JP6037983B2 - Crack opening behavior acquisition method, crack opening behavior acquisition device, and crack opening behavior acquisition program - Google Patents

Description

  The present invention relates to a crack opening behavior acquisition method, a crack opening behavior acquisition device, and a crack opening behavior acquisition program.

  If the crack generated on the surface of the structure propagates, the structure may be damaged, and it is important to detect the crack that may propagate in advance for safe use of the structure. In particular, since cracks that occur in a structure propagate by repeating the opening and closing, detecting crack opening behavior such as whether the crack has opened or not can be used to detect cracks that may develop. It becomes necessary.

  For example, in Patent Document 1, the first strain gauge is attached to the tip of the crack, the second strain gauge is attached to a position away from the crack, and the output of the strain gauge is obtained from two different points. Discloses a method for detecting a change in the amount of strain in a range in which the aperture is open. By using such a method, an effective stress intensity factor in a range where the crack is opened is obtained, and crack growth prediction is performed to improve the accuracy of device life prediction.

JP 63-122928 A

  However, the above-described method has a problem that it is difficult to accurately detect the opening of the crack because the tip of the crack is measured. In particular, in the case of a minute crack, the amount of opening at the tip of the crack is minute, and the amount of change is too small, so that it is difficult to accurately detect the opening behavior of the crack.

  The present invention has been made to solve the above-described problems, and provides a crack opening behavior acquisition method, a crack opening behavior acquisition device, and a crack opening capable of accurately detecting the crack opening behavior. An object is to provide an opening behavior acquisition program.

In order to solve the above problems, the present invention proposes the following means.
In one aspect of the present invention, the crack opening behavior acquisition method is such that the crack is straddled across a region that includes the center of the crack extension direction on the surface of the test object in a direction crossing the extension direction. A first mounting step for providing a first strain gauge; a second mounting step for providing a second strain gauge at a location spaced from the crack on the surface of the test object; and a load on the test object. An output acquisition step of acquiring the outputs of the first strain gauge and the second strain gauge, and a difference calculation for calculating a difference between the outputs of the first strain gauge and the second strain gauge. And a correction step of matching the slopes of the output of the first strain gauge and the output of the second strain gauge in the elastic region between the step and the output acquisition step and the difference calculation step .

  According to such a crack opening behavior acquisition method, the first strain gauge can acquire the strain amount at the center portion of the crack where the deformation amount when the crack opens is the largest in the output acquisition step. . That is, it is possible to acquire the strain amount in the portion where the change in the strain amount when the crack is opened is most easily recognized. In the output acquisition step, the standard strain amount of the test object can be acquired by acquiring with the second strain gauge. After that, by calculating the difference in the difference calculation step, the difference in change between the standard strain amount of the test object when the crack opens and the strain amount in the region including the center of the crack is calculated. can do. The difference calculated in the difference calculation step is calculated because the difference between the strain amount in the region including the center of the crack that has the largest change when the crack opens and the standard strain amount of the test object is calculated. Becomes bigger. As a result, changes can be clarified. And since a change becomes clear, the stress and distortion amount at the time of a crack opening can be acquired with high precision, and the opening behavior of a crack can be detected accurately.

  According to such a crack opening behavior acquisition method, the error due to the test condition can be corrected by correcting the output of the first strain gauge and the output of the second strain gauge in the correction step. That is, in the elastic region, which is the region until the crack opens, the hysteresis loop corrects using the fact that the amount of strain changes linearly with respect to the stress. As a result, the output of the first strain gauge and the output of the second strain gauge in the elastic region can be matched to eliminate the error until the crack opens, and the amount of strain when the crack opens can be reduced. Even if the change is minute, it can be easily detected. Thereby, the opening behavior of the crack can be acquired with higher accuracy.

  Furthermore, in the crack opening behavior acquisition method according to another aspect of the present invention, in the first attachment step, the first strain gauge may be attached so as to cover the entire crack.

  According to such a crack opening behavior acquisition method, the opening behavior can be detected by detecting the strain amount as a whole of the crack extending to the test object. Thereby, the opening behavior of the crack can be acquired with high accuracy even for a crack having a complicated shape whose central portion is unknown.

  Further, the crack opening behavior acquisition method according to another aspect of the present invention is based on the difference between the outputs of the first strain gauge and the second strain gauge based on the difference calculated in the difference calculation step. Based on the opening start point calculation step for calculating an opening start point at which the crack can be considered to start opening, and the difference calculated in the difference calculation step, the maximum value of the difference from the opening start point is calculated as the threshold value. A coefficient calculating step of calculating the opening amount of the crack and calculating a stress intensity factor from the calculated opening amount.

  According to such a crack opening behavior acquisition method, it is possible to accurately detect the point in time when the crack starts to open. In other words, by detecting the timing at which the crack begins to open as the opening start point where the crack can be considered to start opening from the difference between the output of the first strain gauge and the output of the second strain gauge, the crack is opened. This can be easily detected with high accuracy. Further, the opening from the opening start point to the maximum difference is calculated as the crack opening amount. Therefore, it can be acquired as the opening amount how much the crack has opened when the crack opens. Further, since the opening amount can be acquired, it is possible to easily acquire a stress intensity factor that is an index for evaluating whether or not the crack is a crack that propagates. Thereby, the opening behavior of the crack can be detected with higher accuracy.

  Furthermore, in the crack opening behavior acquisition method according to another aspect of the present invention, the stress intensity factor calculated in the coefficient calculating step is a reference stress intensity at which a crack growth rate starts increasing. You may have the crack growth determination process which determines whether it exceeds the coefficient.

  According to such a crack opening behavior acquisition method, it is possible to determine with high accuracy whether or not the crack of the test object is a developing crack. This makes it possible to easily determine with high accuracy whether or not the crack formed on the test object is a harmful crack that has an adverse effect.

  Further, in the crack opening behavior acquisition method according to another aspect of the present invention, the stress intensity factor is determined when it is determined that the stress intensity factor exceeds the reference stress intensity factor in the crack propagation determining step. The crack growth rate is calculated from the above, the length of the crack with the passage of time is estimated, and the time to reach the allowable crack length allowed by the test object is calculated. May be.

  According to such a crack opening behavior acquisition method, the crack growth rate can be easily calculated, and it is possible to easily detect how fast the crack is growing. Based on the calculated crack growth rate, the number of repetitions is calculated, and the crack opening behavior, which is the crack length with the passage of time, is estimated by time conversion from the period in which the load is applied to the test object. Can do. Therefore, it is possible to easily estimate the time until the test object reaches the allowable crack length. Thereby, it is possible to calculate the time until the test object reaches an allowable crack length. That is, it is possible to easily calculate and estimate the time until the test object cannot be used due to a crack formed in the test object. Thereby, it is possible to predict a period until the test object is inspected, a period until the test object is replaced, and the like, and it is possible to take measures before the test object has a fatal effect on the test object.

