90 based on the fatigue degree. In this case, appropriate maintenance of the rolling part 90 can be performed based on the accurately estimated fatigue degree.

In the fatigue degree estimation program, the acquiring step (step (S110)) may include a step of measuring the fatigued portion of the rolling element 90 to obtain third data related to the surface shape. The fatigue degree estimation program may cause the computer to execute a step (steps (S151) to (S154)) of estimating a second fatigue degree related to surface-originating damage of the rolling element 90 based on the data acquired in the acquiring step (step (S110)). The step of estimating the second fatigue degree may include a step (step (S152)) of estimating the contact stress repeatedly acting on the fatigued portion of the rolling element 90 based on the second data and the third data, a step (step (S153)) of estimating the life from the contact stress based on a predetermined relationship between the contact stress and the life, and a step (step (S154)) of estimating the second fatigue degree of the rolling element 90 from the number of rotations and the life of the rolling element 90. Furthermore, the fatigue level estimation program may cause the computer to execute a step (step (S155)) of determining the larger value of the first fatigue level and the second fatigue level as the fatigue level of the rolling part.

In this case, by taking into consideration both the first fatigue degree related to the internal origin type damage and the second fatigue degree related to the surface origin type damage, the fatigue degree of the rolling element 90 can be estimated more accurately.

The fatigue level estimation program may further cause the computer to execute a step (step S161) of notifying the user whether or not the rolling part 90 requires replacement, or notifying the user when to replace the rolling part 90, based on the fatigue level. In this case, information to be used for maintenance of the rolling part 90 can be notified based on the accurately estimated fatigue level.

The rolling part fatigue degree estimation device 14 may include a contact stress estimation unit 51, a life estimation unit 53, a second fatigue degree estimation unit 54, and a fatigue degree determination unit 55. The contact stress estimation unit 51 estimates the contact stress acting repeatedly on the fatigued part of the rolling part 90 based on the second data and third data on the surface shape obtained by measuring the fatigued part of the rolling part 90. The life estimation unit 53 estimates the life from the contact stress based on the relationship (SN diagram) between the predetermined contact stress and the life for an arbitrary probability of failure. The second fatigue degree estimation unit 54 estimates the second fatigue degree of the rolling part 90 from the number of rotations and life of the rolling part 90. The fatigue degree determination unit 55 determines the larger value of the first fatigue degree and the second fatigue degree as the fatigue degree of the rolling part 90.

In this case, the fatigue degree of the rolling part 90 can be estimated more accurately by considering both the first fatigue degree related to the internally originating damage and the second fatigue degree related to the surface originating damage.

(Embodiment 3)
<Procedure for estimating fatigue level>
Fig. 8 is a flowchart showing the procedure of a fatigue level estimation process. Note that a fatigue level estimation system including a fatigue level estimation device according to embodiment 3 that performs the fatigue level estimation process shown in Fig. 8 basically has a similar configuration to the fatigue level estimation system according to embodiment 2. Hereinafter, the fatigue level estimation process in the fatigue level estimation system according to the present embodiment will be described with reference to Fig. 8.

The fatigue degree estimation process shown in FIG. 8 basically has the same configuration as the fatigue degree estimation process shown in FIG. 7, but the process when it is determined that a tissue change has occurred in step (S120) is different from the fatigue degree estimation process shown in FIG. 7. That is, in the fatigue degree estimation process shown in FIG. 8, when it is determined that a tissue change has occurred in the above step (S120), a contact stress estimation step (S171) is performed. In this step (S171), the load estimation unit 32 (see FIG. 6) estimates the contact stress in the fatigue part of the rolling part 90 based on the measurement data of the depth distribution of the diffraction intensity variation with respect to the central angle of the annular diffracted X-ray in the fatigue part of the rolling part 90 included in the second data. For example, the load estimation unit 32 may determine the first depth at which the value of the diffraction intensity variation is maximum based on the measurement data of the depth distribution, which is the distribution data in the depth direction of the diffraction intensity variation with respect to the central angle of the annular diffracted X-ray, as described later. The load estimation unit 32 may use the first depth to estimate the minor axis radius of the contact ellipse, which is the contact portion between the fatigue portion and another member.

The depth distribution measurement data described above may be obtained in step (S110) by measuring the entire annular diffracted X-rays using a two-dimensional detector, or by measuring the entire annular diffracted X-rays by scanning a detector that detects a portion of the annular diffracted X-rays. In addition, in the above step (S110), X-rays may be irradiated from a direction perpendicular to the surface of the fatigue portion of the rolling part 90 or from a direction inclined to the surface.

