A method and device for correcting an MMC fracture model

Abstract

The application discloses a kind of MMC fracture model correction method and device, first based on the fitting MMC initial point obtained by a plurality of fitting of tensile test to initial MMC fracture curve is obtained, secondly, the initial fracture curve is divided according to preset division rule to obtain first, second, third segment data interval, finally, the second, third segment data interval is linearly adjusted to obtain adjusted MMC fracture curve.Compared with prior art, the adjusted MMC fracture curve of the application can have greater freedom to adjust MMC fracture curve on the basis of preserving linear characteristics and curve smoothness.If it is combined with optimization algorithm, the force-displacement curve error between simulation and experiment is minimized as the goal to carry out automatic feature point adjustment, optimization iteration can be completed faster, and better optimization effect and shorter optimization cycle can be achieved.

Description

Technical Field

[0001] This application relates to the field of materials testing technology, and more specifically, to a method and apparatus for correcting MMC fracture models based on data deviation ratio. Background Technology

[0002] The MMC (Modified Mohr-Coulomb) fracture model is a model proposed in 2007 based on the Mohr-Coulomb fracture mechanism. It obtains the stress triaxiality and equivalent plastic strain at fracture time under different failure states, and further performs parameter fitting to finally obtain the MMC fracture failure model (fracture curve), which can characterize the fracture failure behavior of materials under complex stress states.

[0003] Further calculations based on the MCC fracture curve can yield the force-displacement curves of various specimens under simulated conditions. However, the simulated force-displacement curves often deviate from the experimental results. Therefore, to address this issue, adjustments to the MCC fracture curve are necessary. A common adjustment method is to optimize the curve fitting points, adjusting the equivalent plastic strain (y-value of the curve) corresponding to the five tests, and then refitting a new MCC curve. While this method strictly adheres to the MCC fracture equation for fitting, the adjustment range is limited. Especially when the deviation between the simulated and experimental results on the force-displacement curve is significant, simply modifying the fitting points may not effectively improve the accuracy of the results. In extreme cases, over-adjustment may even lead to the curve not being properly fitted. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of existing technologies and provide a method and apparatus for correcting the MMC fracture model. This method allows for greater freedom in adjusting the MMC fracture curve while preserving linear characteristics and curve smoothness. When combined with optimization algorithms to automatically adjust feature points with the goal of minimizing the force-displacement curve errors in simulation and experiment, it can complete optimization iterations more quickly, achieving better optimization results and a shorter optimization cycle.

[0005] The objective of this application is achieved through the following technical solution:

[0006] Firstly, this application proposes a method for correcting an MMC fracture model, the method comprising:

[0007] The initial MMC fracture curve is obtained by fitting multiple fitted initial MMC points obtained from the tensile test based on the MMC fracture model.

[0008] The initial fracture curve is divided into first, second, and third data intervals according to a preset division rule;

[0009] The adjusted MMC fracture curve is obtained by linearly adjusting the second and third data intervals.

[0010] In one possible implementation, the horizontal axis of the initial MMC fracture curve is the stress triaxiality, and the vertical axis is the fracture equivalent plastic strain.

[0011] In one possible implementation, the functional equation of the MMC fracture model is:

[0012]

[0013] in

[0014]

[0015] ε f It is the fracture equivalent plastic strain, η is the stress triaxiality, K, C, f and n are both material constants.

[0016] In one possible implementation, the preset partitioning rule is:

[0017] The second inflection point of the initial MMC fracture curve is taken as the standard point, and the minimum point of the third segment of the initial MMC fracture curve is taken as the first adjustment feature point. Based on the standard point and the first adjustment feature point, the initial MMC fracture curve is divided into the first, second and third data intervals.

[0018] In one possible implementation, the adjusted data curve used for linear adjustment of the second data interval. The formula is: Where y0 is the standard point, y c1 As the first adjustment feature point, For the first adjusted feature point, y i For each data point before adjustment.

