A method and system for obtaining stress-strain curve of cold-bent steel

Abstract

The present invention provides a method and system for obtaining a stress-strain curve of a cold-bent steel, which belongs to the field of cold-bent steel performance analysis. The method includes the following steps: obtaining basic material property data of the corner of the cold-bent steel, constructing a first parameter calculation model according to the basic material property data, and using the first parameter calculation model to calculate the key mechanical parameters of the cold-bent steel corner strain; constructing a second parameter calculation model according to the key mechanical parameters, and using the second parameter calculation model to calculate the first strengthening index, the second strengthening index and the correlation coefficient; constructing a stress-strain model of the corner of the cold-bent steel, inputting the first strengthening index, the second strengthening index and the correlation coefficient into the stress-strain model, and generating a stress-strain curve of the corner of the cold-bent steel. The present invention only requires a small amount of basic material property data and combines it with the constructed model to generate a stress-strain curve. The entire process does not require a tensile test, which is convenient and quick.

Description

Technical Field

[0001] The invention belongs to the field of cold-bent steel performance analysis, and in particular relates to a method and system for obtaining a stress-strain curve of a cold-bent steel. Background Art

[0002] Cold-formed steel is widely used in construction projects. After cold-bending, the performance of the corners of the cold-processed area will change, with yield strength and tensile strength increasing but ductility decreasing, which in turn affects the mechanical properties of the structure. The stress-strain curve is an important means of mechanical property analysis of cold-formed steel and is also the key to structural performance design based on finite element analysis. Therefore, it is very necessary to obtain the stress-strain curve of cold-formed steel.

[0003] At present, the stress-strain curve of cold-bending steel is generally obtained through tensile testing of cold-bending area materials. The stress-strain curve obtained by this method is usually of high accuracy, but this method also has some disadvantages. For example, due to the geometric characteristics of the corners of the cold-bent structure, the processing of the tensile specimens at the corners of the cold-bent steel is more complicated than that of ordinary tensile specimens. In addition, in the process of tensile testing, in order to ensure the test accuracy, it is necessary to consider the problems of force eccentricity and area measurement of tensile specimens in the tensile test, which makes the test process difficult and time-consuming. At the same time, the tonnage and accuracy requirements of equipment such as tensile machines and extensometers used in tensile tests are high. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a method for obtaining a stress-strain curve of a cold-bent steel material, comprising the following steps:

[0005] Obtain basic material property data of the corner of the cold-bent steel, construct a first parameter calculation model based on the basic material property data, and use the first parameter calculation model to calculate the key mechanical parameters of the cold-bent steel corner where strain occurs; wherein the basic material property data is the yield strength f of the cold-bent steel corner yc Or the yield strength of the parent material f yf And cold bending degree i / t;

[0006] Constructing a second parameter calculation model according to the key mechanical parameters, and using the second parameter calculation model to calculate the first strengthening index, the second strengthening index and the correlation coefficient;

[0007] A stress-strain model for the corner of the cold-formed steel is constructed, and the first strengthening index, the second strengthening index and the correlation coefficient are input into the stress-strain model to generate a stress-strain curve for the corner of the cold-formed steel.

[0008] Preferably, the key mechanical parameters include: the tensile strength f of the corner of the cold-bent steel uc 、The ultimate strain of the corner of cold-formed steel εuc , 0.05% nominal stress f at the corner of cold-formed steel 0.05c and the elastic modulus E of the corner of the cold-formed steel c .

[0009] Preferably, when the basic material property data is the yield strength f of the corner of the cold-bent steel yc When, the first parameter calculation model is specifically as follows:

[0010]

[0011] fuc / fyc=1+(130fyc) 1.4 ,

[0012]

[0013] In the formula, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of cold-bent steel.

[0014] Preferably, when the basic material property data is the yield strength f of the parent material yf And cold bending degree i / t, the first parameter calculation model is as follows:

[0015] fuf / fyf=1+(200fyf) 1.75 ,

[0016]

[0017]

[0018]

[0019] In the formula, f uf is the tensile strength of the base material, f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-bent steel, r i is the inner corner radius of the cold-formed steel corner, and t is the thickness of the cold-formed steel.