Next, a load estimation step (S172) is performed. In this step (S172), the load estimation unit 32 estimates the load in the fatigued part of the rolling part 90 based on measurement data of the depth distribution of the variation in diffraction intensity with respect to the central angle of the annular diffracted X-ray in the fatigued part of the rolling part 90. In the above steps (S171) and (S172), the load estimation unit 32 estimates the contact stress and the load by a method that is different from the estimation method in steps (S131) and (S132) of Fig. 8 and is suitable for a state in which a structural change is occurring as described above. Details will be described in the examples below.

Next, a step (S173) of estimating a 10% life (L ₁₀ ) is performed. In this step (S173), the life calculation unit 33 calculates the 10% life (L ₁₀ ) based on the load and the usage conditions of the rolling element 90. The process in step (S173) is basically the same as the process in step (S133).

Next, a calculation step (S174) of an internal fatigue degree (first fatigue degree) is performed. In this step (S174), the first fatigue degree calculation unit 34 calculates the first fatigue degree (N/ _L10 ) of the rolling element 90 from the number of rotations N of the rolling element 90 and the 10% life ( _L10 ) described above. Note that the usage time of the rolling element 90 may be used instead of the number of rotations N.

In the fatigue level estimation process shown in FIG. 8, depending on the result of the determination in step (S120), either step (S131) to step (S134) or the above-mentioned steps (S171) to (S174) are performed to obtain a first fatigue level related to internally originating damage.

Furthermore, similar to the fatigue degree estimation process shown in FIG. 7, by performing steps (S151) to (S155) and step (S161) shown in FIG. 8, it is possible to estimate the fatigue degree of the rolling part 90 and perform a diagnosis based on the fatigue degree.

<Action and effect>
A method for estimating fatigue degree of a rolling component according to the present disclosure includes a step of acquiring data for estimating fatigue degree of the rolling component from the rolling component to which a repeated load due to rotation is applied (step (S110)). The acquiring step (step (S110)) includes a step of acquiring first data on the microstructure of the rolling component, and a step of acquiring second data, which is measurement data of X-ray analysis values on the rolling component, by irradiating a fatigued portion of the rolling component with X-rays. The method for estimating fatigue degree of a rolling part further includes a step (step (S120)) of judging whether or not a structural change has occurred in the fatigued portion of the rolling part based on the data obtained in the acquiring step (step (S110)), and a step (steps (S131) to (S134) and steps (S171) to (S174)) of estimating a first fatigue degree related to internally originating damage of the rolling part based on the judgment result in the judging step (step (S120)) and the data obtained in the acquiring step (step (S110)). The second data includes distribution data in the depth direction of X-ray analysis values related to the rolling part. In the step of estimating the first fatigue degree, if it is determined in the step of determining (step (S120)) that no structural change has occurred, the following steps are performed: a step of estimating the load acting on the rolling part based on the second data (steps (S131, S132)), a step of calculating a life based on the load and the use conditions of the rolling part (step (S133)), and a step of calculating the first fatigue degree of the rolling part from the number of rotations and the life of the rolling part. If it is determined in the step of determining (step (S120)) that a structural change has occurred, the following steps are performed: a step of estimating the load acting on the rolling part based on the distribution data in the depth direction (steps (S171, S172)), a step of calculating a life based on the load and the use conditions of the rolling part (step (S173)), and a step of calculating the first fatigue degree of the rolling part from the number of rotations and the life of the rolling part (step (S174)).

In this way, like the fatigue degree estimation method in the first embodiment of the present invention, the above-mentioned rolling part fatigue degree estimation method can use a different fatigue degree estimation method corresponding to each state depending on whether the progression of rolling fatigue has reached the third stage or not, and therefore the fatigue degree of the rolling part can be estimated with high accuracy.

In the above method for estimating the degree of fatigue of a rolling part, the distribution data in the depth direction is distribution data in the depth direction of data showing the variation in diffraction intensity versus the central angle of the annular diffracted X-ray diffracted at the fatigued part of the rolling part. In this case, since the distribution data in the depth direction has a certain relationship with the load acting on the rolling part when fatigue at the fatigued part has entered the third stage, the load can be estimated based on the distribution data. As a result, the first fatigue degree can be calculated based on the load even when the progression of fatigue has reached the third stage.

