High-temperature compression testing device for composite sheet and application of high-temperature compression testing device

Abstract

The invention discloses a high-temperature compression testing device for a composite thin plate and application of the high-temperature compression testing device, and belongs to the technical field of composite material high-temperature testing. In order to solve the problems of sample buckling, expansion damage, end crushing and the like in the high-temperature compression test process of the composite thin plate, the technical means such as wedge block angle design, L-shaped side surface clamping block structure, adjustable positioning bolts and a lower clamping block with a relatively large inclination angle are mainly adopted. Lateral force can be automatically applied in the temperature rising process, sample buckling is prevented, sample expansion and end damage are effectively avoided, and it is ensured that the working section of the sample is complete. The device is simple and easy to use, can realize accurate positioning of the sample, and provides a reliable high-temperature compression test result.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature testing of composite materials, and particularly relates to a high-temperature compression testing device for composite thin plates and its application. Background Technique

[0002] Carbon fiber reinforced resin matrix composites have excellent high-temperature mechanical properties, thermal stability and radiation resistance, and have gradually become the key materials for high-temperature structural components in aerospace aircraft. During actual service, long-term aerodynamic pressure and heat flux can easily lead to local failure of the composite material products. Therefore, it is necessary to test and characterize their basic high-temperature compression mechanical properties (generally at a high temperature of 500 °C) to provide key data support for the development and production of materials and the structural design of aircraft.

[0003] The current thin plate compression performance test methods can be generally divided into three categories according to the loading method: (1) End loading, such as the C-type fixture in ASTM D695, SRM-1R, and GB / T 5852; (2) Shear loading: such as the A-type fixture in ASTM D3410 and GB / T 5852; (3) Mixed end and shear loading: such as the B-type fixture in ASTM D6641 and GB / T 5852. Under room temperature conditions, these three types of test methods and devices can well obtain the compression performance parameters of the composite material, but there are certain limitations when performing high-temperature tests. To prevent the clamping section or the end of the sample from being crushed, compression test specimens usually need to paste reinforcement sheets on both sides of the clamping part. However, there is a lack of available adhesives for pasting during high-temperature tests; or the specimen is processed into a dog-bone shape to increase the end size for protection. For example, in Patent CN 115046850 A, a dog-bone-shaped specimen is used for high-temperature compression. However, unidirectional carbon fiber reinforced resin matrix composites are limited by the material characteristics and can only be processed into straight specimens. At the same time, the spring pressing device used in this patent must adjust the pressing force between the front and rear anti-buckling plates through the combined use of different disc spring washers to ensure that the fixture can both clamp the specimen and slide relative to the specimen, so that the compression load is transmitted to the working section of the specimen to obtain an effective failure mode. The number and combination method of the used disc spring washers are relatively complex. In addition, the test device also needs to have a high-temperature guiding function. The commonly used bolt locking structure or the guiding shaft / hole structure will both cause the specimen to have a small deflection angle during compression due to thermal expansion. Although there are already some methods to improve it, for example, in Patent CN202111111039.7, a wedge block group is added to the guiding column and the guiding through hole, which can continue to apply constraints to the guiding column when there is a gap between the shaft and the hole due to thermal expansion. However, the sizes of the 8 wedge blocks are extremely likely to be different after high-temperature oxidation. Coupled with the large failure load of unidirectional carbon fiber reinforced resin matrix composites, it leads to eccentric loading and additional frictional forces affecting the test accuracy, and the operation difficulty of assembling and using the 8 wedge blocks is also relatively large. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-temperature compression test device for composite material thin plates and its application, to solve the problems that the previous fixtures are prone to cause unreasonable specimen damage, lack of high-temperature guiding function, and the operation difficulty of the fixtures is relatively large.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A high-temperature compression test device for composite material thin plates includes a sleeve, a first upper clamp block, a second upper clamp block, a lower clamp block, and a wedge block;

[0007] The upper end of the sleeve is a cylinder, containing a cavity with an open top. The cavity contains an inclined surface. The lower end of the sleeve is a semi-cylinder, and the cavity at the upper end of the sleeve communicates with the lower end.

[0008] The first upper clamping block and the second upper clamping block cooperate to clamp the specimen to form a specimen assembly, and are installed in the cavity of the sleeve.

[0009] The wedge block is placed in the cavity of the sleeve. One of its inclined surfaces abuts against the inclined surface of the cavity, and the other vertical straight surface abuts against the specimen assembly.

[0010] The lower clamping block is installed on the semi-cylindrical part at the lower end of the sleeve to clamp the specimen passing through the cavity.

