Evaluation device, evaluation method, and program

Abstract

To provide a device, method and program that can evaluate an opening point of a crack on the basis of test information on a fatigue crack development test.SOLUTION: An opening point evaluation device comprises: an acquisition unit that acquires a first relation between a test force when test forces of an arbitrary number of times are loaded with respect to a test piece 100 and a crack opening displacement in the fatigue crack development test; a first calculation unit that calculates reference compliance of the test piece 100 on the basis of the first relation; a second calculation unit that extracts a plurality of second ranges from the maximum test force of the first relation and minimum test force thereof, and calculates part compliance as to each second range; a third calculation unit that calculates a deviation value indicative of a ratio of a deviation with respect to the reference compliance as for each part compliance; and an opening point determination unit that determines the test force when the deviation value becomes a deviation value of a preset ratio with respect to the maximum value of the deviation value in a second relation between the deviation value and the test force, or the test force corresponding to a medium value of the deviation value as an opening test force corresponding to an opening point of the crack.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for evaluating opening points in a fatigue crack growth test, and a program for implementing the same. [Background technology]

[0002] The fatigue crack growth characteristics of a material are an important index for evaluating the performance of a product. The fatigue crack growth characteristics of a material can be evaluated from the relationship between the stress intensity factor range and the crack growth length obtained by performing a fatigue crack growth test.

[0003] In a fatigue crack propagation test, for example, a compliance method is used as a method for measuring the crack length (see, for example, Patent Document 1). In the compliance method, the crack length is indirectly measured using the ratio (compliance) of the change in crack opening displacement to the change in test force. Specifically, the compliance can be calculated, for example, by dividing the change in crack opening displacement by the change in test force. In addition, for example, the compliance may be calculated by linear approximation of a curve showing the relationship between the crack opening displacement and the test force. The compliance calculated in this way based on the test data is substituted into a predetermined formula showing the relationship between compliance and crack length, thereby calculating the crack length. Using the crack length calculated in this way, the relationship between the stress intensity factor range and the crack propagation length can be obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-250866 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a fatigue crack growth test, the crack tip of a test piece closes when unloading and opens when loading, but when focusing on the intermediate stages of unloading and loading, there is a period during which the crack tip is closed even if a tensile force is acting on the test piece. In this regard, it is known that when the test force acting on the test piece reaches a certain magnitude, the crack tip begins to open during loading and begins to close during unloading. The timing at which the crack tip begins to open and close is called the opening point.

[0006] The fatigue crack growth characteristics of materials are generally organized in terms of the stress intensity factor range corresponding to the variation range of the test force, but in reality, the stress intensity factor above the opening point is effective. This range of variation of the stress intensity factor above the opening point is called the effective stress intensity factor range, and is used as an evaluation index of fatigue crack growth characteristics. In order to improve the fatigue crack growth characteristics of materials, it is useful to consider separately whether the fatigue crack growth characteristics measured in fatigue crack growth tests are due to crack opening and closing or due to the effective stress intensity factor range.

[0007] In addition, the fatigue crack growth characteristics organized by the stress intensity factor range differ depending on the stress ratio of the fatigue crack growth test. Therefore, in order to use the fatigue crack growth characteristics organized by the stress intensity factor range to predict the crack growth behavior of an actual part, it is necessary to perform tests at multiple stress ratios according to the use conditions and evaluate the fatigue crack growth characteristics for each stress ratio. On the other hand, it is known that when the fatigue crack growth characteristics at various stress ratios are organized by the effective stress intensity factor range, the fatigue crack growth characteristics (i.e., the relationship between the crack growth rate and the effective stress intensity factor range) show similar characteristics regardless of the stress ratio. Considering this point, if the fatigue crack growth characteristics organized by the effective stress intensity factor range can be obtained, it can be said that it is possible to estimate the fatigue crack growth characteristics by the stress intensity factor at various stress ratios based on the fatigue crack growth characteristics. Although the fatigue crack growth test requires a lot of effort and time, if the test can be performed at a specific stress ratio and the fatigue crack growth behavior at other stress ratios can be predicted based on the test results, the effort and time required for the test can be significantly reduced.

[0008] For these reasons, it is important to evaluate the crack opening point in fatigue crack growth tests.

[0009] Therefore, an object of the present invention is to provide an evaluation device, an evaluation method, and a program capable of evaluating the crack opening point based on test information from a fatigue crack growth test. [Means for solving the problem]

[0010] The present inventors carried out fatigue crack growth tests on metal test pieces and attempted to evaluate the crack opening point using the unloading elastic compliance method. The tests carried out by the present inventors are described below.

[0011] First, the inventors prepared a test piece 100 shown in FIG. 1 and performed a fatigue crack propagation test. The test piece 100 is a known CT (Compact Tension) test piece used as a tensile fatigue test piece, and has a notch 100a. The notch 100a is a notch for crack generation that is formed so that a crack 100b propagates in a propagation direction intersecting the plate thickness direction and the tensile direction by applying a force to the test piece 100 in a tensile direction perpendicular to the plate thickness direction. The notch 100a is formed in the center of the test piece 100 in the tensile direction.

[0012] The test piece 100 was made of pure iron with a 0.2% yield strength of 83 MPa, a tensile strength of 223 MPa, an elongation of 64%, and a reduction in area of ​​95%. The thickness (B) of the test piece 100 was 8 mm, and the width (W) was 50 mm.

[0013] In the fatigue crack propagation test, a pre-crack with a length of 1 mm was introduced into the test piece 100 with a stress ratio R of -1, and then a stress intensity factor decreasing test (load decreasing test) was performed with stress ratios R set to 0.05, 0.5, and 0.7. In this test, a load was repeatedly applied in the tensile direction shown in Fig. 1. In this test, the displacement of the width of the notch 100a (crack opening displacement) was measured using a clip gauge (not shown).

[0014] From the data obtained from the above fatigue crack growth test, the inventors have created a graph showing the relationship between the fatigue crack growth rate (da / dN) and the stress intensity factor range (ΔK), as shown in Figure 2. From the relationship shown in Figure 2, the lower limit of the stress intensity factor range ΔK (lower limit stress intensity factor range ΔK th ) was 8.1 MPa√m when the stress ratio R was 0.05, 5.8 MPa√m when the stress ratio R was 0.5, and 3.9 MPa√m when the stress ratio R was 0.7.

[0015] Next, the inventors evaluated the opening point according to ASTM E647-13a.

[0016] Fig. 3 shows the relationship between the test force and the crack opening displacement when unloading in a fatigue crack growth test in which the stress ratio R was set to 0.05. Note that Fig. 3 shows the relationship between the test force and the crack opening displacement when unloading in a fatigue crack growth test in which the number of repeated loads was 8.70 × 10 6 The relationship between the test force and the crack opening displacement at the time of unloading (when the crack is judged to have stopped propagating and the test is terminated) is shown.

[0017] Referring to FIG. 3, the inventors first determined the compliance in range A where a crack is considered to be open (hereinafter, referred to as reference compliance C) in the relationship between the crack opening displacement when unloading and the test force. B The maximum test force P max and minimum test force P min The difference between this and the test force range ΔP is (0.7ΔP+P min )~(0.95ΔP+P min ) test force range. Compliance means the ratio of the change in crack opening displacement to the change in test force. Therefore, the standard compliance C B means the ratio of the change in crack opening displacement to the change in test force in range A. The compliance is calculated, for example, by linearly approximating the curve showing the relationship between the crack opening displacement and the test force.