[0019] In one possible implementation, the end point of the initial MMC break curve is used as the second adjustment feature point, and the adjusted data curve is used for linear adjustment of the third data segment. The formula is: Where y c1 As the first adjustment feature point, y c2 For the second adjustment feature point, For the first adjusted feature point, y i For each data point before adjustment, This is the second adjusted feature point.

[0020] In one possible implementation, the tensile test includes pure shear, R5 notch tension, R10 notch tension, center hole tension, and cupping.

[0021] Secondly, this application proposes an MMC fracture model correction device, the device comprising:

[0022] The fitting module is used to fit multiple fitted MMC initial points obtained from tensile tests based on the MMC fracture model to obtain the initial MMC fracture curve.

[0023] The segmentation module is used to divide the initial fracture curve into first, second, and third data intervals according to a preset segmentation rule;

[0024] The adjustment module is used to linearly adjust the second and third data segments to obtain the adjusted MMC fracture curve.

[0025] In one possible implementation, the horizontal axis of the initial MMC fracture curve is the stress triaxiality, and the vertical axis is the fracture equivalent plastic strain.

[0026] In one possible implementation, the functional equation of the MMC fracture model is:

[0027]

[0028] in

[0029]

[0030] ε f It is the fracture equivalent plastic strain, η is the stress triaxiality, K, C, f and n are both material constants.

[0031] The main solution and its various further alternatives described above can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application; furthermore, the (non-conflicting alternatives) can also be freely combined with each other and with other alternatives. Those skilled in the art, after understanding the solution of this application, will realize from the prior art and common general knowledge that there are many combinations, all of which are technical solutions to be protected by this application, and will not be exhaustively listed here.

[0032] This application discloses a method and apparatus for correcting an MMC fracture model. First, based on the MMC fracture model, multiple fitted initial MMC points obtained from tensile experiments are fitted to obtain an initial MMC fracture curve. Second, the initial fracture curve is divided into first, second, and third data intervals according to a preset division rule. Finally, the second and third data intervals are linearly adjusted to obtain the adjusted MMC fracture curve. Compared with existing technologies, the adjusted MMC fracture curve of this application has greater freedom to adjust the MMC fracture curve while preserving linear characteristics and curve smoothness. If combined with optimization algorithms, and with the goal of minimizing the force-displacement curve error in simulation and experiment for automated feature point adjustment, faster optimization iterations can be completed, achieving better optimization results and a shorter optimization cycle. Attached Figure Description

[0033] Figure 1 A schematic flowchart of the MMC fracture model correction method provided in the embodiments of this application is shown.

[0034] Figure 2 A schematic diagram of the initial MMC fracture curve proposed in the embodiments of this application is shown.

[0035] Figure 3 A schematic diagram of the data point distribution on the initial fracture curve provided in the embodiments of this application is shown.

[0036] Figure 4 The illustration shows a schematic diagram of the MMC curves of the prior art and the MMC fracture model correction method provided in the embodiments of this application.

[0037] Figure 5 A warning diagram of MMC fitting proposed in the embodiments of this application is shown. Detailed Implementation

[0038] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0039] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] In existing technologies, force-displacement curves for various specimens under simulated conditions can be obtained through further calculations based on the MCC fracture curve. However, the simulated force-displacement curves often deviate from the experimental results. Therefore, to address this issue, adjustments to the MCC fracture curve are necessary. A common adjustment method is to optimize the curve fitting points, adjusting the equivalent plastic strain (y-value of the curve) corresponding to the five tests, and then refitting a new MCC curve. While this method strictly adheres to the MCC fracture equation for fitting, the adjustment range is limited. Especially when the deviation between the simulated and experimental results on the force-displacement curve is significant, simply modifying the fitting points may not effectively improve the accuracy of the results. In extreme cases, over-adjustment may even lead to the curve not being properly fitted.