[0011] Furthermore, the upper end cylinder of the sleeve includes an inclined bottom surface, which intersects with the vertical straight surface of the lower end semi-cylinder of the sleeve. The formed intersection line is the lower edge of the inclined bottom surface.

[0012] Furthermore, the upper side surface of the lower clamping block is an inclined top surface, and the connection part of the inclined top surface and the lower end semi-cylinder of the sleeve is located at the upper edge of the inclined top surface.

[0013] Furthermore, there is a distance between the inclined bottom surface of the upper end cylinder of the sleeve and the inclined top surface of the lower clamping block.

[0014] Furthermore, both the first upper clamping block and the second upper clamping block have an L-shaped side surface. The L-shaped side surfaces of these two upper clamping blocks are mutually attached and fixed to form a vertical strip-shaped cavity. The cross-section of the strip-shaped cavity is rectangular for placing the specimen.

[0015] Furthermore, the side surface of the upper end cylinder of the sleeve contains at least two screw holes for installing positioning bolts. The positioning bolts are installed in the screw holes, and the ends abut against the side surface of the second upper clamping block to fix the specimen assembly.

[0016] Furthermore, there are several cooperating through holes on both the first upper clamping block and the second upper clamping block. The locking bolts pass through the through holes and are locked by locking washers to fix the first upper clamping block and the second upper clamping block.

[0017] Furthermore, the through hole on the first upper clamping block is a U-shaped hole, and the locking bolt can be horizontally adjusted in the U-shaped hole.

[0018] Furthermore, there are several cooperating through holes on both the vertical straight surfaces of the lower clamping block and the lower end semi-cylinder of the sleeve. The fastening bolts pass through the through holes and are locked by fastening washers to fix the lower clamping block on the lower end semi-cylinder of the sleeve.

[0019] Furthermore, the angle α of the inclined surface of the cavity of the sleeve relative to the horizontal plane is 55° ≤ α ≤ 76°.

[0020] Application of a high-temperature compression test device for composite thin plates, used for high-temperature compression tests of composite thin plates.

[0021] The beneficial effects achieved by the present invention are as follows:

[0022] 1. By reasonably designing the angle of the wedge block, the present invention can fill the gap generated by thermal expansion during the heating process, continuously apply a lateral force to the specimen, prevent buckling, and meet the friction self-locking function to avoid the upward sliding of the wedge block under the action of the specimen buckling force.

[0023] 2. The L-shaped side surface of the upper clamp block group of the present invention fits the width surface and thickness surface of the specimen without gaps, preventing the specimen from being damaged by expansion. Moreover, the upper end surface is flush with the upper end surface of the specimen, jointly bearing the compression load, avoiding premature failure at the end, and ensuring the integrity of the working section of the specimen.

[0024] 3. Through the U-shaped through-hole in the first upper clamp block, the present invention can adapt to specimens of different widths, adjust the position of the clamp block to achieve fitting, and ensure fastening through the locking bolt, improving the accuracy and stability of the test.

[0025] 4. The angle of the wedge block of the present invention is reasonable, avoiding the influence of additional friction on the test results and ensuring the accuracy of high-temperature guidance and experimental data.

[0026] 5. The large inclination angle design of the lower clamp block and the sleeve of the present invention not only provides sufficient lateral support to prevent the specimen from moving laterally, but also avoids blocking the optical path during DIC measurement of deformation, ensuring the effectiveness of the experiment.

[0027] 6. The position of the locking bolt of the present invention can be adjusted to ensure the precise centering of the specimen in the width direction, and the lower clamp block, the specimen and the sleeve are fixed together through the bolt and washer to prevent relative sliding, simplifying the assembly process of the device and improving the stability of the device. Description of the Drawings

[0028] Figure 1 is the assembly drawing of a high-temperature compression test device (including wedge block) for composite thin plates in the embodiment.

[0029] Figure 2 is the assembly drawing of a high-temperature compression test device (excluding wedge block) for composite thin plates in the embodiment.

[0030] Figure 3 is the exploded view of a high-temperature compression test device for composite thin plates in the embodiment.

[0031] Figure 4 is the partial assembly drawing of a high-temperature compression test device for composite thin plates in the embodiment.

[0032] Figure 5It is a process diagram for assembling a high-temperature compression test device for a composite thin plate in an embodiment.

[0033] Figure 6 It is a diagram showing the assembly relationship between the specimen and the first upper clamping block in an embodiment.