The effects of the above-mentioned rolling part fatigue degree estimation method will be described in more detail below. As already mentioned, when fatigue reaches the third stage, a structural change occurs in the fatigued part of the rolling part. In the part where this structural change occurs, the crystals are oriented in a specific direction. Therefore, the variation in diffraction intensity with respect to the central angle of the circular diffracted X-ray (hereinafter, the diffraction intensity variation) increases. The diffraction intensity variation has a distribution in the depth direction of the rolling contact part. The inventor has found that the depth showing the peak value of the above-mentioned distribution in the diffraction intensity variation has a corresponding relationship with the minor axis radius of the contact ellipse. Based on this finding, the contact stress and the load can be estimated from the distribution of the diffraction intensity variation, similar to the method of estimating contact stress from the residual stress distribution in Non-Patent Document 1. Then, the 10% life can be calculated based on the estimated load and the operating conditions of the bearing (for example, the rotation speed, operating temperature, lubricant type, and lubricant contamination level). Furthermore, the fatigue degree can be calculated from the ratio of the number of rotations or operating time of the bearing to the above-mentioned 10% life.

The fatigue degree estimation program according to the present disclosure is a rolling part fatigue degree estimation program executed by the CPU 15 of the fatigue degree estimation device 14 in the second embodiment of the present invention, and causes the computer to execute a step (step (S110)) of acquiring data for estimating fatigue degree from a rolling part to which a repeated load due to rotation is applied. The acquiring step (step (S110)) includes a step of acquiring first data regarding the microstructure of the rolling part, and a step of acquiring second data, which is measurement data of X-ray analysis values regarding the rolling part, by irradiating X-rays to the fatigue part of the rolling part. The fatigue degree estimation program causes the computer to execute a step (step (S120)) of determining whether or not a structural change has occurred in the fatigue part of the rolling part 90 based on the data acquired in the acquiring step (step (S110)), and a step of estimating a first fatigue degree regarding internal origin type damage of the rolling part 90 based on the judgment result in the judging step (step (S120)) and the data acquired in the acquiring step (step (S110)). The second data includes distribution data in the depth direction of the X-ray analysis values for the rolling part 90. In the step of estimating the first fatigue degree, when it is determined in the determining step (step (S120)) that no structural change has occurred, the step of estimating the load acting on the rolling part based on the second data (steps (S131, S132)), the step of calculating the life based on the load and the usage conditions of the rolling part (step (S133)), and the step of calculating the first fatigue degree of the rolling part 90 from the number of rotations and the life of the rolling part 90 (step (S134)) are performed. In the step of estimating the first fatigue level, if it is determined in the step of determining (step (S120)) that a structural change has occurred, the steps of estimating the load acting on the rolling part 90 based on the distribution data in the depth direction (steps (S171, S172)), calculating the life based on the load and the usage conditions of the rolling part 90 (step (S173)), and calculating the first fatigue level of the rolling part 90 from the number of rotations and life of the rolling part 90 (step (S174)) are performed. In this case, the same effect as the fatigue level estimation program in the second embodiment of the present invention can be obtained.

The fatigue degree estimation device 14 according to the present disclosure includes a judgment unit 31, a load estimation unit 32, a life calculation unit 33, and a first fatigue degree calculation unit 34. The judgment unit 31 judges whether or not a structural change has occurred in the fatigued part of the rolling component 90 based on at least one of first data on the microstructure of the rolling component 90 and second data, which is measurement data of X-ray analysis values on the rolling component 90 obtained by irradiating the fatigued part of the rolling component 90 with X-rays. The load estimation unit 32 estimates the load acting on the rolling component 90 based on the second data. The life calculation unit 33 calculates the life based on the load and the use conditions of the rolling component 90. The first fatigue degree calculation unit 34 calculates the first fatigue degree of the rolling component 90 from the number of rotations and life of the rolling component 90. The second data includes distribution data in the depth direction of the X-ray analysis values on the rolling component 90. When the determination unit 31 determines that no tissue change has occurred, the load estimation unit 32 estimates the load acting on the rolling element 90 based on the second data. When the determination unit 31 determines that a tissue change has occurred, the load estimation unit 32 estimates the load acting on the rolling element 90 based on the distribution data in the depth direction. In this case, it is possible to obtain the same effect as the fatigue level estimation device 14 in the second embodiment of the present invention.

