Flexible material high and low temperature compression test method

Abstract

The invention relates to a high and low temperature compression test method for a flexible material, and aims to solve the problems that in the high and low temperature compression test of the flexible material, the lower end is bent and deformed when an S-shaped sensor is pressed down, and a lengthening rod is adopted in a high and low temperature box, so that the side slip of a clamp is aggravated, deflection, instability and uneven stress are caused, and finally, the test data are out of alignment. According to the test method, a compression clamp is included, and the clamp is composed of a lower pressing disc, at least three pin shafts fixed to the lower pressing disc through threads and an upper pressing disc provided with a through hole; the hole diameter of the through hole is slightly greater than the diameter of the pin shaft; meanwhile, the invention also comprises a compensation algorithm for correcting inaccurate test data caused by experimental equipment by utilizing a mechanical formula. The flexible material compression test device is convenient to clamp, accurate in centering and high in unbalance loading resistance, and the accuracy and reliability of a flexible material compression test are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material testing, in particular to a high-low temperature compression test method for flexible materials. BACKGROUND

[0002] A material testing machine is a precision testing instrument for measuring the mechanical properties, process properties, internal defects, and dynamic unbalance of rotating parts of metal materials, non-metal materials, mechanical parts, and engineering structures under various conditions and environments. In the process of researching and exploring new materials, new processes, new technologies, and new structures, a material testing machine is an indispensable important detection instrument.

[0003] During the use of the material testing machine, the S-shaped sensor gradually increases the force borne during the pressing process, and then bends and deforms. Due to the use of the lengthening rod, the lateral sliding amplitude of the clamp increases, which causes a large friction force between the pin column and the through hole, thereby affecting the measured experimental data. Therefore, a high-low temperature compression test method for flexible materials is needed.

[0004] At present, there is no effective solution in the compression test method in the related art. SUMMARY

[0005] In view of the problems in the related art, the present application provides a high-low temperature compression test method for flexible materials to overcome the above technical problems existing in the prior art.

[0006] The technical scheme of the present application is as follows:

[0007] In a first aspect, the present application provides a clamp, which includes two parts. One part is composed of a pressing disc (1) and three pin shafts (3). The pin shafts (3) are connected to the pressing disc (1) by threads. This connection method is not only stable and reliable, but also easy to disassemble, which facilitates cleaning and maintenance of the clamp. The three pin shafts (3) are evenly distributed on the upper surface of the pressing disc (1), ensuring that the pressure applied to the sample during compression is evenly distributed.

[0008] The other part is also a pressing disc structure with a through hole in the center, and the diameter of the through hole is slightly larger than the diameter of the pin shaft. This design facilitates the use of the two clamps together. During the test, the flexible material sample is placed between the two clamps, and the axial compression and fixation of the sample are realized through the cooperation of the pin shaft (3) and the through hole (6). The diameter of the through hole is slightly larger than the diameter of the pin shaft, which can ensure that the pin shaft can be smoothly inserted into the through hole, and on the other hand, it also provides a certain space for the deformation of the sample during compression, avoiding damage to the sample due to too tight fit.

[0009] In a second aspect, the present application provides an experimental data compensation method, and the steps are as follows:

[0010] First, the structure is analyzed and simplified, assuming that AB in the figure is the fixed end (providing horizontal, vertical constraints and bending moment), and the lower part is composed of vertical rods (AC, BD, CE, DI) and horizontal beams (EJ, IJ) to form a multi-span statically determinate structure. Because the structure is symmetrical and the vertical rods (AC, CE, DI) are rigid (assuming no axial deformation, only transmitting vertical force), the vertical displacement at E and I is 0, so the horizontal beam EJ can be regarded as a cantilever beam with E as the fixed end (no displacement at E, the constraint is fixed end).

[0011] Then the force and angle of the cantilever beam EJ are calculated. The length of the cantilever beam EJ is (J to E distance), the bending stiffness is EI, and the point J is subjected to an upward concentrated force F. The bending moment distribution of the cantilever beam EJ is:

[0012]

[0013] In the above formula, is the distance from E to the calculation section, 0 ≤ ≤

[0014] Using the unit load method (virtual work principle): apply a unit force couple at point J = 1, the corresponding unit bending moment distribution =1; the bending moment distribution under actual load:

[0015]

[0016] The angle of rotation is the integral of the actual bending moment and the unit bending moment divided by EI, that is:

[0017] .

[0018] The friction coefficient between the pin shaft and the through hole is µ, and the lengthening rod is a rigid member. The force measured by the testing machine is The direction is vertically upward, and according to the above calculated angle of rotation , the friction force :

[0019]

[0020] Therefore, the vertical force (direction vertically upward) generated during the compression of the specimen is:

[0021]

[0022] Because of the angle of rotation, the real force that the experiment should get is the force along the lengthening rod :

[0023]

[0024] That is, the real strength to be obtained.

