A composite pressure vessel joint test fixture and test method

Abstract

The present invention discloses a composite pressure vessel joint test tool and test method in the field of composite pressure vessel joint test technology. The tool includes a base plate, a support cylinder and a pressure-bearing cover plate. The support cylinder includes a first connection end and a support end. The first connection end is connected to the base plate. The support end is used to support the shoulder of the composite pressure vessel joint test piece and has a profile that matches the shoulder of the composite pressure vessel joint test piece. The pressure-bearing cover plate includes a second connection end and a pressure-bearing end. The second connection end is connected to the end face of the composite pressure vessel joint test piece. The pressure-bearing end is used to bear external pressure and transfer the pressure to the shoulder of the composite pressure vessel joint test piece through the second connection end and the end face of the composite pressure vessel joint test piece in sequence. The present invention can simulate the load conditions of the composite joint in the actual working process, and is used to test the composite joint separately, reducing research and development costs.

Description

Technical Field

[0001] The invention belongs to the technical field of composite pressure vessel joint testing, and in particular relates to a composite pressure vessel joint testing tool and a testing method. Background Art

[0002] The present invention belongs to the field of aerospace lightweight all-composite pressure vessel design, and specifically relates to a composite pressure vessel joint test fixture and test method, which are used for performance verification of composite pressure vessel joints in the design stage.

[0003] Compared to metal pressure vessels, composite pressure vessels offer advantages such as light weight, high specific strength and modulus, high reliability, safe failure modes, short manufacturing cycles, corrosion resistance, and long life. Currently, mature technologies are based on the combination of metal joints and composite shells. Driven by the demand for high performance, low cost, long life, and high reliability in aerospace vehicles, pressure vessels are moving towards fully composite materials. Further composite joints are a key development trend for high-performance, all-composite pressure vessels.

[0004] Pressure vessel joints are crucial components connecting the pressure vessel to the igniter and nozzle, subject to complex forces. Using high-strength, high-modulus carbon fiber composites to manufacture pressure vessel joints can effectively improve the joint's mechanical properties and reduce the weight of the joint and the entire pressure vessel, significantly improving the pressure vessel's volumetric efficiency. Therefore, theoretical calculations combined with experimental verification of composite joint performance are essential. While hydraulic blasting is currently the primary method for verifying the performance of entire pressure vessels, and is relatively well established, research specifically focused on verifying the performance of composite joints is limited. Summary of the Invention

[0005] To address the deficiencies in the prior art, the present invention provides a test fixture and test method for composite pressure vessel joints, which can simulate the load conditions of composite joints during actual working processes and be used to test composite joints individually, thereby reducing R&D costs.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, a composite pressure vessel joint test fixture is provided, comprising a base plate, a support cylinder and a pressure-bearing cover plate, wherein the support cylinder comprises a first connecting end and a supporting end, the first connecting end being connected to the base plate, the supporting end being used to support the shoulder of the composite pressure vessel joint test piece, and having a profile matching the shoulder of the composite pressure vessel joint test piece; the pressure-bearing cover plate comprises a second connecting end and a pressure-bearing end, the second connecting end being connected to the end face of the composite pressure vessel joint test piece, the pressure-bearing end being used to bear external pressure and transfer the pressure to the shoulder of the composite pressure vessel joint test piece via the second connecting end and the end face of the composite pressure vessel joint test piece in sequence.

[0008] Furthermore, the first connecting end is connected to the base plate via bolts.

[0009] Furthermore, the second connection end is connected to the end surface of the composite pressure vessel joint test piece by means of bolts.

[0010] In a second aspect, a composite pressure vessel joint test method is provided, which adopts the composite pressure vessel joint test tool described in the first aspect, including: according to the test requirements, affixing a number of strain gauges on the end face and bottom surface of the composite pressure vessel joint test piece; installing the support cylinder on the base plate, and installing the base plate on the testing machine, and then connecting the end face of the composite pressure vessel joint test piece with the second connecting end of the pressure cover plate, and placing the shoulder of the composite pressure vessel joint test piece on the supporting end of the support cylinder; starting the testing machine, and pre-pressurizing the pressure end of the pressure cover plate according to the set first pressurization condition; after the pre-pressurization is qualified, loading the pressure end of the pressure cover plate according to the set second pressurization condition until the connection interface of the composite pressure vessel joint test piece or the connecting bolt of the second connecting end is damaged; processing the pressure and strain data collected during the pressurization process to obtain performance data of the composite pressure vessel joint test piece.