[0034] Figure 7 It is a diagram showing the assembly relationship between the specimen and all the upper clamping blocks in an embodiment.

[0035] Figure 8 It is a structural diagram of the first upper clamping block in an embodiment.

[0036] Figure 9 It is a structural diagram of the second upper clamping block in an embodiment.

[0037] Figure 10 It is a half-sectional view of the sleeve in an embodiment.

[0038] Figures 11-13 It is a mechanical schematic diagram of the specimen and the wedge block.

[0039] Explanation of reference numerals:

[0040] 1: Sleeve; 2: First upper clamping block;

[0041] 3: Second upper clamping block; 4: Lower clamping block;

[0042] 5: Wedge block; 6: Positioning bolt;

[0043] 7: Locking bolt; 8: Locking nut;

[0044] 9: Fastening bolt; 10: Fastening washer. Detailed implementation manner

[0045] To make the technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and understandable, the following will be described in detail with reference to the embodiments and the drawings.

[0046] This embodiment specifically discloses a high-temperature compression test device for a composite thin plate, as shown in Figures 1-3 The main components include a sleeve 1, a first upper clamping block 2, a second upper clamping block 3, a lower clamping block 4, and a wedge block 5, as well as positioning bolts 6, locking bolts 7, locking nuts 8, fastening bolts 9, and fastening washers 10 for fixing these components. Among them, the upper end of the sleeve 1 is a cylinder, containing a cavity with an opening at the top. The cavity is used to place the assembly of the first upper clamping block 2, the second upper clamping block 3, and the specimen (hereinafter referred to as the specimen assembly) and the wedge block 5. The cavity contains an inclined surface that fits the inclined surface of the wedge block (see Figure 10)。The lower end of the sleeve 1 is a semi-cylinder, and the vacant part opposite the semi-cylinder is used to install the lower clamping block 4. The cavity of the cylinder is connected above the semi-cylinder, which is used to pass through the specimen, and the lower end of the specimen is fixed by the lower clamping block 4. There is a large inclination angle between the sleeve 1 and the lower clamping block 4 at the working section of the specimen, that is, the upper side of the lower clamping block 4 is an inclined top surface that slopes downward, and the bottom surface of the upper end cylinder of the sleeve 1 above the lower clamping block 4 is an inclined bottom surface that slopes upward. These two inclined surfaces form a horizontal V shape, and there can be a certain distance between the inclined bottom surface and the inclined top surface to prevent blocking the camera and the illumination optical path when using digital image correlation technology (DIC) to measure deformation.

[0047] Figures 4-5 The brief assembly process of the sleeve 1, the specimen assembly, and the lower clamping block 4 is shown. After the specimen assembly is placed in the cavity of the sleeve 1, it is fixed by the positioning bolt 6. The position of the positioning bolt 6 is opposite to the side of the second upper clamping block 3, which can achieve the centering in the width direction of the specimen. The lower clamping block 4 is installed at the lower end of the sleeve 1 through the fastening bolt 9 to fix the lower end of the specimen. The end of the fastening bolt 9 is fastened through a fastening washer 10 (not shown in the figure).

[0048] As Figures 6-7 shown, the specimen assembly is composed of the first upper clamping block 2 and the second upper clamping block 3 clamping the specimen in the middle, and is fixed by the locking bolt 7 and the locking nut 8. The structure of the first upper clamping block 2 is as Figure 8 shown, and the structure of the second upper clamping block 3 is as Figure 9 shown. Both contain an L-shaped side, and there are multiple through holes on the side for passing the fastening bolt 7. When the L-shaped sides of the first upper clamping block 2 and the second upper clamping block 3 are assembled in a fitting manner, a strip-shaped cavity for accommodating the specimen is left vacant, and the specimen is fixed in this cavity. The L-shaped sides of the two upper clamping blocks fit the width surface and the thickness surface of the specimen, and the upper end surface is flush with the upper end surface of the specimen. There is no relative sliding between the upper clamping block and the specimen. During the compression process, the upper clamping block and the upper end surface of the specimen jointly bear the compression load to prevent the ineffective failure mode of end crushing. Among them, the through hole on the first upper clamping block 2 is a U-shaped hole, and by adjusting the left and right positions of the first upper clamping block 2, the thickness surface of specimens with different widths can be made to fit the side of the clamping block group.

