Compression clamp for L-shaped beam of composite laminated plate in extreme high-temperature environment and test method of compression clamp

Abstract

The invention provides a compression clamp for an L-shaped beam of a composite laminated plate in an extreme high-temperature environment, which comprises an upper fixing unit, a lower fixing unit and inner fixing pieces, the upper fixing unit is connected with the lower fixing unit through a guide rod, the inner sides of the upper fixing unit and the lower fixing unit are connected with the inner fixing pieces, the inner fixing pieces are L-shaped plates, and the lower fixing unit is connected with the lower fixing unit through a guide rod. The upper part of the test piece is clamped and fixed between the inner fixing piece and the upper fixing unit, and the lower part of the test piece is clamped and fixed between the inner fixing piece and the lower fixing unit. The fixing problem of the L-shaped beam test piece in the compression test can be effectively solved, abrasion of the clamp to the test piece in the test process is avoided, meanwhile, the centering problem of the test piece under the compression load is solved, and the possibility of instability in the compression test is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of profile compression testing, and in particular relates to a compression fixture for an L-shaped beam of a composite laminate in an extreme high temperature environment and a testing method thereof. Background Art

[0002] The new generation of hypersonic aircraft has high performance, new indicators and great design difficulty. It must not only adapt to the extreme force / heat load environment, but also meet the stringent requirements of light weight, high efficiency, low cost and rapid response, which puts extremely high demands on the performance of aircraft materials. With the growing demand for lightweight and high-performance structural parts in the aerospace field, high-temperature composite materials have become one of the indispensable materials for the new generation of hypersonic aircraft in the modern aerospace field due to their advantages such as high temperature resistance, high specific strength, high specific stiffness and strong designability. Special-shaped components such as L-beams are widely used in key parts such as aircraft wing rudders and engine support structures due to their excellent mechanical properties and spatial adaptability. The compression performance of L-beams (especially the yield strength under extreme high temperature conditions) has become the core indicator of their reliability evaluation. At present, the compression strength evaluation of L-beams is generally carried out in the form of simulation analysis, but due to the limitations of simulation analysis theory, the reliability of the results is poor. It is urgent to carry out experimental work to fully grasp the compression performance of L-beams.

[0003] During the compression performance test of L-beam specimens, due to their unique right-angle structure, the compression load is unevenly distributed, and additional bending moments are generated during the compression process. The flat pressure block design of conventional fixtures cannot eliminate the offset, and the measured buckling load contains large errors. In addition, the difference in thermal expansion coefficients between conventional fixture materials (such as nickel-based high-temperature alloys) and composite specimens under high temperature environments causes contact surface gaps, and the friction coefficient will decay under high temperature, which significantly increases the risk of specimen slippage. The compression performance of L-beam components (especially the yield strength under extreme high temperature conditions) has become a core indicator of its reliability evaluation, and it is urgent to solve the technical gap, which is of great significance to the research on compression tests of L-beam specimens. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a compression fixture and a test method for an L-beam of a composite laminate under an extremely high temperature environment in response to the deficiencies of the above-mentioned prior art, which can effectively solve the problem of fixing the L-beam specimen in the compression test, avoid the wear of the specimen by the fixture during the test, and also solve the problem of the centration of the specimen under the compression load, greatly reducing the possibility of instability in the compression test.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A compression fixture for a composite laminate L-beam in an extremely high temperature environment, characterized by comprising an upper fixing unit, a lower fixing unit and an inner fixing member. The upper fixing unit is connected to the lower fixing unit through a guide rod. Inner fixing members are connected to the inner sides of both the upper fixing unit and the lower fixing unit. The inner fixing member is an L-shaped plate. The upper part of the specimen is clamped and fixed between the inner fixing member and the upper fixing unit, and the lower part of the specimen is clamped and fixed between the inner fixing member and the lower fixing unit.

[0006] Preferably, the specimen is an L-beam specimen. Upper and lower grooves adapted to the specimen are respectively formed on the upper fixing unit and the lower fixing unit. The side walls of the upper and lower grooves are sandblasted to make the surface roughness Ra≥1.6μm.

[0007] Preferably, four upper horizontal round holes are symmetrically formed on the outer side wall of the upper fixing unit, and four lower horizontal round holes are symmetrically formed on the outer side wall of the lower fixing unit. Four inner screw holes are formed on the two inner fixing members at positions corresponding to the upper and lower horizontal round holes. Horizontal bolts are connected between the inner screw holes and the upper horizontal round holes, and between the inner screw holes and the lower horizontal round holes. End fasteners are arranged at one ends of the horizontal bolts extending out of the upper and lower horizontal round holes.

