Material hardening curve fitting method for CAE simulation

Abstract

The invention relates to a material hardening curve fitting method for CAE (computer aided engineering) simulation, which comprises the following steps of: respectively calculating tangent slopes from two points to a plurality of points at the tail end of an effective stress-strain curve, acquiring the maximum slope, determining the slope range of an upper fitting curve and the slope range of a lower fitting curve, and calculating the maximum slope. Fitting a plurality of points at the tail end of the effective stress-strain curve by adopting a hardening model to form an upper fitting curve of which the slope is gradually reduced, connecting the effective stress-strain curve with the upper fitting curve to form an upper simulation curve, inserting a point of which the stress is the same as that of the tail end point at the tail end of the effective stress-strain curve, the strain is 105%-120% of the strain of the tail end point, fitting a lower fitting curve with an upper fitting curve method, and determining whether an upper simulation curve or a lower simulation curve is adopted for output according to a slope range; the method solves the problems of complex resultant curve calculation, long time consumption, difficulty in algorithm editing and expensive software, is simple in implementation method, is not limited by steel types, and effectively saves manpower and material resources.

Description

Technical Field

[0001] The invention relates to the technical field of metal sheet forming, and in particular to a material hardening curve fitting method for CAE simulation. Background Art

[0002] When performing CAE simulation, it is necessary to first determine the input curve and verify whether the input curve can make the simulation output curve and the test curve have the best fit. This requires continuous adjustment of parameters to form different input curves. The input curve is a curve fitted based on the test curve. The commonly used fitting hardening model is Swift-Hockett-Shery. The manual editing algorithm of this hardening model is relatively complex, time-consuming and difficult. The use of professional processing software such as Matlab is relatively expensive, and is limited by the fixed parameters of the model. The fitting effect for some steel grades is relatively poor.

[0003] A Chinese patent with publication number CN115292995A discloses a method for fitting a hardening curve of a metal material, comprising the following steps: S1, performing a uniaxial tensile test on the material to obtain a force-displacement curve and an engineering stress-strain curve of the test; S2, based on data points before the peak point of the engineering stress-strain curve, calculating the true stress-plastic strain curve of the material and using it as the first part of the hardening curve; S3, fitting the extension to obtain the second part of the hardening curve; S4, merging the first part and the second part; S5, establishing a finite element model, performing simulation calculations, and obtaining a simulated force-displacement curve; S6, comparing the simulated force-displacement curve with the test force-displacement curve, if the error between the two is within a set threshold, curing the hardening curve of S4 as the hardening curve of the material; if the error between the two is not within the set threshold, returning to S3, optimizing the parameter value until the error is within the set threshold; while improving the fitting accuracy, the convenience of fitting is also improved; but the invention does not involve a specific hardening curve fitting method. Summary of the invention

[0004] The invention provides a material hardening curve fitting method for CAE simulation, which solves the problems that the calculation of the hardening model Swift-Hockett-Shery fitting curve is complex, time-consuming, and the editing algorithm is difficult, while the professional processing software such as MATLAB is expensive. The invention can realize the function of the invention based on WPS or Office by using VBA or any free programmable software, and the implementation method is simpler, is not limited by the steel type, and can effectively save manpower and material resources.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A material hardening curve fitting method for CAE simulation includes the following steps:

[0007] S1. Calculate the tangent slopes from two points at the end of the effective stress-strain curve to multiple points respectively, obtain the maximum slope, determine the slope range of the upper fitting curve, and determine the slope range of the lower fitting curve at the same time;

[0008] S2. The hardening model is used to fit multiple points at the end of the effective stress-strain curve to form an upper fitting curve with a gradually decreasing slope. The effective stress-strain curve is connected to the upper fitting curve to form an upper simulation curve.

