Method for analyzing mechanical properties of sample plate

Abstract

The embodiment of the invention relates to the technical field of testing the mechanical property of a sample by applying stable tensile force, in particular to a method for analyzing the mechanical property of a sample plate, which comprises the following steps: S10, loading the sample plate to be analyzed to preset equipment; s20, stretching the to-be-analyzed sample plate to a preset stretching length to obtain a change relationship between the applied tension and the stretching length; s30, determining the change rate of the tensile force and the tensile length according to the change relation; and S40, determining the mechanical property of the sample plate according to the change rate. According to the method provided by the embodiment of the invention, the tensile force is applied to the sample plate, so that the sample plate is stretched to the preset stretching length, and the change relationship between the applied tensile force and the stretching length is obtained, so that the mechanical property of the sample plate is analyzed, and non-destructive detection on the mechanical property of the sample plate is realized; the accuracy of the analysis result of the mechanical property of the sample plate is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of testing the mechanical properties of a sample by applying a stable tensile force, and in particular to a method for analyzing the mechanical properties of a sample plate. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The mechanical properties of sample plates are one of the important means to detect and evaluate product quality, among which tensile test is the most widely used method for evaluating mechanical properties.

[0004] At present, the traditional method for analyzing the mechanical properties of sample plates is usually to apply tensile force to the sample plates to stretch them until they break, and then evaluate the load-bearing capacity and fracture characteristics of the sample plates before they break, so as to determine the mechanical properties of the sample plates. However, due to improper production process control during the preparation of the sample plates, the sample plates may have uneven tissues. At this time, when the traditional method is used for tensile testing, it is easy for the sample plates to break at the weakest position of the performance, and the true load-bearing capacity of the sample plates cannot be reflected, thus affecting the accuracy of the analysis results of the mechanical properties of the sample plates.

[0005] On the other hand, due to the high cost of the sample plate, after the mechanical properties are tested, if the performance meets the requirements, the sample plate will be reused. If the evaluation method of stretching to fracture is adopted, the sample plate will be wasted. Summary of the invention

[0006] A brief overview of the present application is provided below in order to provide a basic understanding of certain aspects of the present application. It should be understood that this overview is not an exhaustive overview of the present application. It is not intended to identify the key or important parts of the present application, nor is it intended to limit the scope of the present application. Its purpose is merely to present certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0007] An embodiment of the present invention provides a method for analyzing the mechanical properties of a sample plate, the method comprising the following steps: S10, loading the sample plate to be analyzed onto a predetermined device; S20, stretching the sample plate to be analyzed to a predetermined stretching length, and obtaining a changing relationship between the applied tension and the stretching length; S30, determining a changing rate of the tension and the stretching length based on the changing relationship; S40, determining the mechanical properties of the sample plate based on the changing rate.

[0008] The method in the embodiments of the present invention is different from the traditional method of applying tension to the sample plate until it breaks to determine the mechanical properties of the sample plate. Instead, tension is applied to the sample plate to stretch it to a predetermined stretching length, and the changing relationship between the applied tension and the stretching length is obtained to analyze the mechanical properties of the sample plate, thereby achieving non-destructive testing of the mechanical properties of the sample plate and improving the accuracy of the analysis results of the mechanical properties of the sample plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other objects and advantages of the present invention will become apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, which will help to provide a comprehensive understanding of the present invention.

[0010] Figure 1 is a flow chart of a method for analyzing mechanical properties of a sample plate according to an embodiment of the present invention.

[0011] Figure 2 is a flow chart of determining a predetermined interval according to an embodiment of the present invention.

[0012] Figure 3 is a flowchart of determining a predetermined interval according to another embodiment of the present invention.

[0013] Figure 4 Schematic diagram of the structure of a fixture of a predetermined device according to an embodiment of the present invention.

[0014] Figure 5 2 is a schematic structural diagram of a fixture of a predetermined device according to another angle of an embodiment of the present invention.

[0015] Figure 6 4 is a curve showing the relationship between the applied tension and the stretched length according to an embodiment of the present invention.

[0016] Figure 7 The graph is a curve showing the relationship between the pulling force and the stretching length when the same sample plate is stretched multiple times without requiring the clamping position of the sample plate and the distance between the two ends of the first clamping member and the second clamping member according to an embodiment of the present invention.

[0017] Figure 8 The present invention is a curve showing the relationship between the tension and the length of the sample plate when the clamping position of the sample plate and the distance between the two ends of the first clamping member and the second clamping member are required.

