A method and apparatus for calculating the stress of a steel plate by measuring its strain.

Abstract

This invention provides a method and apparatus for calculating the stress of a steel plate by measuring the strain of the steel plate. The method is based on the strain data collected by a triaxial strain rosette attached to the steel plate, and calculates the stress in the two stages before and after the steel plate yields. By calculating the stress of the steel plate at a specific location, the entire process of stress development in the steel plate under plane stress is analyzed, and the influence of various parameters on the mechanical properties of the steel plate can be analyzed.

Description

Technical Field

[0001] This invention relates to a method and apparatus for calculating the stress of a steel plate by measuring its strain. Background Technology

[0002] Steel plates, as a high-quality building material, are widely used in the field of building structures due to their excellent physical properties and ease of processing. In practical applications, steel plates are often under plane stress, bearing biaxial normal stress and in-plane shear stress. When the steel plate deforms significantly, it may yield, undergo plastic deformation, or even fracture, which can have a significant impact on the performance and safety of structures and equipment. Existing experimental methods for measuring and calculating steel plate stress typically involve first measuring the strain of the steel plate using strain gauges, and then calculating the stress based on this strain. However, this method can only calculate the stress in the elastic stage of the steel plate and lacks a method for calculating the stress in the elastoplastic stage, thus failing to further assess the stress state of the steel plate after yielding. Summary of the Invention

[0003] In view of this, the object of the present invention is to provide a method and apparatus for calculating the stress of a steel plate by measuring the strain of the steel plate, so as to solve the above problems.

[0004] The present invention adopts the following solution:

[0005] This application provides a method for calculating the stress of a steel plate by measuring its strain, comprising the following steps:

[0006] Step 1: Measure the mechanical properties of the steel sheet component by uniaxial tensile testing;

[0007] Step 2: Obtain the strain of the three-dimensional strain rosette of the steel plate under plane stress; calculate the axial, circumferential and tangential strain of the steel plate based on the measured strain in the three directions;

[0008] Step 3: Based on the principles of elastoplastic mechanics and measured strain data, calculate the stress development in the steel plate at each moment;

[0009] Since there is no stress in the thickness direction, the steel plate is in a plane stress state. The stress of the steel plate is divided into two stages according to the stress state: elastic and elastoplastic. The stress of the steel plate in each stage has a different calculation method. The yield point of the steel plate can be used as the dividing point between these two stages. The axial, circumferential and tangential stresses of the steel plate in each stage are calculated to obtain the stress of the steel plate in the plane stress state.

[0010] Further, step 1 includes: measuring the Poisson's ratio, yield strength, and elastic modulus of the steel plate through a uniaxial tensile test; wherein, for metallic materials that do not exhibit obvious yielding phenomena, the stress value that produces 0.2% residual deformation is taken as its yield limit.

[0011] Further, step 2 includes:

[0012] Step 2-1: The axial, circumferential, and tangential strains of the steel plate are determined by the normal strain conversion formula:

[0013]

[0014] In the formula, ε sa ε sh and γ ah These represent the axial strain, circumferential strain, and tangential strain of the steel plate, respectively, with α being the angle.

[0015] Step 2-2: Attach one pair of 120Ω 45° triaxial strain rosettes at each location on the steel plate where stress needs to be measured to measure the strain. Compare the angles α1 = 0°, α2 = 45°, and α3 = 90° with the strain ε measured by the triaxial strain rosettes. 0° ε 45° and ε 90° Substituting these values ​​into the normal strain transformation formula, we obtain the strain models for the steel plate in the axial, circumferential, and tangential directions as follows:

[0016]

[0017] In the formula, ε sa ε sh and γ ah ε represents the axial strain, circumferential strain, and tangential strain of the steel plate, respectively. 0° ε 45° and ε 90° The strains are measured by the triaxial strain gauge.

