Loading method to improve control accuracy of tensile test

Abstract

The present invention provides a loading method for improving the control accuracy of a tensile test, including: providing at least two identical specimens, one of which is used as a test piece; calculating the crossbeam stretching speed of the test piece; stretching the test piece according to the crossbeam stretching speed of the test piece to obtain a center gauge length-time variation curve; obtaining the i-th moment when the crossbeam displacement growth trend turns according to the center gauge length-time variation curve; calculating the elastic correction control parameters from the 0th moment to the i-th moment, and the plastic correction control parameters from the i-th moment to the end of the tensile test; performing a tensile test on the specimen with the elastic correction control parameters from the 0th moment to the i-th moment, and with the plastic correction control parameters from the i-th moment to the end of the tensile test. The optimal loading scheme of the specimen is obtained through the test piece, which effectively improves the test control accuracy and solves the abnormal situation that the center deformation of the tensile test specimen in displacement control is insufficient.

Description

Technical Field

[0001] The present invention relates to the technical field of metal stretching, and in particular, to a loading method for improving the control accuracy of a tensile test. Background Art

[0002] When studying the basic mechanical properties of metal materials, tensile tests of the materials are often carried out. By carrying out unidirectional tensile tests, the material's stress-strain curve, yield strength, tensile strength, elongation and other mechanical performance indicators can be obtained. However, since the actuator arm of the tensile testing machine will produce a certain amount of elastic deformation during the test, the center of the specimen often has an abnormal situation of insufficient deformation during stretching. The actual deformation rate of the material is far from the ideal state, and the testing machine cannot complete the required tensile test according to the set test parameters. Since metal materials have obvious strain rate sensitivity, if the actual strain rate of the tensile test does not meet the test design requirements, it will have a serious impact on the mechanical properties of the material, resulting in the inability of the test personnel to accurately obtain the mechanical performance indicators of the material. Therefore, it is very important to develop a loading method to improve the control accuracy of the tensile test.

[0003] At present, there are two commonly used control methods for tensile tests: strain control and displacement control. During the test, the strain control requires the extensometer to be placed against the surface of the specimen. The impact generated during the test fracture can easily damage the extensometer, and it can only be barely applicable to tensile tests of low-strength materials. The displacement control method does not rely on the extensometer and can be applied to tensile tests of materials of various strength levels. However, due to the insufficient deformation at the center of the tensile specimen, the mechanical properties of the material cannot be accurately obtained according to the set test parameters, and cannot meet the needs of scientific research experiments and engineering.

[0004] In summary, the present invention provides a loading method for improving the control accuracy of a tensile test. Summary of the invention

[0005] According to the technical problem of insufficient deformation of the center of the specimen in the tensile test mentioned above, a loading method for improving the control accuracy of the tensile test is provided. The present invention mainly reduces the difference between the actual deformation rate of the material and the set parameters to effectively improve the test control accuracy, thereby avoiding the abnormal situation of insufficient deformation of the center of the specimen in the displacement-controlled tensile test, and meeting the application requirements of scientific research experiments and other engineering practices.

[0006] The technical means adopted by the present invention are as follows:

[0007] The present invention provides a loading method for improving the control accuracy of a tensile test, comprising:

[0008] Providing at least two identical samples, one of which is used as a test piece;

[0009] Obtaining the gauge length and preset strain rate of the test piece;

[0010] Calculating the crossbeam stretching speed of the test piece according to the gauge length and the preset strain rate;

[0011] Stretching the test piece according to the stretching speed of the crossbeam of the test piece to obtain a center gauge length-time variation curve;

[0012] According to the center gauge length-time variation curve, the i-th moment when the growth trend of the beam displacement turns is obtained;

[0013] Calculate the elastic correction control parameters from the 0th moment to the ith moment and the plastic correction control parameters from the ith moment to the end of the tensile test;

[0014] The tensile test is performed on the sample with the elastic correction control parameter from the 0th moment to the i-th moment, and with the plastic correction control parameter from the i-th moment to the end of the tensile test.