[0018] Description of reference numerals:

[0019] 10. First clamping member; 11. Clamping hole; 21. Clamping hole; 20. Second clamping member; 30. First tensile connector; 40. Second tensile connector; 50. First matching member; 51. Notch; 61. Notch; 52. Scale; 62. Scale; 60. Second matching member; 70. Fixed matching member; 80. Fixed member.

[0020] It should be noted that the drawings are not necessarily drawn to scale, but are merely shown in a schematic manner that does not affect the reader's understanding. DETAILED DESCRIPTION

[0021] Exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all features of the actual implementation are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the process of developing any such actual implementation in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and these constraints may vary from implementation to implementation. In addition, it should be understood that although the development work may be very complex and time-consuming, it is only a routine task for those skilled in the art who benefit from the content of this application.

[0022] It is also necessary to explain here that, in order to avoid obscuring the present invention due to unnecessary details, only the device structure and / or processing steps closely related to the solution according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0023] An embodiment of the present invention provides a method for analyzing the mechanical properties of a sample plate, such as Figure 1 As shown, the method includes the following steps S10 to S40.

[0024] S10: Loading the sample plate to be analyzed into a predetermined device.

[0025] S20: stretching the sample plate to be analyzed to a predetermined stretching length, and obtaining a relationship between the applied tension and the stretching length.

[0026] S30: Determine the change rate of the pulling force and the stretching length according to the change relationship.

[0027] S40: Determine the mechanical properties of the sample plate according to the change rate.

[0028] The method provided by the embodiments of the present invention is different from the traditional method of applying tension to a sample plate until it breaks to determine the mechanical properties of the sample plate. Instead, a tension is applied to the sample plate to stretch it to a predetermined stretching length, and the changing relationship between the applied tension and the stretching length is obtained to analyze the mechanical properties of the sample plate, thereby achieving non-destructive testing of the mechanical properties of the sample plate and improving the accuracy of the analysis results of the mechanical properties of the sample plate.

[0029] In some embodiments, in step S10 , the sample plate to be analyzed may be loaded into a predetermined position of a predetermined device, while ensuring the loading stability of the sample plate, so that the predetermined device can apply a uniform pulling force to the sample plate.

[0030] In some embodiments, in step S20, the sample plate to be analyzed can be stretched at a predetermined speed until a predetermined stretching length is reached, the tension applied to the sample plate at this time is determined, and the changing relationship between the tension applied during the stretching process and the stretching length is obtained.

[0031] In some embodiments, in step S20, the change relationship can be plotted as a curve, and the curve can be linearly fitted within a predetermined interval to obtain a straight line that characterizes the change relationship within the predetermined interval; the linear equation of the straight line is obtained, and the change rate in step S30 is determined based on the linear equation.

[0032] In this embodiment, linear fitting is performed on the variation relationship curve within a predetermined interval to simplify the variation relationship between the applied tension and the stretched length into a linear relationship, so that the variation rate of the tension and the stretched length can be determined according to the linear relationship between the two.

[0033] like Figure 2 As shown, in some embodiments, the predetermined interval can be determined using the following steps S21 to S25.

[0034] S21: Select a new sample plate that has not been tested.

[0035] S22: stretching the new sample plate to a plurality of predetermined lengths to obtain a plurality of variation relationships between applied tension and stretched length.

[0036] S23: According to the relationship determined in step S22, a plurality of curves representing the relationship are determined.

[0037] S24: Determine, based on the multiple curves, an interval in which the multiple curves overlap.

[0038] S25: Determine a predetermined interval according to the intervals where the multiple curves overlap. In some embodiments, the "minimum stretching length including the predetermined interval" is selected as the stretching length (eg, a specific stretching length of 5 mm).

[0039] In this embodiment, by stretching the new sample plate to multiple predetermined lengths, a curve characterizing the changing relationship between multiple applied tensile forces and stretched lengths is obtained, and the predetermined interval is determined based on the interval where the multiple curves overlap, so that the interval where the multiple curves overlap in the new sample plate is used as a reference for the predetermined interval of the sample plate to be analyzed.

[0040] In some embodiments, in step S22, when the new sample plate is stretched to a plurality of predetermined lengths, the sample plate to be analyzed is stretched to the selected predetermined length and predetermined interval to verify the validity and reliability of the determined predetermined interval.

[0041] In some embodiments, step S25 also includes the following steps S251 to S252.