[0008] Preferably, two upper vertical round holes are symmetrically formed on the bottom surface of the upper fixing unit, and a lower screw hole corresponding to the upper vertical round hole is formed on the top surface of the lower fixing unit. A guide rod is connected between the upper vertical round hole and the lower screw hole. An M12×1.75 external thread is arranged on one side of the guide rod connected to the lower screw hole.

[0009] Preferably, after the surface of the guide rod is deburred and polished, a tungsten carbide coating is applied to make the surface roughness Ra≤0.4μm of the guide rod. The clearance between the guide rod and the upper horizontal round hole is ≤0.01mm.

[0010] Preferably, the upper fixing unit, the lower fixing unit, the inner fixing member, the guide rod, the horizontal bolt and the end fastener are all made of 2520 austenitic heat-resistant steel. The high-temperature strength (tensile strength ≥520MPa at 450°C) and oxidation resistance (oxidation weight gain rate ≤0.1g / m 2 ·h) of this steel can work stably in an extremely high temperature environment for a long time.

[0011] Preferably, a pressure relief hole is arranged at the bottom of the upper vertical round hole to balance the air pressure inside and outside the fixture during the compression process. The specification of the horizontal bolt is M8×1.25, and the head is designed as a 12mm internal hexagonal structure. The end fastener is an annular butterfly washer, and the cooperation between the horizontal bolt and the end fastener maintains the stability of both sides of the specimen.

[0012] A compression test method for a composite laminate L-beam in an extremely high temperature environment includes the following steps:

[0013] S1. Pretreatment of the specimen: Polish the specimen with sandpaper;

[0014] S2. Assemble the compression fixture and the specimen: Fix the specimen in the upper and lower grooves simultaneously, tighten the transverse bolts and the end fasteners, and ensure that the two end faces of the specimen are flush with the top and bottom surfaces of the compression fixture during assembly;

[0015] S3. High-temperature compression test: Install the compression fixture with the specimen at the center position of the spherical support of the MTS fatigue testing machine. Adjust the positions of the crossbeam, chuck and the angle of the spherical support of the MTS fatigue testing machine to ensure that the surface of the spherical support is in full contact with the bottom surface of the compression fixture, and the chuck is in full contact with the top surface of the compression fixture. Then start the high-temperature environmental chamber. After the environmental chamber heats up to the test temperature, keep it constant for 30 minutes. Set the loading rate and the data acquisition frequency, and monitor the load-displacement curve in real time during the test until the specimen breaks;

[0016] S4. Collect and process the test data to draw a test conclusion.

[0017] The present invention has the following advantages compared with the prior art:

[0018] 1. The present invention is applicable to carry out the compression test of L-shaped beams in extremely high-temperature environments. The fixture can work stably in high-temperature environments for a long time, meeting the test requirements of high-temperature compression tests. The contact surfaces between the fixture and the specimen of the present invention are all sandblasted to provide stable clamping and fixing of the specimen. While the upper fixing unit, the lower fixing unit and the inner fixing piece cooperate to fix and clamp the specimen, the coincidence of the centroid of the cross-section of the L-shaped beam specimen and the centroid of the fixture is also achieved, as well as the extremely small clearance between the high-precision guide rod and the guide circular hole. It can effectively eliminate the influence of additional bending moments and also effectively reduce the offset of the L-shaped beam specimen during the compression process. The fixture adopts a split design, which is quickly assembled and can be adapted to L-shaped beam specimens of different sizes. The modular concept combines the test requirements for lightweight and special-shaped components in the aerospace field to achieve "one fixture for multiple uses".

[0019] 2. The present invention clamps both the upper and lower parts of the L-shaped beam specimen in a coordinated manner by using double units on the inner and outer sides. To make the friction coefficient stable, all the contact surfaces between the fixture and the L-shaped beam specimen are sandblasted to make the surface roughness Ra≥1.6μm. Under the uniform load provided by multiple groups of high-temperature resistant transverse bolts and end fasteners, the specimen can be effectively prevented from slipping and stress concentration. At the same time, the present invention realizes a dynamic centering adjustment mechanism through adjustable fixing on the inner and outer sides, on the basis of ensuring that the cross-section of the specimen is located at the geometric center of the overall compression fixture, to ensure that the offset of the L-shaped beam specimen during the axial compression process is ≤0.1mm. While eliminating the influence of additional bending moments, it further reduces the measurement error of the buckling load.