Furthermore, the crack opening behavior acquisition device according to one aspect of the present invention spans the crack in a direction crossing the extending direction in a region including the center of the extending direction of the crack on the surface of the test object. The first strain gauge attached in this way, the second strain gauge attached at a location away from the crack on the surface of the test object, and when the load is applied to the test object A control unit that estimates an opening behavior of the crack based on outputs of the first strain gauge and the second strain gauge, and the control unit outputs the output of the first strain gauge and the second strain gauge. a difference calculation unit for calculating a correction unit for matching the slope, the difference between the output of the correction unit said first strain gauge and the second strain gauge corrected by the elastic strain range of the output of the gauge, Based on the difference calculated by the difference calculating unit, an opening start point for calculating an opening start point at which the crack can be considered to start opening from a difference in output between the first strain gauge and the second strain gauge Based on the difference calculated by the point calculation unit and the difference calculation unit, the maximum value of the difference from the opening start point is calculated as the opening amount of the crack, and the stress intensity factor is calculated from the calculated opening amount. And a coefficient calculation unit for calculating.

  According to such an opening behavior acquisition device for a crack, it is possible to detect with high accuracy when the crack starts to open. In other words, by detecting the timing at which the crack begins to open as the opening start point where the crack can be considered to start opening from the difference between the output of the first strain gauge and the output of the second strain gauge, the crack is opened. This can be easily detected with high accuracy. Further, the opening from the opening start point to the maximum difference is calculated as the crack opening amount. Therefore, it can be acquired as the opening amount how much the crack has opened when the crack opens. Further, since the opening amount can be acquired, it is possible to easily acquire a stress intensity factor that is an index for evaluating whether or not the crack is a crack that propagates. Thereby, the opening behavior of the crack can be detected with higher accuracy.

  Further, in the crack opening behavior acquisition device according to another aspect of the present invention, the control unit increases a crack growth rate in which the stress intensity factor calculated by the coefficient calculation unit is a rate at which the crack progresses. You may have the crack growth determination part which determines whether it exceeds the reference | standard stress intensity | strength coefficient which begins to do.

  According to such a crack opening behavior acquisition device, it is possible to determine with high accuracy whether or not the crack of the test object is a developing crack. This makes it possible to easily determine with high accuracy whether or not the crack formed on the test object is a harmful crack that has an adverse effect.

  Furthermore, in the crack opening behavior acquisition device according to another aspect of the present invention, when the control unit determines that the stress intensity factor exceeds the reference stress intensity factor in the crack growth determination unit. , Calculating the crack growth rate from the stress intensity factor, estimating the crack length over time, and calculating the time to reach the allowable crack length allowed by the test object You may have a time calculation part.

  According to such a crack opening behavior acquisition device, the crack propagation speed can be easily calculated, and it is possible to easily detect how fast the crack progresses. Based on the calculated crack growth rate, the number of repetitions is calculated, and the crack opening behavior, which is the crack length with the passage of time, is estimated by time conversion from the period in which the load is applied to the test object. Can do. Therefore, it is possible to easily estimate the time until the test object reaches the allowable crack length. Thereby, it is possible to calculate the time until the test object reaches an allowable crack length. That is, it is possible to easily calculate and estimate the time until the test object cannot be used due to a crack formed in the test object. Thereby, it is possible to predict a period until the test object is inspected, a period until the test object is replaced, and the like, and it is possible to take measures before the test object has a fatal effect on the test object.

Further, the crack opening behavior acquisition program according to one aspect of the present invention is a crack opening behavior acquisition program for acquiring the crack opening behavior on the surface of the test object by a computer, using the computer input device. The first output outputted by the first strain gauge arranged on the crack of the test object and the second strain gauge arranged at a position separated from the crack of the test object outputted An input step for acquiring a second output, a correction step for matching the slopes of the first output acquired in the input step and the second output in an elastic region, and the first output corrected in the correction step The crack starts opening from the difference between the first output and the second output based on the difference calculated in the difference calculating step and the difference calculated in the difference calculating step. Shi Based on the difference calculated in the difference calculation step, the opening start point calculation step for calculating the opening start point that can be regarded as, and calculating the maximum value of the difference from the opening start point as the opening amount of the crack, A coefficient calculating step for calculating a stress intensity factor from the calculated opening amount, and a reference stress intensity factor at which a crack growth rate at which the stress intensity factor calculated in the coefficient calculating step starts is increasing. If the stress intensity factor is determined to exceed the reference stress intensity factor in the crack extension determination step and the crack extension determination step, it is determined from the stress intensity factor. A progress time calculating step of calculating a crack growth rate, estimating a crack length with time, and calculating a time required to reach an allowable crack length allowed by the test object; An output step of outputting the calculation result in the time calculation step from the output device of the computer, the causes the computer to perform.

  According to such a crack opening behavior acquisition program, the crack growth rate can be easily calculated, and it can be easily detected how fast the crack progresses. Based on the calculated crack growth rate, the number of repetitions is calculated, and the crack opening behavior, which is the crack length with the passage of time, is estimated by time conversion from the period in which the load is applied to the test object. Can do. Therefore, it is possible to easily estimate the time until the test object reaches the allowable crack length. Thereby, it is possible to calculate the time until the test object reaches an allowable crack length. That is, it is possible to easily calculate and estimate the time until the test object cannot be used due to a crack formed in the test object. Thereby, it is possible to predict a period until the test object is inspected, a period until the test object is replaced, and the like, and it is possible to take measures before the test object has a fatal effect on the test object.

Further, the crack opening behavior acquisition program according to one aspect of the present invention is a crack opening behavior acquisition program for acquiring the crack opening behavior on the surface of the test object by a computer, and the computer uses an input device of the computer. The first output outputted by the first strain gauge arranged on the crack of the test object and the second strain gauge arranged at a position separated from the crack of the test object outputted An input step for acquiring a second output, a correction step for matching the slopes of the first output acquired in the input step and the second output in an elastic region, and the first output corrected in the correction step The crack starts opening from the difference between the first output and the second output based on the difference calculated in the difference calculating step and the difference calculated in the difference calculating step. Based on the difference calculated in the difference calculation step, the opening start point calculation step for calculating the opening start point that can be considered as the maximum, the maximum value of the difference from the opening start point is calculated as the opening amount of the crack, A coefficient calculating step for calculating a stress intensity factor from the calculated opening amount, and a reference stress intensity factor at which a crack growth rate at which the stress intensity factor calculated in the coefficient calculating step starts is increasing. And causing the computer to execute a crack growth determination step for determining whether or not the value exceeds the value, and an output step for outputting the determination result in the crack growth determination step from the output device of the computer.

  According to such an opening behavior acquisition program for a crack, it is possible to determine with high accuracy whether or not the crack of the test object is a developing crack. This makes it possible to easily determine with high accuracy whether or not the crack formed on the test object is a harmful crack that has an adverse effect. And by outputting after a crack growth determination process, it can be judged whether the crack currently formed in the test object is a crack which has a bad influence in a short time.

  According to the crack opening behavior acquisition method of the present invention, it is possible to detect the crack opening behavior with high accuracy by detecting the strain amount in the region including the center of the crack.

