Analysis method for detecting plastic strain ratio of automobile sheet steel

Abstract

The invention relates to an analysis method for detecting the plastic strain ratio of an automobile thin steel plate, and belongs to the technical field of metal processing methods. According to the technical scheme, the method comprises the following steps: establishing a three-dimensional model of a uniaxial tensile sample, and analyzing a deformation path of the sample through uniaxial tensile simulation of the sample; acquiring primary strain and secondary strain data of the same position of the sample by using a grid strain analysis method; fitting a primary and secondary strain curve according to the identified primary and secondary strain relationship through the obtained primary strain and secondary strain data to obtain a straight line about primary and secondary strain, and calculating the plastic strain ratio, namely R value, of the plate through fitting the slope K of the straight line; and comparing the calculated R value with the R value detected by the actual uniaxial tensile test. According to the method, uniaxial tensile simulation is carried out on the sample to obtain main strain and secondary strain data, so that the plastic strain ratio of the plate is calculated, the data is accurate, and the error is small.

Description

Technical Field

[0001] The invention relates to an analysis method for detecting the plastic strain ratio of an automobile thin steel plate, and belongs to the technical field of metal processing methods. Background Art

[0002] With the rapid development of the automobile industry, automobile styling has gradually become internationalized, resulting in more complex structural designs for automobile parts, and higher requirements for the formability of metal sheet materials. The plastic strain ratio, or R value, is an important indicator for evaluating the forming of metal stamping sheets. The common traditional method is to subject the strip-shaped specimen to a tensile testing machine to a 10%-15% tensile deformation. The ratio of the strain in the width direction of the plate to the strain in the thickness direction is called the plastic strain ratio of the plate, or R value. It can evaluate the ability of metal sheets to resist thinning or thickening when subjected to tensile stress or compressive stress. As the automotive industry gradually promotes lightweighting, high-strength steel is gradually being promoted and used. Because the deformation of high-strength steel is small, the R value of the material cannot be detected on the tensile testing machine. Therefore, the R value of the material cannot be obtained by a traditional tensile testing machine for high-strength steel materials.

[0003] During the automobile design stage, it is necessary to perform simulation analysis on automobile parts. Based on the simulation requirements of automobile parts, simulation data cards need to be produced according to the mechanical properties, yield model, fracture model, etc. of metal materials. The R value plays an indispensable role in the simulation data cards. The R value is the ability to resist thinning or thickening. When automobile parts are stamped and formed, the R value is an important indicator for evaluating the formability of parts. Summary of the invention

[0004] The purpose of the present invention is to provide an analytical method for detecting the plastic strain ratio of automobile thin steel plates. By establishing a three-dimensional model of a uniaxial tensile specimen, simulating the uniaxial tensile of the specimen, obtaining the principal strain and secondary strain data, the plastic strain ratio of the plate is calculated. The data is accurate and the error is small, which effectively solves the above-mentioned problems existing in the background technology.

[0005] The technical solution of the present invention is: an analysis method for detecting the plastic strain ratio of a thin automobile steel plate, comprising the following steps:

[0006] (1) Establish a three-dimensional model of the uniaxial tensile specimen, analyze the specimen deformation path through uniaxial tensile simulation, derive the primary and secondary strain data, and identify the relationship between the primary and secondary strains;

[0007] (2) preparing a uniaxial tensile specimen and printing grid points on the specimen;

[0008] (3) Stretching the sample with grid points on a tensile testing machine;

[0009] (4) Using the grid strain analysis method, obtain the principal strain and secondary strain data at the same position of the specimen;

[0010] (5) fitting the major and minor strain curves according to the major and minor strain relationships identified in step (1) using the acquired major and minor strain data to obtain straight lines about the major and minor strains, and calculating the plastic strain ratio of the plate, i.e., the R value, using the slope K of the fitting line;

[0011] (6) Compare the calculated R value with the R value detected by the actual uniaxial tensile test.

[0012] In the step (3), the sample with grid points is stretched on a tensile testing machine according to deformation amounts of 5%, 10%, 15% and 20%.