[0025] Compared with the prior art, the present application has the following beneficial technical effects:

[0026] 1、 The present application solves the problem of easy deflection, instability, uneven stress and distorted test data caused by the need to use a lengthening rod in the high and low temperature flexible material compression test in the prior art.

[0027] 2、 The structure of the clamp is simple and convenient to operate, only need to place the sample between the two clamps, and then through the cooperation of the pin shaft and the through hole, the fixing of the sample can be completed, which greatly improves the test efficiency.

[0028] 3、 The pin shaft and the pressure plate are connected through threads, which is convenient for disassembly and replacement, and is convenient for cleaning and maintenance of the clamp, prolonging the service life of the clamp.

[0029] 4、 It can realize compression test under different temperature environment, different loading rate (from quasi-static to dynamic) and cyclic loading condition, and is suitable for various types of flexible materials, and is convenient for studying material properties. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a high and low temperature flexible material compression test operation table drawing.

[0031] Figure 2 It is a flexible material high and low temperature compression experiment clamp structure drawing.

[0032] Figure 3 It is a local enlarged view of the clamp.

[0033] Figure 4 It is a top view of the clamp 2.

[0034] Figure 5 It is a structure drawing of the clamp 1.

[0035] Figure 6 It is an A-A sectional view of Figure 5 .

[0036] Figure 7 It is a structure drawing of the pin shaft.

[0037] Figure 8 It is a compression clamp operation drawing.

[0038] Figure 9 It is a force analysis drawing of the sensor.

[0039] Figure 10 It is a force analysis drawing of the clamp

[0040] 1 - lower platen; 2 - upper platen; 3 - pin shaft; 4 - locking nut; 5 - positioning flange; 6 - through hole; 7 - guide slot; 8 - auxiliary positioning device; 9 - connector; 10 - dowel pin; 11 - extension rod; 12 - sensor; 13 - high-low temperature chamber; 15 - testing machine. DETAILED DESCRIPTION

[0041] First, the flexible material needs to be processed into a cylindrical sample according to standard specifications. The diameter of the sample is denoted as d, and the height is denoted as h. According to the material testing specification, the h / d ratio is recommended to be controlled within the range of 1-3. During sample preparation, it is necessary to ensure that the two end faces of the sample are precisely machined to meet the standard of being flat and parallel to each other, in order to ensure the accuracy of the test data.

[0042] Then, the preparation stage of the high-low temperature compression test of flexible materials is carried out, and two main components of the test device need to be prepared in advance: the lower clamp assembly (which is composed of the lower platen (1) and the matching pin shaft (3)) and the upper clamp assembly (which includes the upper platen (2) and the through hole (6) structure). The machining precision and assembly quality of these two clamps will directly affect the accuracy of the subsequent test results.

[0043] Next, the flexible material sample to be tested is placed flat on the lower platen (1) of the lower clamp. Special attention should be paid to adjusting the position of the sample during operation to ensure that the center point is completely coincident with the geometric center of the platen. This precise centering operation can avoid eccentric loads during the subsequent compression process and ensure the reliability of the test data.

[0044] Next, the pin shaft (3) of the lower clamp needs to be precisely aligned with the through hole (6) of the upper clamp. During operation, the upper clamp should be slowly and smoothly lowered, and the pin shaft (3) should be accurately inserted into the through hole (6) along the vertical direction, so that the positioning flange (5) cooperates with the guide slot (7). Since the test is conducted in a high-low temperature environment, the experiment needs to be carried out in a high-low temperature chamber (13). The clamps are connected to the testing machine through an extension rod, and each component is locked by a locking nut (4). This assembly process realizes the compression and fixation of the flexible material sample, and establishes a stable loading condition for subsequent performance testing.

[0045] Before the formal compression test, the sample is first treated according to the requirements of the experiment, so that the temperature of the sample reaches the preset temperature, and then the required speed and other requirements of the test machine (14) are tested. During the compression process, two key aspects of information need to be observed and recorded synchronously: one is the change of the strain of the sample under the action of the load (a high-precision video extensometer is used for recording to ensure the test accuracy), and the other is the mechanical property data collected by the test equipment. Through the comparative analysis of these test phenomena, the mechanical performance of the flexible material under the action of the compression load can be comprehensively evaluated.

[0046] After the test is completed, the device needs to be disassembled. At this time, the pin shaft (3) should be rotated in the counterclockwise direction to loosen it from the fixed position of the compression disc. This detachable design not only facilitates the thorough cleaning of the parts of the clamp after the test, but also provides convenient conditions for the regular maintenance of the equipment, ensuring that the clamp remains in good working condition for a long time.

[0047] The experimental data is processed by data compensation, according to the following calculation method:

[0048] First, assume that the lower end of the S-shaped sensor (12) is a cantilever beam, and calculate the bending angle :

[0049]

[0050] Then calculate the friction between the pin column (4) and the through hole (6) :

[0051]

[0052] Further calculate the real force obtained by the test :

[0053]

[0054] That is, the real force to be obtained.