It is process drawing explaining the opening behavior acquisition method of the crack which concerns on 1st embodiment of this invention. It is process drawing explaining the opening behavior acquisition program of the crack in the computer calculation process in FIG. It is a schematic diagram explaining the opening behavior acquisition apparatus of the crack which concerns on 1st embodiment of this invention. It is a graph showing the hysteresis loop obtained at the output acquisition process in FIG. It is a graph showing the hysteresis loop obtained by the correction process in FIG. It is a graph showing the hysteresis loop obtained at the difference calculation process in FIG. 3 is a graph showing a relationship between a stress intensity factor and a crack growth rate in FIG. 2. It is a graph showing the relationship between the crack length and the number of repetitions in the crack opening behavior acquisition method according to the first embodiment of the present invention. It is explanatory drawing which shows the data structure of the evaluation table in FIG. It is a schematic diagram explaining the position of the strain gauge attached in the 1st attachment process and the 2nd attachment process in the opening behavior acquisition method of the crack which concerns on 2nd embodiment of this invention. It is process drawing explaining the opening behavior acquisition program of the crack in the computer calculation process of the opening behavior acquisition method of the crack which concerns on 3rd embodiment of this invention.

Hereinafter, a first embodiment according to the present invention will be described with reference to FIGS.
The crack opening behavior acquisition method according to the first embodiment is implemented using a crack opening behavior acquisition device.

  As shown in FIG. 3, the crack opening behavior acquisition device is installed on a test object 1 having a rectangular plate shape on which a crack 2 is formed. The crack 2 formed on the surface of the test object 1 is a micro crack having a width of 1 mm or less and a radius of curvature of the tip portion of 0, and the short direction of the test object 1 having a rectangular plate shape (FIG. 1 paper surface). (Horizontal direction) is extended in parallel. Here, the short direction of the test object 1 in which the crack 2 extends is defined as the extending direction.

  The crack opening behavior acquisition device 5 in this embodiment is a device that acquires the opening behavior of a microcrack on the surface of the test object 1. The crack opening behavior acquisition device 5 is disposed at a position separated from the crack 2 on the surface of the test object 1 and the first strain gauge 3 disposed on the crack 2 on the surface of the test object 1. A second strain gauge 4 and an acquisition device main body 50 that calculates the opening behavior of the crack 2 based on outputs from the first strain gauge 3 and the second strain gauge 4.

  The first strain gauge 3 intersects the crack 2 perpendicularly to the extending direction over a region including the center in the extending direction of the crack 2 on the surface of the test object 1 and a region including one end of the crack 2. It is attached so as to straddle the direction (vertical direction in FIG. 3). The 1st strain gauge 3 uses the well-known strain gauge which can measure the distortion | strain of arbitrary places. That is, the first strain gauge 3 applies a constant load to the test object 1 and outputs a strain amount ε with respect to the loaded load. This strain amount ε is output as a hysteresis loop by drawing it as a stress-strain curve. Here, the output from the first strain gauge 3 is defined as a first output D1.

  The second strain gauge 4 is affixed at a location spaced apart from the crack 2 on the surface of the test object 1. The second strain gauge 4 is the same strain gauge as the first strain gauge 3 and outputs a strain amount ε with respect to the load applied to the test object 1. Here, the output from the second strain gauge 4 is defined as a second output D2.

  The acquisition device main body 50 is a computer, a CPU 6 that performs various calculations, a memory 51 that serves as a work area of the CPU 6, an auxiliary storage device 7 such as a hard disk drive device, a manual input device 52 such as a keyboard and a mouse, Strain for transmitting and receiving data among the display device 53 (output device), the manual input device 52 and the input / output interface 54 of the display device 53, and the first strain gauge 3 and the second strain gauge 4. A gauge interface 55 (input device), a communication interface 56 for communicating with the outside via a network I such as the Internet, and a storage / reproduction device 57 for performing data storage processing and reproduction processing on the disk-type storage medium D And.

  The auxiliary storage device 7 has a crack opening for acquiring the opening behavior of the crack 2 from the first output D1 and the second output D2 actually measured by the first strain gauge 3 and the second strain gauge 4. A behavior acquisition program 71 and an OS (Operating System) program 72 are stored in advance. The crack opening behavior acquisition program 71 and the OS program 72 are taken into the auxiliary storage device 7 from the disk type storage medium D via the storage / reproduction device 57, for example. The crack opening behavior acquisition program 71 and the OS program 72 may be taken into the auxiliary storage device 7 from an external device via the communication interface 56.

  The auxiliary storage device 7 further stores various data in the course of executing the crack opening behavior acquisition program 71. Specifically, the first output D1 output from the first strain gauge 3, the second output D2 output from the second strain gauge 4, and the auxiliary storage device 7 further include an execution program execution process. Thus, an evaluation table 73 as shown in FIG. 9 is created, and data related to the opening behavior of the crack 2 are stored in the evaluation table 73.

Further, the auxiliary storage device 7 stores the data of the reference stress intensity factor ΔK _th determined for each material and the allowable crack length determined for each test object 1 before executing the crack opening behavior acquisition program 71. the specific data to be a function of the material and shape of the test object 1 such as data of a _m is manual input device 52, it is stored by being input by the communications interface 56 and the storage and playback device 57.

The CPU 6 is a control unit in the acquisition apparatus main body 50 and has a plurality of functional units. The CPU 6 corrects by the input unit 61 that acquires the first output D1 and the second output D2, the correction unit 62 that corrects the inclinations in the elastic regions of the first output D1 and the second output D2, and the correction unit 62. And a difference calculating unit 63 that calculates a difference between the first output D1 and the second output D2. The CPU 6 calculates the opening start point A from the first output D1 and the second output D2 based on the difference obtained by the difference calculation unit 63, and the difference obtained by the difference calculation unit 63. The CPU 6 includes a coefficient calculation unit 65 that calculates a stress intensity factor ΔK based on the above, and a crack propagation determination that determines whether the stress intensity factor ΔK calculated by the coefficient calculator 65 exceeds the reference stress intensity factor ΔK _th and parts 66, with the progress time calculator 67 for calculating the time to reach acceptable crack length a _m based on the judging result of the crack propagation determination unit 66, displays the calculated results in the development time calculator 67 53 And an output unit 68 to be displayed.

  Each of these functional units functions when the CPU 6 executes the crack opening behavior acquisition program 71 stored in the auxiliary storage device 7.

  Next, a crack opening behavior acquisition method using the crack opening behavior acquisition device 5 described above will be described with reference to the process diagram shown in FIG.

  As shown in FIG. 1, the crack opening behavior acquisition method S <b> 10 includes a first attachment step S <b> 1 in which a first strain gauge 3 is provided in a region including the center in the extending direction of the crack 2 on the surface of the test object 1. And the 2nd attachment process S2 which provides the 2nd strain gauge 4 in the location away from the crack 2 in the surface of the test object 1, and the output of the 1st strain gauge 3 and the 2nd strain gauge 4 is acquired. An output acquisition step S3 and a computer calculation step S4 for calculating and acquiring the opening behavior of the crack 2 by a computer based on the outputs of the first strain gauge 3 and the second strain gauge 4 obtained in the output acquisition step S3. And have.

  As shown in FIG. 3, the first attachment step S <b> 1 is a direction that intersects the crack 2 perpendicularly to the extending direction over a region including the center in the extending direction of the crack 2 and a region including one end of the crack 2. 1st strain gauge 3 is stuck so that it may straddle. That is, in the first attachment step S1, the first strain gauge 3 is attached to the crack 2 on the surface of the test object 1 so as to cover a range beyond the center portion from the tip of the crack 2. ing.