[0041] Therefore, in order to solve the above problems, this application proposes an MMC fracture model correction method and apparatus. Based on the fracture curve obtained by fitting, the equivalent plastic strain at the curve feature position is directly adjusted, and the surrounding data points are appropriately adjusted according to a certain proportion. It can adjust the MMC fracture curve with greater freedom while preserving linear characteristics and curve smoothness. The following is a detailed description of the method.

[0042] Please refer to Figure 1 , Figure 1 The flowchart of the MMC fracture model correction method provided in the embodiments of this application is shown, including the following steps:

[0043] S100. Based on the MMC fracture model, the initial MMC fracture curve is obtained by fitting multiple fitted MMC initial points obtained from the tensile test.

[0044] Tensile tests include pure shear, R5 notch tension, R10 notch tension, center hole tension, and cupping. Based on the tensile tests and experimental samples, the fracture equivalent plastic strain and stress triaxiality corresponding to the tensile tests (pure shear, R5 notch tension, R10 notch tension, center hole tension, and cupping) are obtained. Figure 2 As shown, Figure 2 A schematic diagram of the initial MMC fracture curve proposed in this application embodiment is shown. The horizontal axis of the initial MMC fracture curve represents the stress triaxiality, and the vertical axis represents the fracture equivalent plastic strain. The MMC fracture model is obtained under two-dimensional stress conditions, not three-dimensional. The points in the figure correspond to pure shear, R5 notch tension, R10 notch tension, center hole tension, and cupping. These five corresponding coordinate points are denoted as five "fitted MMC initial points." This means that through these five points, the parameters in the function equation of MMC can be optimized to make the function model as close as possible to (fit) the given five initial points.

[0045] The functional equation of the MMC fracture model is:

[0046]

[0047] in

[0048]

[0049] ε f It is the fracture equivalent plastic strain, η is the stress triaxiality, K, C, f and n are both material constants.

[0050] By inputting multiple sets (η, ε) f Curve fitting of the values ​​can be performed using methods such as direct fitting or least squares fitting to obtain material constants. In the MMC fracture model, there are five constants to be fitted: K, C, ... f and n. It's worth noting that the values ​​of parameters K and n are obtained by fitting the stress-strain curves from the uniaxial tensile test using the Swift hardening model. Therefore, we assume K and n are known initially, and the specific values ​​obtained from the corresponding Swift hardening model fitting will be substituted into the calculation. The material parameters that actually need to be fitted are C and n. f.

[0051] Based on five fitted initial MMC points, the material parameters are determined, and the MMC fracture curve equation is obtained. Then, a uniformly spaced numerical sequence is generated within the stress triaxiality interval [-0.66, 0.66] using code. In one possible embodiment, 500 equally spaced numerical sequences are generated within the [-0.66, 0.66] interval. Each sequence is used as an x-value and input into the obtained fracture curve equation to obtain the corresponding fracture equivalent plastic strain. Based on this, 500 data coordinate points generated based on the MMC fracture curve equation can be obtained. The initial MMC fracture curve can be obtained by plotting using Python.

[0052] S200. The initial fracture curve is divided into the first, second, and third data intervals according to the preset division rules.

[0053] The default partitioning rules are:

[0054] The second inflection point of the initial MMC fracture curve is taken as the standard point, and the minimum point of the third segment of the initial MMC fracture curve is taken as the first adjustment feature point. Based on the standard point and the first adjustment feature point, the initial MMC fracture curve is divided into the first, second and third data intervals.

[0055] Please refer to this again. Figure 2 According to the aforementioned preset division rules, the initial fracture curve is divided into three data intervals, and the second and third data intervals are adjusted respectively.

[0056] S300. Linear adjustment is performed on the second and third data segments to obtain the adjusted MMC fracture curve.

[0057] The adjusted data curve used for linear adjustment of the second data interval The formula is: Where y0 is the standard point, y c1 As the first adjustment feature point, For the first adjusted feature point, y i For each data point before adjustment.

