Method for testing cut-off end of laterally-supported stringer under unidirectional load

Abstract

The invention discloses a method for testing the cut-off end of a laterally-supported stringer under a one-way load, and belongs to the technical field of structural member testing. In order to solve the problem that the bearing capacity of a stringer in a composite stiffened wallboard is difficult to accurately evaluate when the stringer stops near a frame, a stringer cut-off end wallboard test piece with the frame is designed, and the size of the test piece and the position relation between the end of the stringer and a clamp are limited, so that a test structure is closer to an actual engineering state; meanwhile, lateral supporting clamps are arranged on the two sides of the frame, so that the frame can slide in the loading direction and is limited in the out-of-plane direction, and out-of-plane deformation and loading eccentricity are effectively restrained; the testing method can be implemented on a universal testing machine, the failure load, the displacement and the damage mode of the stringer cut-off end can be accurately obtained, compared with a clamp-free or multi-rib testing scheme, the testing method has the advantages of being simple in structure, reliable in result, low in cost, high in universality and the like, and the testing method is suitable for analysis and verification of the structural performance of the stringer cut-off end of the stiffened wall plate.

Description

Technical Field

[0001] This invention belongs to the field of structural component testing technology, specifically relating to a testing method for the unidirectional load on the cut-off end of a laterally supported stringer. Background Technology

[0002] Composite stiffened panels are widely used in aerospace structures. When the stringer terminates near the frame, rib, or other parts, its cut-off end is prone to become a weak area under in-plane unidirectional load, especially at the interface between the stringer flange and the skin, where failures such as delamination and peeling are likely to occur. How to accurately reflect the stress state and load-bearing capacity of the stringer cut-off end under test conditions is a key technical problem in current structural testing.

[0003] Existing mechanical testing methods for stiffened panels mostly target integral stiffened panels or simplified specimens, lacking specialized testing schemes for the critical local structure of the girder termination. On the one hand, existing methods typically do not clearly define the size range of framed specimens or the relative position of the girder end and the fixture, resulting in test results being greatly affected by boundary conditions and failing to reflect actual structural performance. On the other hand, without lateral constraints or with unreasonable constraint methods, the frame and panel are prone to significant out-of-plane deformation, causing loading eccentricity, resulting in lower test load-bearing capacity or distorted failure modes. Furthermore, while using multiple girder or complex fixtures can improve the overall load-bearing capacity, the specimens are complex to manufacture, costly, and difficult to effectively evaluate individual girder terminations.

[0004] To address the aforementioned issues, a testing method is urgently needed to meet the testing requirements of composite reinforced panels. Summary of the Invention

[0005] To address the aforementioned issues, this application aims to provide a testing method for the end of a stringer with lateral support structure under unidirectional load. This method includes designing a framed end panel test specimen for the stringer and modifying the fixture design to enable mechanical testing using a universal testing machine, thereby obtaining the destructive load more accurately.

[0006] A test method for the unidirectional load on the truss end with lateral support, used to test the load-bearing capacity of a framed, stringer-supported stiffened wall panel, includes the following steps:

[0007] A support member I is installed on the testing machine to laterally constrain the frame on the test piece, so that the test piece is unconstrained along the loading direction and the support member I, and the test piece is rigidly constrained in the horizontal direction perpendicular to the loading direction;

[0008] On the other side of the test specimen, a support member II is provided to laterally constrain the test specimen, so that the test specimen is unconstrained along the loading direction and the support member II, and the test specimen is rigidly constrained in the horizontal direction perpendicular to the loading direction;

[0009] Apply a unidirectional in-plane load to the test specimen until the specimen fails;

[0010] Obtain the corresponding load, displacement, and / or strain data;