[0018] Furthermore, step 3 includes:

[0019] Step 3-1: In the elastic stage, the stress in the steel plate can be determined using the following calculation model for steel plate stress:

[0020]

[0021] Where, σ sa σ sh and τ ah These represent the axial stress, circumferential stress, and tangential stress of the steel plate, respectively; ε sa ε sh and γ ah These represent the axial strain, circumferential strain, and tangential strain of the steel plate, respectively; E s and υ s These represent the elastic modulus and Poisson's ratio of the steel plate, respectively. The steel plate begins to yield when the calculated stress satisfies the von Mises yield criterion:

[0022]

[0023] Step 3-2: After the steel plate yields, it enters the elastic-plastic stage. The total strain increment can be divided into elastic strain increment and plastic strain increment, that is:

[0024]

[0025] In the formula, dε sa ,dε sh and dγ ah dε represents the axial, circumferential, and tangential strain increments of the steel plate, respectively. e sa ,dε e sh and dγ e ah dε represents the axial, circumferential, and tangential elastic strain increments of the steel plate, respectively. p sa ,dε p sh and dγ p ah These represent the axial, circumferential, and tangential plastic strain increments of the steel plate, respectively.

[0026] The relationship model between stress increment and elastic strain increment is as follows:

[0027]

[0028] Therefore, in order to obtain the elastic strain increment, it is necessary to determine the plastic strain increment. Based on the correlation flow rule, the following relationship can be obtained:

[0029]

[0030] In the formula, dλ is the proportionality coefficient, which is greater than 0 during the elastoplastic loading stage;

[0031] S sa and S sh The axial and circumferential deviatoric stresses of the steel plate are respectively determined by the following formula:

[0032]

[0033] The calculation model for effective plastic strain increment is as follows:

[0034]

[0035] Based on the condition of plastic incompressibility of metals, under small deformations, it can be assumed that only linear strain causes changes in side length and volume, while the changes in side length and volume caused by shear strain are high-order infinitesimal quantities and can be ignored. Therefore, the plastic strain increment dε in the thickness direction of the steel plate is... p sr The calculation model is as follows:

[0036]

[0037] The plastic strain increment dε in the thickness direction of the steel plate p sr The effective plastic strain increment is calculated by substituting the calculation model into the calculation model of the effective plastic strain increment:

[0038]

[0039] In the elastoplastic stage, in order to calculate dε p sa ,dε p sh and dγ p ah We must assume dλ and satisfy the von Mises yield condition, which is a variation of the von Mises yield condition:

[0040]

[0041] Among them, f se The effective stress of a steel plate depends on the current effective plastic strain ε. sp ;f se and ε sp The relationship can be determined by measuring the uniaxial stress-strain relationship of the steel sheet material.

[0042] Given the current stress, effective plastic strain, and total strain increment, the plastic strain increment will simultaneously affect the values ​​on both sides of the above deformation form. Therefore, when the stress does not meet the yield condition, the plastic strain increment is solved by iterating the value of the proportional coefficient dλ, thereby determining the stress increment and corresponding stress when the steel plate enters the elastic-plastic stage.

[0043] Furthermore, the value of the adjustment ratio coefficient dλ is: taking the dλ values ​​from the first two iterations to make the von Mises yield function have opposite signs, and then using the bisection method to take the subsequent dλ values ​​until the calculation meets the accuracy requirements.

[0044] This application also provides a device for calculating the stress of a steel plate by measuring its strain, comprising:

[0045] Mechanical performance measuring device, used to measure the mechanical properties of steel plate materials through experiments;

[0046] The strain calculation device is used to obtain the strain of the three-dimensional strain curves of a steel plate under plane stress; and to calculate the axial, circumferential and tangential strains of the steel plate based on the measured strains in the three directions.

[0047] The stress calculation device is used to calculate the stress development in a steel plate at each moment based on the principles of elastoplastic mechanics and measured strain data. Since there is no stress in the thickness direction, the steel plate is in a plane stress state. The stress of the steel plate is divided into two stages according to the stress state: elastic and elastoplastic. The stress of the steel plate in each stage has a different calculation method. The yield point of the steel plate can be used as the dividing point between these two stages. The axial, circumferential and tangential stresses of the steel plate in each stage are calculated to obtain the stress of the steel plate under plane stress state.