[0058] The end point of the initial MMC break curve is used as the second adjustment feature point, and the adjusted data curve is used for linear adjustment of the third data segment. The formula is: Where y c1 As the first adjustment feature point, y c2 For the second adjustment feature point, For the first adjusted feature point, y i For each data point before adjustment, This is the second adjusted feature point.

[0059] based on Figure 2 Please refer to Figure 3 , Figure 3 This illustration shows a schematic diagram of the data point distribution on the initial fracture curve provided in an embodiment of this application. c1 and y c2 These are the feature points that need adjustment, and y0 is the standard point. First, perform linear adjustment on the second segment of the curve, and then adjust the y... c1 and y c2 They are respectively denoted as and After interpolation, y0 and y c1 There are multiple data points between them, denoted as y. i We can calculate y using the following formula. c1 Adjusted to After that, for each data point y i Adjusted to Value: Next, the curve adjustment for the third segment is performed. Using the same method and based on the following formula, the result can be calculated. Plot the adjusted data curve as a curve.

[0060] Please refer to Figure 4 , Figure 4The present application provides a schematic diagram of the MMC curves of the prior art and the MMC fracture model correction method, which verifies the aforementioned MMC fracture model correction method:

[0061] Based on the MMC fracture model correction method combined with an optimization algorithm (Bayesian optimization), two feature points that need adjustment are set as variable parameters. The goal is to automatically adjust these feature points to minimize the force-displacement curve error between simulation and experiment. In one possible embodiment, the MMC curve adjustment based on the data deviation ratio is obtained through Bayesian optimization, and this is compared with the "simulation-experiment" force-displacement error obtained by directly changing the fitting points and refitting the MMC curve. The desired outcome is that the "simulation-experiment" force-displacement error of each optimized sample is less than 5%. If this is achieved, the optimization iteration will stop early; if not, all set iterations will be performed, and the maximum error value for each sample will be recorded during each iteration. The minimum value among these maximum values ​​will be selected as the optimal result for this optimization iteration.

[0062] The results obtained through calculation and verification are shown in Table 1:

[0063] Table 1

[0064]

[0065] According to the data shown in Table 1, the MMC fracture model correction method proposed in this application successfully achieved its predetermined goal after seven iterations, thus terminating the iteration process early. Through this optimization, the maximum error of the force-displacement curve was significantly reduced from 14.31% in the initial state to 4.56%. This result demonstrates that the adopted correction method has achieved significant results in correcting the accuracy of simulation results.

[0066] When adjusting the MMC fracture model using the method of adjusting the fitting points, the method performed a predetermined 20 complete iterations. During the 20 iterations, the first requirement set was not met, namely, the force-displacement error consistently failed to decrease below 5%. In the best iteration result, although the maximum error of the force-displacement curve was reduced to 6.59%, its improvement effect was relatively weak compared to the new correction method proposed in the embodiments of this application.

[0067] Furthermore, during the optimization iteration process, warning messages indicating poor MMC fitting results appeared multiple times. For example... Figure 5 As shown, these warnings are triggered based on a set standard where the r-square value is below 0.6, indicating to the user that there may be a risk of program errors during the fitting process.

[0068] Based on again Figure 4By comparing the MMC curves generated by the existing technology and the MMC fracture model correction method proposed in this application, it can be concluded that the existing technology has a long optimization cycle, limited optimization effect, and multiple prompts of poor MMC fitting during the optimization process. In contrast, the MMC curves generated by the MMC fracture model correction method proposed in this application have better optimization effect and shorter optimization cycle, and can achieve the optimization goal in advance.

[0069] The following is a possible implementation of an MMC fracture model correction device, which is used to perform the various execution steps and corresponding technical effects of the MMC fracture model correction method shown in the above embodiments and possible implementations. The device includes:

[0070] The fitting module is used to fit multiple fitted MMC initial points obtained from tensile tests based on the MMC fracture model to obtain the initial MMC fracture curve.

