JPH08201257A - Method for measuring degree of fatigue damage - Google Patents

Abstract

PURPOSE: To provide a method by which the degree of fatigue damage of a structural member can be recognized and the remaining service life of the member can be estimated in early stage after the use of the member is started. CONSTITUTION: After the relation between the root-mean-square roughness Rrms, average center-line roughness, or average ten-point roughness and the degree of fatigue damage of the surface of a test piece is found by repetitively applying a fatigue load to the test piece, the surface dimension of a used structural member is measured and the fluctuation of the root-mean-square roughness Rrms, average center-line roughness, or average ten-point roughness is found from the measured results of the surface dimension. Then the degree of fatigue damage of the structural member is found by applying the fluctuation to the relation found from the test piece. Therefore, the fatigue damage and remaining service life of the used structural member can be quantitatively recognized in an early stage by using such a simple method as the measurement of the surface dimension.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a degree of fatigue damage applied to a machine structure or the like which is subjected to a low cycle fatigue load.

[0002]

2. Description of the Related Art Fatigue damage degree of a conventional mechanical structure or the like subjected to repeated fatigue load (repeated number of uses N × 100 / repeated number of breaks N)
Regarding f), there were some that were measured by measuring the temperature, pressure, stress, etc. applied to the structure, etc.
There is no one that measures the degree of fatigue damage by measuring the surface shape and evaluates the remaining life.

[0003]

The conventional measurement of the degree of fatigue damage of a structure or the like has been performed by measuring the temperature, pressure, stress, etc. applied to the structure or the like as described above.

However, whichever measuring method is used, it is difficult to accurately predict the remaining life of a structure or the like based on the measurement results, and it is impossible to predict it particularly at the early stage of the life. Was close to The present invention is intended to solve the above problems.

[0005]

[Means for Solving the Problems]

(1) In the fatigue damage level measuring method of the present invention, the relationship between the root mean square roughness of the surface and the fatigue damage level is obtained in advance for the test piece of the structural member subjected to repeated fatigue loading, and the structural member in use is measured. After finishing the surface of the part to a mirror surface, the surface shape is measured linearly in the direction of maximum load, the root mean square roughness is calculated from this measurement result, and the variation of this root mean square roughness from the initial state is calculated. After that, the fatigue damage degree of the structural member is calculated from the previously obtained relation between the root mean square roughness and the fatigue damage degree.

(2) The present invention is characterized in that the center line average roughness is used in place of the root mean square roughness in the fatigue damage degree measuring method according to the above-mentioned invention (1).

(3) The present invention is characterized in that, in the fatigue damage level measuring method according to the above-mentioned invention (1), ten-point average roughness is used instead of the root mean square roughness.

[0008]

[Function] When a structural member that initially had a smooth surface is subjected to repeated fatigue loading, first a slip band appears due to plastic deformation on the surface, then irregularities such as protrusions and intrusions appear, and micro cracks occur.・ Growth, generation of macro cracks ・ Failure after growth.

In the above-mentioned invention (1), as a result of repeating various experiments focusing on this point, it is found that there is a correlation between the root mean square roughness of the surface of the structural member in use and the degree of fatigue damage. This is due to the findings.

Therefore, the relationship between the root mean square roughness of the test piece and the degree of fatigue damage is obtained in advance, the surface shape of the structural member in use is measured, and the root mean square roughness of the surface is obtained from this. By calculating the amount of change from the initial state and applying it to the above relationship, the degree of fatigue damage of the structural member can be obtained from the initial stage of use, and the remaining life can be predicted.

The above invention (2) is based on the finding that there is a correlation between the center line average roughness of the surface of the structural member in use and the degree of fatigue damage as a result of repeated experiments. By carrying out the measuring method of the present invention in the same procedure as the above-mentioned invention (1), from the relationship between the center line average roughness of the surface of the structural member and the degree of fatigue damage, the above-mentioned invention (1) is obtained.
Similarly to the above, it is possible to obtain the fatigue damage degree of the structural member from the initial stage of use, and it is possible to predict the remaining life.

The invention (3) is based on the finding that, as a result of various experiments, there is a correlation between the ten-point average roughness of the surface of the structural member in use and the degree of fatigue damage. By performing the measuring method of the present invention in the same procedure as in the above-mentioned invention (1), it is used in the same manner as in the above-mentioned invention (1) from the relationship between the ten-point average roughness of the surface of the structural member and the degree of fatigue damage. It is assumed that the fatigue damage degree of the structural member can be obtained from the initial stage of starting the, and the remaining life can be predicted.

[0013]

The procedure of the method for measuring the degree of fatigue damage of a structural member according to the first embodiment of the present invention will be described below.

First, for a structural member that is subjected to repeated fatigue loading, the surface of the measurement target site is mirror-finished by bubbling with a diamond grindstone of 1 μm, and then the surface shape of the measurement target site is linearly measured in the maximum load direction. To do. At this time, a contact-type measuring method such as a stylus method or a non-contact measuring method such as laser measurement is used for the measurement.

Next, with respect to the surface shape of the measurement target portion of the structural member obtained by this measurement, the root mean square roughness Rrms
To calculate. Finally, the fatigue damage degree is obtained by applying the above calculation result to the relational diagram of the root mean square roughness Rrms and the fatigue damage degree of the test piece prepared in advance in the laboratory to predict the remaining life.