[0048] By adopting the above technical solution, the present invention can achieve the following technical effects:

[0049] This invention uses strain data collected by triaxial strain gauges attached to a steel plate to calculate the stress in the two stages before and after the steel plate yields. By calculating the stress in the steel plate at a specific location, the entire process of stress development in the steel plate under plane stress is analyzed, and the influence of various parameters on the mechanical properties of the steel plate can be analyzed. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0051] Figure 1 This is a flowchart of a method for calculating the stress of a steel plate by measuring the strain of the steel plate according to an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram of the steel plate structure according to an embodiment of the present invention;

[0053] Figure label: Triaxial strain flower 1. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Example

[0056] This embodiment provides a method and apparatus for calculating the stress of a steel plate by measuring its strain.

[0057] Example 1, as Figure 1 and Figure 2 As shown, this embodiment of the invention provides a method for calculating the stress of a steel plate by measuring its strain. This method can be performed by a device for calculating the stress of a steel plate by measuring its strain (hereinafter referred to as: stress calculation device). Specifically, it is performed by one or more processors in the stress calculation device to implement steps 1 to 3.

[0058] Step 1: Measure the basic mechanical properties of the steel plate material through experiments;

[0059] Step 2: Obtain the strain of each of the three strain gauges 1 in the steel plate under plane stress. Calculate the axial, circumferential, and tangential strains of the steel plate based on the measured strains in the three directions.

[0060] Step 3: Based on the principles of elastoplastic mechanics and measured strain data, calculate the stress development in the steel plate at each moment. Since there is no stress in the thickness direction, the steel plate is in a plane stress state. The stress in the steel plate is divided into two stages according to the stress state: elastic and elastoplastic. The stress in each stage has a different calculation method. The yield point of the steel plate can be used as the dividing point between these two stages. Calculate the axial, circumferential, and tangential stresses in each stage to obtain the stress of the steel plate under plane stress.

[0061] It is understood that the stress calculation device can be an electronic device with computing capabilities, such as a portable laptop computer, desktop computer, server, smartphone, or tablet computer.

[0062] Step 1: Measure the Poisson's ratio, yield strength, and elastic modulus of the steel plate through a uniaxial tensile test; for metallic materials without obvious yielding phenomenon, the stress value that produces 0.2% residual deformation is taken as its yield limit.

[0063] Step 2: Attach one pair of 120Ω 45° triaxial strain gauges (1) to each location on the steel plate where stress needs to be measured to measure the strain. Obtain the strain of each triaxial strain gauge (1) under plane stress. Calculate the axial, circumferential, and tangential strains of the steel plate based on the measured strains in the three directions.

[0064] Step 2-1: The axial, circumferential, and tangential strains of the steel plate are determined by the normal strain conversion formula:

[0065]

[0066] In the formula, εsa, εsh and γah represent the axial strain, circumferential strain and tangential strain of the steel plate, respectively, and α is the angle;

[0067] Step 2-2: Compare angles α1 = 0°, α2 = 45°, and α3 = 90° with the strain ε measured by triaxial strain roser 1. 0° ε 45° and ε 90° Substituting these values ​​into the normal strain transformation formula, we obtain the strain models for the steel plate in the axial, circumferential, and tangential directions as follows:

[0068]

[0069] In the formula, ε sa ε sh and γ ah ε represents the axial strain, circumferential strain, and tangential strain of the steel plate, respectively. 0° ε 45° and ε 90° The strains are measured by triaxial strain gauge 1.

[0070] Step 3: Based on the principles of elastoplastic mechanics and measured strain data, calculate the stress development in the steel plate at each moment. Since there is no stress in the thickness direction, the steel plate is in a plane stress state. The stress in the steel plate is divided into two stages according to the stress state: elastic and elastoplastic. The stress in each stage has a different calculation method. The yield point of the steel plate can be used as the boundary between these two stages. Calculate the axial, circumferential, and tangential stresses in each stage to obtain the stress of the steel plate under plane stress.

[0071] Step 3-1: In the elastic stage, the stress in the steel plate can be determined using the following calculation model for steel plate stress:

[0072]

[0073] Where, σ sa σ sh and τ ah These represent the axial stress, circumferential stress, and tangential stress of the steel plate, respectively; ε sa ε sh and γ ah These represent the axial strain, circumferential strain, and tangential strain of the steel plate, respectively; E s and υ s These represent the elastic modulus and Poisson's ratio of the steel plate, respectively.