[0020] 3. Guide rods are arranged between the upper and lower clamping ends of the test piece of the present invention according to the principle of geometric center symmetry. The clearance between the high-precision guide rod and the upper round hole on the guide is ≤0.01 mm. In addition, 2520 austenitic heat-resistant steel exhibits excellent creep resistance in an extremely high-temperature environment, offsetting the difference in thermal expansion of the material and ensuring the stability of the fixture structure.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0022] Figure 1 is a three-dimensional assembly structure schematic diagram of the compression fixture and the test piece of the present invention.

[0023] Figure 2 is a front view assembly structure schematic diagram of the compression fixture and the test piece of the present invention.

[0024] Figure 3 is a top view assembly structure schematic diagram of the compression fixture and the test piece in the present invention.

[0025] Figure 4 is a three-dimensional structure schematic diagram of the upper fixing unit in the present invention.

[0026] Figure 5 is a three-dimensional structure schematic diagram of the lower fixing unit in the present invention.

[0027] Figure 6 is a top view structure schematic diagram of the upper fixing unit in the present invention.

[0028] Figure 7 is a top view structure schematic diagram of the lower fixing unit in the present invention.

[0029] Figure 8 is a three-dimensional structure schematic diagram of the inner fixing piece in the present invention.

[0030] Figure 9 is a structure schematic diagram of the guide rod in the present invention.

[0031] Figure 10 is a structure schematic diagram of the test piece in the present invention.

[0032] Figure 11 is a structure schematic diagram of the transverse bolt in the present invention.

[0033] Figure 12 is a structure schematic diagram of the end fastener in the present invention.

[0034] Description of the reference numerals:

[0035] 1 - upper fixing unit; 2 - lower fixing unit; 3 - inner fixing piece;

[0036] 4—Guide rod; 5—Transverse bolt; 6—End fastener;

[0037] 7—Specimen; 8—Upper horizontal round hole; 9—Upper vertical round hole;

[0038] 10—Upper groove; 11—Lower horizontal round hole; 12—Lower screw hole;

[0039] 13—Lower groove; 14—Internal screw hole. Detailed implementation mode

[0040] Example 1

[0041] As Figures 1 to 12 shown, this embodiment provides a compression fixture for a composite laminate L-beam in an extreme high temperature environment, including an upper fixing unit 1, a lower fixing unit 2 and an internal fixing member 3. The upper fixing unit 1 is connected to the lower fixing unit 2 through a guide rod 4. The inner sides of the upper fixing unit 1 and the lower fixing unit 2 are both connected to the internal fixing member 3. The internal fixing member 3 is an L-shaped plate. The upper part of the specimen 7 is clamped and fixed between the internal fixing member 3 and the upper fixing unit 1, and the lower part of the specimen 7 is clamped and fixed between the internal fixing member 3 and the lower fixing unit 2.

[0042] In this embodiment, the specimen 7 is an L-beam specimen. Upper grooves 10 and lower grooves 13 adapted to the specimen 7 are respectively provided on the upper fixing unit 1 and the lower fixing unit 2. The side walls of the upper grooves 10 and the lower grooves 13 are sandblasted so that the surface roughness Ra≥1.6μm.

[0043] In this embodiment, four upper horizontal round holes 8 are symmetrically provided on the outer side wall of the upper fixing unit 1, four lower horizontal round holes 11 are symmetrically provided on the outer side wall of the lower fixing unit 2, and four internal screw holes 14 are provided on the two internal fixing members 3 at positions corresponding to the upper horizontal round holes 8 and the lower horizontal round holes 11. Transverse bolts 5 are connected between the internal screw holes 14 and the upper horizontal round holes 8, and between the internal screw holes 14 and the lower horizontal round holes 11. End fasteners 6 are provided at one ends of the transverse bolts 5 extending out of the upper horizontal round holes 8 and the lower horizontal round holes 11.

[0044] In this embodiment, two upper vertical round holes 9 are symmetrically provided on the bottom surface of the upper fixing unit 1, lower screw holes 12 corresponding to the upper vertical round holes 9 are provided on the top surface of the lower fixing unit 2. Guide rods 4 are connected between the upper vertical round holes 9 and the lower screw holes 12. An M12×1.75 external thread is provided on one side of the guide rod 4 connected to the lower screw hole 12.