[0020] Preferably, the second parameter calculation model is as follows:

[0021]

[0022] m=2.179·exp(f yc / f uc )-4.742,

[0023] m=exp(-0.781·(r i / t)ln(f uf / f yf )),

[0024]

[0025] In the formula, n is the first reinforcement index, m is the second reinforcement index, K is the correlation coefficient, and f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, r i / t is the degree of cold bending, f yf is the yield strength of the parent material, f uf is the tensile strength of the base material, E c is the elastic modulus of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of cold-bent steel.

[0026] Preferably, the stress-strain model is as follows:

[0027]

[0028]

[0029] In the formula, ε p is the plastic strain at the corner of the cold-bent steel, f yc is the yield strength of the corner of the cold-formed steel, E c is the elastic modulus of the corner of the cold-formed steel, n is the first strengthening index, m is the second strengthening index, K is the correlation coefficient, ε is the strain of the corner of the cold-formed steel, and σ is the stress of the corner of the cold-formed steel.

[0030] The present invention also provides a system for acquiring stress-strain curves of corners of cold-bent steel materials, comprising:

[0031] The first parameter calculation model building module is used to obtain the basic material property data of the cold-bent steel corner, build the first parameter calculation model according to the basic material property data, and use the first parameter calculation model to calculate the key mechanical parameters of the cold-bent steel corner strain; wherein the basic material property data is the yield strength f of the cold-bent steel corner yc Or the yield strength of the parent material f yf And cold bending degree i / t;

[0032] A second parameter calculation model construction module is used to construct a second parameter calculation model according to key mechanical parameters; and use the second parameter calculation model to calculate the first strengthening index, the second strengthening index and the correlation coefficient;

[0033] The stress-strain curve generation module is used to construct a stress-strain model for the corner of the cold-bent steel; the first strengthening index, the second strengthening index and the correlation coefficient are input into the stress-strain model to generate a stress-strain curve for the corner of the cold-bent steel.

[0034] The method and system for obtaining the stress-strain curve of cold-bent steel provided by the present invention have the following beneficial effects:

[0035] The present invention only requires basic material property data: the yield strength f of the corner of the cold-bent steel yc Or the yield strength of the parent material f yf And cold bending degree i / t, the key mechanical parameters of the strain at the corner of the bent steel can be obtained. This process does not require tensile testing and is simple and direct. The second parameter calculation model constructed based on the key mechanical parameters can calculate the first strengthening index, the second strengthening index and the correlation coefficient. The stress-strain model of the cold-bent steel corner constructed by inputting the first strengthening index, the second strengthening index and the correlation coefficient can generate the stress-strain curve of the cold-bent steel corner. The whole process is simple, fast and very convenient. There is no need to use test equipment, let alone consider issues such as force eccentricity and test equipment accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiment of the present invention and its design scheme, the following briefly introduces the drawings required for this embodiment. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 is a flow chart of obtaining a stress-strain curve according to an embodiment of the present invention;

[0038] Figure 2 It is known that f yc The stress-strain curve prediction effect diagram;

[0039] Figure 3 It is known that f yf With r i / t stress-strain curve prediction effect diagram. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the scope of protection of the present invention.

[0041] Example

[0042] The present invention provides a method for obtaining a stress-strain curve of a cold-bent steel material, specifically, Figure 1 As shown, the following steps are included:

[0043] Step 1: Obtain basic material property data of the corner of the cold-formed steel, build a first parameter calculation model based on the basic material property data, and use the first parameter calculation model to calculate key mechanical parameters of the strain occurring in the corner of the cold-formed steel.

[0044] Among them, the basic material property data is the yield strength f of the cold-formed steel corner yc Or the yield strength of the parent material f yf And cold bending degree i / t.

[0045] Key mechanical parameters include: tensile strength f of cold-formed steel corners uc 、The ultimate strain of the corner of cold-formed steel ε uc , 0.05% nominal stress f at the corner of cold-formed steel 0.05c and the elastic modulus E of the corner of the cold-formed steel c According to different known conditions, the methods for obtaining key mechanical parameters are specifically divided into the following two cases.

[0046] (1) When the basic material property data is the yield strength f of the cold-formed steel corner yc When , the first parameter calculation model is as follows:

[0047]

[0048] fuc / fyc=1+(130fyc) 1.4 (2)

[0049]

[0050] In the formula, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of cold-bent steel.