  As shown in FIG. 3, the second attachment step S <b> 2 is provided by attaching a second strain gauge 4 to a location at a certain distance from the crack 2 on the surface of the test object 1. The second strain gauge 4 may be placed anywhere as long as it is separated from the crack 2, but in order to avoid the influence of the crack 2, a place separated from the crack 2 by one or more widths of the strain gauge. It is preferable to arrange in.

In the output acquisition step S3, after performing the first attachment step S1 and the second attachment step S2, a constant load is applied to the test object 1, and the first output D1 of the first strain gauge 3 corresponding to the loaded load. And the 2nd output D2 of the 2nd strain gauge 4 is acquired. The first output D1 and the second output D2 are strain amounts ε obtained by a strain gauge under a loaded load, and are output as a hysteresis loop as shown in FIG. 4 by drawing as a stress-strain curve.
As shown in FIG. 4, when the hysteresis loops of the first output D1 and the second output D2 obtained in the output acquisition step S3 are compared, the first output D1 obtained by measuring the strain amount ε of the crack 2 When 2 opens, the stress σ does not increase even when a load is applied, and only the strain amount ε increases. Therefore, although the first strain gauge 3 and the second strain gauge 4 are provided on the same test object 1 and are loaded with the same load, the first output D1 is more than the second output D2. Also, the maximum strain amount ε _max is output large.
The load applied to the test object 1 may be any load that displaces the crack 2 in the direction to open the crack 2, and is simply orthogonal to the extending direction of the crack 2 with respect to the test object part. A tensile test may be performed in the direction in which the test object 1 is bent, and a bending test may be performed so that the test object 1 is bent.

Next, the computer calculation step S4, which is the operation of the acquisition apparatus main body 50, will be described together with details of each functional unit of the CPU 6 according to the step diagram shown in FIG.
In the computer calculation step S4, the first output D1 and the second output D2 acquired in the output acquisition step S3 are taken into the acquisition device body 50, and the opening behavior of the crack 2 is processed by the acquisition device body 50, which is a computer. Run to get. The computer calculation step S4 includes an input step S41 for capturing the first output D1 and the second output D2 acquired in the output acquisition step S3 by the input device of the acquisition device body 50, the first output D1 obtained in the input step S41, and A correction step S42 for matching the slopes of the second output D2 in the elastic region and a difference calculation step S43 for calculating a difference between the first output D1 and the second output D2 corrected in the correction step S42. The computer calculation step S4 calculates an opening start point calculation step for calculating an opening start point A from which the crack 2 starts opening from the difference between the first output D1 and the second output D2 from the difference obtained in the difference calculation step S43. S44 and a coefficient calculation step S45 for calculating the stress intensity factor ΔK from the difference obtained in the difference calculation step S43. Computer calculation step S4 is crack 2 is crack propagation rate-out determines whether increased start reference stress intensity factor [Delta] K _th stress intensity factor [Delta] K was calculated exceeds crack growth evaluation step at a speed S46 of progress When, can on the basis of the determination result in crack growth determination step S46, the allowable-out and development time calculation step S47 of calculating the time to reach crack length a _m, acquiring apparatus the calculated time body to allow the test object 1 Output step S48 to output from 50 display devices 53. The computer calculation step S4 is performed by the acquisition device body 50 by executing the crack opening behavior acquisition program 71 through the above-described plurality of steps.

  In the input step S41, the first output D1 output from the first strain gauge 3 arranged in the first attachment step S1 on the crack 2 of the test object 1 and the position separated from the crack 2 of the test object 1. The second output D2 output from the second strain gauge 4 arranged in the second attachment step S2 is acquired by the output acquisition step S3, and then acquired by the acquisition device body 50 by the input unit 61.

  Specifically, in the input step S <b> 41, the first output D <b> 1 and the second output D <b> 2 captured by the strain gauge interface 55 that is an input device of the acquisition device main body 50 are stored in the auxiliary storage device 7. In the present embodiment, the input unit 61 is one of functional units of the CPU 6.

  In the correction step S42, as shown in FIG. 5, the second output D2 acquired in the output acquisition step S3 and taken into the acquisition device main body 50 in the input step S41 is made to coincide with the inclination of the first output D1 in the elastic region. The correction unit 62 corrects the error.

  Specifically, in the correction step S42, the correction unit 62 matches the slope in the elastic region of the hysteresis loop drawn as the stress-strain curve by the first output D1 and the second output D2 acquired by the input unit 61. Correct the value. And the correction | amendment part 62 correct | amends so that the 2nd output D2 may be multiplied, and makes the elastic region which is a linear part of the hysteresis loop of the 2nd output D2 correspond with the elastic region of the 1st output D1. This utilizes the fact that the first output D1 and the second output D2 are outputs from a strain gauge provided on the same test object 1. That is, in the elastic region that is a region until the crack 2 is opened, theoretically, the strain amount ε of the hysteresis loop linearly changes with respect to the stress σ. Therefore, in the correction step S42, the correction unit 62 performs the second adjustment so that the inclination of the elastic region of the hysteresis loop obtained by the first output D1 and the inclination of the elastic region of the hysteresis loop obtained by the second output D2 match. Correction is performed by multiplying the value of the output D2 by an arbitrary multiplier. The correction unit 62 in the present embodiment is one of the function units of the CPU 6.

  In the difference calculating step S43, as shown in FIG. 6, the difference calculating unit 63 calculates the difference between the second output D2 and the first output D1 corrected by the correcting step S42 so that the slopes in the elastic region of the hysteresis loop coincide with each other. calculate.

  Specifically, in the difference calculation step S43, the difference calculation unit 63 draws a stress-strain curve based on the difference between the first output D1 and the second output D2 corrected by the correction unit 62, thereby correcting the step S42. Thus, in the elastic region where the first output D1 and the second output D2 are matched, a differential hysteresis loop having a strain of 0 can be obtained even if the stress σ changes. In the difference calculation step S <b> 43, the difference calculation unit 63 calculates a difference strain amount Δε that is a difference between the corrected second output D <b> 2 and the first output D <b> 1 and stores it in the evaluation table 73 of the auxiliary storage device 7. Then, even if the stress σ changes in the elastic region in the range in which the first output D1 and the second output D2 coincide with each other based on the calculated differential strain amount Δε, the difference calculation unit 63 does not change the differential strain amount Δε. Calculate a differential hysteresis loop of zero. The difference calculation unit 63 in the present embodiment is one of functional units of the CPU 6.

  In the opening start point calculating step S44, as shown in FIG. 6, based on the difference calculated in the difference calculating step S43, it can be considered that the crack 2 has started opening from the difference between the first output D1 and the second output D2. The opening start point A is calculated by the opening start point calculation unit 64.

  Specifically, in the opening start point calculating step S44, the opening start point calculating unit 64 uses the first output D1 from the difference hysteresis loop drawn by the difference calculating step S43 based on the difference calculated by the difference calculating unit 63. A change point where the difference εε starts to change and the difference strain εε changes is calculated as an opening start point A. The opening start point calculation unit 64 in the present embodiment is one of the functional units of the CPU 6.