The method for estimating contact stress of a rolling part according to the present disclosure includes a step (step (S110)) of obtaining distribution data in the depth direction of the variation in diffraction intensity versus the central angle of the ring-shaped diffracted X-rays diffracted at the fatigue part by irradiating X-rays from the surface to the inside of the fatigue part of the rolling part 90, and a step (step (S171)) of estimating the contact stress repeatedly acting on the fatigue part of the rolling part 90 based on the distribution data in the depth direction. In this way, since the distribution data in the depth direction has a certain relationship with the contact stress acting on the rolling part when fatigue at the fatigue part has entered the third stage, the contact stress can be estimated based on the distribution data.

In the above contact stress estimation method, the step of estimating the contact stress (step (S171)) may include a step of determining a first depth at which the value of the diffraction intensity variation is maximum based on the distribution data in the depth direction, estimating the minor axis radius of the contact portion with another member in the fatigue portion using the first depth, and a step of estimating the contact stress based on the minor axis radius.

In the contact stress estimation method, in the step of obtaining distribution data in the depth direction (step (S110)), the entire annular diffracted X-rays may be measured using a two-dimensional detector. In the contact stress estimation method, in the step of obtaining distribution data in the depth direction (step (S110)), the entire annular diffracted X-rays may be measured by scanning a detector that detects a portion of the annular diffracted X-rays.

In the above contact stress estimation method, in the step of obtaining distribution data in the depth direction (step (S110)), X-rays may be irradiated from a direction perpendicular to the surface of the fatigued portion of the rolling part 90. In the above contact stress estimation method, in the step of obtaining distribution data in the depth direction (step (S110)), X-rays may be irradiated from a direction inclined to the surface of the fatigued portion of the rolling part 90.

Example 1
The fatigue degree of the test specimen after the life test using the line contact tester was estimated according to the present disclosure. The test conditions are shown in Table 1.

The results are explained below.
<Fatigue level estimation when fatigue progression has not reached the third stage>
(1) Determination of the peak position of residual stress When the progression of fatigue has not yet reached the third stage, the contact stress and load are estimated from the measurement results of the depth distribution of residual stress. In the following example, the equivalent stress of residual stress is used, but it is also possible to estimate the load using the circumferential residual stress and the axial residual stress.

Figure 9 is a graph showing the depth distribution of the equivalent stress of residual stress. The horizontal axis of Figure 9 indicates the depth from the surface of the sample, in units of μm. The vertical axis of the graph in Figure 9 indicates the equivalent stress of residual stress, in units of MPa. The test time for the sample from which the data shown in Figure 9 was obtained using a line contact tester was 148 minutes. As shown in Figure 9, the residual stress distribution is approximated by a quadratic function. The position where the approximate curve shows a peak is taken as the peak position of the equivalent stress (depth showing the maximum value) Zσeq. In Figure 9, the peak position Zσeq is 210 μm.

(2) Estimation of Contact Stress and Load It is known that the position where the residual stress is maximum and the position _Z45 where the maximum shear stress τmax generated inside the rolling element is maximum are almost the same (Zσeq ≒ _Z45 ). In addition, in the case of line contact, the relationship between the minor axis radius b of the contact ellipse and _Z45 is expressed by the following formula (2). Note that since the ratio of the major axis to the minor axis of the contact ellipse for most bearings is 10 or more, there is no problem in using formula (2) regardless of the shape of the rolling element.

When the two rolling elements in contact are two parallel cylinders, the relationship between the minor axis radius b and the load P is given by the following formula (3).

Here, l denotes the contact length between the two cylindrical rolling elements 1 and 2. R ₁ and R ₂ denote the radii of curvature of rolling elements 1 and 2, respectively. υ ₁ and υ ₂ denote the Poisson's ratios of rolling elements 1 and 2, respectively. E ₁ and E ₂ denote the Young's moduli of rolling elements 1 and 2, respectively.

If rolling elements 1 and 2 are made of the same material, the above formula (3) can be transformed into the following formula (4).

From the above equations (2) and (4), the following equation (5) is derived.

Therefore, the contact stress P _max is given by the following equation (6).

Substituting the test piece specifications shown in Table 2 below and the value of _Z45 obtained in the previous section into the above formula (5), a value of P = 18.84 kN is obtained. Also, using the above formula (6), a value of contact stress _Pmax = 4.02 GPa is obtained.