[0051] Yield strength f at the corner of cold-formed steel yc Under known conditions, the 0.05% nominal stress f of the corner of the cold-formed steel can be calculated by formulas (1) and (2) respectively. 0.05c and tensile strength f uc ; The tensile strength f of the corner of the cold-bent steel is obtained uc After that, the ultimate strain ε of the corner of the cold-bent steel can be calculated according to formula (3): uc .

[0052] In addition, the elastic modulus E of the corner of the cold-formed steel c A statistical value of 197 GPa may be used.

[0053] (2) When the basic material property data is the yield strength f of the parent material yf And cold bending degree i / t, the first parameter calculation model is as follows:

[0054] f uf / f yf =1+(200f yf ) 1.75 (4)

[0055]

[0056]

[0057] In the formula, f uf is the tensile strength of the base material, f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-bent steel, r i is the inner corner radius of the cold-formed steel corner, and t is the thickness of the cold-formed steel.

[0058] The yield strength of the parent material is f yf And cold bending degree i / t is known, the tensile strength f of the parent material can be calculated by formula (4) uf ; After obtaining the tensile strength f of the base material uf Then, the yield strength f of the corner of the cold-formed steel can be calculated by formula (5): yc , the yield strength f of the corner of the cold-bent steel is obtained yc After that, the 0.05% nominal stress f of the corner of the cold-formed steel can be calculated according to formula (1): 0.05c , the tensile strength f of the corner of the cold-bent steel can be calculated by formula (6): uc , in order to obtain the tensile strength f of the corner of the cold-bent steel uc After that, the ultimate strain ε of the corner of the cold-bent steel can be calculated according to formula (3): uc .

[0059] In addition, if the elastic modulus E of the base material f It is known that the elastic modulus E of the corner of the cold-bent steel c =0.95E f Otherwise, E f Use statistical value 206GPa or E c Use a statistical value of 197 GPa.

[0060] Step 2: Construct a second parameter calculation model based on the key mechanical parameters, and use the second parameter calculation model to calculate the first strengthening index, the second strengthening index and the correlation coefficient.

[0061] The second parameter calculation model is as follows:

[0062]

[0063] m=2.179·exp(f yc / f uc )-4.742 (8),

[0064] m=exp(-0.781·(r i / t)ln(f uf / f yf )) (9),

[0065]

[0066] In the formula, n is the first reinforcement index, m is the second reinforcement index, K is the correlation coefficient, and f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, r i / t is the degree of cold bending, f yf is the yield strength of the parent material, f uf is the tensile strength of the base material, E c is the elastic modulus of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of cold-bent steel.

[0067] The key mechanical parameters f obtained by step 1 0.05c and f yc According to formula (7), the first strengthening index n can be calculated; when the basic material property data is the yield strength f of the corner of the cold-formed steel yc When the base material property data is the yield strength f of the parent material, the second strengthening index m is calculated according to formula (8); yf And cold bending degree i / t, calculate the second strengthening index m according to formula (9); after obtaining m, combine the key mechanical parameters E obtained in step 1 c 、f yc 、f uc , ε uc and m, the correlation coefficient K can be calculated according to formula (10).

[0068] Step 3: Construct a stress-strain model for the corner of the cold-formed steel, input the first strengthening index, the second strengthening index and the correlation coefficient into the stress-strain model, and generate a stress-strain curve for the corner of the cold-formed steel.

[0069] The stress-strain model is as follows:

[0070]

[0071]

[0072] In the formula, ε p is the plastic strain at the corner of the cold-bent steel, f yc is the yield strength of the corner of the cold-formed steel, E c is the elastic modulus of the corner of the cold-formed steel, n is the first strengthening index, m is the second strengthening index, K is the correlation coefficient, ε is the strain of the corner of the cold-formed steel, and σ is the stress of the corner of the cold-formed steel.

[0073] In equations (11) and (12), ε p is the plastic strain of the corner of the cold-bent steel. By giving the plastic strain 0~ε pu , the corresponding strain and stress can be calculated, and then the stress-strain curve is generated, where ε pu f is the tensile strength of the corner of the cold-formed steel uc The corresponding plastic strain.