[0074] The steel plate begins to yield when the calculated stress satisfies the von Mises yield criterion as follows:

[0075]

[0076] Step 3-2: After the steel plate yields, it enters the elastic-plastic stage. The total strain increment can be divided into elastic strain increment and plastic strain increment, that is:

[0077]

[0078] In the formula, dε sa ,dε sh and dγ ah dε represents the axial, circumferential, and tangential strain increments of the steel plate, respectively. e sa ,dε e sh and dγ e ah dε represents the axial, circumferential, and tangential elastic strain increments of the steel plate, respectively. p sa ,dε p sh and dγ p ah These represent the axial, circumferential, and tangential plastic strain increments of the steel plate, respectively.

[0079] The relationship model between stress increment and elastic strain increment is as follows:

[0080]

[0081] Therefore, in order to obtain the elastic strain increment, it is necessary to determine the plastic strain increment. Based on the correlation flow rule, the following relationship can be obtained:

[0082]

[0083] In the formula, dλ is the proportionality coefficient, which > 0 during the elastoplastic loading stage; S sa and S sh The axial and circumferential deviatoric stresses of the steel plate are respectively calculated by the following formula:

[0084]

[0085] The calculation model for effective plastic strain increment is as follows:

[0086]

[0087] Based on the condition of plastic incompressibility of metals, under small deformations, it can be assumed that only linear strain causes changes in side length and volume, while the changes in side length and volume caused by shear strain are high-order infinitesimal quantities and can be ignored. Therefore, the plastic strain increment dε in the thickness direction of the steel plate is... p sr The calculation model is as follows:

[0088]

[0089] The plastic strain increment dε in the thickness direction of the steel plate p sr Substituting the calculation model of effective plastic strain increment into the calculation model of effective plastic strain increment, we obtain the following deformation calculation model of effective plastic strain increment:

[0090]

[0091] In the elastoplastic stage, in order to calculate dε p sa ,dε p sh and dγ p ah We must assume dλ and satisfy the von Mises yield condition, which is a variation of the von Mises yield condition:

[0092]

[0093] Among them, f se The effective stress of a steel plate depends on the current effective plastic strain ε. sp ;f se and ε sp The relationship can be determined by measuring the uniaxial stress-strain relationship of the steel sheet material.

[0094] Given the current stress, effective plastic strain, and total strain increment, the plastic strain increment will simultaneously affect the values ​​on both sides of the above deformation form. Therefore, when the stress does not meet the yield condition, the plastic strain increment is solved by iterating the value of the proportional coefficient dλ, thereby determining the stress increment and corresponding stress when the steel plate enters the elastic-plastic stage.

[0095] Furthermore, the value of the adjustment ratio coefficient dλ is as follows: dλ1 is set to 0, and f1 is calculated at this time; dλ2 is set as follows: if f2 and f1 have opposite signs at this time, the subsequent dλ is determined by the bisection method of the following formula. i If f2 and f1 have the same sign at this point, then take dλ3 = 2dλ2 and continue the calculation until f i The sign is opposite to f1; the subsequent dλ i+1 The following bisection method is used to determine the value until the accuracy requirement of the yield condition is met. The von Mises yield function is:

[0096]

[0097] The value of dλ2 is:

[0098]

[0099] Where dε eThe equivalent change increment at which yielding begins; σ e The equivalent stress at the moment before yielding; dε sr For the strain increment in the thickness direction, the elastic stage can be determined by the following formula:

[0100]

[0101] Satisfy f i The value of dλ after f1 has the opposite sign is determined by the bisection method of the following formula (if f2 has the opposite sign to f1, it is determined by the first formula; if f2 has the same sign to f1, it is determined by the following two formulas in sequence):

[0102] dλ i+1 =(dλ1+dλ) i ) / 2

[0103] dλ i+2 =(dλ i +dλ i+1 ) / 2

[0104] To facilitate understanding of the present invention, a specific example will be used for illustration below.