[0018] Next, the maximum test force P max and minimum test force P min Multiple test force ranges from a to i (i = 1 to n) were extracted. i In the example shown in FIG. 3, the 20 ranges a1, a2, a3, . . . a are arranged in order from the side with the highest test force. 20 More specifically, in the example shown in FIG. i The size of ΔP a In this case, the adjacent range a in terms of the magnitude relationship of the test force i Each other is 0.5ΔP a Multiple test force ranges a to overlap i The following is extracted.

[0019] Next, extract multiple ranges a i Compliance C i (i=1~n) (hereinafter, partial compliance C i (hereinafter referred to as "(1 / 2)") was calculated.

[0020] Next, each partial compliance C i About Compliance C B Deviation value C, which indicates the deviation ratio offset,i (i = 1 to n) was calculated. Specifically, the deviation value C offset,i was calculated. C offset,i =(C B -C i ) / C B ... (1)

[0021] Figure 4 shows the test force and the displacement C offset In order to create the relationship line shown in Figure 4, first, one axis is set to the deviation value C offset On the coordinate system with the other axis as the test force P, each partial compliance C i The deviation value C corresponding to offset,i and test force P i (range a i The points that indicate the intermediate value of the test force (i = 1 to n) are plotted. Then, the points that are adjacent in terms of the magnitude relationship of the test force (Coffset,i and the point indicating the test force) are connected by a straight line. This allows the test force and the deviation value C offset The relation line is obtained. i The midpoint of the range a i The average value of the maximum and minimum test forces is given.

[0022] According to ASTM E647-13a, the test force and the displacement value C offset In the relationship line, the deviation value C offset The test force at which the deviation value C becomes 1%, 2% or 4% is determined to be the test force at the opening point. offset The test force at which the value of OP (Hereinafter, the opening test force P OP The opening test force P OP The stress intensity factor calculated based on the stress intensity factor K OP and the maximum test force P max The stress intensity factor calculated based on the stress intensity factor K max Based on the following formula (2), the effective stress intensity factor range ΔK eff was calculated. ΔK eff =K max -K OP (2)

[0023] In addition, in Figures 3 and 4, the number of repetitions is 8.70 × 10 6 The test data is for the number of cycles, but the inventors have also calculated the effective stress intensity factor range ΔK eff As shown in FIG. 5, the inventors calculated the relationship between the fatigue crack growth rate (da / dN) and the effective stress intensity factor range (ΔK eff ) was created. For comparison, Fig. 5 also shows the relationship between the fatigue crack growth rate (da / dN) and the stress intensity factor range (ΔK) when the stress ratios R are 0.05 and 0.7 (data shown in Fig. 2).

[0024] As shown in Fig. 5, the effective stress intensity factor range ΔK calculated by the above method eff is considerably smaller than the stress intensity factor range ΔK when the stress ratio R is 0.7. offset The test force at which the stress intensity factor is 4% is defined as the test force at the opening point, and the effective stress intensity factor range ΔK eff A similar trend was observed when calculating

[0025] Generally, in a high stress ratio test where the crack is in a completely open state, the minimum test force P min and the opening test force P OP Therefore, the lower limit of the stress intensity factor range ΔK calculated in a test with a high stress ratio (for example, R = 0.7) (the lower limit of the stress intensity factor range ΔK th ) is the effective stress intensity factor range ΔK in a test with a stress ratio of 0.05 eff Lower limit of stress intensity factor range ΔK eff,th However, as shown in Fig. 5, the effective stress intensity factor range ΔK eff was significantly smaller than the stress intensity factor range ΔK when the stress ratio was 0.7. This suggests that the above method may not be able to properly evaluate the opening point.

[0026] Therefore, the inventors have determined that the effective stress intensity factor range ΔK eff A detailed study was conducted to determine why there was a large difference between the stress intensity factor range ΔK when the stress ratio was 0.7 and the stress intensity factor range ΔK when the stress ratio was 0.7. In this study, the inventors focused on the effect of the difference in the number of cycles in the fatigue crack growth test on the crack opening displacement. This will be explained in detail below.

[0027] Figure 6 shows the fatigue crack propagation test with a load repetition rate of 9.16×10 3 Test force and displacement value C created from the data when unloading offset The relationship line shown in FIG. 4 (where the number of repetitions is 8.70×10 6When comparing the data from the first time with the relationship line shown in Figure 6, the deviation value C offset Although not shown in the figure, the number of repeated loads in the fatigue crack growth test was 1.46 × 10 5 Test force and displacement value C created from the data when unloading offset The relationship line also shows the deviation value C offset The maximum value of is the deviation value C of the relationship line shown in Figure 4. offset Thus, the inventors' investigation revealed that the deviation value C offset It was found that there were differences in the occurrence of

[0028] The inventors have determined that the deviation value C offset The inventors considered that the difference in the occurrence state of the cracks may be the reason why the opening point cannot be appropriately evaluated. Specifically, the inventors considered that the difference in the deviation value C offset Even though there are differences in the occurrence of the openings, the opening point is judged using the same criteria without taking these differences into account (deviation value C offset It was thought that even if the test force at which the opening point is 1%, 2% or 4% was determined to be the opening test force, the opening point would not be evaluated appropriately.

[0029] Therefore, the inventors have determined that the deviation value C offset We tried to determine the opening point based on the criteria according to the occurrence of the test force and the displacement value C offset In the relationship line, the test force when the deviation value is a preset ratio to the maximum deviation value (in this study, the deviation value is 1 / 3 of the maximum deviation value) was determined to be the opening test force (first determination criterion). The inventors then determined the effective stress intensity factor range ΔK eff was calculated based on the opening test force determined by the above criteria. As a result, the effective stress intensity factor range ΔK eff Lower limit value ΔK eff,th is the lower limit ΔK of the stress intensity factor range ΔK calculated in a test with a stress ratio of 0.7. th became equivalent to the value.

[0030] In addition, the inventors have determined the relationship between the test force and the displacement value C offset In relation to the deviation value C offset,i The test force corresponding to the median of (i = 1 to n) is judged as the opening test force (second judgment criterion), and the effective stress intensity factor range ΔK in the test with a stress ratio of 0.05 is eff In this case, the effective stress intensity factor range ΔK in the test with a stress ratio of 0.05 was also calculated. eff Lower limit value ΔK eff,th is the lower limit ΔK of the stress intensity factor range ΔK calculated in a test with a stress ratio of 0.7. th became equivalent to the value.

[0031] From the above results, the test force (first judgment criterion) when the deviation value is a preset percentage of the maximum deviation value, or the deviation value C offset,i The deviation value C is obtained by determining the test force (second judgment criterion) corresponding to the median value of (i = 1 to n) as the opening test force. offset It was found that the opening point can be appropriately evaluated regardless of differences in the occurrence conditions.

[0032] The "ratio" of the deviation value at which the opening test force is obtained relative to the maximum deviation value can be determined in advance by experiment for each type of metal material (e.g., types classified according to alloy components, etc.). For example, fatigue crack growth tests are performed on multiple types of metal materials at arbitrary stress ratios (e.g., stress ratios R = 0.05 or R = 0.5) and high stress ratios (e.g., stress ratios R = 0.7), and the effective stress intensity factor range ΔK obtained in tests at the arbitrary stress ratios is calculated for each metal material. eff However, it is sufficient to determine the "deviation ratio" that is approximately equal to the stress intensity factor range ΔK obtained in a high stress ratio test at the corresponding crack growth rate. Note that the high stress ratio fatigue crack growth test does not need to be continued for a long period of time until the crack stops propagating, and it is sufficient to carry out the test in a limited range where the "deviation ratio" can be determined.