[0011] To address the technical problem in existing reinforced panel tests where unreasonable boundary conditions at the girder termination end under unidirectional in-plane loads easily lead to out-of-plane deformation and loading eccentricity of the frame and panel, making it difficult to accurately reflect their load-bearing capacity and failure characteristics, this technical solution addresses this issue by setting laterally constrained supports I and II on both sides of the test specimen. These supports rigidly constrain the frame in the horizontal direction perpendicular to the loading direction while allowing free sliding in the loading direction. This ensures the frame only bears in-plane forces consistent with actual engineering conditions and does not participate in non-target bending. This symmetrical lateral support method effectively suppresses frame warping during the test. The additional stress and eccentricity effect caused by the instability of the curved or wall panel overcome the defects of conservative test results and distorted failure modes when there is no lateral support or the constraint method is inappropriate. Under this controlled boundary condition, a unidirectional in-plane load is applied to the test piece and load, displacement and / or strain data are acquired simultaneously. This allows the stress concentration caused by the sudden change in stiffness at the end of the stringer to become the dominant failure factor. This enables an effective characterization of the load-bearing capacity, deformation response and failure process of the end of the framed stringer under unidirectional load. The result is a clear test stress state, a clear failure location and test results that are representative and repeatable in engineering.

[0012] The technical solution provided in this application also has the following technical features:

[0013] Preferably, in one embodiment of this application, the lateral support assembly includes support member I and support member II; support member I and support member II are respectively disposed on both sides of the test specimen, and the contact forces of support member I and support member II on the test specimen cancel each other out.

[0014] Preferably, in one embodiment of this application, the support member I, the support member II and the test specimen are in surface contact, the frame is provided with a clearance groove for the stringer, and the test specimen is allowed to move relative to the load direction.

[0015] Preferably, in one embodiment of this application, the support member I is in surface contact with the frame, and the outward displacement of the frame's contact surface is restricted, and the frame and the support member I form a sliding pair along the load direction.

[0016] Preferably, in one embodiment of this application, the test piece is a composite material wall panel test piece, including a skin, at least one stringer with a cut-off end, and a frame with through holes corresponding to the stringer, wherein the frame, skin, and stringer are connected as a whole.

[0017] Preferably, in one embodiment of this application, the stringer is configured as a T-shape, an L-shape, or an Ω-shape.

[0018] Preferably, in one embodiment of this application, the frame is symmetrically arranged and is formed by combining two L-shaped members or two C-shaped members.

[0019] Preferably, in one embodiment of this application, the geometric dimensions of the test piece satisfy the following conditions: in the test structure of the terminal scenario in which the test piece is applied, the width of the test piece is not less than the minimum stringer spacing in the structure under test, the length of the test piece is between 1.25 times and 2 times the adjacent frame spacing, and the distance between the stringer and the clamp of the testing machine is less than one-fifth of the frame spacing, the stringer spacing is the adjacent spacing width between adjacent stringers, and the frame spacing is the distance between adjacent frames.

[0020] Preferably, in one embodiment of this application, the lateral support assembly includes a connecting plate, an L-shaped base, and a sliding support member. The L-shaped base is used to connect to the testing machine, and the two ends of the connecting plate are connected to the L-shaped base. The connecting plate is provided on both sides of the test piece. The sliding support member is provided on one side of the test piece via the connecting plate, and a stringer and frame are provided on the other side of the test piece.

[0021] One side of the test piece is supported by an abutment sliding support, and the other side of the test piece is supported on the connecting plate by a frame.

[0022] Preferably, in one embodiment of this application, the position where the sliding support abuts the test piece and the position where the frame connects to the test piece are respectively located at corresponding positions on both sides of the test piece, so that the abutting forces of the sliding support and the frame on both sides of the test piece are canceled out.

[0023] Preferably, in one embodiment of this application, a strain measuring device is arranged on the skin and / or stringer of the test piece, and strain data is collected synchronously during loading for quantitative analysis of the failure process at the end of the stringer.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0025] Compared with the prior art, the technical solution of this application has achieved the following technical advancements:

[0026] 1. This application addresses the problem in existing test methods that make it difficult to stably reflect the stress and failure characteristics of the stringer end under unidirectional in-plane loads due to unclear test boundary conditions. By using a framed stringer end panel test specimen and limiting the width, length, and relative position of the stringer end to the frame and fixture, the test boundary conditions are made clear and repeatable. This facilitates obtaining test results of the failure load and failure location of the stringer end and reduces the dispersion of test results.