[0105] Step A involves obtaining the steel plate material parameters through testing, conducting a uniformly distributed load test on the I-beam, and obtaining triaxial strain rosette data. The specific process is as follows:

[0106] Combined with appendix Figure 2 First, a uniaxial tensile test was conducted on the steel plate to obtain the stress-strain curve of the steel plate and material parameters such as yield stress, elastic modulus, and Poisson's ratio of the steel. Then, a uniformly distributed load test was conducted on the I-beam, and the 0°, 45° and 90° strains of 45° triaxial strain rosette 1 at each 120Ω stress point were collected at the stress points to be analyzed.

[0107] Step B calculates the axial stress, circumferential stress, and tangential stress of the web during the elastic stage (before yielding) according to the given formula. The specific process is as follows:

[0108] Based on the 0° strain ε collected by the triaxial strain roser 1 0° 45° strain ε 45° and 90° strain ε 90° The web strain can be determined using the following strain models for axial, circumferential, and tangential directions:

[0109]

[0110] Where, ε sa ε sh and γ ah These represent the axial strain, circumferential strain, and tangential strain of the web, respectively.

[0111] The web stress in the elastic stage can be determined using the following calculation model for steel plate stress:

[0112]

[0113] Where, σ sa σ sh and τ ah E represents the axial stress, circumferential stress, and tangential stress of the web, respectively. s and υ s These represent the elastic modulus and Poisson's ratio of the steel plate, respectively.

[0114] Step C: The web enters the elastoplastic stage (after yielding). Assuming a proportionality constant dλ, the axial, circumferential, and tangential stresses of the web are calculated based on the relationship between stress increment and elastic strain increment. The specific process is as follows:

[0115] First, the web begins to yield when the calculated stress satisfies the von Mises yield criterion:

[0116]

[0117] Then, based on the axial strain increment (dε) at the moment of entering the elastoplastic stage sa ) n Circumferential strain increment (dε) sh ) n and tangential strain increment (dγ) ah ) n (The strain increment is obtained by subtracting the strain at this moment from the strain at the next moment); the axial stress at the current moment (σ) sa ) n Circumferential stress (σ) sh ) n , Tangential stress (τ) ah ) n and effective plastic strain (ε sp ) n Assume the scaling factor dλ is 0 in the first iteration (i=1), and the scaling factor dλ is 0 in the second iteration (i=2):

[0118]

[0119] Calculate the plastic strain increment based on the value of dλ2. and The calculation formula is as follows:

[0120]

[0121] Among them, S sa and S sh , , represent the axial and circumferential deviatoric stresses of the web, respectively; dλ is the proportionality coefficient, which is greater than 0 during the elastoplastic loading stage.

[0122] Next, based on the fact that the total strain increment in the elastoplastic stage can be divided into elastic strain increment and plastic strain increment, the elastic strain increment is calculated:

[0123]

[0124] Next, based on the relationship between stress increment and elastic strain increment, the stress increment at that moment is calculated:

[0125]

[0126] Finally, by adding the stress increment of the web obtained from the above formula to the stress at that moment, the web stress at the next moment can be obtained:

[0127]

[0128] Step D determines whether the calculated axial, circumferential, and tangential stresses of the web meet the accuracy requirements of the von Mises yield function. If they do, the calculation of the web stress at the next moment continues; otherwise, the process returns to step C to re-assume the proportionality constant dλ. The specific process is as follows:

[0129] First, calculate the effective plastic strain increment, as shown in the following formula:

[0130]

[0131] Then, the effective stress f is determined based on the current effective plastic strain εsp. se (fse and ε) sp The relationship can be determined by measuring the uniaxial stress-strain relationship of the steel.