[0013] In the step (5), the calculation formula of R value is R=ε w / ε t , according to the volume invariance principle, ε t =-ε l -ε w , that is, R = ε w / (-ε l -ε w ), that is, R = -1 / (K+1), K is ε w / ε l , where ε l represents the true principal strain, ε w represents the true secondary strain, ε t represents the true through-thickness strain.

[0014] The beneficial effects of the present invention are as follows: by establishing a three-dimensional model of a uniaxial tensile specimen, simulating the uniaxial tensile of the specimen, obtaining principal strain and secondary strain data, and thus calculating the plastic strain ratio of the plate, the data is accurate and the error is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of the method of the present invention;

[0016] Figure 2 is a linear relationship diagram of the primary and secondary strains in uniaxial tension of an embodiment of the present invention;

[0017] Figure 3 is a schematic diagram of a uniaxial tensile specimen according to an embodiment of the present invention;

[0018] Figure 4 It is a fitted primary and secondary strain diagram of an embodiment of the present invention;

[0019] Figure 5 It is the true major and minor strain cloud diagram of the 2#, 3#, 4# and 5# specimens after stretching of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the invention implementation cases clearer, the technical solutions in the implementation cases of the present invention will be clearly and completely described below in conjunction with the drawings in the implementation cases. Obviously, the implementation cases described are only a small part of the implementation cases of the present invention, rather than all the implementation cases. Based on the implementation cases in the present invention, all other implementation cases obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] An analysis method for detecting the plastic strain ratio of a thin automobile steel plate comprises the following steps:

[0022] (1) Establish a three-dimensional model of the uniaxial tensile specimen, analyze the specimen deformation path through uniaxial tensile simulation, derive the primary and secondary strain data, and identify the relationship between the primary and secondary strains;

[0023] (2) preparing a uniaxial tensile specimen and printing grid points on the specimen;

[0024] (3) Stretching the sample with grid points on a tensile testing machine;

[0025] (4) Using the grid strain analysis method, obtain the principal strain and secondary strain data at the same position of the specimen;

[0026] (5) fitting the major and minor strain curves according to the major and minor strain relationships identified in step (1) using the acquired major and minor strain data to obtain straight lines about the major and minor strains, and calculating the plastic strain ratio of the plate, i.e., the R value, using the slope K of the fitting line;

[0027] (6) Compare the calculated R value with the R value detected by the actual uniaxial tensile test.

[0028] In the step (3), the sample with grid points is stretched on a tensile testing machine according to deformation amounts of 5%, 10%, 15% and 20%.

[0029] In the step (5), the calculation formula of R value is R=ε w / ε t , according to the volume invariance principle, ε t =-ε l -ε w , that is, R = ε w / (-ε l -ε w ), that is, R = -1 / (K+1), K is ε w / ε l , where ε l represents the true principal strain, ε w represents the true secondary strain, ε t represents the true through-thickness strain.

[0030] Example:

[0031] The present invention adopts the following steps.

[0032] (1) Through the uniaxial tensile simulation analysis of the DC52D+Z material performance data of Handan Iron and Steel, the uniaxial tensile major and minor strain data of the sample were derived and combined with FLC comparative analysis. The results showed that the major and minor strains of the sample were linearly related, such as Figure 2 ;

[0033] (2) The galvanizing production line takes DC52D+Z material and processes 5 tensile specimens perpendicular to the rolling direction according to the national standard GBT228.1-2010. They are marked as 1#, 2#, 3#, 4#, and 5#, and grid points are printed on the 2#, 3#, 4#, and 5# tensile specimens respectively. No processing is done on 1#. Figure 3 .