[0045] In this embodiment, after the surface of the guide rod 4 is deburred and polished, a tungsten carbide coating is applied so that the surface roughness Ra≤0.4μm of the guide rod 4, and the clearance between the guide rod 4 and the upper horizontal round hole 8≤0.01mm.

[0046] In this embodiment, the upper fixing unit 1, the lower fixing unit 2, the inner fixing member 3, the guide rod 4, the transverse bolt 5 and the end fastener 6 are all made of 2520 austenitic heat-resistant steel. The high-temperature strength of this steel has a tensile strength ≥ 520 MPa at 450 °C and an oxidation weight gain rate ≤ 0.1 g / m 2 ·h and can work stably in an extremely high-temperature environment for a long time.

[0047] In this embodiment, a pressure relief hole is provided at the bottom of the upper vertical circular hole 9 to balance the air pressure inside and outside the fixture during the compression process. The specification of the transverse bolt 5 is M8×1.25, and the head is designed with a 12 mm internal hexagonal structure. The end fastener 6 is an annular butterfly washer, and the cooperation of the transverse bolt 5 and the end fastener 6 is used to maintain the stability of both sides of the specimen 7 inside and outside.

[0048] Embodiment 2

[0049] This embodiment provides a compression test method for a composite laminate L-shaped beam in an extremely high-temperature environment, including the following steps:

[0050] S1. Pretreatment of the specimen 7: Polish the specimen 7 with 600-mesh sandpaper;

[0051] S2. Assemble the compression fixture and the specimen 7: Place the surface where the upper horizontal circular hole 9 is located facing up and the inner fixing member 3 on a smooth glass plate. Invert the upper end of the specimen 7 and place it between the upper fixing unit 1 and the inner fixing member 3, ensuring that the inner and outer sides of the specimen 7 are closely attached to the rough surface of the inner fixing member 3 and the upper groove 10 respectively. Push the three back and forth gently on the smooth glass plate until the upper end surface of the specimen 7, the upper reference surface of the upper fixing unit 1 and the upper reference surface of the inner fixing member 3 are flush. Initially tighten the four transverse bolts 5 in a diagonal order to ensure that the specimen 7 does not slide when the upper fixing unit 1 and the inner fixing member 3 are moved. Check and adjust again whether the upper end surface of the specimen 7, the upper reference surface of the upper fixing unit 1 and the upper reference surface of the inner fixing member 3 are flush. After it is correct, use a torque wrench, set the torque value within the test permission range, and tighten the transverse bolt 5. After the torque is correct, place the device aside for later use; Connect and fix the guide rod 4 to the lower screw hole 12 by threading, and place it on a smooth glass plate together with another inner fixing member 3. Through the cooperation of the guide rod 4 and the upper vertical circular hole 9, assemble the installed part of the fixture with the lower fixing unit 2. After clamping the lower end of the specimen 7 with the inner fixing member 3, push it back and forth gently on the smooth glass plate to make the lower end surface of the specimen, the lower reference surface of the lower fixing unit 2 and the lower reference surface of the inner fixing member 3 flush. Initially tighten it in a diagonal order using the transverse bolt 5 in cooperation with the end fastener 6 to ensure that the specimen does not slide when the lower fixing unit 2 and the inner fixing member 3 are moved. Check and adjust again whether the lower end surface of the specimen, the lower reference surface of the lower fixing unit 2 and the lower reference surface of the inner fixing member 3 are flush. After it is correct, use a torque wrench, set the torque value within the test permission range, and tighten the transverse bolt 5 on the lower fixing unit 2. After the torque is correct, the assembly work of the compression fixture and the specimen is completed;

[0052] S3. High-temperature compression test: Install the compression fixture with the test piece 7 at the center position of the spherical bearing of the MTS fatigue testing machine. Adjust the position of the crossbeam, chuck and the angle of the spherical bearing of the MTS fatigue testing machine to ensure that the surface of the spherical bearing is in full contact with the bottom surface of the compression fixture, and the chuck is in full contact with the top surface of the compression fixture. Then start the high-temperature environmental chamber, heat it up to the target temperature at a rate of 15 °C / min and keep it constant for 30 min. After setting the loading rate of 2 mm / min and the data acquisition frequency of 2 Hz, use the pressure plate of the MTS testing machine to apply a compression load to the fixture. During the test, monitor the temperature uniformity of the fixture through an infrared thermal imager with a temperature difference ≤ 15 °C, and monitor the load-displacement curve in real time until the test piece breaks;

[0053] S4. Collect and process the test data to draw a test conclusion.