[0033] When determining the opening test force, either the first or second criterion may be used. Note that fatigue crack growth tests are performed on multiple types of metal materials at arbitrary stress ratios (e.g., stress ratios R = 0.05 or R = 0.5) and high stress ratios (e.g., stress ratios R = 0.7), and the effective stress intensity factor range ΔK obtained in the tests at the arbitrary stress ratios for each metal material is calculated. eff However, it is preferable to determine which of the first and second criteria is closer to the stress intensity factor range ΔK obtained in a test at a high stress ratio at the corresponding crack growth rate.

[0034] The present invention has been made based on the above findings, and includes the following evaluation device, evaluation method, and program.

[0035] (1) an acquisition unit that acquires a first relationship between a test force applied to a test piece multiple times in a fatigue crack growth test and a numerical value related to the displacement of a predetermined portion of the test piece when the test force is applied to the test piece an arbitrary number of times; and a first calculation unit that calculates a reference compliance of the test piece from a change in a numerical value related to the displacement in a first range of the test force during a period in which a crack in the test piece is open, based on the first relationship acquired by the acquisition unit; a second calculation unit that extracts a plurality of second ranges of the test force between a maximum test force and a minimum test force when the test force is applied to the test piece an arbitrary number of times based on the first relationship acquired by the acquisition unit, and calculates a partial compliance from a change in a numerical value related to the displacement for each of the extracted plurality of second ranges; a third calculation unit that calculates a deviation value indicating a ratio of deviation from the reference compliance calculated by the first calculation unit for each of the plurality of partial compliances calculated by the second calculation unit; an opening point determination unit that generates a second relationship between the deviation value calculated by the third calculation unit for each partial compliance and the test force, and determines, in the second relationship, the test force when the deviation value is a preset percentage of the maximum deviation value, or the test force corresponding to a median of the deviation values, as an opening test force corresponding to the opening point of a crack.

[0036] (2) the first calculation unit determines the first range according to a stress ratio in the fatigue crack growth test, The evaluation device according to (1) above, wherein the second calculation unit determines the plurality of second ranges depending on the stress ratio.

[0037] (3) The evaluation device according to (1) or (2) above, wherein the opening point determination unit calculates a comparative compliance from a change in the numerical value relating to the displacement in a third range of the test force, the third range being wider than the first range and having a minimum value smaller than the minimum value of the first range, based on the first relationship acquired by the acquisition unit, and when the comparative compliance is greater than the reference compliance, determines the minimum test force to be the opening test force, instead of the test force when the deviation value is a preset percentage of the maximum deviation value in the second relationship or the test force corresponding to the median of the deviation value in the second relationship.

[0038] (4) The evaluation device according to any one of (1) to (3), wherein, when a value obtained by dividing the test force when the deviation value in the second relationship is a preset percentage relative to the maximum deviation value by the maximum test force exceeds a preset threshold value, the opening point determination unit determines the minimum test force to be the opening test force, rather than the test force when the deviation value in the second relationship is a preset percentage relative to the maximum deviation value or the test force corresponding to a median of the deviation values ​​in the second relationship.

[0039] (5) The evaluation device according to any one of (1) to (4) above, wherein the first relationship indicates a relationship between the test force and a numerical value related to the displacement when unloaded.

[0040] (6) The evaluation device according to any one of (1) to (5) above, wherein the test piece is a CT test piece, and the numerical value relating to the displacement of the specified portion is a crack opening displacement or a strain on the back surface of the test piece.

[0041] (7) The evaluation device according to any one of (1) to (6), wherein the second calculation unit extracts the multiple second ranges so that portions of adjacent second ranges overlap in terms of the magnitude relationship of the test forces.

[0042] (8) The evaluation device according to any one of (1) to (7) above, wherein the predetermined ratio is set according to test conditions of a fatigue crack growth test.

[0043] (9) The evaluation device according to any one of (1) to (8) above, further comprising a fourth calculation unit that calculates an effective stress intensity factor range based on the opening test force determined by the opening point determination unit.

[0044] (10) A method for evaluating a crack opening point of a test piece in a fatigue crack growth test by a computer, comprising: (a) obtaining a first relationship between a test force applied to a test piece multiple times in a fatigue crack growth test and a numerical value related to the displacement of a predetermined portion of the test piece when the test force is applied to the test piece an arbitrary number of times; (b) calculating a reference compliance of the test specimen from a change in the numerical value of the displacement in the first range of the test force during a period during which a crack in the test specimen is open based on the first relationship obtained in the step (a); (c) extracting a plurality of second ranges of the test force between the maximum test force and the minimum test force when the test force is applied to the test piece an arbitrary number of times based on the first relationship obtained in the step (a), and calculating a partial compliance from a change in the numerical value related to the displacement for each of the extracted plurality of second ranges; (d) calculating a deviation value indicating a deviation ratio of each of the plurality of partial compliances calculated in the step (c) to the reference compliance calculated in the step (b); (e) generating a second relationship between the deviation value calculated for each of the partial compliances in the step (d) and the test force, and determining the test force when the deviation value is a preset ratio to the maximum deviation value in the second relationship, or the test force corresponding to the median of the deviation value in the second relationship, as an opening test force corresponding to the opening point of the crack; The method for evaluating an aperture point comprises:

[0045] (11) In the step (b), the first range is determined according to a stress ratio in the fatigue crack growth test; The evaluation method according to (10) above, wherein in the step (c), the plurality of second ranges are determined according to the stress ratio.

[0046] (12) The evaluation method according to (10) or (11) above, in which in the step (e), a comparative compliance is calculated based on the first relationship obtained in the step (a) from a change in the numerical value related to the displacement in a third range of the test force, the third range being wider than the first range and having a minimum value smaller than the minimum value of the first range, and when the comparative compliance is greater than the reference compliance, the minimum test force is determined to be the opening test force, instead of the test force when the deviation value is a preset percentage of the maximum deviation value in the second relationship or the test force corresponding to the median of the deviation value in the second relationship.

[0047] (13) The evaluation method according to any one of (10) to (12), wherein in the step (e), if a value obtained by dividing the test force when the deviation value in the second relationship is a preset percentage of the maximum deviation value by the maximum test force exceeds a preset threshold value, the minimum test force is determined to be the opening test force, instead of the test force when the deviation value in the second relationship is a preset percentage of the maximum deviation value or the test force corresponding to the median of the deviation value in the second relationship.

[0048] (14) The evaluation method according to any one of (10) to (13) above, wherein the first relationship indicates a relationship between the test force and a numerical value related to the displacement when unloaded.

[0049] (15) The evaluation method according to any one of (10) to (14) above, wherein the test piece is a CT test piece, and the numerical value relating to the displacement of the specified portion is a crack opening displacement or a strain on the back surface of the test piece.

[0050] (16) The evaluation method according to any one of (10) to (15) above, wherein in the step (c), the second ranges are extracted so that parts of the second ranges adjacent to each other in terms of the magnitude relationship of the test forces overlap.

[0051] (17) The evaluation method according to any one of (10) to (16) above, wherein the predetermined ratio is set according to test conditions of a fatigue crack growth test.