[0049] This device is used for high-temperature compression testing of composite thin plates, and the operation process is as follows:

[0050] 1) Fit the upper end of the specimen to the L-shaped sides of the first upper clamping block 2 and the second clamping block 3, and clamp the specimen through the locking bolt 7 and the locking nut 8 to form a specimen assembly;

[0051] 2) Place the specimen assembly into the cavity of the sleeve 1, and the lower end of the specimen fits the wall surface of the sleeve 1, and pay attention to ensuring that the specimen is vertical in the front-back direction;

[0052] 3) Fix the lower clamping block 4 on the sleeve 1 through the fastening bolt 9 and the fastening washer 10. Similarly, the specimen is fitted to the wall surface of the lower clamping block 4.

[0053] 4) Place the wedge block 5 into the cavity of the sleeve 1. One side of the inclined surface of the wedge block 5 is fitted to the inner inclined surface of the cavity of the sleeve 1, and the other side is fitted to the second clamping block 3.

[0054] 5) Place the assembled whole device on the compression plate of the testing machine, and start heating up and testing.

[0055] The design principle of the wedge block angle of this device is as follows:

[0056] By designing the wedge block angle, during the heating process of this device, when a gap appears between the wedge block and the specimen due to thermal expansion, the wedge block can freely fall due to gravity, fill the gap, and then continuously apply a lateral force to the specimen to prevent the specimen from buckling. This angle satisfies frictional self-locking and cannot slide upward when subjected to the buckling force of the specimen; during the compression process, this angle satisfies that it cannot be driven downward by the specimen to prevent the frictional force between it and the specimen from canceling out the compression force, resulting in incorrect transmission of the load to the working section of the specimen.

[0057] At high temperature, the friction coefficient μ between the wedge block and the sleeve 1 is approximately 0.7.

[0058] ① When a gap appears between the wedge block and the specimen due to thermal expansion of this device, its force analysis is as Figure 11 shown:

[0059] The wedge block can automatically slide downward under the action of gravity, and it needs to satisfy:

[0060] G·sinα ≥ μ·Gcosα

[0061] μ ≤ tanα

[0062] α ≥ 35°

[0063] ② When the specimen buckles during the compression process and applies a force horizontally to the right on the wedge block, its force analysis is as Figure 12 shown:

[0064] The forces perpendicular to the inclined plane downward for F and G are Fsinα and Gcosα respectively, and the resultant force T = Fsinα + Gcosα, from which a downward frictional force μ 1 (Fsinα + Gcosα) is generated; the component of F along the inclined plane upward is Fcosα, and the component of G along the inclined plane downward is μGsinα. At this time, the wedge block needs to satisfy frictional self-locking and cannot slide obliquely upward, and it needs to satisfy:

[0065] Gsinα + μ 1 (Fsinα + Gcosα) ≥ Fcosα

[0066] That is,

[0067] Gsinα + μ 1 Fsinα + μ 1 Gcosα ≥ Fcosα (1)

[0068] When the specimen undergoes deflection deformation and pushes the wedge block to the right, F can change continuously, that is, F in the above formula is constantly changing. Therefore, an α cannot be directly obtained 0 , so simplify the above formula. First, without considering the influence of gravity, it satisfies:

[0069] Fcosα ≤ μ 1 Fsinα

[0070] That is,

[0071]

[0072] When holds, due to the frictional force generated by F and the influence of the self - gravity component of the wedge block, formula (1) is automatically satisfied. At this time:

[0073] α ≥ 55°

[0074] ③ When the specimen is compressed and moves downward, to prevent it from dragging the wedge block downward, resulting in the two getting stuck tighter and tighter and the frictional force between them increasing, which interferes with the mechanical property test of the specimen. At this time, the wedge block needs to meet the following requirements: when the specimen moves downward, it will not drag the wedge block downward. The force analysis of the wedge block is as follows Figure 13 shown as:

[0075] 1) In the initial state, the specimen is stationary, and the wedge block is restricted by the specimen and the inclined plane and remains stationary.

[0076] At this time, N 1 sinα = F, N 1 cosα = G, that is, F = G·tanα;

[0077] There is no frictional force between the wedge block and the specimen, and between the wedge block and the inclined plane.

[0078] 2) When the specimen starts to move downward, assume that the static friction coefficients between the wedge block and the inclined plane, and between the wedge block and the specimen are μ1 and μ2 respectively.

[0079] The wedge block is subjected to the downward frictional force f 2 = μ 2 ·F = μ 2 ·G·tanα.