[0042] S251: In an interval where multiple curves overlap, linear fitting is performed on each curve to obtain a straight line representing a change relationship in the overlapped interval.

[0043] S252: Obtain a linear equation of the straight line, determine the rate of change in step S30 based on the linear equation, and determine a predetermined interval based on the rate of change.

[0044] In this embodiment, by performing linear fitting on each curve within the overlapping interval, a linear equation of the straight line representing the change relationship is obtained, and the change rate is determined based on the linear equation, and the predetermined interval is determined based on the change rate, thereby achieving determination of the predetermined interval based on the overlapping interval of multiple curves.

[0045] In some embodiments, in step S252, the overlapping intervals with consistent change rates are predetermined intervals, so as to ensure that after linear fitting of the curve within the predetermined interval, the straight line obtained can accurately characterize the changing relationship between the applied tension and the stretching length.

[0046] For example, in step S20, when determining the predetermined interval, a new sample plate that has not been tested can be selected, and the new sample plate can be stretched by 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12 mm, and 14 mm respectively to obtain six corresponding change relationships between applied tension and stretched length, and six curves representing the relationship are determined according to the change relationships, such as Figure 6 shown.

[0047] Furthermore, according to the six curves representing the change relationship, it can be judged that the curvature overlap of the curves is high in the 2-4mm range, so the interval of curve overlap is determined to be 2-4mm. In this interval, a linear fit is performed on each curve to obtain a straight line representing the change relationship. The fitting data is shown in Table 1 below:

[0048] Table 1 The curve of the change relationship is fitted to the data in the range of 2-4mm

[0049]

[0050]

[0051] Further, a linear equation of the straight line is obtained based on the fitting data, and the change rate in step S30 is determined based on the linear equation. Based on the change rate, overlapping intervals with consistent change rates are determined as predetermined intervals.

[0052] like Figure 3 As shown, in some embodiments, the predetermined interval may also be determined by the following steps S21' to S26'.

[0053] S21': Select a new sample plate that has not been tested.

[0054] S22': stretching the new sample plate to a plurality of predetermined lengths to obtain the length of the new sample plate after stretching.

[0055] S23': According to the length predetermined in step S22' and the length obtained, determine the maximum value of the predetermined length at which the length of the new sample plate remains unchanged after stretching.

[0056] S24': stretch the new sample plate to a length equal to the maximum value of the length predetermined in step S23', and obtain the relationship between the tension and the stretched length.

[0057] S25': According to the relationship determined in step S24', determine a curve representing the relationship.

[0058] S26': perform linear fitting on the curve to obtain a linear equation of the approximate straight line segment of the curve, determine the rate of change in step S30 based on the linear equation, and determine the predetermined interval based on the rate of change.

[0059] In this embodiment, the new sample plate is stretched to multiple predetermined lengths, the lengths of the new sample plate before and after stretching are compared, and the maximum value of the predetermined length at which the length of the new sample plate remains unchanged after stretching is determined, so as to determine the maximum value of the stretching length that the new sample plate can withstand, thereby ensuring lossless stretching; then, the new sample plate is stretched to the predetermined length to obtain a curve of the relationship between the applied tension and the stretching length, and a linear fitting is performed to obtain a linear equation of the approximate straight line segment, and the rate of change is determined based on the linear equation, and the predetermined interval is determined based on the rate of change, so as to determine the predetermined interval of the sample plate to be analyzed based on the relationship between the maximum value of the stretching that the new sample plate can withstand and the change in tension.

[0060] Specifically, in step S23', based on the predetermined length and the length obtained in step S22', the maximum value of the predetermined length at which the length of the new sample plate remains unchanged after stretching is determined, that is, the length of the new sample plate before stretching is compared with the length actually obtained after the new sample plate is stretched according to the predetermined length, and the maximum value of the predetermined length corresponding to the situation where the actual length obtained of the new sample plate after stretching is equal to or has a smaller change than the length of the new sample plate before stretching is determined.

[0061] For example, in step S22' and step S23', the new sample plate is stretched by 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12 mm, and 14 mm, respectively, to obtain the lengths of the new sample plate before and after stretching, as shown in Table 2 below:

[0062] Table 2 Comparison of the length of the new sample before and after stretching to a predetermined length

[0063]

[0064] According to the data in Table 2, within the range of the predetermined stretching length being less than or equal to 7.5 mm, the length of the new sample plate before and after stretching is almost unchanged. When the predetermined stretching length is 10 mm, the length of the new sample plate after stretching is significantly increased compared to the length before stretching. Therefore, the maximum value of the predetermined length is 7.5 mm, that is, to ensure lossless stretching, the selected stretching length should be less than 7.5 mm.