[0052] (18)(f) The evaluation method according to any one of (10) to (17) above, further comprising a step of calculating an effective stress intensity factor range based on the opening test force determined in the step (e).

[0053] (19) A program for causing a computer to execute the evaluation method according to any one of (10) to (18) above. Effect of the Invention

[0054] According to the present invention, the opening point of a crack can be evaluated based on test information from a fatigue crack growth test. [Brief description of the drawings]

[0055] [Figure 1] FIG. 1 is a diagram showing a test piece used in a fatigue crack growth test. [Diagram 2] FIG. 2 is a graph showing the relationship between fatigue crack growth rate and stress intensity factor range. [Diagram 3] FIG. 3 shows the relationship between the test force and the crack opening displacement when the load is removed. [Figure 4] FIG. 4 is a graph showing the relationship between the test force and the deviation value (deviation of the partial compliance from the reference compliance). [Diagram 5] FIG. 5 is a graph showing the relationship between the fatigue crack growth rate and the effective stress intensity factor range (ΔKeff). [Figure 6] FIG. 6 is a graph showing the relationship between the test force and the deviation value (deviation of the partial compliance from the reference compliance). [Figure 7] FIG. 7 is a block diagram showing a schematic configuration of an evaluation device according to an embodiment of the present invention. [Figure 8] FIG. 8 is a diagram illustrating an example of the second relationship. [Figure 9] FIG. 9 is a block diagram specifically showing the configuration of an evaluation device according to one embodiment of the present invention. [Figure 10] FIG. 10 is a flow diagram showing the operation of the evaluation device according to this embodiment. [Figure 11] FIG. 11 is a block diagram showing an example of a computer that realizes an evaluation device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] [Device configuration] Fig. 7 is a block diagram showing a schematic configuration of an evaluation device according to an embodiment of the present invention. As shown in Fig. 7, the evaluation device 10 according to this embodiment includes an acquisition unit 12, a first calculation unit 14, a second calculation unit 16, a third calculation unit 18, and an opening point determination unit 20. In the following, a case where a fatigue crack growth test is performed using the above-mentioned test piece 100 as a test piece will be described. The fatigue crack growth test may be performed according to ASTM E647, for example. The fatigue crack growth test may be a stress intensity factor decreasing test (load decreasing test) or a stress intensity factor increasing test (constant load range test).

[0057] The acquisition unit 12 acquires a relationship (hereinafter referred to as the first relationship) between the test force and the numerical value relating to the displacement when the test force is applied to the test piece 100 an arbitrary number of times, from among test information including the test force applied to the test piece 100 multiple times in a fatigue crack propagation test and numerical values ​​relating to the displacement of a specified portion of the test piece 100.

[0058] In this embodiment, the numerical value related to the displacement of a predetermined portion of the test piece 100 in the test information is the crack opening displacement measured by a clip gauge attached to the notch 100a. Therefore, in this embodiment, the test information includes the relationship between the test force repeatedly applied to the test piece 100 and the crack opening displacement when the test force is applied. In this embodiment, the first relationship is, for example, the relationship between the test force and the crack opening displacement when unloaded when a test force is applied an arbitrary number of times in a fatigue crack growth test, as shown in FIG. 3.

[0059] In the present embodiment, the acquiring unit 12 may acquire test information from an external device, and extract the first relationship for each number of repetitions of the test force from the acquired test information. The acquiring unit 12 may also acquire the first relationship created for each number of repetitions of the test force in the external device, for example.

[0060] The first calculation unit 14 calculates the reference compliance C of the test piece 100 from a change in the crack opening displacement (a numerical value related to the displacement) in the first range of the test force during the period in which the crack 100b of the test piece 100 is open, based on the first relationship acquired by the acquisition unit 12. B In this embodiment, for example, the maximum test force P max and minimum test force P min The difference between this and the test force range ΔP is (0.7ΔP+P min )~(0.95ΔP+P min ) is set as the first range. In the example shown in FIG. 3, range A corresponds to the first range. Note that the method for setting the first range is not limited to this example, and a range of test forces in which the crack 100b is considered to be open can be set as the first range. Other examples of setting the first range will be described later.

[0061] In this embodiment, compliance means the ratio of the change in crack opening displacement to the change in test force. Therefore, the reference compliance C B means the ratio of the change in crack opening displacement to the change in test force in the first range. The compliance may be calculated, for example, by linearly approximating a curve showing the relationship between the crack opening displacement and the test force, or by dividing the change in crack opening displacement by the change in the test force.

[0062] The second calculation unit 16 calculates the maximum test force P when the test force is applied to the test piece 100 for an arbitrary number of times based on the first relationship acquired by the acquisition unit 12. max and minimum test force P min A plurality of second ranges of test force from i (i = 1 to n). In the example shown in FIG. 3, the range a1, a2, a3, . . . a 20 respectively correspond to the second range.

[0063] In this embodiment, a plurality of second ranges a i The magnitudes of the second range a are equal to each other. iThe magnitude of the test force range ΔP is set to, for example, 0.1 times the test force range ΔP. In this embodiment, for example, the second range a i (In the example shown in Figure 3, the maximum value of the range a1) is the maximum test force P max A plurality of second ranges a are set so that the value is 0.95 times or more of i In this embodiment, for example, the second range a on the side where the test force is the lowest is extracted. i (In the example shown in Figure 3, range a 20 ) and the minimum test force P min The difference between this and the second range a i A plurality of second ranges a, each of which has a size less than i is extracted.

[0064] In the present embodiment, the second calculation unit 16 calculates, for example, a second range a i Multiple second ranges a are created so that some of them overlap. i In this embodiment, for example, the second range a adjacent to each other in terms of the magnitude relationship of the test force is extracted. i The two are in the second range a i Multiple second ranges a are created so that they overlap by half the size of i is extracted.

[0065] The method for setting the second range is not limited to the above example, and the second range may be set according to the test conditions. Other examples of setting the second range will be described later.

[0066] The second calculation unit 16 calculates the extracted second ranges a i For each, the partial compliance C was calculated from the change in the crack opening displacement (displacement value). i (i=1 to n) is calculated. In this embodiment, the partial compliance C i The second range a i It means the ratio of the change in crack opening displacement to the change in test force in

[0067] The third calculation unit 18 calculates the partial compliances C iFor each of them, the reference compliance C calculated by the first calculation unit 14 B Deviation value C, which indicates the deviation ratio offset,i In this embodiment, the third calculation unit 18 calculates the deviation value C based on the following formula (1): offset,i Calculate. C offset,i =(C B -C i ) / C B ... (1)

[0068] The opening point determination unit 20 determines whether the third calculation unit 18 calculates the partial compliance C i The deviation value C calculated for each offset,i A relationship between the test force and the deviation value C (hereinafter referred to as the second relationship) is generated. offset 2 shows an example of the second relationship between

[0069] In this embodiment, the aperture point determination unit 20 sets one axis to a deviation value C offset On the coordinate system with the other axis as the test force P, each partial compliance C i The deviation value C corresponding to offset,i and test force P i (range a i The points indicating the intermediate value of the test force (i=1 to n) are plotted. Furthermore, the opening point determination unit 20 connects adjacent points in the magnitude relationship of the test force among the multiple points plotted as described above with straight lines. In this embodiment, the second relationship means a set of multiple line segments generated as described above.

