Determination method of biaxial tensile effective strength

Abstract

The invention provides a biaxial tensile effective strength measuring method which comprises the following steps: S1, manufacturing four types of biaxial tensile samples based on a position relationship between a plate rolling direction and a tensile arm; s2, based on the biaxial tensile sample, determining a tensile proportionality coefficient of the biaxial tensile test; s3, carrying out a biaxial tensile test, and determining a strength value Bzx corresponding to the strain point Azx; s4, calculating a mean value Bzxj of the strength corresponding to the stretching directions X of the biaxial stretching curves of the current two stretching ratios; and S5, sequentially calculating a strength mean value Bzxj of the biaxial tension curve in the tension direction X under each sample type, and calculating the minimum value of the strength mean value Bzxj of the biaxial tension curve in the tension direction X under each sample type, wherein the minimum value is the biaxial tension effective strength of the sample. According to the method, the effective deformation characteristics of the plate under the biaxial tension loading condition can be accurately represented in forming simulation analysis, and the forming precision and manufacturing efficiency of automobile parts are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sheet material simulation analysis, and in particular to a method for measuring biaxial tensile effective strength. Background Art

[0002] Automotive parts are often manufactured using stamping processes, which involve feeding sheet metal into a specialized die and applying a certain amount of pressure to achieve the desired part shape. To accurately design the die structure and manufacturing process, simulation software is required to analyze and design a suitable forming process for the sheet metal. The sheet metal's biaxial tensile deformation characteristics during the forming process must be accurately input to ensure accurate simulation analysis. Inaccurate sheet metal deformation characteristics input during simulation analysis can lead to significant errors in the part's forming process parameters.

[0003] Currently, the industry often uses the uniaxial tensile deformation characteristics of sheet metal in forming simulation analysis to approximate the biaxial deformation the sheet metal will experience during forming. However, the mechanical properties of sheet metal under uniaxial and biaxial tension differ significantly. Using uniaxial tensile analysis results to design forming dies for parts will inevitably lead to inaccurate die designs, resulting in extensive die repair work, significantly increasing repair costs and time, and failing to meet actual production requirements. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to propose a method for measuring the effective strength of biaxial tension to solve the problems of large analysis errors and high mold repair costs in existing methods.

[0005] The technical means adopted in the present invention are as follows: A method for determining effective biaxial tensile strength, comprising the following steps: S1. Based on the positional relationship between the sheet rolling direction and the first, second, third, and fourth tensile arms, four types of biaxial tensile specimens are prepared. S2. Determine the tensile ratio coefficient Z=X / Y of the biaxial tensile test based on the biaxial tensile specimen; S3. Perform a biaxial tensile test on the biaxial tensile specimen according to the tensile ratio coefficient to obtain a biaxial tensile curve for each tensile ratio, and determine the maximum limit strain point A of the biaxial tensile curve with the tensile direction Y under a single tensile ratio. zy The absolute value of the maximum limit strain point A zy As a benchmark, find the strain point A corresponding to the biaxial tensile curve with the tensile direction X zx , determine the strain point A zx The corresponding intensity value B zx ; S4, sequentially obtain the strength B of the biaxial stretching curve in the stretching direction X for each stretching ratio zx If the strength change value of two consecutive stretching ratios exceeds the specified value, continue to increase the proportional coefficient in S2 and repeat S3 until the strength change value of two consecutive stretching ratios does not exceed the specified value. Calculate the mean value B of the strength corresponding to the stretching direction X of the biaxial stretching curve of the current two stretching ratios. zxj ; S5. Calculate the mean strength value B of the biaxial tensile curve in the tensile direction X for each sample type. zxj Calculate the mean strength B of the biaxial tensile curve in the tensile direction X for each sample type zxj The minimum value is the effective biaxial tensile strength of the sample.