[0027] 2. This application addresses the problem that frames and wall panels are prone to out-of-plane deformation and loading eccentricity under conditions of no lateral constraint or insufficient constraint. By setting lateral support structures on both sides of the frame, the frame can slide freely in the loading direction and be restricted in the out-of-plane direction perpendicular to the loading direction, thereby suppressing non-target out-of-plane deformation. This makes the stress state of the test specimen during the test closer to the unidirectional in-plane load condition, which is conducive to obtaining more reasonable failure modes and load-bearing capacity test results.

[0028] 3. This application addresses the problem that when testing multiple stringers or complex fixture schemes, the test specimen structure is complex, the manufacturing cost is high, and it is not conducive to the performance evaluation of the cut-off end of a single stringer. It proposes a test method that uses the cut-off end of a single stringer combined with lateral support. Under the premise of meeting the requirements of test stability and constraint, it simplifies the structure of the test specimen and fixture, reduces the test cost, and improves the applicability and versatility of the test method in engineering applications. The test results are consistent with the simulation.

[0029] 4. This application, by comparing and analyzing the lateral support scheme, the fixture-free scheme, and the multi-reinforced scheme under the same material system and loading conditions, can quantitatively compare the performance of the stringer end structure under different constraints in terms of load-bearing capacity, displacement response, and failure mode, and provides a basis for evaluating the effectiveness of the testing method. Attached Figure Description

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0031] Figure 1 This is a perspective view of the test apparatus and test piece for a test method of a laterally supported stringer end under unidirectional load, according to one embodiment.

[0032] Figure 2 This is a perspective view of a framed stringer end test specimen of a test method for testing the laterally supported stringer end under unidirectional load, according to one embodiment.

[0033] Figure 3 This is a displacement cloud diagram of a test method for the laterally supported stringer end under unidirectional load, according to one embodiment.

[0034] Figure 4 This is a stress cloud diagram of a test method for the laterally supported stringer end under unidirectional load, according to one embodiment.

[0035] Figure 5 A fixture-free displacement contour plot;

[0036] Figure 6 Stress cloud diagram of a fixture-free solution;

[0037] Figure 7 This is a displacement contour diagram of a three-ribbed scheme;

[0038] Figure 8 This is a stress cloud diagram of a three-ribbed design.

[0039] Components in the diagram:

[0040] 1. Connect the tablet

[0041] 2. L-shaped base

[0042] 3. Sliding support component

[0043] 4. Testing machine

[0044] 5. Frame

[0045] 6. Skin

[0046] 7. Long beam. Detailed Implementation

[0047] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings. These embodiments are only for illustrating this application and are not intended to limit the invention.

[0048] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0050] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0051] "Stringer termination point" refers to the position in aircraft stiffened panels where the stringer (stiffening rib) must terminate on the skin due to structural layout, opening or docking requirements. Because the stringer suddenly "breaks off", the stiffness at this point changes abruptly, which can easily lead to stress concentration, causing the stringer to delaminate or delaminate. Therefore, in engineering, this small termination area is analyzed and tested separately and is called "stringer termination point".

[0052] T-shaped stringer: A "vertical plate" is perpendicular to the skin, with a narrow edge strip on top, and the cross-section looks like the capital letter T;

[0053] L-shaped (angle-shaped) stringer shape: The cross-section is "right angle" or "hook" shaped, with only one leg bonded to the skin and the other leg pointing upwards;

[0054] Ω-shaped (hat-shaped) stringer shape: closed "hat" section, with the two sides of the feet bonded to the skin, and the middle arched;

[0055] To address the shortcomings of existing technologies, it is necessary to propose a method that can effectively constrain and test the cut-off end of a framed stringer under unidirectional load conditions, making the test boundary conditions closer to actual working conditions. By rationally designing the size of the test piece and the lateral support method, the out-of-plane deformation of non-target parts can be suppressed while ensuring structural stability, thereby obtaining more realistic and repeatable failure loads and failure locations.

[0056] While ensuring the accuracy of structural strength testing, the complexity and cost of test specimens and fixtures are reduced; by comparing the load-bearing capacity, displacement level and failure mode under different constraint conditions, the results are made quantifiable and comparable; while taking into account versatility and adaptability, the testing method can be applied to different stringer configurations and material systems; these indicators provide technical inspiration for subsequent optimization of testing methods and expansion of related patent solutions.