[0070] In the example shown in FIG. 8, the partial compliance C 19 Deviation value C offset,19 The maximum deviation value C offset,max Partial Compliance C 19 is the 19th second range a counting from the high test force side 19 is the ratio of the change in crack opening displacement to the change in test force in

[0071] Referring to FIG. 8, the opening point determination unit 20 determines the maximum deviation value Coffset,max A preset percentage deviation value C offset,th The test force at which this occurs is defined as the opening test force P OP This will be described in detail below. In the example of FIG. 8, the deviation value C offset,th is the maximum deviation value C offset,max It is set to one-third of the value.

[0072] In this embodiment, the opening point determination unit 20 determines the opening test force P according to the following conditions, for example: OP With reference to FIG. 8, among the multiple line segments included in the second relationship, the deviation value C offset,th A point corresponding to a deviation value smaller than offset,th The target line segment is a line segment that connects a point (hereinafter referred to as the second point) corresponding to a deviation value larger than the first point and in which the test force corresponding to the first point is larger than the test force corresponding to the second point. In the example of FIG. 8, the lines L8 and L 13 , L 17 are the target segments. Target segments L8, L 13 , L 17 Among them, the target line L corresponding to the lowest test force 17 In the deviation value C offset,th The test force at which this occurs is the opening test force P OP Let us assume that.

[0073] The process performed by the opening point determination unit 20 does not have to be a process that follows the above conditions as is. Specifically, when the opening point determination unit 20 determines that the opening test force P OP The test force that is judged to be the second relationship and the deviation value C offset,th Therefore, in the process executed by the aperture point determination unit 20, it is not necessary to actually create a plurality of line segments as the second relationship, but a collection of linear functions corresponding to the plurality of line segments is used as the second relationship, and the second relationship and the deviation value C offset,th Based on the opening test force P OP may be calculated.

[0074] As described above, the evaluation device 10 according to this embodiment can evaluate the crack opening point from the test information obtained in the fatigue crack growth test. In this embodiment, the deviation value C offset,th is the maximum deviation value C offset,max This allows the deviation value C to be calculated according to the number of repeated loads in the fatigue crack growth test. offset The occurrence status (more specifically, the maximum deviation value C offset,max ) even if there is a difference in the deviation value C offset The opening point can be determined based on a criterion according to the occurrence status of the opening point. As a result, the opening point can be appropriately evaluated.

[0075] Next, a specific configuration of the evaluation device 10 will be described. Fig. 9 is a block diagram specifically showing the configuration of the evaluation device 10 according to one embodiment of the present invention.

[0076] 9, the evaluation device 10 further includes a storage unit 22 and a fourth calculation unit 24 in addition to the above-mentioned acquisition unit 12, first calculation unit 14, second calculation unit 16, third calculation unit 18, and opening point determination unit 20. Below, the storage unit 22 will be described, and then the operation of the acquisition unit 12 and the like will be described. Note that with regard to the acquisition unit 12, first calculation unit 14, second calculation unit 16, third calculation unit 18, and opening point determination unit 20, operations similar to those of the above-mentioned embodiment will be briefly described.

[0077] The memory unit 22 stores the size of the first range, the size of the second range, and the deviation value C used to determine the aperture point. offset,th The ratio for setting is stored according to the test conditions. In this embodiment, the test conditions include the stress ratio in the fatigue crack growth test and the type of the metallic material to be tested. First, the size of the first range stored in the memory unit 22 and the size of the second range stored in the memory unit 22 will be described.

[0078] The larger the stress ratio in the fatigue crack growth test, the smaller the change in test force. Therefore, in order to improve the evaluation accuracy, it is preferable to make the ratios of the first and second ranges to the test force range ΔP larger in a test with a large stress ratio than in a test with a small stress ratio. Therefore, in this embodiment, the first and second ranges are set according to the stress ratio.

[0079] Specifically, the first range is set, for example, as follows. In the following, R indicates a stress ratio, P max indicates the maximum test force at any number of repetitions, and P min indicates the minimum test force at any number of repetitions, and ΔP indicates the test force range (the difference between the maximum test force and the minimum test force). Note that the first and second ranges described below are merely examples, and fatigue crack growth tests can be performed on various metallic materials, and the first and second ranges that allow appropriate evaluation of the opening point can be set for each type of metallic material.

[0080] (First range) R<0, R=0~0.1: (0.70ΔP+P min )~(0.95ΔP+P min ) 0.1 <R<0.3:(0.65ΔP+P min )~(0.95ΔP+P min ) 0.3≦R<0.5:(0.60ΔP+P min )~(0.95ΔP+P min ) R = 0.5: (0.55ΔP+P min )~(0.95ΔP+P min ) 0.5 <R<0.7:(0.50ΔP+P min )~(0.95ΔP+P min ) 0.7≦R:(0.45ΔP+P min )~(0.95ΔP+P min )

[0081] The size of the second range is set, for example, as follows.

[0082] (Size of the second range) R<0, R=0~0.1: 0.10ΔP 0.1 <R<0.3:0.13ΔP 0.3≦R<0.5:0.15ΔP R=0.5:0.17ΔP 0.5 <R<0.7:0.19ΔP 0.7≦R:0.20ΔP

[0083] Next, the offset value C used to determine the aperture point offset,th The ratio for setting is described below. In this embodiment, for example, fatigue crack growth tests are performed on multiple types of metal materials at an arbitrary stress ratio (for example, stress ratio R = 0.05 or R = 0.5) and a high stress ratio (for example, stress ratio R = 0.7). Then, for each type of metal material, the effective stress intensity factor range ΔK obtained in the test at the arbitrary stress ratio is eff However, a "deviation ratio" is calculated so as to be approximately equal to the stress intensity factor range ΔK obtained in a high stress ratio test at a corresponding crack growth rate. In this embodiment, the "deviation ratio" calculated as described above is stored for each type of metallic material in the memory unit 22. Note that the high stress ratio fatigue crack growth test does not need to be continued for a long period of time until the crack stops propagating, and may be carried out within a limited range where the "deviation ratio" can be calculated.

[0084] The acquisition unit 12 acquires the first relationship in the same manner as in the above-described embodiment. The first calculation unit 14 calculates the reference compliance C B In this embodiment, the first calculation unit 14 is provided with a stress ratio for a fatigue crack growth test as a test condition. In this embodiment, for example, a user of the evaluation device 10 inputs the stress ratio by operating an input unit (not shown). The first calculation unit 14 selects a first range corresponding to the given stress ratio from among a plurality of first ranges stored in the storage unit 22, and calculates a standard compliance C based on the selected first range. B Calculate.

[0085] The second calculation unit 16 calculates a plurality of second ranges a i (i = 1 to n) is extracted, and each second range a i Regarding Partial Compliance C i (i=1 to n). In this embodiment, the second calculation unit 16 is also provided with a stress ratio for a fatigue crack growth test, similar to the first calculation unit 14. The second calculation unit 16 selects a second range size corresponding to the provided stress ratio from a plurality of second range sizes stored in the storage unit 22, and calculates a plurality of second ranges a based on the selected second range size. i Extract.

[0086] The third calculation unit 18 calculates each partial compliance C i About Compliance C B Deviation value C, which indicates the deviation ratio offset,i Calculate (i=1 to n).