[0065] S23': According to the length predetermined in step S22' and the length obtained, determine the maximum value of the predetermined length at which the length of the new sample plate remains unchanged after stretching.

[0066] like Figure 4 As shown, in some embodiments, the predetermined device has a clamp, and the clamp includes a first clamp 10 and a second clamp 20, the first clamp 10 and the second clamp 20 are arranged in a vertical direction, the sample plate is clamped by the first clamp 10 and the second clamp 20, and the sample plate is located between the first clamp 10 and the second clamp 20. In step S10, the clamping position of the sample plate is adjusted so that the gravity of the sample plate does not act on the second clamp 20 and there is no upward pulling force, and the initial stress state of the sample plate is consistent, so as to ensure that when the same sample plate is stretched to the same stretching length for multiple times, the curves of the obtained change relationship are the same, and are not affected by the gravity of the sample plate itself and the friction with the second clamp 20, thereby improving the accuracy of the mechanical property test of the sample plate.

[0067] In some embodiments, in step S10, the distance between the two ends of the first clamp 10 and the two ends of the second clamp 20 can be measured, and based on the measurement results, the positions of the first clamp 10 and the second clamp 20 in the predetermined device are adjusted to make the distance between the two ends of the first clamp 10 and the two ends of the second clamp 20 equal.

[0068] In this embodiment, the distances between the two ends of the first clamping member 10 and the two ends of the second clamping member 20 are adjusted to be equal so as to align the axes of the first clamping member 10 and the second clamping member 20, thereby ensuring that the forces on the two ends of the sample plate at the stretching starting point remain consistent when performing multiple tensile tests, and the direction in which the tensile force is applied to the sample plate is accurate and not eccentric, further ensuring that when the same sample plate is stretched to the same stretching length multiple times, the curves of the obtained change relationship are the same.

[0069] The following illustrates the requirements and limitations in the above-mentioned embodiments, and the necessity for obtaining accurate and effective data and improving the accuracy of mechanical property testing of the sample plate, by comparing the variation relationship curve obtained when no requirements are set for the clamping position of the sample plate and the distance between the two ends of the first clamping member 10 and the second clamping member 20, and the variation relationship curve obtained when requirements and adjustments are set for the clamping position of the sample plate and the distance between the two ends of the first clamping member 10 and the second clamping member 20.

[0070] See also Figure 7 , Figure 7 The figure shows the relationship between the pulling force and the stretching length of the same sample plate when no requirements are placed on the clamping position of the sample plate and the distance between the first clamping member 10 and the second clamping member 20. Figure 7 It can be seen that the curves do not completely overlap, and when fitting in the same displacement range (5-8 mm), the slopes of the straight lines obtained also have obvious differences. The relative standard deviation of the same sample plate stretched 6 times is 10.2%, as shown in Table 3 below:

[0071] Table 3 Curve fitting of tensile force and tensile length of sample plate after repeated stretching of 10 mm

[0072]

[0073] See also Figure 8 , Figure 8 The figure shows the relationship between the pulling force and the stretched length of the same sample plate when the clamping position of the sample plate is adjusted to make the gravity of the sample plate have no effect on the second clamping member 20 and the distance between the two ends of the first clamping member 10 and the two ends of the second clamping member 20 are adjusted to be equal. Figure 8It can be seen that the directions and trends of the curves are very similar, and when fitting in the same displacement range (2-4 mm), the slopes of the straight lines obtained are similar. The relative standard deviation of the six stretches of the same sample plate is 1.58%, as shown in Table 4 below:

[0074] Table 4 Linear fitting of the tensile force and tensile length curve of the sample plate after repeated stretching of 10 mm

[0075]

[0076] Therefore, it is necessary to require and adjust the clamping position of the sample plate and the distance between the first clamping member 10 and the second clamping member 20 in order to obtain accurate and effective data and improve the accuracy of the mechanical property test of the sample plate.

[0077] like Figure 4 As shown, in some embodiments, the clamp of the predetermined device may further include: a first tensile connector 30 , a second tensile connector 40 , a first matching member 50 and a second matching member 60 .