  When the crack 2 starts to open, the displacement due to the opening of the crack 2 is output as the first output D1 of the first strain gauge 3 in addition to the elongation of the material. Therefore, when the crack 2 is opened, the first output D1 starts to deviate from the second output D2, which is the standard strain amount ε of the test object 1. Therefore, it is possible to determine that the crack 2 has been opened by detecting, as the opening start point A, the changing point at which a difference in the differential strain amount Δε starts to occur in the differential hysteresis loop.

  Then, the opening start point calculation unit 64 calculates, as the opening start point A, a change point at which the differential strain amount Δε that is the difference stored in the evaluation table 73 starts to change, and stores it in the evaluation table 73 of the auxiliary storage device 7. .

Thereafter, in the opening start point calculating step S44, the opening start point A is calculated by the opening start point calculating unit 64, and the opening stress σ _A and the opening strain amount ε _A are calculated.

Specifically, in the opening start point calculating step S44, as shown in FIG. 6, the opening start point calculating unit 64 calculates the stress σ at the opening start point A from the differential hysteresis loop and the opening stress at which the crack 2 starts to open. Calculated as σ _A.

Here, the opening stress σ _A is obtained from the differential strain amount Δε at the opening start point A among the differential strain amounts Δε calculated as the difference between the strain amount ε of the first output D1 and the strain amount ε of the second output D2. This is the calculated stress σ. At the same time, as shown in FIG. 5, the opening strain amount ε _A corresponding to the opening stress σ _A and the strain amount ε at which the crack 2 starts to open corresponding to the opening start point _A is calculated.

In the opening start point calculating step S44, the opening start point calculating unit 64 calculates the stress σ corresponding to the differential strain amount Δε at the opening start point A stored in the evaluation table 73 as the opening stress σ _A , and stores the auxiliary memory. Stored in the evaluation table 73 of the device 7. Further, the opening start point calculation unit 64 calculates the strain amount ε corresponding to the opening stress σ _A from the first output D1 as the opening strain amount ε _A and stores it in the evaluation table 73 of the auxiliary storage device 7. As a result, in the opening start point calculation step S44, the opening stress σ _A and the opening strain amount ε _A when the crack 2 opens are acquired.

  As shown in FIG. 6, the coefficient calculation step S45 is a coefficient as the opening amount δ of the crack 2 based on the difference calculated in the difference calculation step S43 and the opening start point A calculated in the opening start point calculation step S44. The calculation unit 65 calculates the stress intensity factor ΔK from the opening amount δ.

Specifically, in the coefficient calculation step S45, the coefficient calculation unit 65 calculates the opening amount δ based on the difference strain amount Δε that is the difference stored in the evaluation table 73 calculated in the difference calculation step S43, It is stored in the evaluation table 73 of the storage device 7. The opening amount δ is calculated as a maximum differential strain amount Δε _max that is a change amount from the differential strain amount Δε at the opening start point A to the maximum value of the differential strain amount Δε. The coefficient calculation unit 65 in the present embodiment is one of functional units of the CPU 6.

  Thereafter, in the coefficient calculation step S45, the coefficient calculation unit 65 calculates the stress intensity factor ΔK using the equation (1) based on the calculated opening amount δ.

Here, the Young's modulus E and the yield stress σ _y are constants depending on the material of the test object 1 and are determined in advance by the test object 1 to be used. Although the Young's modulus E and the yield stress σ _y are not shown, they may be manually input to the auxiliary storage device 7 by the manual input device 52, and are automatically input by the communication interface 56 and the storage / reproduction device 57. May be entered.

Then, the coefficient calculation unit 65 calculates the stress intensity factor ΔK using the above equation (1) based on the opening amount δ, the Young's modulus E and the yield stress σ _y stored in the auxiliary storage device 7. And stored in the evaluation table 73 of the auxiliary storage device 7.

In the crack growth determination step S46, it is determined whether or not the stress intensity factor ΔK calculated in the coefficient calculation step S45 exceeds the reference stress intensity factor ΔK _{th at} which the crack growth rate, which is the rate at which the crack 2 propagates, starts to increase. The crack propagation determination unit 66 makes the determination.

As shown in FIG. 7, the crack growth rate begins to increase the stress intensity factor [Delta] K exceeds the reference stress intensity factor [Delta] K _th. When the crack growth rate increases, the crack 2 will grow. However, if the crack growth rate does not increase, the crack 2 does not propagate. That is, when the calculated stress intensity factor ΔK does not exceed the reference stress intensity factor ΔK _th , the crack growth rate does not increase, and the crack 2 for which the stress intensity factor ΔK is calculated has a longer crack length. It turns out that it is the crack 2 which does not propagate to a. Conversely, when the calculated stress intensity factor ΔK exceeds the reference stress intensity factor ΔK _th , the crack growth rate increases, and the crack 2 for which the stress intensity factor ΔK is calculated is equal to or greater than the crack length a. It can be seen that this crack 2 propagates.

Therefore, in the crack growth determination step S46, the crack growth determination unit 66 compares the stress intensity factor ΔK stored in the auxiliary storage device 7 with the reference stress intensity factor ΔK _th so that the crack 2 It is determined whether or not the above progresses. If the crack propagation determination unit 66 determines that the stress intensity factor ΔK exceeds the reference stress intensity factor ΔK _th , a signal is output to the propagation time calculation unit 67, and then the propagation time calculation step S47 is performed. On the other hand, in the crack growth determination step S46, if it is determined that the stress intensity factor [Delta] K does not exceed the reference stress intensity factor [Delta] K _th, and outputs a signal to the input unit 61, carrying out the input step S41 again.

The reference stress intensity factor ΔK _th is a constant that depends on the material of the test object 1 to be used, and is determined in advance by the test object 1 to be used. The reference stress intensity factor ΔK _th may be manually input to the auxiliary storage device 7 by the manual input device 52, or may be automatically input to the auxiliary storage device 7 by the communication interface 56 or the storage / reproduction device 57.

In the progress time calculation step S47, the crack growth rate is calculated by the progress time calculation unit 67 from the stress intensity factor ΔK based on the determination result in the crack growth determination step S46. The evolution in time calculation step S47, the time elapsed and estimating crack 2 crack length a of Ki caused, the test object 1 progress time to reach acceptable crack length a _m tolerated time calculator 67 Calculate with

Acceptable crack length a _m is a value determined depending on the material and shape of the test object 1, is predetermined by the test object 1 to be used. That is, the allowable crack length a _m is the crack length a of the acceptable limit on the use of the test object 1. Exceeding the crack length a _m, the crack 2 that is formed in the test structure, the function of the test object 1 is considered corrupted impaired. Acceptable crack length a _m may be manually entered into the auxiliary storage device 7 by manual input device 52 may be entered automatically in the auxiliary storage device 7 by the communication interface 56 and the storage and playback device 57.

Specifically, first, in the progress time calculating step S47, when it is determined in the crack progress determining step S46 that the stress intensity factor ΔK exceeds the reference stress intensity factor ΔK _th , the progress time calculating unit 67 Using the equation (2), the crack growth rate is calculated from the stress intensity factor ΔK stored in the auxiliary storage device 7 and stored in the evaluation table 73 of the auxiliary storage device 7.
The crack growth rate is the amount of crack 2 developed when a constant load is applied to the test object 1 for one cycle in the output acquisition step S3.