[0071] The segmentation module is used to divide the initial fracture curve into the first, second, and third data intervals according to a preset segmentation rule;

[0072] The adjustment module is used to linearly adjust the second and third data segments to obtain the adjusted MMC fracture curve.

[0073] In one possible implementation, the horizontal axis of the initial MMC fracture curve represents the stress triaxiality, and the vertical axis represents the fracture equivalent plastic strain.

[0074] In one possible implementation, the functional equation of the MMC fracture model is:

[0075]

[0076] in

[0077]

[0078] ε f It is the fracture equivalent plastic strain, η is the stress triaxiality, K, C, f and n are both material constants.

[0079] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for correcting an MMC fracture model, characterized in that, The method includes: The initial MMC fracture curve is obtained by fitting multiple fitted initial MMC points obtained from the tensile test based on the MMC fracture model. The initial MMC fracture curve is divided into first, second, and third data intervals according to a preset division rule, which is as follows: The second inflection point of the initial MMC fracture curve is taken as the standard point, and the minimum point of the third segment of the initial MMC fracture curve is taken as the first adjustment feature point. Based on the standard point and the first adjustment feature point, the initial MMC fracture curve is divided into the first, second and third data intervals. Linear adjustment of the second and third data segments yields the adjusted MMC fracture curve; The adjusted data curve used for linear adjustment of the second data interval The formula is: ,in As the standard point, As the first adjustment feature point, This is the first adjusted feature point. For each data point before adjustment; The adjusted data curve used to linearly adjust the third data segment is obtained by taking the end point of the initial MMC fracture curve as the second adjustment feature point. The formula is: ,in As the first adjustment feature point, For the second adjustment feature point, This is the first adjusted feature point. For each data point before adjustment, This is the second adjusted feature point.

2. The MMC fracture model correction method as described in claim 1, characterized in that, The horizontal axis of the initial MMC fracture curve represents the stress triaxiality, and the vertical axis represents the fracture equivalent plastic strain.

3. The MMC fracture model correction method as described in claim 2, characterized in that, The functional equation of the MMC fracture model is: ； in ; ； It is the fracture equivalent plastic strain, and η is the stress triaxiality. , , , , All of these are material constants.

4. The MMC fracture model correction method as described in claim 1, characterized in that, The tensile tests include pure shear, R5 notch tensile, R10 notch tensile, center hole tensile, and cupping.

5. A device for correcting MMC fracture models, characterized in that, The device includes: The fitting module is used to fit multiple fitted MMC initial points obtained from tensile tests based on the MMC fracture model to obtain the initial MMC fracture curve. The segmentation module is used to divide the initial MMC fracture curve into first, second, and third data intervals according to a preset segmentation rule. The preset segmentation rule is as follows: The second inflection point of the initial MMC fracture curve is taken as the standard point, and the minimum point of the third segment of the initial MMC fracture curve is taken as the first adjustment feature point. Based on the standard point and the first adjustment feature point, the initial MMC fracture curve is divided into the first, second and third data intervals. The adjustment module is used to linearly adjust the second and third data intervals to obtain the adjusted MMC fracture curve. The adjusted data curve used for linear adjustment of the second data interval The formula is: ,in As the standard point, As the first adjustment feature point, This is the first adjusted feature point. For each data point before adjustment; The adjusted data curve used to linearly adjust the third data segment is obtained by taking the end point of the initial MMC fracture curve as the second adjustment feature point. The formula is: ,in As the first adjustment feature point, For the second adjustment feature point, This is the first adjusted feature point. For each data point before adjustment, This is the second adjusted feature point.

6. The MMC fracture model correction device as described in claim 5, characterized in that, The horizontal axis of the initial MMC fracture curve represents the stress triaxiality, and the vertical axis represents the fracture equivalent plastic strain.

7. The MMC fracture model correction device as described in claim 6, characterized in that, The functional equation of the MMC fracture model is: ； in ; ； It is the fracture equivalent plastic strain, and η is the stress triaxiality. , , , , All of these are material constants.

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