(3) Calculation of Fatigue Degree Here, the relationship between the contact stress and the life is expressed by the following formula (7).

In past tests conducted by the inventors, data was obtained showing that _L10 = 2400 minutes in the case of a line contact test with _Pmax = 4.2 GPa. Using this data and the relationship in the above formula (7), the estimated life _L10est. and the estimated fatigue degree t/ _L10est. are calculated. Here, t represents the test time. The results were _L10est. = 3452.5 minutes, and t/ _L10est. = 148/3452.5 = 0.0429.

<Fatigue level estimation when fatigue progression reaches the third stage>
The fatigue degree is estimated from the X-ray stress measurement results using a database of fatigue degrees obtained in a rolling fatigue life test previously performed and X-ray stress measurement results of test pieces that were rolled up to that fatigue degree. Here, data obtained from a line contact test with P _max = 4.2 GPa is used. The number of test pieces in this test is 22.

Figure 10 is a graph showing the relationship between the variance in diffraction intensity obtained with circumferential incidence and the test time. The horizontal axis of Figure 10 is the test time in minutes. The vertical axis of Figure 10 shows the variance in diffraction intensity. The diffraction intensity was measured at a depth of 600 μm from the surface of the test piece. The plot in Figure 10 shows the measured values, and the solid line is the regression curve. Using the regression curve in Figure 10, for example, when the variance in diffraction intensity is 15,000, it can be estimated that the test time for that test piece is approximately 1,500 to 2,400 minutes. The dashed line in Figure 10 is the lower limit of the test time estimated from the measured values. Using this dashed line makes it possible to estimate the fatigue level on the safe side, taking into account the variance in the data.

For example, when the degree of fatigue t/ _L10 is estimated based on FIG. 10 when the value of the variation in diffraction intensity is 15,000, it is given as t/L10=1500/2400-2400/2400=0.625-1.

Next, a case will be considered in which the retained austenite is used as an index of fatigue degree. Fig. 11 is a graph showing the relationship between the reduction rate of retained austenite and test time. The horizontal axis of Fig. 11 indicates the test time in minutes. The vertical axis of Fig. 11 indicates the reduction rate of retained austenite in %. In Fig. 11, data at a depth of 210 µm is shown with a diamond legend, and data at a depth of 600 µm is shown with a square legend. A regression line is shown for each data. Here, the reduction rate of retained austenite is defined as follows:

When the reduction rate of the retained austenite is used as an index of the degree of fatigue, as can be seen from FIG. 11, the slope of the graph is larger when the measured value is used at an inner depth (e.g., 600 μm depth) than the depth where fatigue is most likely to progress (e.g., Z ₄₅ = 210 μm), and the sensitivity of the reduction rate of the retained austenite to the test time is high. The following reasons are considered for this. That is, when the fatigue enters the third stage, the amount of retained austenite near Z ₄₅ is almost 0%, and the amount of retained austenite at that depth does not change thereafter. On the other hand, in the region at a depth of 600 μm, the contact stress is smaller than that at Z ₄₅ described above, so the structural change progresses more slowly. Therefore, as shown in FIG. 11, the data at the region at a depth of 600 μm is more sensitive to the test time.

Using the regression line shown in Figure 11, it can be estimated that when the reduction rate of retained austenite is 30%, for example, the test time for that test piece is approximately 1,400 to 2,400 minutes. Here, the dashed line shown in Figure 11 is the lower limit of the test time estimated from the measured values. Using this dashed line makes it possible to estimate the degree of fatigue on the safe side, taking into account the variability in the data.

For example, when the fatigue degree t/ _L10 is estimated based on FIG. 11 when the reduction rate of the retained austenite is 30%, it is t/L10=1400/2400-2400/2400=0.583-1.

As described above, it was found that in some cases it is possible to accurately evaluate the degree of fatigue by using the measured value at a depth where fatigue progresses slowly, rather than the measured value at Z ₄₅ where fatigue progresses quickly. The same is true for other X-ray analysis values such as half-width and residual stress.

Example 2
In relation to the fatigue level estimating method according to the third embodiment described above, the following experiment was carried out.

(1) Estimation of contact stress (Pmax) <Preparation of test specimen>
X-ray analysis was carried out on the test specimens that had been subjected to a life test using a line contact type fatigue testing machine or a bearing life testing machine. The test conditions for the life test using the line contact type fatigue testing machine are shown in Table 3, and the test conditions for the life test using the bearing life testing machine are shown in Table 4. Hereinafter, the former test specimen will be referred to as the "first test specimen" and the latter test specimen as the "second test specimen."