[0011] Furthermore, several strain gauges are respectively affixed to the end face and bottom face of the composite pressure vessel joint test piece, including: on the end face of the composite joint test piece, the strain gauge is a single piece, the direction of which is perpendicular to the layers, and is used to verify whether the plies are delaminated when the end face of the composite joint test piece is subjected to stress; on the bottom face of the composite joint test piece, the strain gauge is a double piece, the directions of which are radial and circumferential, respectively, the radial direction is perpendicular to the fiber direction, and the circumferential direction is parallel to the fiber direction, and is used to detect the actual radial and circumferential strain values ​​under stress.

[0012] Furthermore, the first pressurizing condition includes: first loading to no more than 30% of the test load at a loading speed of 0.5 to 1 mm / min, then unloading to 0, and repeating once.

[0013] Furthermore, the second pressurization condition includes: first, gradually loading the composite pressure vessel joint test piece with a loading gradient of no more than 10% of the test load to 70%-80% of the test load, then gradually loading the composite pressure vessel joint test piece with a loading gradient of no more than 5% of the test load to 105%-110% of the test load, and maintaining the load for at least 1 minute. If the composite pressure vessel joint test piece does not fail, continue loading the composite pressure vessel joint test piece with a loading gradient of 2% of the test load until the connection interface or the second connection end connecting bolt of the composite pressure vessel joint test piece fails.

[0014] Furthermore, the performance data of the composite pressure vessel joint test piece includes: the end face delamination pressure of the composite pressure vessel joint test piece, the deviation between the bottom surface radial strain measurement value and the theoretical value, the deviation between the bottom surface circumferential strain measurement value and the theoretical value, and the safety factor.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention can simulate the load conditions of composite material joints in actual working process through the base plate, support cylinder and pressure cover plate, and is used to test composite material joints separately, thereby reducing R&D costs;

[0017] (2) The present invention can replace the water pressure test verification method. The test method is safe and reliable and can ensure the accuracy of the test results. It can be used for performance verification of composite pressure vessel joints in the design stage and provide effective data support for the structural and layup optimization design of composite joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the three-dimensional structure of a composite pressure vessel joint test fixture provided by an embodiment of the present invention;

[0019] Figure 2 This is a schematic cross-sectional view of a composite pressure vessel joint test fixture provided by an embodiment of the present invention;

[0020] Figure 3 1 is a schematic diagram of the three-dimensional structure of a composite pressure vessel joint test piece used for testing in an embodiment of the present invention;

[0021] Figure 4 Schematic diagram of the position and orientation of the bottom patch of a composite pressure vessel joint test piece according to an embodiment of the present invention;

[0022] Figure 5 Schematic diagram of the position and orientation of the end face patch of a composite pressure vessel joint test piece according to an embodiment of the present invention;

[0023] Figure 6 2. It is a schematic diagram of the direction of force when loading a composite pressure vessel joint test piece in an embodiment of the present invention;

[0024] In the figure: 1, bottom plate; 2, supporting cylinder; 21, first connecting end; 22, supporting end; 3, pressure-bearing cover plate; 31, second connecting end; 32, pressure-bearing end; 4, composite pressure vessel joint test piece; 41, shoulder; 42, end face; 43, bottom face. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0026] Example 1:

[0027] like Figures 1 to 3 As shown, a composite pressure vessel joint test fixture includes a base plate 1, a support cylinder 2 and a pressure cover plate 3, the support cylinder 2 includes a first connecting end 21 and a supporting end 22, the first connecting end 21 is connected to the base plate 1, the supporting end 22 is used to support the shoulder 41 of the composite pressure vessel joint test piece 4, and has a profile matching the shoulder 41 of the composite pressure vessel joint test piece 4; the pressure cover plate 3 includes a second connecting end 31 and a pressure end 32, the second connecting end 31 is connected to the end face 42 of the composite pressure vessel joint test piece 4, the pressure end 32 is used to bear external pressure, and transfer the pressure to the shoulder 41 of the composite pressure vessel joint test piece 4 through the second connecting end 31 and the end face 42 of the composite pressure vessel joint test piece 4 in sequence.