[0015] Furthermore, the beam stretching speed of the test piece is calculated in the following manner:

[0016] The beam stretching speed of the test piece=the gauge length×the preset strain rate.

[0017] Furthermore, the elastic correction control parameter and the plastic correction control parameter are calculated in the following manner:

[0018] The center gauge length-time variation curve is divided from the 0th moment to the ith moment into the first part, and the ith moment to the stretching end moment into the second part;

[0019] Performing a linear regression analysis on the first part to obtain an elastic regression coefficient, and performing a linear regression analysis on the second part to obtain a plastic regression coefficient;

[0020] The elastic correction control parameter is obtained according to the elastic regression coefficient and the beam stretching speed of the test piece, and the plastic correction control parameter is obtained according to the plastic regression coefficient and the beam stretching speed of the test piece.

[0021] Furthermore, when performing linear regression analysis on the second part, in the center gauge length-time variation curve, the second part is translated so that the starting point of the second part corresponds to the zero point of the center gauge length-time variation curve;

[0022] A linear regression analysis is performed on the second part after translation.

[0023] Furthermore, the elastic correction control parameter is calculated in the following manner:

[0024] The elastic correction control parameter=the beam stretching speed of the test piece / the elastic regression coefficient×the beam stretching speed of the test piece.

[0025] Furthermore, the plasticity correction control parameter is calculated in the following manner:

[0026] The plastic correction control parameter=the beam stretching speed of the test piece÷the plastic regression coefficient×the beam stretching speed of the test piece.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The loading method for improving the control accuracy of tensile tests provided by the present invention includes: providing at least two identical specimens, one of which is used as a test piece; obtaining the gauge length and preset strain rate of the test piece; calculating the crossbeam stretching speed of the test piece according to the gauge length and the preset strain rate; stretching the test piece according to the crossbeam stretching speed of the test piece to obtain a center gauge length-time variation curve; obtaining the i-th moment when the crossbeam displacement growth trend turns according to the center gauge length-time variation curve; calculating the elastic correction control parameters from the 0th moment to the i-th moment and the plastic correction control parameters from the i-th moment to the end of the tensile test; performing a tensile test on the specimen with the elastic correction control parameters from the 0th moment to the i-th moment and with the plastic correction control parameters from the i-th moment to the end of the tensile test. The optimal loading scheme of the specimen is obtained through the test piece, which greatly reduces the difference between the actual deformation rate of the material and the set parameters, effectively improves the test control accuracy, and solves the abnormal situation that the center deformation of the tensile test specimen under displacement control is insufficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

[0030] Figure 1 A flow chart of a loading method for improving tensile test control accuracy provided by the present invention.

[0031] Figure 2 This is a comparison diagram of the test curve before correction and the target parameters provided by the present invention.

[0032] Figure 3 This is a comparison diagram of the modified test curve and target parameters provided by the present invention. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme 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 described embodiments 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 creative work should fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "first", "second", etc. in the specification 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 data 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 that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0035] Reference Figure 1 , Figure 1 A flow chart of a loading method for improving the control accuracy of a tensile test provided by the present invention is provided to illustrate a specific embodiment of the loading method for improving the control accuracy of a tensile test provided by this embodiment, including:

[0036] Provide at least two identical specimens, one of which is used as the test piece;

[0037] Obtain the gauge length and preset strain rate of the test piece;

[0038] Calculate the crossbeam stretching speed of the test piece according to the gauge length and the preset strain rate;

[0039] The crossbeam stretching speed of the test piece is calculated as follows:

[0040] The beam stretching speed of the test piece = gauge length × preset strain rate.