[0006] Furthermore, the central axis of the first stretching arm and the second stretching arm is the same, which is the first central axis; the central axis of the third stretching arm and the fourth stretching arm is the same, which is the second central axis; the first central axis is perpendicular to the second central axis.

[0007] Furthermore, four types of biaxial tensile specimens are as follows: For the first specimen type, the sheet material has a rolling direction parallel to the first central axis; For the second specimen type, the rolling direction of the sheet is parallel to the second central axis; For the third specimen type, the rolling direction of the sheet material is at an angle of 45 degrees to the first central axis; For the fourth sample type, the rolling direction of the sheet material is at an angle of 45 degrees to the second central axis.

[0008] Furthermore, in S2: The stretch ratio coefficient Z=X / Y starts from 1 and increases by 1 times each time. The stretch ratio of each specimen type shall be increased at least 2 times; The X direction is the direction of the first tensile arm and the second tensile arm in the sheet material of the first sample type; the Y direction is the direction of the third tensile arm and the fourth tensile arm in the sheet material of the first sample type; The X direction is the direction of the third tensile arm and the fourth tensile arm in the second sample type sheet; the Y direction is the direction of the first tensile arm and the second tensile arm in the second sample type sheet; The X direction is the direction of the first tensile arm and the second tensile arm in the third sample type of sheet material; the Y direction is the direction of the third tensile arm and the fourth tensile arm in the third sample type of sheet material; The X direction is the direction of the third tensile arm and the fourth tensile arm in the fourth sample type of the sheet material; the Y direction is the direction of the first tensile arm and the second tensile arm in the fourth sample type of the sheet material.

[0009] Furthermore, in S4, the prescribed value is 10 MPa.

[0010] Compared with the prior art, the present invention has the following advantages: The present invention discloses a determination and determination method of biaxial tensile effective strength, which can accurately characterize the effective deformation characteristics of sheet metal under biaxial tensile loading conditions in forming simulation analysis, overcomes the difficulties of large analysis errors and high mold repair costs using traditional methods, greatly improves the forming accuracy and manufacturing efficiency of automotive parts, and widely meets the actual application requirements of engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0012] Figure 1 Flow chart of the method of the present invention.

[0013] Figure 2 Schematic diagram of sample preparation of the present invention.

[0014] Figure 3 Schematic diagram of the tensile direction of the sample of the present invention.

[0015] Figure 4 The stretching ratio of the present invention is 1:1. 1x Confirm the diagram. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0017] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0018] like Figure 1 As shown, the present invention provides a method for determining the effective strength of biaxial tension. Based on the complex biaxial loading mechanism of metal materials, the complex mechanical behavior of the material is associated with the finite element calculation principle. By cleverly combining the loading mechanism of the biaxial tensile test with the finite element theory, a method for accurately characterizing the effective strength characteristics of the material is formed. The specific method and steps are as follows: S1. Prepare four types of biaxial tensile specimens. For the first type of specimen, the sheet rolling direction is parallel to the center lines of the first and second tensile arms. For the second type of specimen, the sheet rolling direction is parallel to the center lines of the third and fourth tensile arms. For the third type of specimen, the sheet rolling direction forms a 45-degree angle with the center lines of the first and second tensile arms. For the fourth type of specimen, the sheet rolling direction forms a 45-degree angle with the center lines of the third and fourth tensile arms. S2. Determine the stretching ratio for the biaxial tensile test as X:Y, where X corresponds to the stretching direction of the first and second stretching arms of the first specimen, the third and fourth stretching arms of the second specimen, the first and second stretching arms of the third specimen, and the third and fourth stretching arms of the fourth specimen in S1. Y is the other stretching direction of the specimen. The proportional coefficient Z = X / Y starts at 1 and increases by 1 each time. The stretching ratio for each specimen type should be increased at least twice. like Figure 2 and 3 As shown, the central axis of the first stretching arm and the second stretching arm is the same, which is the first central axis; the central axis of the third stretching arm and the fourth stretching arm is the same, which is the second central axis; the first central axis is perpendicular to the second central axis.