For the X-ray measurements, a two-dimensional detector type X-ray stress measurement device, μ-X360 (manufactured by Pulstec Industries Co., Ltd.), was used. The X-ray measurement conditions are shown in Table 5.

When performing X-ray measurement, the coordinate system was defined as shown in FIG. 12. FIG. 12 is a schematic diagram for explaining the coordinate system when performing X-ray measurement. FIG. 12 shows a case where X-rays are irradiated onto the outer periphery of a rolling element 90 as a sample while the rolling element 90 is rotated in the direction indicated by an arrow 81. By rotating the rolling element 90, X-rays are irradiated onto a fatigued portion 82 where fatigue has occurred on the outer periphery of the rolling element 90. In the following, a case where the X-ray irradiation direction (ψ, φ ₀ ) indicated by an arrow α in FIG. 12 is (0, 0) is defined as normal incidence, and a case where the X-ray irradiation direction (ψ, φ
When the X-ray irradiation direction (ψ,φ _{0 ) is (30,0), it is called circumferential incidence, and when the X-ray irradiation direction (ψ,φ 0 )} is (30,90), it is called axial incidence. Also, as shown in FIG. 13, diffracted X-rays are generated to form a conical surface β with the X-ray irradiation portion as the apex. Here, FIG. 13 is a schematic diagram of diffracted X-rays. As shown in FIG. 13, diffracted X-rays can be detected by X-ray detector 12 including a planar detection portion. Also, diffracted X-rays may be detected by scanning detector 83 that detects a portion of the diffracted X-rays.

When using an X-ray detector 12 (two-dimensional detector) including the planar detection unit shown in FIG. 13, annular diffracted X-rays as shown in FIG. 14 are obtained. These are called "annular diffracted X-rays." Here, FIG. 14 is a schematic diagram of the measured annular diffracted X-rays. FIG. 15 is a schematic diagram for explaining the variation in diffraction intensity. The horizontal axis of the graph on the left side of FIG. 15 indicates the central angle α of the diffracted X-rays shown in FIG. 14, and the vertical axis indicates the diffraction intensity of the diffracted X-rays. The vertical axis of the graph on the right side of FIG. 15 indicates the diffraction intensity of the diffracted X-rays, and the horizontal axis indicates the number of diffraction intensity data. The graph on the right side of FIG. 15 shows the frequency distribution of the diffraction intensity.

Referring to Figures 14 and 15, the parameter "diffraction intensity variation" described later is defined as "standard deviation of diffraction intensity with respect to the central angle α of the annular diffracted X-ray (standard deviation S shown in the graph on the right side of Figure 15)." The above-mentioned diffraction intensity variation can also be obtained using detector 83, which is a zero-dimensional or one-dimensional detector shown in Figure 13, that detects a portion of the annular diffracted X-ray.

<Measurement results for the first test piece in the life test using a line contact type fatigue testing machine>
The measurement results regarding the first test specimen will be described with reference to Figs. 16 and 17. Fig. 16 is a graph showing the depth direction distribution of the circumferential residual stress, which is the result of the X-ray measurement of the first test specimen. Fig. 17 is a graph showing the depth direction distribution of the variation of the diffraction intensity, which is the result of the X-ray measurement of the first test specimen. Note that, for the first test specimen from which the measurement results shown in Figs. 16 and 17 were obtained, the test time of the life test using the line contact type fatigue tester was 1700 minutes. In addition, as a result of performing a structural observation after the X-ray measurement of the first test specimen, it was confirmed that the first test specimen had reached the third stage of fatigue.

The horizontal axis of FIG. 16 and FIG. 17 indicates the depth from the surface of the test piece, and the unit is mm. The vertical axis of FIG. 16 indicates the value of the circumferential residual stress, and the unit is MPa. The vertical axis of FIG. 17 indicates the variation in diffraction intensity. From FIG. 16, it can be seen that the depth at which the circumferential residual stress shows the maximum value is about 0.4 mm, which is a position deeper than Z _45. Also, from FIG. 17, the variation in the diffraction intensity obtained by normal incidence shows a maximum value near Z ₀ , and the variation in the diffraction intensity obtained by axial incidence shows a maximum value between Z ₀ and Z _45. On the other hand, the variation in the diffraction intensity obtained by circumferential incidence has a smaller change compared to the data of the variation in the diffraction intensity obtained by incidence from the other two directions, and does not show a clear maximum value. In addition, when the same measurement was performed on 21 other first test pieces other than the exemplified test piece, a distribution in which the variation in the diffraction intensity obtained by normal incidence and axial incidence was maximum near Z ₀ was obtained, as with the first test piece shown in FIG. 17.