[0074] Taking the tensile test results of different steel grades as an example, the method provided by the present invention is used to obtain the stress-strain curve of the corner of the cold-bent steel to verify the effectiveness of the method. Table 1 shows the measured material properties of the base material of the specimens with different steel grades, the measured cold bending degree of the corner of the cold-bent steel, and the measured key mechanical parameters of the corner of the cold-bent steel.

[0075] In order to verify the effectiveness of the method, this embodiment obtains stress-strain curves for different known basic material property data, and compares the obtained stress-strain curves with the stress-strain curves obtained by the experiment. The details are as follows:

[0076] (1) Only the yield strength f of the corner of the cold-formed steel is known yc .

[0077] First, the method of the present invention is combined with the yield strength f of the corner of the cold-bent steel material. yc Calculate the remaining key mechanical parameters, and then calculate the first strengthening index n, the second strengthening index m and the correlation coefficient K through the obtained key mechanical parameters. Then input the obtained first strengthening index n, the second strengthening index m and the correlation coefficient K into the stress-strain model to generate the stress-strain curve, such as Figure 2 As shown in the figure, it can be seen that the prediction curve obtained by this method is in good agreement with the experimental curve.

[0078] (2) Only the yield strength f of the parent material is known yf And cold bending degree i / t.

[0079] First, by the method of the present invention and combining the yield strength f of the base material yf And cold bending degree i / t calculates the key mechanical parameters, and then calculates the first strengthening index n, the second strengthening index m and the correlation coefficient K through the obtained key mechanical parameters, and then inputs the obtained data into the stress-strain model to generate the stress-strain curve, such as Figure 3 As shown in the figure, it can be seen that the curve obtained by this method is in good agreement with the experimental curve.

[0080] Table 1 Measured parameter data of parent material and cold-bent steel of different steel grade specimens

[0081]

[0082] The present invention also provides a system for acquiring stress-strain curves of corners of cold-bent steel materials, comprising:

[0083] The first parameter calculation model building module is used to obtain the basic material property data of the cold-bent steel corner, build the first parameter calculation model according to the basic material property data, and use the first parameter calculation model to calculate the key mechanical parameters of the cold-bent steel corner strain; wherein the basic material property data is the yield strength f of the cold-bent steel corner yc Or the yield strength of the parent material f yf And cold bending degree i / t;

[0084] A second parameter calculation model construction module is used to construct a second parameter calculation model according to key mechanical parameters; and use the second parameter calculation model to calculate the first strengthening index, the second strengthening index and the correlation coefficient;

[0085] The stress-strain curve generation module is used to construct a stress-strain model for the corner of the cold-formed steel; the first strengthening index, the second strengthening index and the correlation coefficient are input into the stress-strain model to generate the stress-strain curve for the corner of the cold-formed steel.

[0086] The embodiments described above are only preferred specific implementation modes of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of the technical solutions that can be obviously obtained by any technician familiar with the field within the technical scope disclosed in the present invention belong to the protection scope of the present invention.