  Here, da / dN is the crack growth rate. The material constant C and the material constant m are constants depending on the material of the test object 1 and are determined in advance by the test object 1 to be used. Although C and m are not shown, they may be manually input to the auxiliary storage device 7 by the manual input device 52, or may be automatically input to the auxiliary storage device 7 by the communication interface 56 or the storage / reproduction device 57. Good.

  And based on (3) Formula and the said (2) Formula, (4) Formula is guide | induced.

  Here, the shape constant f is a constant depending on the shape of the test object 1 and is determined in advance by the test object 1 to be used. Although not shown, the shape constant f may be manually input to the auxiliary storage device 7 by the manual input device 52, or may be automatically input to the auxiliary storage device 7 by the communication interface 56 or the storage / reproduction device 57. Good.

In progress time calculation step S47, based on the (4) equation, calculated the progress time calculator 67, the repetition number N required to develop into crack length a _x-1 Crack 2 brat crack length a _x And stored in the evaluation table 73 of the auxiliary storage device 7.
Similarly, the relationship between the number of repetitions N and the crack length a calculated by the progress time calculation unit 67 based on the equation (4) over a plurality of times for each predetermined crack length a is as shown in FIG. Become. Thereby, in progress time calculation process S47, the change of the crack length a accompanying the increase in the repetition number N is estimated. And the repetition number N can be converted into the time t from the period which loads a test object 1 in output acquisition process S3. Therefore, the propagation time calculation unit 67 can estimate the opening behavior of the crack 2 that is the propagation length of the crack 2 over time. Thereby, in progress time calculation process S47, the progress time calculation part 67 calculates time t based on the graph of FIG. 8, and stores it in the evaluation table 73 of the auxiliary storage device 7.

Thereafter, development time calculator 67 calculates the allowable number of repetitions N _m to reach the permissible crack length a _m. By converting the calculated allowable number of iterations N _m, progress time calculator 67 calculates the allowable time t _m is the time t required to reach the acceptable crack length a _m.

  In the output step S48, data of the evaluation table 73 as shown in FIG. 9 in which the time t which is the calculation result in the progress time calculation step S47 is stored is output from the display device 53 of the acquisition device main body 50 by the output unit 68.

Specifically, in the output step S48, the output unit 68 causes the acquisition device body 50 to execute the crack opening behavior acquisition program 71 in the computer calculation step S4, the differential strain amount Δε, the opening start point A, An opening stress σ _A , an opening strain amount ε _A , an opening amount δ, a stress intensity factor ΔK, a crack growth rate, a repetition rate N, and a time t are output. That is, the output unit 68 causes the display device 53 to display and output the evaluation table 73 stored in the auxiliary storage device 7 by the input / output interface 54 that is the output device of the acquisition device main body 50.

According to the crack opening behavior acquisition method S10 as described above, in the first attachment step S1, the center in the extending direction of the crack 2 is included so as to cover the range beyond the center portion from the tip of the crack 2. The first strain gauge 3 can be provided so as to straddle the crack 2 in a direction perpendicular to the extending direction of the region. Therefore, by the output acquisition step S3, the strain amount ε at the center of the crack 2 where the amount of deformation when the crack 2 opens can be acquired as the first output D1 by the first strain gauge 3. . That is, it is possible to obtain the strain amount ε at the portion where the change in the strain amount ε when the crack 2 opens is most easily recognized.
Moreover, in output acquisition process S3, it acquires as 2nd output D2 with the 2nd strain gauge 4 provided in the position spaced apart from the crack 2 with the 1st output D1 which is the output of the 1st strain gauge 3. FIG. Thus, the standard strain amount ε of the test object 1 that is the strain amount ε in the region without the crack 2 can be obtained.

Thereafter, in the difference calculation step S43, a standard strain amount of the test object 1 when the crack 2 is opened is obtained by obtaining a differential strain amount Δε which is a difference between the first output D1 and the second output D2. The difference in change between ε and the strain amount ε in the region including the center in the extending direction of the crack 2 can be calculated. Since the difference between the strain amount ε in the region including the center in the extending direction of the crack 2 having the largest change amount when the crack 2 is opened and the standard strain amount ε of the test object 1 is calculated. The difference between the first output D1 and the second output D2 calculated in the difference calculation step S43 becomes large, and the opening start point A becomes clear and can be detected accurately. Since the opening start point A can be detected accurately, the opening stress σ _A and the opening strain amount ε _A when the crack 2 opens can be obtained with high accuracy, and when the crack 2 has opened. The opening behavior of the crack 2 can be accurately detected. As a result, the opening behavior of the crack 2 can be detected with high accuracy.

  Further, by correcting and matching the first output D1 output from the first strain gauge 3 and the second output D2 output from the second strain gauge 4 by the correction step S42, errors due to test conditions are reduced. It can be corrected. That is, even if the first strain gauge 3 and the second strain gauge 4 are provided by being attached to the same test object 1, some errors occur when the tensile test or the like is actually performed. This error always occurs due to various factors such as the test environment and how to attach the strain gauge. Therefore, in the elastic region, which is the region until the crack 2 opens, the hysteresis loop changes the strain amount ε linearly with respect to the stress σ, and the first output D1 and the second output in the correction step S42. It correct | amends so that the inclination in the elastic region with D2 may be united. As a result, the first output D1 and the second output D2 in the elastic region can be matched, and errors due to the test environment until the crack 2 opens can be removed, and the strain amount ε when the crack 2 opens Even if the change of is small, it can be easily detected. Thereby, the opening behavior of the crack 2 can be acquired with higher accuracy.

Furthermore, by calculating the opening start point A where the difference between the first output D1 and the second output D2 starts to occur based on the difference strain amount Δε calculated in the difference calculating step S43, the time point when the crack 2 starts to open Can be detected with high accuracy. That is, by detecting the timing at which the crack 2 starts to open as the opening start point A at which the difference between the first output D1 and the second output D2 starts to occur, it is easy to detect that the minute crack 2 that cannot be visually observed has opened. It can be detected with high accuracy. Then, by calculating the stress σ and the strain amount ε at the opening start point A as the opening stress σ _A and the opening strain amount ε _A , information on the crack 2 at the time when the crack 2 opened can be obtained with high accuracy. . As a result, the opening behavior of the crack 2 can be detected with higher accuracy.

Further, from the differential strain amount Δε at the opening start point A to the maximum value of the differential strain amount Δε based on the differential strain amount Δε calculated in the difference calculating step S43 and the opening start point A calculated in the opening start point calculating step S44. Is calculated as the opening amount δ of the crack 2. Therefore, not only the opening stress σ _A and the opening strain amount ε _A at the time when the crack 2 opens, but also how much the crack 2 has opened can be acquired as the opening amount δ. In addition, since the opening amount δ can be acquired, the stress intensity factor ΔK that is an index for evaluating whether the crack 2 is a crack 2 that propagates can be easily acquired. Thereby, the opening behavior of the crack 2 can be detected with higher accuracy.