[0080] f 2 , the normal pressures of G, F perpendicular to the inclined plane downward:

[0081] T = F·sinα+(f 2 +G)·cosα = G·sinα·tanα+(μ 2 F + G)·cosα

[0082] The upward force of the wedge along the inclined plane is the component Fcosα of F, and the frictional force μ 1 generated by T. The downward force along the inclined plane is the component (f 2 +G) of (f 2 +G)sinα.

[0083] When the specimen moves downward, if the wedge is not dragged downward, the following condition should be satisfied:

[0084] (f 2 +G)sinα ≤ μ 1 T + F·cosα

[0085] (μ 2 F + G)sinα ≤ μ 1 [Fsinα+(f 2 +G)cosF]+Fcosα

[0086] (μ 2 ·G·tanα + G)sinα ≤ μ 1 [G·tanα·sinα+(μ 2 ·G·tanα + G)cosα]+G·tanα·cosα

[0087] Simplifying gives:

[0088] (μ 1 -μ 2 )secα + μ 1 μ 2 sinα + μ 2 cosα ≥ 0

[0089] Taking μ 1 = 0.7 and μ 2 = 0.9, we get:

[0090] α ≤ 76°

[0091] In summary, the angular range is 55° ≤ α ≤ 76°.

[0092] Although the present invention has been disclosed above by way of examples, it is not intended to limit the present invention. Any appropriate modification or equivalent replacement of the technical solutions of the present invention by those of ordinary skill in the art shall be covered within the protection scope of the present invention, and the protection scope of the present invention shall be defined by the claims.

Claims

1. A high temperature compression test device for composite thin plates, characterized in that: It includes a sleeve, a first upper clamping block, a second upper clamping block, a lower clamping block and a wedge block; The upper end of the sleeve is a cylinder, containing a cavity with an open top, the cavity containing an inclined surface, and the lower end of the sleeve is a semi-cylinder, the cavity of the upper end of the sleeve is connected with the lower end; The first upper clamping block cooperates with the second upper clamping block to clamp the sample to form a sample assembly, and is installed in the cavity of the sleeve; The wedge block is placed in the cavity of the sleeve, with one side of the wedge block leaning against the inclined surface of the cavity, and the other side of the wedge block leaning against the sample assembly; The lower clamping block is installed on the semi-cylindrical body at the lower end of the sleeve to clamp the sample passing through the cavity.

2. The high temperature compression test device for composite sheets according to claim 1, characterized in that: The cylindrical body at the upper end of the sleeve comprises an inclined bottom surface, which intersects with the vertical straight surface of the semi-cylindrical body at the lower end of the sleeve, and the intersection line formed is the lower edge of the inclined bottom surface.

3. The high temperature compression test device for composite sheets according to claim 1, characterized in that: The upper side surface of the lower clamping block is an inclined top surface, and the connection between the inclined top surface and the semi-cylindrical body at the lower end of the sleeve is located at the upper edge of the inclined top surface.

4. The high temperature compression test device for composite sheet according to claim 1, characterized in that: The first upper clamp block and the second upper clamp block both have an L-shaped side surface, and the L-shaped side surfaces of the two upper clamp blocks are fitted and fixed to each other to form a vertical strip-shaped cavity, and the cross section of the strip-shaped cavity is rectangular for placing the sample.

5. The high temperature compression test device for composite sheets according to claim 1, characterized in that: The side surface of the cylindrical body at the upper end of the sleeve contains at least two screw holes for installing positioning bolts; the positioning bolts are installed in the screw holes, and the ends thereof are pressed against the side surface of the second upper clamping block to fix the sample assembly.

6. The high temperature compression test device for composite sheet according to claim 1, characterized in that: The first upper clamp block and the second upper clamp block both have a plurality of matching through holes, through which locking bolts pass and are locked by locking washers to fix the first upper clamp block and the second upper clamp block.

7. The high temperature compression test device for composite sheets according to claim 6, characterized in that: The through hole on the first upper clamping block is a U-shaped hole, and the locking bolt can be adjusted laterally in the U-shaped hole.

8. The high temperature compression test device for composite sheets according to claim 1, characterized in that: The lower clamp block and the vertical straight surface of the lower semi-cylinder of the sleeve both contain a plurality of matching through holes, through which fastening bolts pass and are locked by fastening washers to fix the lower clamp block on the lower semi-cylinder of the sleeve.

9. The high temperature compression test device for composite sheets according to claim 1, characterized in that: The angle α of the inclined surface of the cavity of the sleeve relative to the horizontal plane is 55°≤α≤76°.

10. An application of the high temperature compression test device for composite sheets according to any one of claims 1 to 9, characterized in that: Used for high temperature compression testing of composite sheets.

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