[0055] According to the above processing method, the final force is processed to obtain the stress, and then the strain measured by the video extensometer is processed to generate the stress-strain curve, so as to obtain the material properties.

[0056] Finally, it should be emphasized that the above-mentioned embodiments are only examples of the technical solutions of the present application, and are not limiting provisions; even if the details of the present application have been described in detail with reference to these embodiments, those skilled in the art should understand that they can adjust the technical solutions of the described embodiments, or make equivalent replacement for part or even all technical features; such adjustment or replacement does not cause the relevant technical solutions to deviate from the scope of the embodiments of the present application.

Claims

1. A high and low temperature compression test method for flexible materials: This paper proposes a compression test method for flexible materials specifically designed for high and low temperature environments to evaluate the compression characteristics of materials at different temperatures. To address issues such as specimen collapse during testing, this method provides a flexible material compression test fixture and a method for compensating for inaccurate data caused by the testing apparatus. Its features include: The test fixture consists of two parts: the lower fixture includes a threaded lower pressure plate (1), a locking nut (4), and at least three evenly distributed pins (3), with a positioning flange (5) at the top of the pins (3) to effectively prevent lateral slippage of the sample; the upper fixture is an upper pressure plate (2) structure with guide grooves (7) and through holes (6) corresponding to the pins (3), which automatically aligns with the positioning flange (5); the two are positioned by insertion to achieve stable fixation of the sample during axial compression. In addition, the data compensation method compensates for the frictional error caused by the bending deformation of the sensor through mechanical formulas: the horizontal beam at the lower end of the S-shaped sensor is abstracted into a cantilever beam model, and the deflection angle is calculated based on the unit load method; then, combined with the friction coefficient µ between the pin and the through hole, and combined with relevant mechanical formulas, the true material mechanical parameters are finally obtained. This scheme, through the combination of structural innovation and algorithm compensation, significantly improves the accuracy and stability of flexible material testing under extreme temperatures.

2. The clamp according to claim 1, characterized in that: The number of pins (3) is 3-5, and they are evenly distributed along the circumference of the lower pressure plate (1). The axis of the pins (3) is parallel to the axis of the lower pressure plate (1) and connected by fine thread. This ensures that the pressure is transmitted evenly when the sample is under pressure, while also improving the connection stability and enabling fine adjustment of the height of the pins (3), and facilitating disassembly.

3. The clamp according to claim 1, characterized in that: The diameter of the through hole (6) is 0.1-0.5 mm larger than the maximum diameter of the pin (3), forming a clearance fit, which makes the pin (3) self-adaptive when inserted, while avoiding installation difficulties caused by interference fit.

4. The clamp according to claim 1, characterized in that: It also includes an auxiliary positioning device (8), which is a ring structure and is detachably installed on the testing machine and sensor (12) by means of an extension rod (11) and a connector (9). It is fixed by a locking nut (4) and a pin (10) to limit the initial placement position of the sample and ensure that the sample is concentrically aligned with the pin (3). At the same time, the upper surface of the locking nut (4) is provided with anti-slip texture or coating to increase the friction with the mounting sleeve and prevent the sample from sliding relative to each other during compression.

5. The data compensation method according to claim 1, characterized in that: First, a structural analysis and simplification are performed. Assume AB is a fixed end (providing horizontal and vertical constraints and bending moments), and the structure below consists of vertical members (AC, BD, CE, DI) and horizontal beams (EJ, IJ). Due to the symmetry of the structure and the rigidity of the vertical members (AC, CE, DI) (assuming no axial deformation, only transmitting vertical force), the vertical displacement at points E and I is zero. Therefore, the horizontal beam EJ can be considered as a cantilever beam with E as its fixed end (no displacement at E, the constraint is a fixed end). Then, the forces and rotation angles of the cantilever beam EJ are calculated. The length of the cantilever beam EJ is... (The distance from J to E), with bending stiffness EI, J is subjected to a concentrated force F upwards, and its bending moment distribution is as follows: ( Let E be the distance from the calculated section, 0 ≤ ≤ Using the unit load method (virtual work principle), a unit moment is applied at point J. =1, corresponding to the unit bending moment distribution =1, the bending moment distribution under actual load is: Corner The integral of the actual bending moment and the unit bending moment divided by EI, i.e. .

6. The data compensation method according to claim 1, characterized in that: The coefficient of friction between the pin and the through hole is µ, and the extension rod is a rigid component. The force measured by the sensor... The direction is vertically upward, based on the angle calculated above. The pressure of the through hole on the pin can be determined. Thus, the frictional force is obtained. Therefore, it can be concluded that the vertical force generated during the compression of the sample... (Direction vertically upward). Due to the rotation angle, the actual force obtained from the experiment should be the force along the direction of the extended rod. That is, the actual force that is to be obtained.

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