[0009] S3. Insert a point with the same stress as the end point at the end of the effective stress-strain curve, and the strain is 105% to 120% of the end point strain to form a new effective stress-strain curve;

[0010] S4, fitting two or more points at the end of the new effective stress-strain curve using the hardening model to form a lower fitting curve with a gradually increasing tangent slope, and the original effective stress-strain curve is connected to the lower fitting curve to form a lower simulation curve;

[0011] S5. When a simulation curve with a specific slope needs to be output, the slope range obtained in the above steps is used to determine whether to use the upper simulation curve or the lower simulation curve for output, and the simulation curve is output using step S2 or step S4.

[0012] Furthermore, the step S1 of determining the slope range of the upper fitting curve includes: fitting the multiple points at the end of the effective stress-strain curve using the hardening model respectively, calculating the slopes of the first two points of the fitting curve, and when the slope of the upper fitting curve is less than or equal to the maximum slope of the effective stress-strain curve and less than the slope calculated last time, if it is the minimum slope, exiting the loop calculation, thereby determining the slope range of the upper fitting curve.

[0013] Furthermore, the formula of the hardening model is as follows:

[0014] y=C·x n (1)

[0015] Among them, y is stress, x is strain, C is coefficient, and n is coefficient.

[0016] Furthermore, the step S4 of forming a lower fitting curve with a gradually increasing tangent slope includes: fitting two to multiple points at the end of the new effective stress-strain curve using a hardening model, calculating the slopes of the first two points of the fitting curve, and when the slope of the lower fitting curve is greater than or equal to 0, less than or equal to the minimum slope of the upper fitting curve, and greater than the slope calculated last time, it is determined to be the maximum slope, then the loop calculation is exited to form a lower fitting curve with a gradually increasing tangent slope.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) This method performs curve fitting based on the effective stress-strain curve to form two curve slope ranges. The simulation curve with a specific slope can be output by selecting the upper simulation curve or the lower simulation curve according to the slope range;

[0019] 2) This method can replace the Swift-Hockett-Shery fitting curve of the hardening model, solving the problem that the Swift-Hockett-Shery calculation is complex, time-consuming, and difficult to edit the algorithm, while the use of professional processing software such as MATLAB is expensive;

[0020] 3) The present invention can realize the above functions based on WPS or Office by using VBA or any free programmable software. The implementation method is simpler, is not limited by the type of steel, and can effectively save manpower and material resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the fitting curve of the present invention. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0023] The present invention discloses a material hardening curve fitting method for CAE simulation. The simulation curve is composed of an effective stress-strain curve and a fitting curve. The fitting curve can be divided into an upper fitting curve and a lower fitting curve. First, the tangent slopes of multiple points at the end of the effective stress-strain curve are calculated to obtain the maximum slope. The two points to multiple points at the end of the effective stress-strain curve are fitted respectively using a hardening model to form an upper fitting curve with a gradually decreasing tangent slope. The tangent slope of the upper fitting curve is calculated using the first two points of the upper fitting curve. The tangent slope of the upper fitting curve is not greater than the maximum slope of the effective stress-strain curve to ensure smooth connection between the effective stress-strain curve and the upper fitting curve. This step can determine the slope range of the upper fitting curve, and can also determine the slope range of the lower fitting curve. The slope range of the curve; secondly, insert a point with the same stress as the end point at the end of the effective stress-strain curve, and the strain is 105% to 120% of the strain at the end point. By fitting two to multiple points at the end of the effective stress-strain curve at this time using the hardening model, a lower fitting curve with a gradually increasing tangent slope can be formed. The tangent slope is calculated using the first two points of the lower fitting curve. The minimum slope of the lower fitting curve is 0, and the maximum slope is the minimum slope of the upper fitting curve. The effective stress-strain curve is connected to the upper fitting curve or the lower fitting curve to form a simulation curve group with a gradually increasing fitting curve slope. The simulation curve with a specific slope can be determined by the slope range to determine whether the upper simulation curve or the lower simulation curve should be output. The method specifically includes the following steps:

[0024] S1. Calculate the tangent slopes from two points at the end of the effective stress-strain curve to multiple points respectively, obtain the maximum slope, fit the multiple points at the end of the effective stress-strain curve respectively using the hardening model, calculate the slopes of the first two points of the fitting curve, and determine whether the slope of the upper fitting curve is less than or equal to the maximum slope of the effective stress-strain curve, whether it is less than the slope calculated last time, and whether it is already the minimum slope. If it is the minimum slope, exit the loop calculation. This step can determine the slope range of the upper fitting curve. The lower range of the curve is 0 to the slope of the lowest curve of the upper curve, so the slope range of the lower fitting curve is determined while determining the range of the upper curve.

[0025] S2. Use the following formula to fit multiple points at the end of the effective stress-strain curve:

[0026] Formula y = C x n (2)

[0027] Among them, y is stress, x is strain, C is coefficient, and n is coefficient;

[0028] An upper fitting curve with a gradually decreasing slope is formed, and the effective stress-strain curve is connected with the upper fitting curve to form an upper simulation curve.

[0029] S3. Insert a point with the same stress as the end point at the end of the effective stress-strain curve, and the strain is 105% to 120% of the end point strain to form a new effective stress-strain curve.

[0030] S4. For two or more points at the end of the new effective stress-strain curve, use the formula y = C x n Fitting is performed, the slopes of the first two points of the fitting curve are calculated, and it is determined whether the slope of the lower fitting curve is greater than or equal to 0, less than or equal to the minimum slope of the upper fitting curve, greater than the slope calculated last time, and the maximum slope. This step forms a lower fitting curve with a gradually increasing tangent slope. The original effective stress-strain curve is connected to the lower fitting curve to form a lower simulation curve.

[0031] S5. When a simulation curve with a specific slope needs to be output, the slope range can be used to determine whether the upper simulation curve or the lower simulation curve should be output, and the output simulation curve is calculated using step S2 or step S4.

[0032] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0033] [Example]

[0034] like Figure 1 The figure is a schematic diagram of the fitting curve of the present invention. The method is based on the effective stress-strain curve L 有效 Perform curve fitting, L 有效 It is obtained by processing experimental data. The first half of the fitting process is L 有效 , the second half is the fitting curve L 拟合 The curve L 仿真i ; Fitting curve L 拟合 Divided into the upper fitting curve L 拟合上i and the lower fitting curve L 拟合下i , curve L 仿真i Divided into upper simulation curve L 仿真上i and the lower simulation curve L 仿真下i , effective stress-strain curve L 有效 The maximum tangent slope of multiple points at the end is k0, and the upper fitting curve L 拟合上i The slope between the first two points is k1 i , the lower fitting curve L 拟合下i The slope between the first two points is k2 i , k1 i The range is k1 min ≤k1 i ≤k0, k2 ranges from 0≤k2i ≤k1 min , L 仿真上i The range is L 仿真上min ≤L 仿真上i ≤L 仿真上max , L 仿真下 The range is L 仿真下min ≤L 仿真下i ≤L 仿真下max , specifically including the following steps:

[0035] S1, calculate the effective stress-strain curve L 有效 The tangent slope from the end point 2 to the 10th point is used to obtain the maximum slope k0 and the effective stress-strain curve L 有效 The multiple points at the end use the formula y = C x n Perform fitting and calculate the fitting curve L 拟合上i The slope k1 of the first two points i , if k1 i ≤k0, then judge k1 i Is it less than the slope k1 calculated last time? i-1 , if k1 i ≤k1 i-1 Then record k1 min =k1 i , the maximum number of cycles is L 有效 points until the whole cycle ends, and k1 can be obtained min The value of k1 is obtained at the same time i If the slope k1 i >k0 or k1 i >k1 i-1 , then give up this calculation, adjust the number of points selected at the end, and use the formula y = C x n Re-fit, this step can determine the upper fitting curve L 拟合上i The slope range is k1 min ≤k1 i ≤k0, and the lower fitting curve L can be determined 拟合下i The slope range is 0≤k2 i ≤k1 min .