[0132] During the elastoplastic stage, the von Mises yield function must be satisfied, i.e.:

[0133]

[0134] The web stress calculated in step C is compared with the effective stress f determined by measuring the uniaxial stress-strain relationship of the steel. se The values ​​are compared to determine if the von Mises yield condition is met. If the von Mises yield condition is not met, then the initial assumption in step C regarding the proportionality coefficient dλ is incorrect. When f1 and f2 have opposite signs, the bisection method of the first formula below is used to obtain the subsequent dλ value for iteration; when f1 and f2 have the same sign, dλ3 = 2dλ2 is taken and the calculation continues until f1 and f2 are equal. i If the signs are opposite, then the bisection method of the following two equations is used to obtain the subsequent dλ values ​​for iteration:

[0135] dλ i+1 =(dλ1+dλ) i) / 2

[0136] dλ i+2 =(dλ i +dλ i+1 ) / 2

[0137] The iteration continues until the value of dλ satisfies the accuracy requirement of the von Mises yield condition, i.e.:

[0138]

[0139] Finally, output the axial stress σ of the web of the I-beam during the entire uniformly distributed load test. sa Circumferential stress σ sh Tangential stress τ ah and effective plastic strain ε sp .

[0140] Based on the above steps, the axial stress σ of the web of the I-beam under plane stress can be obtained. sa Circumferential stress σ sh and tangential stress τ ah .

[0141] Using triaxial strain rosettes at other angles (such as 60° triaxial strain rosette 1), the axial stress σ of the steel plate under plane stress state can also be obtained by following the same steps. sa Circumferential stress σ sh and tangential stress τ ah .

[0142] Example 2: This embodiment of the invention provides a device for calculating the stress of a steel plate by measuring its strain, comprising:

[0143] Mechanical performance measuring device, used to measure the mechanical properties of steel plate materials through experiments;

[0144] A strain calculation device is used to obtain the strain of a steel plate under plane stress in each of the three strain gauges. The axial, circumferential, and tangential strains of the steel plate are calculated based on the measured strains in the three directions.

[0145] The stress calculation device is used to calculate the stress development in a steel plate at each moment based on the principles of elastoplastic mechanics and measured strain data. Since there is no stress in the thickness direction, the steel plate is in a plane stress state. The stress in the steel plate is divided into two stages according to the stress state: elastic and elastoplastic. The stress in each stage has a different calculation method. The yield point of the steel plate can be used as the boundary point between these two stages. The axial, circumferential, and tangential stresses in each stage are calculated separately to obtain the stress of the steel plate under plane stress.

[0146] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of the present invention are within the scope of protection of the present invention.

[0147] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0148] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0149] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0150] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

Claims

1. A method for calculating the stress of a steel plate by measuring its strain, characterized in that, Includes the following steps: Step 1: Measure the mechanical properties of the steel sheet component by uniaxial tensile testing; Step 2: Obtain the strain of the three-dimensional strain rosette of the steel plate under plane stress; calculate the axial, circumferential and tangential strain of the steel plate based on the measured strain in the three directions; Step 3: Based on the principles of elastoplastic mechanics and measured strain data, calculate the stress development in the steel plate at each moment; Step 2 includes: Step 2-1: The axial, circumferential, and tangential strains of the steel plate are determined by the normal strain conversion formula: In the formula, ε sa ε sh and γ ah These represent the axial strain, circumferential strain, and tangential strain of the steel plate, respectively, with α being the angle. Step 2-2: Attach one pair of 120Ω 45° triaxial strain rosettes at each location on the steel plate where stress needs to be measured to measure the strain. Compare the angles α1 = 0°, α2 = 45°, and α3 = 90° with the strain ε measured by the triaxial strain rosettes. 0° ε 45° and ε 90° Substituting these values ​​into the normal strain transformation formula, we obtain the strain models for the steel plate in the axial, circumferential, and tangential directions as follows: In the formula, ε sa ε sh and γ ah ε represents the axial strain, circumferential strain, and tangential strain of the steel plate, respectively. 0° ε 45° and ε 90° The strains were measured by the triaxial strain rosette. The calculation model for the effective plastic strain increment is as follows: dε p sa ,dε p sh and dγ p ah These represent the axial, circumferential, and tangential plastic strain increments of the steel plate, respectively. Based on the condition of plastic incompressibility of metals, under small deformations, it is assumed that only linear strain causes changes in side length and volume, while the changes in side length and volume caused by shear strain are high-order infinitesimals and can be ignored. Therefore, the plastic strain increment dε in the thickness direction of the steel plate is... p sr The calculation model is as follows: The plastic strain increment dε in the thickness direction of the steel plate p sr The effective plastic strain increment is calculated by substituting the calculation model into the calculation model of the effective plastic strain increment: In the elastoplastic stage, in order to calculate dε p sa ,dε p sh and dγ p ah We must assume dλ and satisfy the von Mises yield condition, which is a variation of the von Mises yield condition: Among them, f se The effective stress of a steel plate depends on the current effective plastic strain ε. sp ;f se and ε sp The relationship between them is determined by measuring the uniaxial stress-strain relationship of the steel sheet material. Given the current stress, effective plastic strain, and total strain increment, the plastic strain increment will simultaneously affect the values ​​on both sides of the above deformation form. Therefore, when the stress does not meet the yield condition, the plastic strain increment is solved by iterating the value of the proportional coefficient dλ, thereby determining the stress increment and corresponding stress when the steel plate enters the elastic-plastic stage.