Claims

1. A method for obtaining a stress-strain curve of a cold-bent steel material, characterized in that: The steps include: Obtain basic material property data of the corner of the cold-bent steel, construct a first parameter calculation model based on the basic material property data, and use the first parameter calculation model to calculate the key mechanical parameters of the cold-bent steel corner where strain occurs; wherein the basic material property data is the yield strength f of the cold-bent steel corner yc Or the yield strength of the parent material f yf And cold bending degree i / t; Constructing a second parameter calculation model according to the key mechanical parameters, and using the second parameter calculation model to calculate the first strengthening index, the second strengthening index and the correlation coefficient; Constructing a stress-strain model for the corner of the cold-formed steel material, inputting the first hardening index, the second hardening index and the correlation coefficient into the stress-strain model, and generating a stress-strain curve for the corner of the cold-formed steel material; The key mechanical parameters include: the tensile strength f of the corner of the cold-bent steel uc 、The ultimate strain of the corner of cold-formed steel ε uc , 0.05% nominal stress f at the corner of cold-formed steel 0.05c and the elastic modulus E of the corner of the cold-formed steel c ; When the basic material property data is the yield strength f of the corner of the cold-formed steel yc When, the first parameter calculation model is specifically as follows: f uc / f yc =1+(130 / f yc ) 1.4 , In the formula, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of the cold-formed steel; When the basic material property data is the yield strength f of the parent material yf And cold bending degree i / t, the first parameter calculation model is as follows: f uf / f yf =1+(200 / f yf ) 1.75 , In the formula, f uf is the tensile strength of the base material, f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, r i is the inner corner radius of the cold-formed steel corner, t is the thickness of the cold-formed steel; The second parameter calculation model is as follows: m=2.179·exp(f yc / f uc )-4.742, m=exp(-0.781·(r i / t)ln(f uf / f yf )), In the formula, n is the first reinforcement index, m is the second reinforcement index, K is the correlation coefficient, and f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, r i / t is the degree of cold bending, f yf is the yield strength of the parent material, f uf is the tensile strength of the base material, E c is the elastic modulus of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of the cold-formed steel; The stress-strain model is as follows: In the formula, ε p is the plastic strain at the corner of the cold-bent steel, f yc is the yield strength of the corner of the cold-formed steel, E c is the elastic modulus of the corner of the cold-formed steel, n is the first strengthening index, m is the second strengthening index, K is the correlation coefficient, ε is the strain of the corner of the cold-formed steel, and σ is the stress of the corner of the cold-formed steel.

2. A system for acquiring stress-strain curves of corners of cold-bent steel, characterized in that: include: The first parameter calculation model building module is used to obtain the basic material property data of the cold-bent steel corner, build the first parameter calculation model according to the basic material property data, and use the first parameter calculation model to calculate the key mechanical parameters of the cold-bent steel corner strain; wherein the basic material property data is the yield strength f of the cold-bent steel corner yc Or the yield strength of the parent material f yf And cold bending degree i / t; A second parameter calculation model construction module is used to construct a second parameter calculation model according to key mechanical parameters; and use the second parameter calculation model to calculate the first strengthening index, the second strengthening index and the correlation coefficient; A stress-strain curve generation module is used to construct a stress-strain model for the corner of the cold-bent steel; the first hardening index, the second hardening index and the correlation coefficient are input into the stress-strain model to generate a stress-strain curve for the corner of the cold-bent steel; Among them, the key mechanical parameters include: the tensile strength f of the corner of the cold-bent steel uc 、The ultimate strain of the corner of cold-formed steel ε uc , 0.05% nominal stress f at the corner of cold-formed steel 0.05c and the elastic modulus E of the corner of the cold-formed steel c ; When the basic material property data is the yield strength f of the corner of the cold-formed steel yc When, the first parameter calculation model is specifically as follows: f uc / f yc =1+(130 / f yc ) 1.4 , In the formula, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of the cold-formed steel; When the basic material property data is the yield strength f of the parent material yf And cold bending degree i / t, the first parameter calculation model is as follows: f uf / f yf =1+(200 / f yf ) 1.75 , In the formula, f uf is the tensile strength of the base material, f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, r i is the inner corner radius of the cold-formed steel corner, t is the thickness of the cold-formed steel; The second parameter calculation model is as follows: m=2.179·exp(f yc / f uc )-4.742, m=exp(-0.781·(r i / t)ln(f uf / f yf )), In the formula, n is the first reinforcement index, m is the second reinforcement index, K is the correlation coefficient, and f yc is the yield strength of the corner of the cold-formed steel, f uc is the tensile strength of the corner of the cold-formed steel, f 0.05c is the 0.05% nominal stress at the corner of the cold-formed steel, r i / t is the degree of cold bending, f yf is the yield strength of the parent material, f uf is the tensile strength of the base material, E c is the elastic modulus of the corner of the cold-formed steel, ε uc is the ultimate strain at the corner of the cold-formed steel; The stress-strain model is as follows: In the formula, ε p is the plastic strain at the corner of the cold-bent steel, f yc is the yield strength of the corner of the cold-formed steel, E c is the elastic modulus of the corner of the cold-formed steel, n is the first strengthening index, m is the second strengthening index, K is the correlation coefficient, ε is the strain of the corner of the cold-formed steel, and σ is the stress of the corner of the cold-formed steel.

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