[0041] The test piece is stretched according to the stretching speed of the crossbeam of the test piece to obtain a center gauge length-time variation curve;

[0042] According to the center gauge length-time variation curve, the i-th moment when the growth trend of beam displacement turns is obtained;

[0043] Calculate the elastic correction control parameters from the 0th moment to the ith moment and the plastic correction control parameters from the ith moment to the end of the tensile test;

[0044] Among them, the elastic correction control parameters and the plastic correction control parameters are calculated in the following way:

[0045] The center gauge length-time variation curve is divided from the 0th moment to the ith moment into the first part, and the ith moment to the stretching end moment into the second part;

[0046] Linear regression analysis is performed on the first part to obtain the elastic regression coefficient, and linear regression analysis is performed on the second part to obtain the plastic regression coefficient;

[0047] Specifically, when performing linear regression analysis on the second part, in the center gauge length-time variation curve, the second part is translated so that the starting point of the second part corresponds to the zero point of the center gauge length-time variation curve;

[0048] Linear regression analysis was performed on the second part after translation.

[0049] The elastic correction control parameter is obtained according to the elastic regression coefficient and the beam stretching speed of the test piece, and the plastic correction control parameter is obtained according to the plastic regression coefficient and the beam stretching speed of the test piece.

[0050] Among them, the elastic correction control parameter is calculated as follows:

[0051] Elastic correction control parameter = beam stretching speed of the test piece ÷ elastic regression coefficient × beam stretching speed of the test piece.

[0052] The plasticity correction control parameters are calculated as follows:

[0053] Plastic correction control parameter = beam stretching speed of the test piece ÷ plastic regression coefficient × beam stretching speed of the test piece.

[0054] The tensile test is performed on the specimen with elastic correction control parameters from the 0th moment to the i-th moment, and with plastic correction control parameters from the i-th moment to the end of the tensile test.

[0055] It can be understood that when the crossbeam tensile specimen of the testing machine stretches the test piece according to the crossbeam tensile speed of the test piece, the unidirectional tensile test of the test piece is carried out in a displacement control mode. The preset strain rate is determined before the test and is the test condition defined by the test personnel for the tensile test. There is an error between the crossbeam tensile speed of the test piece calculated according to the preset strain rate and the actual deformation rate. Therefore, it is necessary to reduce the error between the crossbeam tensile speed of the test piece and the actual deformation rate. Specifically, the center gauge length-time variation curve is obtained according to the tensile test of the test piece, and the center gauge length-time variation curve is divided into the first The elastic regression coefficient of the first part and the plastic regression coefficient of the second part are calculated respectively. The elastic correction control parameter and the plastic correction control parameter are obtained according to the elastic regression coefficient, the plastic regression coefficient and the beam stretching speed of the test piece. The tensile test is carried out on the specimen from the 0th moment to the ith moment with the elastic correction control parameter, and from the ith moment to the end of the tensile test with the plastic correction control parameter, so that the actual deformation rate of the specimen is closer to the preset strain rate, thereby greatly improving the control accuracy of the specimen tensile test and effectively improving the situation of insufficient deformation of the specimen center during the tensile test.

[0056] In some optional embodiments, referring to Figure 1 , Figure 2 and Figure 3 , Figure 2 A comparison diagram of the test curve before correction and the target parameters provided by the present invention, Figure 3 A comparison diagram of the modified test curve and the target parameter provided by the present invention is used to illustrate a specific embodiment of the loading method for improving the control accuracy of the tensile test provided by this embodiment, including:

[0057] Provide at least two identical specimens, one of which is used as the test piece;

[0058] Taking the preset strain rate of the test piece as 0.001 and the gauge length of the test piece as 50 mm as an example, according to the beam stretching speed of the test piece = gauge length × preset strain rate, the beam stretching speed of the test piece is calculated to be 0.05 mm / s.

[0059] The uniaxial tensile test is carried out by stretching the test piece at a speed of 0.05 mm / s to obtain the center gauge length-time variation curve, such as Figure 2 As shown, the V theory is the beam stretching speed of the test piece. According to the center gauge length-time variation curve, the turning point of the beam displacement growth trend is 110 seconds. The center gauge length-time variation curve is divided from 0 seconds to 110 seconds as the first part, and from 110 seconds to the end of stretching as the second part.