2. The method for calculating the stress of a steel plate by measuring strain in a steel plate according to claim 1, characterized in that, Step 1 includes: measuring the Poisson's ratio, yield strength, and elastic modulus of the steel plate through a uniaxial tensile test; wherein, for metallic materials that do not show obvious yielding phenomenon, the stress value that produces 0.2% residual deformation is taken as its yield limit.

3. The method for calculating the stress of a steel plate by measuring the strain of the steel plate according to claim 1, characterized in that, Step 3 includes: Step 3-1: In the elastic stage, the stress in the steel plate can be determined using the following calculation model for steel plate stress: Where, σ sa σ sh and τ ah These represent the axial stress, circumferential stress, and tangential stress of the steel plate, respectively; ε sa ε sh and γ ah These represent the axial strain, circumferential strain, and tangential strain of the steel plate, respectively; E s and υ s These represent the elastic modulus and Poisson's ratio of the steel plate, respectively; the steel plate begins to yield when the calculated stress satisfies the von Mises yield criterion as follows: Step 3-2: After the steel plate yields, it enters the elastic-plastic stage. The total strain increment can be divided into elastic strain increment and plastic strain increment, that is: In the formula, dε sa ,dε sh and dγ ah dε represents the axial, circumferential, and tangential strain increments of the steel plate, respectively. e sa ,dε e sh and dγ e ah These represent the axial, circumferential, and tangential elastic strain increments of the steel plate, respectively. The relationship model between stress increment and elastic strain increment is as follows: Therefore, in order to obtain the elastic strain increment, it is necessary to determine the plastic strain increment. Based on the correlation flow rule, the following relationship can be obtained: In the formula, dλ is the proportionality coefficient, which is greater than 0 during the elastoplastic loading stage; S sa and S sh The axial and circumferential deviatoric stresses of the steel plate are respectively determined by the following formula:

4. The method for calculating the stress of a steel plate by measuring the strain of the steel plate according to claim 3, characterized in that, The value of the adjustment ratio coefficient dλ is: take the dλ of the first two iterations to make the von Mises yield function have opposite signs, and then use the bisection method to take the subsequent dλ values ​​until the calculation meets the accuracy requirements.

5. An apparatus for calculating the stress of a steel plate by measuring its strain, which can implement the method for calculating the stress of a steel plate by measuring its strain as described in any one of claims 1-4, characterized in that, include: Mechanical performance measuring device, used to measure the mechanical properties of steel plate materials through experiments; The strain calculation device is used to obtain the strain of the three-dimensional strain curves of a steel plate under plane stress; and to calculate the axial, circumferential and tangential strains of the steel plate based on the measured strains in the three directions. The stress calculation device is used to calculate the stress development in a steel plate at each moment based on the principles of elastoplastic mechanics and measured strain data. Since there is no stress in the thickness direction, the steel plate is in a plane stress state. The stress of the steel plate is divided into two stages according to the stress state: elastic and elastoplastic. The stress of the steel plate in each stage has a different calculation method. The yield point of the steel plate can be used as the dividing point between these two stages. The axial, circumferential and tangential stresses of the steel plate in each stage are calculated to obtain the stress of the steel plate under plane stress state.

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