[0054] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes and equivalent changes made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A compression fixture for a composite laminate L-beam in an extreme high-temperature environment, characterized in that The invention comprises an upper fixing unit (1), a lower fixing unit (2) and an inner fixing member (3); the upper fixing unit (1) is connected to the lower fixing unit (2) via a guide rod (4); the inner sides of the upper fixing unit (1) and the lower fixing unit (2) are both connected to the inner fixing member (3); the inner fixing member (3) is an L-shaped plate; the upper part of a test piece (7) is clamped and fixed between the inner fixing member (3) and the upper fixing unit (1); and the lower part of the test piece (7) is clamped and fixed between the inner fixing member (3) and the lower fixing unit (2).

2. The compression fixture for the composite laminate L-beam in an extreme high-temperature environment according to claim 1, characterized in that, The test piece (7) is an L-shaped beam test piece, and the upper fixing unit (1) and the lower fixing unit (2) are respectively provided with an upper groove (10) and a lower groove (13) adapted to the test piece (7), and the side walls of the upper groove (10) and the lower groove (13) are sandblasted to achieve a surface roughness Ra of ≥1.6 μm.

3. The compression fixture for the composite laminate L-beam in an extremely high temperature environment according to claim 1, characterized in that Four upper transverse circular holes (8) are symmetrically formed on the outer wall of the upper fixing unit (1), and four lower transverse circular holes (11) are symmetrically formed on the outer wall of the lower fixing unit (2). Four inner screw holes (14) are formed on the two inner fixing members (3) at positions corresponding to the upper transverse circular holes (8) and the lower transverse circular holes (11). Transverse bolts (5) are connected between the inner screw holes (14) and the upper transverse circular holes (8) and between the inner screw holes (14) and the lower transverse circular holes (11). One end of the transverse bolt (5) extending out of the upper transverse circular hole (8) and the lower transverse circular hole (11) is provided with an end fastener (6).

4. The compression fixture for the composite laminate L-beam in an extremely high temperature environment according to claim 3, characterized in that The bottom surface of the upper fixing unit (1) is symmetrically provided with two upper vertical circular holes (9), the top surface of the lower fixing unit (2) is provided with lower screw holes (12) corresponding to the upper vertical circular holes (9), a guide rod (4) is connected between the upper vertical circular holes (9) and the lower screw holes (12), and an external thread is provided on one side of the guide rod (4) connected to the lower screw holes (12).

5. The compression fixture for the composite laminate L-beam in an extremely high temperature environment according to claim 4, characterized in that The surface of the guide rod (4) is deburred and polished, and then coated with a tungsten carbide coating so that the surface roughness Ra of the guide rod (4) is less than or equal to 0.4 μm, and the matching clearance between the guide rod (4) and the upper transverse circular hole (8) is less than or equal to 0.01 mm.

6. The compression fixture for the composite laminate L-beam in an extreme high temperature environment according to any one of claims 1-5 is used in a compression test method for the composite laminate L-beam in an extreme high temperature environment, characterized in that The following steps are involved: S1. Pretreatment of the specimen (7): grinding the specimen (7) with sandpaper; S2. Assemble the compression fixture and the test piece (7): fix the test piece (7) in the upper groove (10) and the lower groove (13) at the same time, tighten the transverse bolt (5) and the end fastener (6), and ensure that the two end surfaces of the test piece (7) are flush with the top and bottom surfaces of the compression fixture during assembly; S3, high temperature compression test: install the compression fixture with the test piece (7) installed at the center of the spherical support, adjust the fatigue testing machine crossbeam, the chuck position and the spherical support angle to ensure that the surface of the spherical support is in full contact with the bottom surface of the compression fixture, and the chuck is in full contact with the top surface of the compression fixture, then start the high temperature environmental chamber, heat the environmental chamber to the test temperature and keep the temperature constant for 30 minutes, set the loading rate and data acquisition frequency, and monitor the load-displacement curve in real time during the test until the test piece breaks; S4. Collect and process test data to draw test conclusions.

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