[0019] S3. Carry out biaxial tensile test on the biaxial tensile specimen prepared in S1 according to the stretching ratio of S2 to obtain the biaxial tensile curve for each stretching ratio, and determine the maximum limit strain point A of the biaxial tensile curve with the stretching direction Y under a single stretching ratio. zyThe absolute value of the limit strain point is used as the reference to find the strain point A corresponding to the tensile direction of the biaxial tensile curve X. zx , determine the strength value B corresponding to the strain point zx ; That is, if the maximum limit strain point A ZY If the strain is 1.0% (in the Y direction), then find the strength value corresponding to 1.0% of the strain point in the biaxial tensile curve with the tensile direction in the X direction. Because strain and stress correspond to each other, there will be stress when there is strain.

[0020] S4. Obtain the strength B of the biaxial stretching curve in the stretching direction X for each stretching ratio according to S3. zx If the strength change value of two consecutive stretching ratios exceeds 10MPa, continue to increase the proportional coefficient in S2 and repeat S3 until the strength change value of two consecutive stretching ratios does not exceed 10MPa. Calculate the mean value B of the strength corresponding to the stretching direction X of the biaxial stretching curve of the current two stretching ratios. zxj ; S5. Calculate the mean strength B of the biaxial tensile curve in the tensile direction X for each sample type according to S3 and S4. zxj Calculate the mean strength B of the biaxial tensile curve in the tensile direction X for each sample type zxj The minimum value is the effective biaxial tensile strength of the sample, and this value can accurately characterize the effective strength characteristics of the current material under biaxial tensile loading conditions.

[0021] Example S1. Prepare four types of biaxial tensile specimens. The sheet rolling direction of the first specimen type is parallel to the center line of the first and second tensile arms. The sheet rolling direction of the second specimen type is parallel to the center line of the third and fourth tensile arms. The sheet rolling direction of the third specimen type is at a 45-degree angle to the center line of the first and second tensile arms. The sheet rolling direction of the fourth specimen type is at a 45-degree angle to the center line of the third and fourth tensile arms. The specimen preparation diagram is shown in FIG. Figure 2 As shown; S2. Determine the stretching ratio of the biaxial tensile test as X:Y, where X corresponds to the stretching direction of the first and second stretching arms of the first sample, the third and fourth stretching arms of the second sample, the first and second stretching arms of the third sample, and the third and fourth stretching arms of the fourth sample in step 1, and Y is the other stretching direction of the sample. The schematic diagram of the stretching direction of the sample is shown in FIG. Figure 3 The proportional coefficient Z=X / Y ranges from 1 to 5, increasing by 1 times each time. The specific stretching ratios are 1:1, 2:1, 3:1, 4:1, and 5:1. S3, carry out biaxial tensile test on the biaxial tensile specimen prepared in step 1 according to the stretching ratio of S2, obtain biaxial tensile curves for each stretching ratio, and determine the maximum limit strain point A of the biaxial tensile curve with a stretching ratio of 1:1 and a stretching direction of Y. 1y The absolute value is 1.08%. Based on this limit strain point, find the strain point A corresponding to the tensile direction X of the biaxial tensile curve. 1x is 1.08%, determine the strength value B corresponding to this strain point 1x 217.6MPa; S4. Obtain the strength B in the stretching direction X of the biaxial stretching curve with a stretching ratio of 1:1, 2:1, 3:1, 4:1, and 5:1 according to S3. 1x 、B 2x 、B 3x 、B 4x 、B 5x They are 217.6MPa, 246.1MPa, 278.2MPa, 302.7MPa, and 308.6MPa respectively. If the strength change value of two consecutive stretching ratios exceeds 10MPa, continue to increase the proportional coefficient in S2 and repeat S3 until the strength change value of two consecutive stretching ratios does not exceed 10MPa. Calculate the mean value Bzxj of the strength corresponding to the stretching direction X of the biaxial stretching curve of the current two stretching ratios; S5. Calculate the mean strength B of the biaxial tensile curve in the tensile direction X for each sample type according to S3 and S4. zxj Calculate the mean strength B of the biaxial tensile curve in the tensile direction X for each sample type zxj The minimum value is the effective biaxial tensile strength of the sample, and this value can accurately characterize the effective strength characteristics of the current material under biaxial tensile loading conditions.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining effective biaxial tensile strength, characterized in that: The steps include: S1. Based on the positional relationship between the sheet rolling direction and the first, second, third, and fourth tensile arms, four types of biaxial tensile specimens are prepared. S2. Determine the tensile ratio coefficient Z=X / Y of the biaxial tensile test based on the biaxial tensile specimen; S3. Perform a biaxial tensile test on the biaxial tensile specimen according to the tensile ratio coefficient to obtain a biaxial tensile curve for each tensile ratio, and determine the maximum limit strain point A of the biaxial tensile curve with the tensile direction Y under a single tensile ratio. zy The absolute value of the maximum limit strain point A zy As a benchmark, find the strain point A corresponding to the biaxial tensile curve with the tensile direction X zx , determine the strain point A zx The corresponding intensity value B zx ; S4, sequentially obtain the strength B of the biaxial stretching curve in the stretching direction X for each stretching ratio zx If the strength change value of two consecutive stretching ratios exceeds the specified value, continue to increase the proportional coefficient in S2 and repeat S3 until the strength change value of two consecutive stretching ratios does not exceed the specified value. Calculate the mean value B of the strength corresponding to the stretching direction X of the biaxial stretching curve of the current two stretching ratios. zxj ; S5. Calculate the mean strength value B of the biaxial tensile curve in the tensile direction X for each sample type. zxj Calculate the mean strength B of the biaxial tensile curve in the tensile direction X for each sample type zxj The minimum value is the effective biaxial tensile strength of the sample.