Furthermore, compared with the calculated stress intensity factor [Delta] K of the crack growth rate expansion increased start reference stress factor [Delta] K _th, determines whether exceeds the reference stress intensity factor [Delta] K _th. Thereby, it is possible to determine with high accuracy whether or not the crack 2 of the test object 1 is the crack 2 that propagates. That is, the crack 2 having the stress intensity factor ΔK does not progress until the stress intensity factor ΔK exceeds the reference stress intensity factor ΔK _{th at} which the crack growth rate starts to increase. Even if such a crack 2 is formed on the surface of the test object 1, there is very little risk of adverse effects such as damage to the test object 1 without taking countermeasures. Therefore, by comparing the stress intensity factor ΔK and the reference stress intensity factor ΔK _th , it is easily determined with high accuracy whether or not the crack 2 formed on the test object 1 is a harmful crack 2 that has an adverse effect. it can.

Further, the crack growth rate can be easily calculated by the stress intensity factor ΔK, and it is possible to easily detect how fast the crack 2 is growing. Then, by calculating the number of repetitions N based on the calculated crack growth rate, the number of repetitions N required until the crack 2 reaches a certain crack length a can be easily calculated. That is, it is possible to easily estimate the change in the crack length a as the number of repetitions N increases. In addition, the number of repetitions N can be time-converted from the period in which the load is applied to the test object 1 in the output acquisition step S3, so that the crack 2 opening behavior that is the crack length a with time can be estimated. Accordingly, it is easily possible to also estimate the time period until the test object 1 reaches the allowable crack length a _m. Accordingly, by calculating the time until the test object 1 reaches the allowable crack length a _m acceptable, the time until the test object 1 can not be used by the crack 2 Taki formed in the test object 1 It can be easily calculated and estimated. That is, it is possible to predict a period until the test object 1 is inspected, a period until it is replaced, and the like, and measures can be taken before the crack 2 causes a fatal influence on the test object 1.

Next, the crack opening behavior acquisition method S10 of the second embodiment will be described with reference to FIG.
In the second embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof is omitted. In the crack opening behavior acquisition method S10 according to the second embodiment, the crack 2 having a complicated shape is formed on the surface of the test target portion, and the position where the first strain gauge 3 is attached to the crack 2 Is different from the first embodiment.

  That is, as shown in FIG. 10, in the second embodiment, the test object 1 is not a crack 2 that extends in a straight line in the extending direction, but a plurality of microcracks 2 gather to form a microcrack group 21. ing. Examples of such a microcrack group 21 include a set of microcracks 2 formed so as to sew gaps between crystal grains during stress σ corrosion cracking.

  And in 1st attachment process S1, unlike the first embodiment, the 1st strain gauge 3 is affixed and provided so that the whole microcrack group 21 may be covered. In the first mounting step S <b> 1 in the second embodiment, the microcracks 21 are formed in a direction perpendicular to the extending direction from one end of the crack 2 to the other end so as to completely cover the microcracks 21. The first strain gauge 3 is pasted in a straddling manner. That is, in the first attachment step S1 in the second embodiment, the first strain gauge 3 is attached and provided so that the microcracks 21 on the surface of the test object 1 are completely hidden.

According to the crack opening behavior acquisition method S10 as described above, the opening behavior is detected by detecting the strain amount ε as a whole of the microcrack group 21 which is the crack 2 extending to the test object 1. can do. That is, for each microcrack 2 forming the microcrack group 21, even if the strain amount ε that changes at the time of opening is small, the microcrack group 21 that is a set of microcracks 2 has a large strain amount ε. Has changed. Therefore, the first strain gauge 3 is attached so as to cover the entire microcrack group 21, thereby detecting a large strain amount ε as the microcrack group 21 that is a set of microcracks 2. Thus, the opening start point A can be accurately detected. Therefore, the opening stress σ _A and the opening strain amount ε _A when the crack 2 opens can be obtained with high accuracy. As a result, the opening behavior of the crack 2 can be obtained with high accuracy even for the microcrack group 21 having a complicated shape in which the central portion of the crack 2 is unknown.
Note that the crack 2 to which the first strain gauge 3 is attached in the first mounting step S1 in the second embodiment is not limited to the microcrack group 21, and for example, as in the first embodiment. It may be a crack 2 extending in the extending direction.

Next, the crack opening behavior acquisition program 71 of the third embodiment will be described with reference to FIG.
In the third embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof is omitted. The crack opening behavior acquisition program 71 of the third embodiment is different from the first embodiment in that the output step S48 is performed after the crack propagation determination step S46.

That is, as shown in FIG. 11, the second computer operation step S40 in the third embodiment performs the second output step S481 without performing the propagation time calculation step S47 after the crack propagation determination step S46.
Unlike the output step S48, the second output step S481 causes the output unit 68 to output the determination result of the crack growth determination step S46 from the display device 53 of the acquisition device main body 50. That is, in the second output step S481, the output unit 68 calculates the differential strain amount Δε, the opening start point A, the opening calculated by the acquisition device body 50 executing the crack opening behavior acquisition program 71 in the computer calculation step S4. The stress σ _A , the opening strain amount ε _A , the opening amount δ, the stress intensity factor ΔK, and the determination result are displayed on the display device 53 and output.

According to the crack opening behavior acquisition program 71 as described above, the calculated stress intensity factor ΔK exceeds the reference stress intensity factor ΔK _th when compared with the reference stress intensity factor ΔK _{th at} which the crack growth rate starts to increase. It is determined whether or not. Thereby, it is possible to determine with high accuracy whether or not the crack 2 of the test object 1 is the crack 2 that propagates. That is, the crack 2 having the stress intensity factor ΔK does not progress until the stress intensity factor ΔK exceeds the reference stress intensity factor ΔK _{th at} which the crack growth rate starts to increase. Even if such a crack 2 is formed on the surface of the test object 1, there is very little risk of adverse effects such as damage to the test object 1 without taking countermeasures. Therefore, by comparing the stress intensity factor ΔK and the reference stress intensity factor ΔK _th , it is easily determined with high accuracy whether or not the crack 2 formed on the test object 1 is a harmful crack 2 that has an adverse effect. it can. Then, by outputting after the crack growth determination step S46, it is possible to determine whether or not the crack 2 formed on the test object in a short time is the crack 2 that has an adverse effect.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and omission of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible. Further, the present invention is not limited by the embodiments, and is limited only by the scope of the claims.

The correction step S42 is not limited to matching the output of the second strain gauge 4 with the output of the first strain gauge 3, and for example, the output of the first strain gauge 3 is reversed to the second. The output of the first strain gauge 3 and the output of the second strain gauge 4 may be corrected together.
The crack 2 may be a scratch or a crack generated on the surface of the material, or may be a minute hole after the inclusion in the material is removed.
Further, the crack 2 is not limited to the one extending in the short direction of the test object 1 in the present embodiment. For example, the crack 2 is inclined with respect to the short direction of the test object 1 in the present embodiment. It may be extended.
Furthermore, each step performed in the computer calculation step S4 is not limited to being automatically performed by a computer, and necessary information may be calculated by manually performing each step.