[0036] S2, effective stress-strain curve L 有效 The multiple points at the end use the formula y = C x n Fitting is performed to form the slope k1 i The gradually decreasing upper fitting curve L 拟合上i , effective stress-strain curve L 有效 Connect the upper fitting curve L 拟合上i Forming the upper simulation curve L 仿真上i .

[0037] S3, effective stress-strain curve L 有效 The strain point is strain i , stress point is stress i , in strain i Then insert a strain i+1 , must satisfy L 有效 The strain interval, i.e. strain i+1 -strain i =strain i -strain i-1 , then in the effective stress-strain curve L 有效 End stress i Then insert a stress of the same magnitude i+1 , namely stress i+1 =stress i , and mark the effective stress-strain curve after the insertion point as L 有效下 .

[0038] S4, for curve L 有效下 From the two points at the end to multiple points, the formula y = C x n Perform fitting and calculate the fitting curve L 拟合下i The slope k2 of the first two points i , if 0<k2 i ≤k1 min , then the output slope k2 i The gradually increasing lower fitting curve L 拟合下i , effective stress-strain curve L 有效 Connect the lower fitting curve L 拟合下i Forming the lower simulation curve L 仿真下i .

[0039] S5. When it is necessary to output a simulation curve L with a specific slope ki 仿真i When the slope range k1 generated by step S1 is min ≤k1 i ≤k0 and 0≤k2 i ≤k1 min Determine whether to use step S2 or step S4 to output the simulation curve L 仿真i .

Claims

1. A material hardening curve fitting method for CAE simulation, characterized in that: The steps include: S1. Calculate the tangent slopes from two points at the end of the effective stress-strain curve to multiple points respectively, obtain the maximum slope, determine the slope range of the upper fitting curve, and determine the slope range of the lower fitting curve at the same time; S2. The hardening model is used to fit multiple points at the end of the effective stress-strain curve to form an upper fitting curve with a gradually decreasing slope. The effective stress-strain curve is connected to the upper fitting curve to form an upper simulation curve. S3. Insert a point with the same stress as the end point at the end of the effective stress-strain curve, and the strain is 105% to 120% of the end point strain to form a new effective stress-strain curve; S4, fitting two or more points at the end of the new effective stress-strain curve using the hardening model to form a lower fitting curve with a gradually increasing tangent slope, and the original effective stress-strain curve is connected to the lower fitting curve to form a lower simulation curve; S5. When a simulation curve with a specific slope needs to be output, the slope range obtained in the above steps is used to determine whether to use the upper simulation curve or the lower simulation curve for output, and the simulation curve is output using step S2 or step S4.

2. The material hardening curve fitting method for CAE simulation according to claim 1, characterized in that: The step S1 of determining the slope range of the upper fitting curve includes: fitting multiple points at the end of the effective stress-strain curve using a hardening model, calculating the slopes of the first two points of the fitting curve, and when the slope of the upper fitting curve is less than or equal to the maximum slope of the effective stress-strain curve and less than the slope calculated last time, if it is the minimum slope, exiting the loop calculation, thereby determining the slope range of the upper fitting curve.

3. The material hardening curve fitting method for CAE simulation according to claim 1, characterized in that: The formula of the hardening model is as follows: y=C·x n (1) Among them, y is stress, x is strain, C is coefficient, and n is coefficient.

4. The material hardening curve fitting method for CAE simulation according to claim 1, characterized in that: The step S4 of forming a lower fitting curve with a gradually increasing tangent slope comprises: fitting two to multiple points at the end of the new effective stress-strain curve using a hardening model, calculating the slopes of the first two points of the fitting curve, and when the slope of the lower fitting curve is greater than or equal to 0, less than or equal to the minimum slope of the upper fitting curve, and greater than the slope calculated last time, determining it as the maximum slope, then exiting the loop calculation to form a lower fitting curve with a gradually increasing tangent slope.

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