In this example, as a result of various experiments, it was found that there is a correlation between the root mean square roughness Rrms of the surface of the structural member in use which is subjected to repeated fatigue loading and the degree of fatigue damage. This is due to the findings. The root mean square roughness Rrms is represented by the following equation.

[0017]

[Equation 1]

FIG. 1 shows part of the results obtained by the above experiment.
2 and FIG. FIG. 1 shows the results of measurement of the change in the surface shape in the axial direction of the test piece at this time (strain range Δε) by applying repeated fatigue load to a round rod uniaxial test piece using SUSF316H which is austenitic stainless steel as a material. = 1
% Hour).

The root mean square roughness Rrms is obtained from the above measurement results, and the relationship between this increase and the fatigue damage degree is shown in FIG. 2. From FIG. 2, the root mean square roughness and the fatigue damage degree of the surface of the test piece are shown. It turns out that there is a correlation between them.

As shown in FIG. 1, the above-mentioned change in surface shape appears from the initial stage of fatigue damage. Therefore, the method of this embodiment determines the degree of fatigue damage in the initial stage of fatigue damage of structural members. It is also extremely effective in predicting the remaining life.

Next, a measuring method according to the second embodiment of the present invention will be described. In the method of the present embodiment, the center line average roughness Ra is used instead of the root mean square roughness Rrms in the first embodiment, and the procedure for carrying out the measuring method is the same as in the first embodiment.

Also in this embodiment, as in the first embodiment,
This is because the centerline average roughness Ra was obtained from the measurement results shown in FIG. 1 and it was found that there is a correlation between the increased amount and the fatigue damage degree as shown in FIG. The center line average roughness Ra is expressed by the following equation.

Ra = A / L Here, A is the sum of the absolute values of the area with respect to the center line of the surface roughness where the amplitude repeats as shown in FIG. 1, and L is the axial length in which the amplitude is measured. That's it.

Next, a measuring method according to the third embodiment of the present invention will be described. In the method of this embodiment, the ten-point average roughness Rz is used in place of the root mean square roughness Rrms in the first embodiment, and the procedure for carrying out the measuring method is the same as in the first embodiment.

Also in this embodiment, as in the first embodiment,
The ten-point average roughness Rz is obtained from the measurement results shown in FIG.
This is due to the fact that there is a correlation between this increase and the degree of fatigue damage, as shown in FIG.

The ten-point average roughness Rz is, as shown in FIG. 1, the average value of the heights of the peaks from the highest peak of the surface roughness where the amplitude repeats to the fifth highest peak, and the lowest valley in order. It is obtained from the difference from the average value of the altitude of the valley bottom up to the fifth valley.

The measuring methods of the first, second, and third embodiments have their respective characteristics, and the respective characteristics will be compared and explained below. In the case of the first embodiment, the calculation is easy and the average feature of all data can be grasped. Second
In the case of the embodiment, the calculation is easy, but at present, other 2
Less accurate than the two methods.

In the case of the third embodiment, since it is based on the data of only 10 points, if the points do not represent the damage situation, the accuracy is lowered. It should be noted that since irregularities due to noise or foreign matter may be measured as surface roughness, a check is required.

[0029]

In the method for measuring the degree of fatigue damage of the present invention, the test piece is subjected to repeated fatigue loading in advance, and the root-mean-square roughness, the centerline average roughness, or the ten-point average roughness and the fatigue damage degree are given. , The surface shape of the structural member in use is measured, and the root-mean-square roughness of the surface from the measurement result,
The center line average roughness, or the change of the ten-point average roughness, by applying this to the relationship previously obtained by the test piece to determine the degree of fatigue damage, by a simple method of surface shape measurement, It enables quantitative understanding of fatigue damage and remaining life of structural members in use, especially in the initial stage.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a surface shape measurement result at each fatigue damage degree according to an embodiment of the present invention.

FIG. 2 is a relationship diagram between root mean square roughness and fatigue damage degree according to the above-mentioned embodiment.

FIG. 3 is a relationship diagram of center line average roughness and fatigue damage degree according to the second embodiment of the present invention.

FIG. 4 is a relationship diagram between ten-point average roughness and fatigue damage degree according to the third embodiment of the present invention.

Claims (3)

[Claims] 1. The relationship between the root-mean-square roughness and the degree of fatigue damage of a test piece of a structural member subjected to repeated fatigue loading is obtained in advance, and the surface of the measurement target site of the structural member in use is mirror-finished. , The surface shape is linearly measured in the direction of the maximum load, the root mean square roughness is calculated from this measurement result, and the change amount from the initial state is further calculated for the root mean square roughness, and then the above-mentioned pre-determination is performed. A method for measuring the degree of fatigue damage, characterized in that the degree of fatigue damage of the structural member is obtained from the relationship between the root mean square roughness and the degree of fatigue damage. 2. The fatigue damage level measuring method according to claim 1, wherein a center line average roughness is used in place of the root mean square roughness. 3. The fatigue damage level measuring method according to claim 1, wherein a ten-point average roughness is used instead of the root mean square roughness.