[0028] In this embodiment, the support cylinder 2 is a rotating body structure with a flange flanging, which is used to support the composite pressure vessel joint test piece 4 during the test. The outer surface of the upper end (support end 22) of the support cylinder 2 is the same as the shoulder 41 of the composite pressure vessel joint test piece 4, and the flange flanging is connected and fixed to the base plate by bolts, nuts, and gaskets.

[0029] The pressure cover plate 3 has a neck flange structure. Its flange (second connection end 31) is integrally connected to the end face 42 of the composite pressure vessel joint test piece 4 via bolts and gaskets. The pressure cover plate 3 is then placed on the support cylinder 2. The shoulder 41 of the composite pressure vessel joint test piece 4 contacts the upper end face of the support cylinder 2. The neck (pressure-bearing end 32) of the pressure cover plate 3 is used for loading the test machine's pressure head. The base plate 1 is bolted to the test machine.

[0030] The present invention can simulate the load conditions of composite material joints in actual working processes through the base plate, support cylinder and pressure cover plate, and is used to test composite material joints separately, thereby reducing R&D costs. It can replace the water pressure test verification method and has the advantages of simple operation, low cost and high safety.

[0031] Example 2:

[0032] Based on the composite pressure vessel joint test tool described in Example 1, this embodiment provides a composite pressure vessel joint test method, using the composite pressure vessel joint test tool described in Example 1.

[0033] Step 1: According to the test requirements, affix several strain gauges to the end and bottom surfaces of the composite pressure vessel joint test piece. Figure 4 、 Figure 5 As shown, strain gauges are attached to the bottom surface 43 and end surface 42 of the composite pressure vessel joint test piece 4. The end surface 42 strain gauges are single, located between holes and oriented perpendicularly to the layers. They are numbered 9# to 14# and are used to verify whether the plies delaminate when the composite pressure vessel joint test piece 4 is subjected to stress. The bottom surface 43 strain gauges are dual, oriented radially (#1 to 4#) and circumferentially (#5 to 8#). The radial direction is perpendicular to the fiber orientation, while the circumferential direction is parallel to the fiber orientation. These gauges are used to detect the actual radial and circumferential strain values ​​under stress and compare them with theoretically calculated values.

[0034] Step 2: Install the support cylinder 2 on the base plate 1, and install the base plate 1 on the testing machine, then connect the end face 42 of the composite pressure vessel joint test piece 4 to the second connecting end 31 of the pressure cover plate 3, and place the shoulder 41 of the composite pressure vessel joint test piece 4 on the supporting end 22 of the support cylinder 2.

[0035] Step 3: Start the testing machine and pre-load the pressure-bearing end of the pressure-bearing cover plate according to the set first pressurization condition. The first pressurization condition includes: first loading at a loading rate of 0.5-1 mm / min to no more than 30% of the test load, then unloading to 0, and repeating. Check the loading and measurement systems for proper condition, as well as the test status of the composite pressure vessel joint test piece 4, and check the repeatability of load and strain.

[0036] Step 4: After the pre-pressing is qualified, the pressure-bearing end of the pressure cover plate is loaded according to the set second pressurization condition until the connection interface of the composite pressure vessel joint test piece or the second connection end connection bolt is broken. Figure 6 The second pressurization condition includes: first, gradually loading the composite pressure vessel joint test piece with a loading gradient of no more than 10% of the test load to 70%-80% of the test load, then gradually loading the composite pressure vessel joint test piece with a loading gradient of no more than 5% of the test load to 105%-110% of the test load, and maintaining the load for at least 1 minute. If the composite pressure vessel joint test piece does not fail, continue loading the composite pressure vessel joint test piece with a loading gradient of 2% of the test load until the connection interface or the second connection end connecting bolt of the composite pressure vessel joint test piece fails.

[0037] Step 5: Data Processing and Analysis: Process the pressure and strain data collected during the pressurization process to obtain performance data for the composite pressure vessel joint test piece. Statistically analyze the strain data between the 42 holes on the end face of the composite pressure vessel joint test piece 4. If the strain data changes suddenly, delamination has occurred, and ply optimization is required (the pressure at the time of the sudden change is the delamination pressure on the end face of the composite pressure vessel joint test piece). Statistically analyze the radial and circumferential strain measurement data, plot a comparison curve between the measured strain values ​​and the theoretical strain values, and determine the deviation between the measured bottom radial strain value and the theoretical value, as well as the deviation between the measured bottom circumferential strain value and the theoretical value. If the measured strain values ​​and the theoretical strain values ​​show the same trend and the difference is within 10% to 20%, the theoretical design and calculation method of the joint are effective. Record the maximum breaking load of the connection interface, and calculate the actual safety factor of the connection interface.