<Measurement results for the second test piece in the life test using a bearing life test machine>
The measurement results regarding the second test specimen will be described with reference to Figs. 18 and 19. Fig. 18 is a graph showing the depth direction distribution of the circumferential residual stress, which is the result of the X-ray measurement of the second test specimen. Fig. 19 is a graph showing the depth direction distribution of the variation of the diffraction intensity, which is the result of the X-ray measurement of the second test specimen. Note that, for the second test specimen from which the measurement results shown in Figs. 18 and 19 were obtained, the test time of the life test using the bearing life tester was 1196.3 hours. In addition, as a result of performing a structural observation after the X-ray measurement of the second test specimen, it was confirmed that the second test specimen had reached the third stage of fatigue.

The vertical and horizontal axes in Fig. 18 and Fig. 19 are the same as those in Fig. 16 and Fig. 17. From Fig. 18, it can be seen that the depth at which the circumferential residual stress shows the maximum value is about 0.2 mm, which is a position deeper than Z _45. From Fig. 19, it can be seen that the variation in the diffraction intensity shows a maximum value near Z ₀ for any incident direction. Note that, when the same measurement was performed on 20 second test specimens other than the exemplified test specimen, a distribution in which the variation in the diffraction intensity was maximum near Z ₀ was obtained, as with the second test specimen shown in Fig. 19.

From the above results, it was found that the distribution of the diffraction intensity variation is maximum near Z _0. As can be seen from Figs. 17 and 19, the first and second test pieces show similar trends. By utilizing this property, it becomes possible to estimate the contact stress (Pmax), which is the load on the bearing, even when fatigue has progressed to the third stage. Note that, when a change is observed in the diffraction intensity variation, it is determined that fatigue in the sample has progressed to the third stage.

<Calculation of contact stress (Pmax)>
The formula for calculating contact stress (Pmax) is shown below. In the case of line contact, the relationship shown in the following formula (9) exists between the minor axis radius b of the contact ellipse and _Z0 . Note that since the ratio of the major axis to the minor axis of the contact ellipse for most bearings is 10 or more, the following formula (9) can be used regardless of the shape of the rolling elements.

When the two rolling elements 1 and 2 in contact are two parallel cylinders, the relationship between the minor axis radius b and the load P is expressed by the following formula (10). Note that the following formula (10) is the same as formula (3) explained in Example 1.

If rolling elements 1 and 2 are made of the same material, the above formula (10) can be transformed into the following formula (11).

From the above formula (9) and formula (11), the following formula (12) is derived.

Therefore, the contact stress P _max is given by the following equation (13).

As mentioned in Example 1, the relationship between the minor axis radius b and the load P is expressed by the following formula (14).

From the above formula (11) and formula (14), the following formula (15) is derived.

Therefore, the contact stress P _max is given by the following equation (16).

_Z0 is the depth at which the diffraction intensity variation is at its maximum, and _Z45 is the depth at which the residual stress is at its maximum. When fatigue is at the first or second stage, for example in step S131 of Figures 7 and 8, the above formula (16) is used to estimate the contact stress Pmax. On the other hand, when fatigue is at the third stage, for example in step S171 of Figure 8, the above formula (13) is used to estimate the contact stress Pmax. The estimated results of Pmax are shown below.

<Pmax Estimation Results for the First Test Piece>
FIG. 20 shows the results of estimating the contact stress Pmax using equation (13) from the measurement results of the first test piece after the test under the conditions shown in Table 6 below.

FIG. 20 is a graph showing the estimated contact stress of the first test piece. The horizontal axis of FIG. 20 indicates the test time for each test piece, in minutes. The vertical axis of FIG. 20 indicates the estimated contact stress Pmax (
20 shows the estimated surface pressure (estimated surface pressure) in GPa. The nominal test surface pressure (contact stress) for the first specimen was 4.2 GPa, whereas the estimated average Pmax was 4.31 GPa with a standard deviation of 0.12 GPa as shown in FIG.