[0087] The opening point determination unit 20 generates the second relationship in the same manner as in the above embodiment, and determines the opening test force P from the generated second relationship. OP In this embodiment, the type of the metal material of the test piece 100 is provided to the opening point determination unit 20 as a test condition. In this embodiment, for example, a user of the evaluation device 10 inputs the type of the metal material by operating an input unit (not shown). The opening point determination unit 20 determines the deviation value C offset,th From among a number of ratios for setting, a ratio corresponding to the given type of metal material is selected, and based on the selected ratio, the deviation value C offset,th The opening point determination unit 20 calculates the deviation value C offset,th Based on the opening test force P OP Although a detailed description is omitted, the "ratio" may be set according to the test conditions, taking into consideration test conditions other than the type of metal material (for example, stress ratio, etc.).

[0088] In this embodiment, the opening point determination unit 20 determines the comparative compliance C from a change in the crack opening displacement (a numerical value related to the displacement) in a third range of test force, which is wider than the first range and has a minimum value smaller than the minimum value of the first range, based on the first relationship acquired by the acquisition unit 12. C The following is a detailed explanation.

[0089] In this embodiment, the stress ratio of the fatigue crack growth test is also given to the opening point determination unit 20, similarly to the first calculation unit 14 and the second calculation unit 16. The opening point determination unit 20 sets a third range corresponding to the given stress ratio and calculates the comparative compliance C C In this embodiment, the third range corresponding to the stress ratio is stored in advance in the storage unit 22. The opening point determination unit 20 selects the third range corresponding to the given stress ratio from among the multiple third ranges stored in the storage unit 22, and calculates the comparative compliance C based on the selected third range. C The third range is set, for example, according to the stress ratio as follows:

[0090] (Third range) 0≦R:P min ~(0.95ΔP+P min ) R<0:0~0.95P max

[0091] In addition, in fatigue crack growth tests where the stress ratio is 0 or more, the maximum test force P max from the minimum test force P min If the crack tip closes while the test force is being removed, the comparative compliance C C is the standard compliance C B Therefore, in this embodiment, in a fatigue crack growth test in which the stress ratio is 0 or more, the comparative compliance C C Compliance with Standards C B If the deviation value is larger than , it is assumed that the crack 100b is in a completely open state, and the deviation value C offset,th Using the opening test force P OP Instead of judging the minimum test force P min The opening test force POP It is determined that:

[0092] In addition, in fatigue crack growth tests where the stress ratio is less than 0, the maximum test force P max If the crack tip closes while the test force is being removed from 0 (kN), the comparative compliance C C is the standard compliance C B Therefore, in the present embodiment, in the fatigue crack growth test where the stress ratio is less than 0, the comparative compliance C C Compliance with standard C B If the maximum test force P is greater than max The crack 100b is considered to be in a completely open state in the test force range from 0 (kN) to 0 (kN), and the deviation value C offset,th Using the opening test force P OP Instead of judging, 0 (kN) is the opening test force P OP It is determined that:

[0093] In this embodiment, the opening point determination unit 20 determines the deviation value C offset,th The test force when max The opening point determination unit 20 determines whether or not a value obtained by dividing the stress ratio by the stress ratio exceeds a preset threshold value. In this embodiment, threshold values ​​corresponding to the stress ratio are stored in advance in the storage unit 22. The opening point determination unit 20 selects a threshold value corresponding to a given stress ratio from among a plurality of threshold values ​​stored in the storage unit 22, and performs the above determination based on the selected threshold value. The threshold value is set, for example, as follows according to the stress ratio.

[0094] (threshold) R≦0.1:0.70 0.1 <R<0.3:0.75 0.3≦R<0.5:0.80 R=0.5:0.85 0.5 <R<0.7:0.87 0.7≦R:0.90

[0095] Based on the inventors' experience, in fatigue crack growth tests where the stress ratio is 0 or more, the maximum test force P max from the minimum test force P min If the crack tip closes while the test force is being removed, the displacement value C in the second relationship offset,th The test force when max It is considered that the value obtained by dividing by is equal to or less than the above threshold value. Therefore, in this embodiment, in the second relationship obtained in the fatigue crack growth test with a stress ratio of 0 or more, the deviation value C offset,th The test force when max If the value obtained by dividing by exceeds the above threshold value, it is considered that the crack 100b is in a completely open state, and the deviation value C offset,th Using the opening test force P OP Instead of judging the minimum test force P min The opening test force P OP It is determined that:

[0096] In addition, based on the inventors' experience, in fatigue crack growth tests where the stress ratio is less than 0, the maximum test force P max If the crack tip closes while the test force is being removed from 0 (kN), the displacement value C in the second relationship is offset,th The test force when max It is considered that the value obtained by dividing by is equal to or less than the above threshold value. Therefore, in this embodiment, in the second relationship obtained in the fatigue crack growth test in which the stress ratio is less than 0, the deviation value C offset,th The test force when max If the value obtained by dividing by exceeds the above threshold value, the maximum test force P max The crack 100b is considered to be in a completely open state in the test force range from 0 (kN) to 0 (kN), and the deviation value C offset,th Using the opening test force P OP Instead of judging, 0 (kN) is the opening test force P OP It is determined that:

[0097] In this embodiment, the deviation value C calculated by the third calculation unit 18 offset,iWhen all of (i=1 to n) are negative values, the opening point determination unit 20 determines that the crack 100b is in a completely open state. In this case, the opening point determination unit 20 determines that the minimum test force P min The opening test force P OP In the fatigue crack growth test where the stress ratio is less than 0, 0 (kN) is set as the opening test force P OP It is determined that:

[0098] The fourth calculation unit 24 calculates the opening test force P OP In this embodiment, for example, a formula for calculating the stress intensity factor based on the test force is stored in advance in the storage unit 22. The fourth calculation unit 24 calculates the effective stress intensity factor range based on the opening test force P OP and maximum test force P max The effective stress intensity factor range is calculated based on the above.

[0099] As described above, in this embodiment, the opening test force P OP can be more appropriately determined.

[0100] [Device operation] Next, the operation of the evaluation device 10 according to the present embodiment will be described. Fig. 10 is a flow diagram showing the operation of the evaluation device 10 according to the present embodiment. Note that the evaluation method according to one embodiment of the present invention is carried out by operating the evaluation device 10.

[0101] In this embodiment, first, the acquisition unit 12 acquires the first relationship as described above (step S1). Next, the first calculation unit 14 calculates the reference compliance C B is calculated (step S2).

[0102] Next, the second calculation unit 16 calculates the second ranges a i and extracting each second range a i Regarding Partial Compliance C i(Step S3). Next, the third calculation unit 18 calculates each partial compliance C i Regarding deviation value C offset,i is calculated (step S4).

[0103] Next, the opening point determination unit 20 determines the opening test force P OP (Step S5). Finally, the fourth calculation unit 24 calculates the effective stress intensity factor range as described above (Step S6). In this embodiment, the processes of Steps S2 to S6 are executed every time the first calculation unit 14 acquires the first relationship when the test force is applied an arbitrary number of times.

[0104] [program] The program according to an embodiment of the present invention may be a program that causes a computer to execute the processes of steps S1 to S6 described above. The evaluation device and evaluation method according to the present embodiment can be realized by installing and executing this program on a computer. In this case, the processor of the computer functions as the acquisition unit 12, the first calculation unit 14, the second calculation unit 16, the third calculation unit 18, the opening point determination unit 20, and the fourth calculation unit 24 to perform the processes.

[0105] In addition, in this embodiment, the memory unit 22 is realized by storing the data files that constitute it in a storage device such as a hard disk provided in the computer, or by installing a recording medium on which these data files are stored in a reading device connected to the computer.