[0038] The present invention can replace the water pressure test verification method. The test method is reliable, easy to operate, low in cost, and high in safety compared to the water pressure test method. It is suitable for verifying the performance of composite material joints in the design stage. It can ensure the accuracy of the test results and be used for performance verification in the design stage of composite material pressure vessel joints. It can evaluate and analyze the stress conditions of composite material pressure vessel joints and the reliability of the connection interface, and judge the effectiveness of the theoretical design and calculation methods of composite material joints, providing effective data support for the structural and layup optimization design of composite material joints.

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A composite pressure vessel joint test method, characterized in that: A composite pressure vessel joint test fixture is used, including a base plate, a supporting cylinder and a pressure cover plate. The supporting cylinder includes a first connecting end and a supporting end, wherein the first connecting end is connected to the bottom plate, and the supporting end is used to support the shoulder of the composite pressure vessel joint test piece and has a profile matching the shoulder of the composite pressure vessel joint test piece; The pressure-bearing cover plate includes a second connecting end and a pressure-bearing end, the second connecting end being connected to the end face of the composite pressure vessel joint test piece, and the pressure-bearing end being used to bear external pressure and transfer the pressure sequentially through the second connecting end and the end face of the composite pressure vessel joint test piece to the shoulder of the composite pressure vessel joint test piece; Methods include: According to the test requirements, several strain gauges are attached to the end face and bottom face of the composite pressure vessel joint test piece, including: on the end face of the composite joint test piece, the strain gauge is a single piece, the direction is perpendicular to the layers, and is used to verify whether the plies are delaminated when the end face of the composite joint test piece is subjected to stress; on the bottom face of the composite joint test piece, the strain gauge is a double piece, the direction is radial and circumferential, respectively, the radial direction is perpendicular to the fiber direction, and the circumferential direction is parallel to the fiber direction, and is used to detect the actual radial and circumferential strain values ​​under stress; Install the support cylinder on the base plate, and install the base plate on the testing machine, then connect the end surface of the composite pressure vessel joint test piece to the second connecting end of the pressure cover plate, and place the shoulder of the composite pressure vessel joint test piece on the supporting end of the support cylinder; Start the testing machine and pre-press the pressure-bearing end of the pressure-bearing cover plate according to the set first pressurization condition; After the pre-pressing is qualified, the pressure-bearing end of the pressure-bearing cover plate is loaded according to the set second pressurization condition until the connection interface of the composite pressure vessel joint test piece or the connecting bolt of the second connection end is broken; The pressure and strain data collected during the pressurization process are processed to obtain the performance data of the composite pressure vessel joint test piece, including: the end face delamination pressure of the composite pressure vessel joint test piece, the deviation between the bottom surface radial strain measurement value and the theoretical value, the deviation between the bottom surface circumferential strain measurement value and the theoretical value, and the safety factor.

2. The composite pressure vessel joint testing method according to claim 1, characterized in that: The first connecting end is connected to the base plate via bolts.

3. The composite pressure vessel joint testing method according to claim 1, characterized in that: The second connection end is connected to the end surface of the composite pressure vessel joint test piece by means of bolts.

4. The composite pressure vessel joint testing method according to claim 1, characterized in that: The first pressurizing condition includes: first loading to no more than 30% of the test load at a loading speed of 0.5 to 1 mm / min, then unloading to 0, and repeating once.

5. The composite pressure vessel joint testing method according to claim 1, characterized in that: The second pressurization condition includes: first loading step by step to 70% to 80% of the test load with a loading gradient of no more than 10% of the test load, then loading step by step to 105% to 110% of the test load with a loading gradient of no more than 5% of the test load, and maintaining the load for no less than 1 minute; if the composite pressure vessel joint test piece is not damaged, finally loading step by step with a loading gradient of 2% of the test load until the connection interface of the composite pressure vessel joint test piece or the connecting bolt of the second connection end is damaged.

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