[0060] Linear regression analysis of the first part results in the first regression equation y=0.016x, so the elastic regression coefficient K1 is 0.016; when linear regression analysis of the second part is performed, in the center gauge length-time variation curve, the second part is translated so that the starting point of the second part corresponds to the zero point of the center gauge length-time variation curve; linear regression analysis of the translated second part results in the second regression equation y=0.0299x, so the elastic regression coefficient K2 is 0.0299.

[0061] According to the elastic correction control parameter = beam stretching speed of the test piece ÷ elastic regression coefficient × beam stretching speed of the test piece, the elastic correction control parameter is calculated to be 0.156 mm / s; according to the plastic correction control parameter = beam stretching speed of the test piece ÷ plastic regression coefficient × beam stretching speed of the test piece, the plastic correction control parameter is calculated to be 0.0836 mm / s.

[0062] In the process of stretching the sample, from 0 to 110 seconds, the elastic correction control parameter is 0.156 mm / s to control the stretching of the sample, and from 110 seconds to the end of stretching, the plastic correction control parameter is 0.0836 mm / s to control the stretching of the sample. Figure 3 ,exist Figure 3 In the figure, V elastic correction refers to the elastic correction control parameter, and V plastic correction refers to the plastic correction control parameter. It can be clearly seen that the actual deformation rate of the sample is closer to the preset strain rate, that is, the tensile test of the sample is carried out using the corrected parameters, and the control accuracy is higher. The method provided in this embodiment utilizes the deformation characteristics of the material and the inherent correlation mechanism of the stiffness of the testing machine system to obtain accurate control parameters, thereby improving the control accuracy of the tensile test of the sample and effectively improving the situation where the center deformation of the sample is insufficient during the tensile test.

[0063] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0064] In the above embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0065] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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 loading method for improving the control accuracy of a tensile test, characterized in that: include: Providing at least two identical samples, one of which is used as a test piece; Conduct a uniaxial tensile test of the test piece in a displacement-controlled manner, and stretch the test piece according to the tensile speed of the beam of the test piece; Obtaining the gauge length and preset strain rate of the test piece; Calculating the crossbeam stretching speed of the test piece according to the gauge length and the preset strain rate; The crossbeam stretching speed of the test piece = the gauge length × the preset strain rate; Stretching the test piece according to the stretching speed of the crossbeam of the test piece to obtain a center gauge length-time variation curve; According to the center gauge length-time variation curve, the i-th moment when the growth trend of the beam displacement turns is obtained; Calculate the elastic correction control parameters from the 0th moment to the ith moment and the plastic correction control parameters from the ith moment to the end of the tensile test; The elastic correction control parameter=the beam stretching speed of the test piece ÷ the elastic regression coefficient × the beam stretching speed of the test piece; The plastic correction control parameter=the beam stretching speed of the test piece ÷ the plastic regression coefficient × the beam stretching speed of the test piece; The center gauge length-time variation curve is divided from the 0th moment to the ith moment into the first part, and the ith moment to the stretching end moment into the second part; Performing a linear regression analysis on the first part to obtain an elastic regression coefficient, and performing a linear regression analysis on the second part to obtain a plastic regression coefficient; The elastic correction control parameter is obtained according to the elastic regression coefficient and the beam stretching speed of the test piece, and the plastic correction control parameter is obtained according to the plastic regression coefficient and the beam stretching speed of the test piece; The tensile test is performed on the sample with the elastic correction control parameter from the 0th moment to the i-th moment, and with the plastic correction control parameter from the i-th moment to the end of the tensile test.

2. The loading method for improving the control accuracy of a tensile test according to claim 1, characterized in that: When performing linear regression analysis on the second part, in the center gauge length-time variation curve, the second part is translated so that the starting point of the second part corresponds to the zero point of the center gauge length-time variation curve; A linear regression analysis is performed on the second part after translation.

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