[0106] The program according to the present embodiment may be executed by a computer system constructed by a plurality of computers, in which case each computer may function as the acquisition unit 12, the first calculation unit 14, the second calculation unit 16, the third calculation unit 18, the opening point determination unit 20, and the fourth calculation unit 24, respectively.

[0107] [Physical configuration] 11 is a block diagram showing an example of a computer that realizes the evaluation device 10 according to one embodiment of the present invention. The computer 110 realizes the evaluation device 10 according to this embodiment by executing a program according to this embodiment.

[0108] 11, the computer 110 includes a CPU 111, a main memory 112, a storage device 113, an input interface 114, a display controller 115, a data reader / writer 116, and a communication interface 117. These components are connected to each other via a bus 121 so as to be able to communicate data with each other. Note that the computer 110 may include a GPU (Graphics Processing Unit) or an FPGA (Field-Programmable Gate Array) in addition to or instead of the CPU 111.

[0109] The CPU 111 loads the programs (codes) in this embodiment stored in the storage device 113 into the main memory 112 and executes them in a predetermined order to perform various calculations. The main memory 112 is typically a volatile storage device such as a DRAM (Dynamic Random Access Memory). The programs in this embodiment are provided in a state stored in a computer-readable recording medium 120. The programs in this embodiment may be distributed over the Internet connected via a communication interface 117.

[0110] Specific examples of the storage device 113 include a hard disk drive and a semiconductor storage device such as a flash memory. The input interface 114 mediates data transmission between the CPU 111 and input devices 118 such as a keyboard and a mouse. The display controller 115 is connected to a display device 119 and controls the display on the display device 119.

[0111] Data reader / writer 116 mediates data transmission between CPU 111 and recording medium 120, reads programs from recording medium 120, and writes processing results in computer 110 to recording medium 120. Communication interface 117 mediates data transmission between CPU 111 and other computers.

[0112] Specific examples of recording medium 120 include general-purpose semiconductor storage devices such as CF (Compact Flash (registered trademark)) and SD (Secure Digital), magnetic recording media such as a flexible disk, or optical recording media such as a CD-ROM (Compact Disk Read Only Memory).

[0113] The evaluation device 10 according to this embodiment may be realized by using hardware corresponding to each part, rather than a computer on which a program is installed. Also, the evaluation device 10 may be realized in part by a program and the remaining part by hardware.

[0114] [Variations] In the above embodiment, the case where the crack opening displacement measured by the clip gauge attached to the notch 100a is used as the numerical value related to the displacement of the predetermined portion of the test piece has been described. However, the numerical value related to the displacement of the predetermined portion of the test piece is not limited to the above example, and may be a numerical value related to the displacement of another portion of the test piece. For example, the strain generated in the center of the back surface 100c (the surface opposite to the surface where the notch 100a is formed) of the test piece 100 may be measured by a strain gauge (back surface gauge). In this case, in the method described in the above embodiment, the strain measured by the strain gauge instead of the crack opening displacement is used as the numerical value related to the displacement of the predetermined portion of the test piece, so that the opening point can be evaluated in the same manner as in the above embodiment.

[0115] In the above embodiment, the deviation value C offset,iIn the second relationship between (i = 1 to n) and the test force, the maximum deviation value C offset,max A preset percentage deviation value C offset,th The test force at which this occurs is the opening test force P OP The first judgment criterion is explained below. OP The criteria for determining the above are not limited to the above examples.

[0116] Specifically, the deviation value C offset,i In the second relationship between and the test force, the deviation value C offset,i The test force corresponding to the median value of the opening test force P OP (second criterion). In this case, the deviation value C offset,i The deviation value C that is the middle of the ranking when the values ​​are sorted by size offset,i The test force corresponding to the opening test force P OP Therefore, the second relationship is the deviation value C offset,i Any information showing the correspondence between the test force and the deviation value C is sufficient, and it is not necessary to use a set of multiple line segments as shown in Figure 8. offset,i If the number of is even, the deviation value C offset,i The two deviation values ​​C that are in the middle when the values ​​are sorted in order of magnitude. offset,i The average of the two test forces corresponding to the opening test force P OP This can be done as follows.

[0117] As shown above, the deviation value C offset,i The test force corresponding to the median value of the opening test force P OP As in the above embodiment, the deviation value C is determined according to the number of repeated loads in the fatigue crack growth test. offset Even if there are differences in the occurrence of offset The opening point can be determined based on a criterion according to the occurrence status of the opening point. As a result, the opening point can be appropriately evaluated.

[0118] In addition, the opening point judgment unit 20 judges the opening test force P OP In the case of judging the comparative compliance C in the fatigue crack growth test with a stress ratio of 0 or more, similarly to the above-mentioned embodiment,C Compliance with Standards C B If it is greater than , the opening test force P calculated according to the second criterion OP Instead, the minimum test force P min The opening test force P OP It may be determined that:

[0119] In addition, the opening point judgment unit 20 is similar to the above embodiment in the fatigue crack growth test where the stress ratio is less than 0, and the comparative compliance C C Compliance with Standards C B If it is greater than , the opening test force P calculated according to the second criterion OP Instead, 0 (kN) is the opening test force P OP It may be determined that:

[0120] In addition, the opening point judgment unit 20, as in the above embodiment, in the second relationship obtained in the fatigue crack growth test with a stress ratio of 0 or more, the opening test force P calculated according to the second judgment criterion OP Maximum test force P max If the value obtained by dividing by exceeds the above-mentioned threshold value, the opening test force P calculated according to the second judgment criterion OP Instead, the minimum test force P min The opening test force P OP It may be determined that:

[0121] In addition, the opening point judgment unit 20 is a second relationship obtained in a fatigue crack growth test in which the stress ratio is less than 0, and the opening test force P calculated according to the second judgment criterion OP Maximum test force P max If the value obtained by dividing by exceeds the above-mentioned threshold value, the opening test force P calculated according to the second judgment criterion OP Instead, 0 (kN) is the opening test force P OP It may be determined that:

[0122] In addition, similarly to the above embodiment, the deviation value C calculated by the third calculation unit 18 offset,i When all of (i = 1 to n) are negative values, the opening point judgment unit 20 judges that the minimum test force Pmin The opening test force P OP In the fatigue crack growth test where the stress ratio is less than 0, 0 (kN) is set as the opening test force P OP It may be determined that:

[0123] In addition, the evaluation device 10 is the opening test force P OP The judgment criterion for judging the opening test force P may be selected from the first judgment criterion and the second judgment criterion described above. In this case, for example, a user of the evaluation device 10 operates an input unit (not shown) to specify a judgment criterion, and the opening point judgment unit 20 judges the opening test force P according to the judgment criterion specified by the user. OP may be determined.