[0078] Among them, the first clamping member 10 is connected to the first tensile connector 30; the second clamping member 20 is connected to the second tensile connector 40; the first clamping member 10 and the second clamping member 20 clamp the sample that needs to be subjected to a mechanical tensile test; the force-applying mechanism applies external force to the first tensile connector 30 and the second tensile connector 40 to perform a mechanical tensile test on the sample; the first matching member 50 and the second matching member 60 are simultaneously connected to the first clamping member 10 and the second clamping member 20, so that at the beginning of the tensile test, the end faces of the first clamping member 10 and the second clamping member 20 are parallel, and the axis of the first clamping member 10 is aligned with the axis of the second clamping member 20.

[0079] The sample here may be a sample plate.

[0080] In this embodiment, a first mating piece 50 and a second mating piece 60 are provided and connected to the first clamping piece 10 and the second clamping piece 20 at the same time, so as to ensure that during the tensile test, the relative positions of the first clamping piece 10 and the second clamping piece 20 are limited so that the axes of the two are aligned, thereby ensuring that when multiple tensile tests are performed, the forces on the sample plate at both ends of the tensile starting point remain consistent, and the direction in which the tensile force is applied to the sample plate is accurate and without eccentricity, thereby improving the accuracy of the test results and reducing errors. At the same time, it is ensured that the sample is clamped stably and straightly, and that the first clamping piece 10 and the second clamping piece 20 apply uniform and appropriate tensile force to the sample, so as to detect the mechanical properties of the sample without breaking the sample.

[0081] In some embodiments, fasteners (e.g., screws) may be used to connect the first clamp 10 and the second clamp 20 to the first tensile connector 30 and the second tensile connector 40, respectively, so that when a mechanical tensile test is performed on the sample, when a force-applying mechanism applies an external force to the first tensile connector 30 and the second tensile connector 40, the first tensile connector 30 and the second tensile connector 40 drive the first clamp 10 and the second clamp 20 to move, thereby achieving stretching of the sample.

[0082] In some embodiments, one end of the first mating piece 50 passes through the first clamping piece 10, and the other end of the first mating piece 50 is fixedly connected to the second clamping piece 20; one end of the second mating piece 60 passes through the first clamping piece 10, and the other end of the second mating piece 60 is fixedly connected to the second clamping piece 20, so that the first mating piece 50 and the second mating piece 60 are assembled on the first clamping piece 10 and the second clamping piece 20, thereby limiting the relative position of the first clamping piece 10 and the second clamping piece 20, so that the end faces of the two are parallel and the axes are aligned.

[0083] like Figure 4 As shown, in some embodiments, the clamp also includes a fixed fitting 70, which is connected to the first clamping member 10 so that the first fitting 50 and the second fitting 60 are fixedly arranged on the first clamping member 10, thereby achieving a fixed connection between the first fitting 50 and the second fitting 60 and the first clamping member 10.

[0084] like Figure 4 As shown, in some embodiments, the first clamping member 10 and the second clamping member 20 are formed with a clamping hole 11 and a clamping hole 21. Through the clamping hole 11 and the clamping hole 21, the first clamping member 10 and the second clamping member 20 clamp the sample that needs to be subjected to a mechanical tensile test to achieve a firm clamping of the sample and avoid displacement of the sample when being stretched.

[0085] Specifically, Figure 4 and Figure 5 As shown, when clamping a sample that needs to undergo a mechanical tensile test, a fixing member 80 is used to pass through the clamping hole 11 and the clamping hole 21, and penetrate through a matching hole corresponding to the clamping hole 21 provided on the sample, so that the first clamping member 10 and the second clamping member 20 can firmly clamp the sample.

[0086] In some embodiments, the clamping holes can be arranged in plurality, and the plurality of clamping holes are arranged in pairs on the first clamping member 10 and the second clamping member 20, and the number of the clamping holes arranged on the first clamping member 10 is equal to the number of the clamping holes arranged on the second clamping member 20, so as to further improve the stability of the sample being clamped.

[0087] like Figure 4As shown, in some embodiments, the clamping holes 11 and the clamping holes 21 are arranged to be spaced apart from each other by a predetermined length so that the clamping holes 11 and the clamping holes 21 are evenly distributed, avoiding stress concentration and causing the sample to break at the clamping holes, while improving the tensile bearing capacity of the sample to further ensure that the sample is not broken.

[0088] like Figure 4 As shown, in some embodiments, a notch 51 and a notch 61 are formed on the first mating piece 50 and the second mating piece 60, and the notch 51 and the notch 61 are configured to install the first mating piece 50 and the second mating piece 60 on the second clamping piece 20, so as to realize the fixed connection between the first mating piece 50 and the second mating piece 60 and the second clamping piece 20. For example, a tool such as a wrench can be used for installation and fixing.