DESCRIPTION OF SYMBOLS 1 ... Test object 2 ... Crack 5 ... Crack opening behavior acquisition apparatus 3 ... 1st strain gauge D1 ... 1st output 4 ... 2nd strain gauge D2 ... 2nd output D ... Disc type storage medium I ... Network 50 ... Acquisition device main body 6 ... CPU 61 ... Acquisition unit σ ... Strain amount ε ... Stress 62 ... Correction unit 63 ... Difference calculation unit Δε ... Differential strain amount 64 ... Opening start point calculation unit A ... Opening start point σ _A ... Opening Stress ε _A ... Opening strain amount 65 ... Coefficient calculation unit δ ... Opening amount Δε _max ... Maximum differential strain amount ΔK ... Stress intensity factor a ... Crack length 66 ... Crack growth determination part ... Reference stress intensity factor 67 ... Progress time calculation Part N ... Number of repetitions a _m ... Permissible crack length t ... Permissible time 68 ... Output part 51 ... Memory 7 ... Auxiliary storage device 71 ... Crack opening behavior acquisition program 72 ... OS program ΔK _th ... Reference stress intensity factor 73 ... Evaluation table 52 ... Manual input device 53 ... Display device 54 ... Input / output interface 55 ... Strain gauge interface 56 ... Communication interface 57 ... Storage / reproduction device S10 ... Method of acquiring crack opening behavior S1 ... First mounting step S2 ... Second Mounting process S3 ... Output process ε _max ... Maximum strain amount S4 ... Computer calculation process S41 ... Acquisition process S42 ... Correction process S43 ... Difference calculation process S44 ... Opening start point calculation process S45 ... Coefficient calculation process S46 ... Crack growth determination process S47 ... Progress time calculation step S48 ... Output step 21 ... Small crack group S40 ... Second computer calculation step S481 ... Second output step

Claims (10)

A first attachment step of providing a first strain gauge in a region including the center of the crack extending direction on the surface of the test object so as to straddle the crack in a direction crossing the extending direction;
A second mounting step of providing a second strain gauge at a location spaced from the crack on the surface of the test object;
An output acquisition step of acquiring outputs of the first strain gauge and the second strain gauge when a load is applied to the test object;
A difference calculating step for calculating a difference between outputs of the first strain gauge and the second strain gauge;
Between the output acquisition step and the difference calculation step, a correction step of matching the slope in the elastic region between the output of the first strain gauge and the output of the second strain gauge;
A crack opening behavior acquisition method comprising: 2. The crack opening behavior acquisition method according to claim 1 , wherein in the first attaching step, the first strain gauge is attached so as to cover the entire crack. Based on the difference calculated in the difference calculation step, an opening start point for calculating an opening start point at which the crack can be considered to start opening from a difference in output between the first strain gauge and the second strain gauge A point calculation step;
A coefficient calculation step of calculating a maximum value of the difference from the opening start point as an opening amount of the crack based on the difference calculated in the difference calculating step, and calculating a stress intensity factor from the calculated opening amount. The crack opening behavior acquisition method according to claim 1 or 2 , wherein: A crack growth determination step of determining whether or not the stress intensity factor calculated in the coefficient calculation step exceeds a reference stress intensity factor at which a crack growth rate at which the crack propagates starts to increase; The crack opening behavior acquisition method according to claim 3 , wherein: When it is determined that the stress intensity factor exceeds the reference stress intensity factor in the crack growth determination step, the crack growth rate is calculated from the stress intensity factor, and the length of the crack over time The crack opening behavior acquisition method according to claim 4 , further comprising a progress time calculation step of calculating a time until the allowable crack length allowed by the test object is reached by estimating the length. A first strain gauge attached to a region including the center of the crack extending direction on the surface of the test object so as to straddle the crack in a direction crossing the extending direction;
A second strain gauge attached to a location spaced from the crack on the surface of the test object;
A controller for estimating the opening behavior of the crack based on the outputs of the first strain gauge and the second strain gauge when a load is applied to the test object;
The controller is
A correction unit that matches the slope in the elastic region between the output of the first strain gauge and the output of the second strain gauge;
A difference calculating unit for calculating a difference between outputs of the first strain gauge and the second strain gauge corrected by the correcting unit ;
Based on the difference calculated by the difference calculation unit, an opening start for calculating an opening start point at which the crack can be considered to start opening from a difference in output between the first strain gauge and the second strain gauge A point calculator,
A coefficient calculation unit that calculates the maximum value of the difference from the opening start point as the opening amount of the crack based on the difference calculated by the difference calculating unit, and calculates a stress intensity factor from the calculated opening amount And a crack opening behavior acquisition device. The control unit determines whether or not the stress intensity factor calculated by the coefficient calculation unit exceeds a reference stress intensity factor at which a crack growth rate at which the crack propagates starts increasing. The crack opening behavior acquisition device according to claim 6 , further comprising a determination unit. The control unit calculates the crack growth rate from the stress intensity factor when the crack intensity determination unit determines that the stress intensity factor exceeds the reference stress intensity factor. The crack according to claim 7 , further comprising a propagation time calculation unit that estimates a length of the accompanying crack and calculates a time required to reach an allowable crack length allowed by the test object. Opening behavior acquisition device. A crack opening behavior acquisition program for acquiring the opening behavior of a crack on the surface of a test object by a computer,
A first output outputted by a first strain gauge arranged on the crack of the test object and a second position arranged at a position separated from the crack of the test object by an input device of the computer. An input process for obtaining a second output outputted by the strain gauge of
A correction step of matching the slopes of the first output and the second output acquired in the input step in an elastic region;
A difference calculating step of calculating a difference between the first output and the second output corrected in the correcting step ;
Based on the difference calculated in the difference calculating step, an opening start point calculating step for calculating an opening start point from which the crack can be considered to start opening from the difference between the first output and the second output;
A coefficient calculation step of calculating a maximum value of the difference from the opening start point as an opening amount of the crack based on the difference calculated in the difference calculating step, and calculating a stress intensity factor from the calculated opening amount. When,
A crack growth determination step of determining whether or not the stress intensity factor calculated in the coefficient calculation step exceeds a reference stress intensity factor at which a crack growth rate at which the crack progresses begins to increase; and
When it is determined in the crack growth determination step that the stress intensity factor exceeds the reference stress intensity factor, the crack growth rate is calculated from the stress intensity factor, and An estimation process for calculating the time to reach the allowable crack length allowed for the test object by estimating the length; and
An output step of outputting the calculation result in the progress time calculation step from the output device of the computer;
To cause the computer to execute a crack opening behavior acquisition program. A crack opening behavior acquisition program for acquiring the opening behavior of a crack on the surface of a test object by a computer,
A first output outputted by a first strain gauge arranged on the crack of the test object and a second position arranged at a position separated from the crack of the test object by an input device of the computer. An input process for obtaining a second output outputted by the strain gauge of
A correction step of matching the slopes of the first output and the second output acquired in the input step in an elastic region;
A difference calculating step of calculating a difference between the first output and the second output corrected in the correcting step ;
Based on the difference calculated in the difference calculating step, an opening start point calculating step for calculating an opening start point from which the crack can be considered to start opening from the difference between the first output and the second output;
A coefficient calculation step of calculating a maximum value of the difference from the opening start point as an opening amount of the crack based on the difference calculated in the difference calculating step, and calculating a stress intensity factor from the calculated opening amount. When,
A crack growth determination step of determining whether or not the stress intensity factor calculated in the coefficient calculation step exceeds a reference stress intensity factor at which a crack growth rate at which the crack progresses begins to increase; and
An output step of outputting a determination result in the crack growth determination step from an output device of the computer;
To cause the computer to execute a crack opening behavior acquisition program.

Images