[0124] In addition, for example, a user of the evaluation device 10 inputs the type of metal material by operating an input unit (not shown), and the opening point determination unit 20 determines the opening test force P based on a determination criterion corresponding to the type of metal material input by the user. OP In this case, the effective stress intensity factor range ΔK may be determined for a plurality of metal materials using the first and second criteria. eff Based on the calculated results, a preferable judgment criterion may be determined in advance for each type of metallic material. Specifically, for example, fatigue crack growth tests may be performed on multiple types of metallic materials at an arbitrary stress ratio (e.g., stress ratio R = 0.05 or R = 0.5) and a high stress ratio (e.g., stress ratio R = 0.7), and the effective stress intensity factor range ΔK obtained in the test at the arbitrary stress ratio may be determined for each metallic material. eff However, it is previously determined which of the first and second judgment criteria is closer to the stress intensity factor range ΔK obtained in a test with a high stress ratio at a corresponding crack growth rate. Then, the relationship between the type of metallic material and the judgment criteria is stored in advance in the storage unit 22. As a result, the opening point judgment unit 20 selects a judgment criterion corresponding to the type of metallic material input by the user based on the above relationship stored in the storage unit 22, and calculates the opening test force P OP It is possible to determine: [Industrial Applicability]

[0125] According to the present invention, the opening point of a crack can be evaluated based on test information from a fatigue crack growth test. [Explanation of symbols]

[0126] 10 Evaluation equipment 12 Acquisition Department 14 First Calculation Section 16 Second Calculation Section 18 Third Calculation Section 20 Opening point determination section 22 Memory section 24 Fourth Calculation Section 100 test pieces 100a notch 100b Crack 100c back

Claims

1. an acquisition unit that acquires a first relationship between a test force applied to a test piece a number of times in a fatigue crack growth test and a numerical value related to the displacement of a predetermined portion of the test piece, the first relationship being obtained when the test force is applied to the test piece an arbitrary number of times; a first calculation unit that calculates a reference compliance of the test piece from a change in a numerical value related to the displacement in a first range of the test force during a period in which a crack in the test piece is open, based on the first relationship acquired by the acquisition unit; and a second calculation unit that extracts a plurality of second ranges of the test force between a maximum test force and a minimum test force when the test force is applied to the test piece an arbitrary number of times based on the first relationship acquired by the acquisition unit, and calculates a partial compliance from a change in a numerical value related to the displacement for each of the extracted plurality of second ranges; a third calculation unit that calculates a deviation value indicating a ratio of deviation from the reference compliance calculated by the first calculation unit for each of the plurality of partial compliances calculated by the second calculation unit; an opening point determination unit that generates a second relationship between the deviation value calculated by the third calculation unit for each of the partial compliances and the test force, and determines, in the second relationship, the test force when the deviation value is a preset percentage of the maximum deviation value, or the test force corresponding to a median of the deviation values ​​in the second relationship, as an opening test force corresponding to the opening point of a crack.

2. The first calculation unit determines the first range according to a stress ratio in the fatigue crack growth test, The evaluation device according to claim 1 , wherein the second calculation unit determines the second ranges depending on the stress ratio.

3. 3. The evaluation device according to claim 1, wherein the opening point determination unit calculates a comparative compliance from a change in a numerical value related to the displacement in a third range of the test force, the third range being wider than the first range and having a minimum value smaller than the minimum value of the first range, based on the first relationship acquired by the acquisition unit, and when the comparative compliance is greater than the reference compliance, determines the minimum test force to be the opening test force, rather than the test force when the deviation value is a preset percentage of the maximum deviation value in the second relationship or the test force corresponding to a median of the deviation value in the second relationship.

4. 4. The evaluation device according to claim 1, wherein when a value obtained by dividing the test force when the deviation value in the second relationship is a preset percentage relative to the maximum deviation value by the maximum test force exceeds a preset threshold value, the opening point determination unit determines the minimum test force to be the opening test force, rather than the test force when the deviation value in the second relationship is a preset percentage relative to the maximum deviation value or the test force corresponding to a median of the deviation values ​​in the second relationship.

5. The evaluation device according to claim 1 , wherein the first relationship indicates a relationship between the test force and a numerical value related to the displacement during unloading.

6. 6. The evaluation device according to claim 1, wherein the test piece is a CT test piece, and the numerical value relating to the displacement of the predetermined portion is a crack opening displacement or a strain on a back surface of the test piece.

7. The evaluation device according to claim 1 , wherein the second calculation unit extracts the second ranges such that adjacent second ranges in terms of the magnitude relationship of the test forces partially overlap each other.

8. The evaluation device according to claim 1 , wherein the predetermined ratio is set according to test conditions of a fatigue crack growth test.

9. 9. The evaluation device according to claim 1, further comprising a fourth calculation unit that calculates an effective stress intensity factor range based on the opening test force determined by the opening point determination unit.

10. A method for evaluating a crack opening point of a test specimen in a fatigue crack growth test by a computer, comprising the steps of: (a) acquiring a first relationship between a test force applied to a test piece multiple times in a fatigue crack growth test and a numerical value related to the displacement of a predetermined portion of the test piece, the test force being applied to the test piece a given number of times; (b) calculating a reference compliance of the test specimen from a change in a numerical value of the displacement in the first range of the test force during a period during which a crack in the test specimen is open based on the first relationship obtained in the step (a); (c) extracting a plurality of second ranges of the test force between a maximum test force and a minimum test force when the test force is applied to the test piece an arbitrary number of times based on the first relationship obtained in the step (a), and calculating a partial compliance from a change in a numerical value related to the displacement for each of the extracted second ranges; (d) calculating a deviation value indicating a deviation ratio of each of the plurality of partial compliances calculated in the step (c) to the reference compliance calculated in the step (b); (e) generating a second relationship between the deviation value calculated for each partial compliance in the step (d) and the test force, and determining the test force when the deviation value is a preset ratio to the maximum deviation value in the second relationship, or the test force corresponding to the median of the deviation value in the second relationship, as an opening test force corresponding to the opening point of the crack; The method for evaluating an aperture point comprises:

11. In the step (b), the first range is determined according to a stress ratio in the fatigue crack growth test; The evaluation method according to claim 10 , wherein in the step (c), the plurality of second ranges are determined in accordance with the stress ratio.

12. 12. The evaluation method according to claim 10, wherein in the step (e), a comparative compliance is calculated based on the first relationship acquired in the step (a) from a change in a numerical value related to the displacement in a third range of the test force, the third range being wider than the first range and having a minimum value smaller than the minimum value of the first range, and when the comparative compliance is greater than the reference compliance, the minimum test force is determined to be the opening test force, instead of the test force when the deviation value is a preset ratio with respect to the maximum deviation value in the second relationship or the test force corresponding to the median of the deviation value in the second relationship.

13. 13. The evaluation method according to claim 10, wherein in the step (e), when a value obtained by dividing the test force when the deviation value in the second relationship is a preset percentage relative to the maximum deviation value exceeds a preset threshold value, the minimum test force is determined to be the opening test force, instead of the test force when the deviation value in the second relationship is a preset percentage relative to the maximum deviation value or the test force corresponding to the median of the deviation value in the second relationship.

14. The evaluation method according to claim 10 , wherein the first relationship indicates a relationship between the test force and a numerical value related to the displacement during unloading.

15. 15. The evaluation method according to claim 10, wherein the test piece is a CT test piece, and the numerical value relating to the displacement of the predetermined portion is a crack opening displacement or a strain on a back surface of the test piece.

16. 16. The evaluation method according to claim 10, wherein in the step (c), the plurality of second ranges are extracted such that adjacent second ranges in terms of the magnitude relationship of the test forces partially overlap each other.

17. The evaluation method according to claim 10 , wherein the predetermined ratio is set according to test conditions of a fatigue crack growth test.

18. 18. The evaluation method according to claim 10, further comprising the step of: (f) calculating an effective stress intensity factor range based on the opening test force determined in the step (e).

19. A program for causing a computer to execute the evaluation method according to any one of claims 10 to 18.

Images