[0089] like Figure 4 As shown, in some embodiments, the first matching member 50 and the second matching member 60 are provided with size scales 52 and 62. When the sample plate is tested, the first clamping member 10, the second clamping member 20 and the sample plate can be connected as one through the action of the first matching member 50 and the second matching member 60, so as to ensure that the relative positions of the first clamping member 10, the second clamping member 20 and the sample plate remain unchanged when the first clamping member 10, the second clamping member 20 and the sample plate are clamped on the mechanical testing machine. And through the scales on the first matching member 50 and the second matching member 60, the changes in the position of the sample corresponding to the scale and the changes in the position of the first clamping member 10 and the second clamping member 20 relative to the scale are observed, so as to determine that the relative positions of the three have not changed relatively during the process of clamping to the mechanical testing machine, that is, there is no movement caused by external force.

[0090] Regarding the embodiments of the present invention, it should also be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to obtain new embodiments.

[0091] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for analyzing the mechanical properties of a sample plate, characterized in that: It includes the following steps: S10: Loading the sample plate to be analyzed into a predetermined device; S20: stretching the sample plate to be analyzed to a predetermined stretching length, and obtaining a relationship between the applied tension and the stretching length; S30: determining the change rate of the pulling force and the stretching length according to the change relationship; S40: Determine the mechanical properties of the sample plate according to the change rate.

2. The method according to claim 1, characterized in that In step S20, the change relationship is plotted as a curve. Performing linear fitting on the curve within a predetermined interval to obtain a straight line representing the change relationship within the predetermined interval; A linear equation of the straight line is obtained, and the rate of change in step S30 is determined according to the linear equation.

3. The method according to claim 2, characterized in that The predetermined interval is determined by the following steps: S21: Select a new sample plate that has not been tested; S22: stretching the new sample plate to a plurality of predetermined lengths to obtain a plurality of variation relationships between applied tensions and the stretching lengths; S23: according to the relationship determined in step S22, determining a plurality of curves representing the relationship; S24: determining, according to the plurality of curves, an interval in which the plurality of curves overlap; S25: Determine the predetermined interval according to the intervals where the multiple curves overlap.

4. The method according to claim 3, characterized in that In the step S25, Also includes: S251: performing linear fitting on each of the curves in an overlapped interval, to obtain a straight line representing the change relationship in the overlapped interval; S252: Obtaining a linear equation of the straight line, and determining the rate of change in step S30 according to the linear equation; The predetermined interval is determined according to the change rate.

5. The method according to claim 4, characterized in that In step S252, The overlapping intervals where the change rates are consistent are the predetermined intervals.

6. The method according to claim 2, characterized in that The predetermined interval is determined by the following steps: S21': select a new sample plate that has not been tested; S22': stretching the new sample plate to a plurality of predetermined lengths to obtain the length of the new sample plate after stretching; S23': determining the maximum value of the predetermined length of the new sample plate at which the length remains unchanged after stretching according to the predetermined length and the length obtained in step S22'; S24': stretching the new sample plate to a maximum length of the predetermined length in step S23', and obtaining a relationship between the tension and the stretching length; S25': according to the relationship determined in step S24', determining a curve representing the relationship; S26': performing linear fitting on the curve to obtain a linear equation of the straight line segment of the curve, determining the change rate in step S30 according to the linear equation, and determining the predetermined interval according to the change rate.

7. The method according to claim 1, characterized in that in, The predetermined device has a clamp, the clamp includes a first clamp and a second clamp, the first clamp and the second clamp are arranged in a vertical direction, the sample plate is clamped by the first clamp and the second clamp, and the sample plate is located between the first clamp and the second clamp, In step S10, The clamping position of the sample plate is adjusted so that the gravity of the sample plate does not act on the second clamping member.

8. The method according to claim 1, characterized in that in, The predetermined device has a clamp, the clamp includes a first clamp and a second clamp, the first clamp and the second clamp are arranged in a vertical direction, the sample plate is clamped by the first clamp and the second clamp, and the sample plate is located between the first clamp and the second clamp, In step S10, The distance between the two ends of the first clamping member and the two ends of the second clamping member is measured, According to the measurement result, the positions of the first clamping member and the second clamping member on the predetermined device are adjusted so that the distances between the two ends of the first clamping member and the two ends of the second clamping member are equal.

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