[0034] (3) Specimens 2#, 3#, 4# and 5# were stretched on a tensile testing machine, and the stroke was set on the tensile testing machine to stop when the specimens were deformed to 5%, 10%, 15% and 20% respectively; Specimen 1# was stretched according to the standard tensile test requirements, and the mechanical properties data of the specimens were collected, as shown in Table 1;

[0035] Table 1 Mechanical properties of DC52D+Z

[0036]

[0037] (4) For the stretched 2#, 3#, 4# and 5# specimens, use a camera to collect grid points on the specimens and identify the deformation cloud map of the specimens, such as Figure 5 , and the grid strain analysis technology is used to analyze the real primary and secondary strain data of the sample. Each sample takes 13 groups of primary and secondary strain data, as shown in Table 2

[0038] Table 2 Actual major and minor strain data of specimen 2#

[0039]

[0040]

[0041] The real major and minor strain data of specimen 3#

[0042] Strain Name Principal strain Secondary strain 1 0.089 -0.065 2 0.087 -0.069 3 0.094 -0.08 4 0.093 -0.065 5 0.096 -0.06 6 0.084 -0.068 7 0.101 -0.058 8 0.096 -0.061 9 0.106 -0.057 10 0.097 -0.059 11 0.083 -0.066 12 0.085 -0.063 13 0.08 -0.06

[0043] The real major and minor strain data of the 4# specimen

[0044]

[0045]

[0046] The real major and minor strain data of the 5# specimen

[0047]

[0048]

[0049] (5) According to the strain data obtained in step (4), the primary and secondary strain curves are fitted and compared with the simulation data in step (1), such as Figure 4 ;

[0050] (6) According to the linear relationship between the major and minor strains obtained in step (5), combined with the R value calculation formula R = -1 / (K+1), K represents the slope, the R value of the sample is calculated to be 2.347969. The R value of the 1# sample tested in the test is 2.349, with an error of 0.44%

[0051] (7) This method was used to verify the accuracy of the calculated R value on 20 brands including DC01, DC06, DC56D+Z, and HC180BD+Z. The error was within 1%, as shown in Table 3.

[0052] Table 3 Calculated R values

[0053]

[0054]

[0055] (8) Since high-strength steel has a small deformation, the tensile testing machine cannot detect the R value. By extending this method to high-strength steel, the R value of high-strength steel is calculated. From the calculation results, it can be seen that with the increase of material strength, the R value shows a decreasing trend. Compared with DP steel, DH steel has a higher R value and better ductility, as shown in Table 4.

[0056] Table 4 Calculation of R value of high strength steel

[0057] Brand Calculating the R value HC340 / 590DP 0.857 HC340 / 590DH 1.1 HC340 / 590DHD+Z 1.02 HC340 / 590DPD+Z 0.9 HC420 / 780DH 0.78 HC420 / 780DHD+Z 0.75 HC420 / 780DP 0.88 HC420 / 780DPD+Z 0.74 HC550 / 980DP 0.8 HC550 / 980DPD+Z 0.78

Claims

1. An analytical method for detecting the plastic strain ratio of automobile thin steel plates, characterized in that The following steps are involved: (1) Establish a three-dimensional model of the uniaxial tensile specimen, analyze the specimen deformation path through uniaxial tensile simulation, derive the primary and secondary strain data, and identify the relationship between the primary and secondary strains; (2) preparing a uniaxial tensile specimen and printing grid points on the specimen; (3) Stretching the sample with grid points on a tensile testing machine; (4) Using the grid strain analysis method, obtain the principal strain and secondary strain data at the same position of the specimen; (5) fitting the major and minor strain curves according to the major and minor strain relationships identified in step (1) using the acquired major and minor strain data to obtain straight lines about the major and minor strains, and calculating the plastic strain ratio of the plate, i.e., the R value, using the slope K of the fitting line; (6) Compare the calculated R value with the R value detected by the actual uniaxial tensile test.

2. The analysis method for detecting the plastic strain ratio of automobile thin steel plates according to claim 1 is characterized in that: In the step (3), the sample with grid points is stretched on a tensile testing machine according to deformation amounts of 5%, 10%, 15% and 20%.

3. The analysis method for detecting the plastic strain ratio of automobile thin steel plates according to claim 1, characterized in that: In the step (5), the calculation formula of R value is R=ε w / ε t , according to the volume invariance principle, ε t =-ε l -ε w , that is, R = ε w / (-ε l -ε w ), that is, R = -1 / (K+1), K is ε w / ε l , where ε l represents the true principal strain, ε w represents the true secondary strain, ε t represents the true through-thickness strain.

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