<Pmax Estimation Results for the Second Test Piece>
FIG. 21 shows the results of estimating the contact stress Pmax using equation (13) from the measurement results of the second test piece after the test under the conditions shown in Table 7 below.

FIG. 21 is a graph showing the estimated contact stress of the second test specimen. The horizontal axis of FIG. 21 shows the test time for each test specimen in hours. The vertical axis of FIG. 21 shows the estimated contact stress Pmax (estimated surface pressure) in GPa. The nominal test surface pressure (contact stress) for the second test specimen was 3.2 GPa, while the average estimated _Pmax as shown in FIG. 21 was 3.44 GPa with a standard deviation of 0.27 GPa.

<Calculating fatigue level>
The fatigue degree is calculated based on the contact stresses for the first and second test specimens estimated in the previous section. The relationship between the contact stress and the life is assumed to be expressed by the following formula (17).

In past tests conducted by the inventors, data was obtained that _L10 = 2400 minutes in a life test using a line contact type fatigue testing machine with _Pmax = 4.2 GPa. Data was also obtained that _L10 = 1622 hours in a life test using a bearing life testing machine with _Pmax = 3.2 GPa. Using these data and the relationship in formula (17) above, the estimated life _L10est. and estimated fatigue degree t/ _L10est. for each sample are obtained. Here, t represents the test time. The results are shown in Tables 6 and 7. As described above, the fatigue degree can be calculated using the contact stress Pmax estimated from the variation in diffraction intensity.

The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

11 irradiation unit, 12 X-ray detector, 12A detection unit, 12B hole, 13 surface shape measuring device, 14 fatigue degree estimation device, 16 memory, 17 input unit, 18 display unit, 21 data preparation unit, 23 microstructure observation unit, 31 judgment unit, 32 load estimation unit, 33 life calculation unit, 34 first fatigue degree calculation unit, 41 first fatigue degree estimation unit, 51 contact stress estimation unit, 53 life estimation unit, 54 second fatigue degree estimation unit, 55 fatigue degree determination unit, 60 control unit, 61 memory unit, 70 diagnosis unit, 81 arrow, 82 fatigue part, 83 detector, 90 rolling part.

Claims (8)

A method for estimating contact stress in a rolling part, comprising the steps of: irradiating X-rays from the surface to the inside of a fatigued part of a rolling part, thereby obtaining distribution data in the depth direction of the variation in diffraction intensity with respect to the central angle of the annular diffracted X-rays diffracted at the fatigued part; and estimating the contact stress repeatedly acting on the fatigued part of the rolling part based on the distribution data in the depth direction. The method for estimating contact stress for rolling parts according to claim 1, wherein the step of estimating the contact stress includes a step of determining a first depth at which the value of the variation in the diffraction intensity is maximum based on the distribution data in the depth direction, estimating the minor axis radius of the contact portion with another member in the fatigue portion using the first depth, and estimating the contact stress based on the minor axis radius. The method for estimating contact stress in rolling parts according to claim 1 or 2, wherein in the step of obtaining distribution data in the depth direction, a two-dimensional detector is used to measure the entire annular diffracted X-rays. The method for estimating contact stress in rolling parts according to claim 1 or 2, wherein in the step of obtaining distribution data in the depth direction, the entire annular diffracted X-rays are measured by scanning a detector that detects a portion of the annular diffracted X-rays. The method for estimating contact stress of a rolling part according to any one of claims 1 to 4, wherein in the step of obtaining distribution data in the depth direction, the X-rays are irradiated from a direction perpendicular to the surface of the fatigue part of the rolling part. The method for estimating contact stress of a rolling part according to any one of claims 1 to 4, wherein in the step of obtaining distribution data in the depth direction, the X-rays are irradiated from a direction inclined with respect to the surface of the fatigue portion of the rolling part. A contact stress estimation program for the rolling component, the contact stress estimation program causing a computer to execute each step described in claim 1. A contact stress estimation device for rolling parts, which acquires distribution data in the depth direction of the diffraction intensity variation with respect to the central angle of the circular diffracted X-rays based on data obtained by irradiating X-rays from the surface to the inside of a fatigue part of a rolling part, and has a judgment unit that judges whether the distribution data in the depth direction has a maximum value inside the fatigue part, and when the judgment unit judges that the distribution data has a maximum value, estimates the contact stress acting on the rolling part based on the distribution data in the depth direction.

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