2. The method for measuring the effective biaxial tensile strength according to claim 1, wherein: The central axis of the first stretching arm and the second stretching arm is the same, which is the first central axis; the central axis of the third stretching arm and the fourth stretching arm is the same, which is the second central axis; the first central axis is perpendicular to the second central axis.

3. The method for measuring the effective biaxial tensile strength according to claim 2, wherein: The four types of biaxial tensile specimens are as follows: For the first specimen type, the sheet material has a rolling direction parallel to the first central axis; For the second specimen type, the rolling direction of the sheet is parallel to the second central axis; For the third specimen type, the rolling direction of the sheet material is at an angle of 45 degrees to the first central axis; For the fourth sample type, the rolling direction of the sheet material is at an angle of 45 degrees to the second central axis.

4. The method for measuring the effective biaxial tensile strength according to claim 1, wherein: In S2: The stretch ratio coefficient Z=X / Y starts from 1 and increases by 1 times each time. The stretch ratio of each specimen type shall be increased at least 2 times; The X direction is the direction of the first tensile arm and the second tensile arm in the sheet material of the first sample type; the Y direction is the direction of the third tensile arm and the fourth tensile arm in the sheet material of the first sample type; The X direction is the direction of the third tensile arm and the fourth tensile arm in the second sample type sheet; the Y direction is the direction of the first tensile arm and the second tensile arm in the second sample type sheet; The X direction is the direction of the first tensile arm and the second tensile arm in the third sample type of sheet material; the Y direction is the direction of the third tensile arm and the fourth tensile arm in the third sample type of sheet material; The X direction is the direction of the third tensile arm and the fourth tensile arm in the fourth sample type of the sheet material; the Y direction is the direction of the first tensile arm and the second tensile arm in the fourth sample type of the sheet material.

5. The method for measuring the effective biaxial tensile strength according to claim 1, wherein: In S4, the prescribed value is 10 MPa.

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