[0057] like Figure 1 A test method for the laterally supported stringer end under unidirectional load, used to test the load-bearing capacity of the stiffened wall panel with frame 5 and stringer 7, includes the following steps:

[0058] A support member I is installed on the testing machine 4 to laterally constrain the frame 5 on the test piece, so that the test piece is unconstrained along the loading direction and the support member I, and the test piece is rigidly constrained in the horizontal direction perpendicular to the loading direction.

[0059] On the other side of the test specimen, a support member II is provided to laterally constrain the test specimen, so that the test specimen is unconstrained along the loading direction and the support member II, and the test specimen is rigidly constrained in the horizontal direction perpendicular to the loading direction;

[0060] Apply a unidirectional in-plane load to the test specimen until the specimen fails;

[0061] Obtain the corresponding load, displacement, and / or strain data;

[0062] The key implementation points of this application are as follows: Focusing on the critical local structure of the "stringer termination point," experimental boundary conditions are constructed that are highly consistent with the actual engineering state under stress. By selecting a framed stiffened wall panel as the test specimen, and rationally controlling the overall dimensions of the specimen and the relative positions between the stringer termination point and the frame and fixtures, the stringer exhibits a genuine stiffness abrupt change at the termination point. Simultaneously, lateral support member I and lateral support member II are arranged on both sides of the testing machine to rigidly constrain the frame in the horizontal direction perpendicular to the loading direction, while allowing free sliding in the loading direction. This effectively suppresses out-of-plane deformation of the frame and wall panel without introducing additional constraint forces. These implementation points ensure a clear and stable force path for the test specimen under unidirectional loads, avoiding non-target failure caused by unreasonable boundary conditions.

[0063] The working process of this application is as follows: During the test, after the test piece is installed on the testing machine, the unidirectional in-plane load is gradually applied along the main force direction of the skin and the stringer; as the load increases, the force is transmitted to the stringer through the skin. At the end of the stringer, due to the abrupt change in cross-section and stiffness, local stress concentration is triggered; the lateral supports I and II restrict the displacement of the frame in the out-of-plane direction, so that the frame only participates in the real in-plane force and does not bend or warp, thereby ensuring that the end of the stringer becomes the main controlled failure area; when the load reaches the critical value, the test piece preferentially debonds, delaminates or fails at the edge / skin interface or adjacent area at the end of the stringer; by synchronously collecting load, displacement and strain data, the failure load, deformation level and failure mode of the end of the stringer under unidirectional load can be clearly obtained, realizing the comparative analysis of the structural performance of different stringer configurations (T-type, L-type, Ω-type) and under different constraint conditions.

[0064] Specifically, in one embodiment of this application, the lateral support assembly includes support member I and support member II; support member I and support member II are respectively disposed on both sides of the test specimen, and the contact forces of support member I and support member II on the test specimen cancel each other out; support member I, support member II and the test specimen are in surface contact; the frame 5 is provided with a clearance groove for the stringer 7, and the test specimen is allowed to move relative to each other along the load direction; support member I is in surface contact with the frame 5, and restricts the outward displacement of the contact surface of the frame 5; the frame 5 and support member I form a sliding pair along the load direction;

[0065] To address the issues of additional bending moments, out-of-plane deformation, and loading eccentricity introduced during unidirectional load testing of the girder's cut-off end due to asymmetrical or unreasonable lateral constraints, a structural feature is adopted: symmetrically arranged support members I and II on both sides of the test specimen. This allows the lateral resistance forces generated by the support members on both sides to cancel each other out, thus avoiding the introduction of additional lateral internal forces. Simultaneously, by employing surface contact between the support members, the test specimen, and the frame, and by incorporating slotted structures on the frame to avoid the girder, relative sliding of the test specimen along the load direction is allowed while ensuring support stiffness. This creates a sliding pair between the frame and the support members in the loading direction, restricting only out-of-plane displacement. This effectively suppresses non-target out-of-plane deformation of the frame and wall panels without constraining actual in-plane deformation, ensuring consistency between the test stress state and engineering conditions. This structure is simple to implement; the support members can be made of engineering plastics or composite materials with sufficient out-of-plane stiffness and low friction. This embodiment achieves the technical effect of effectively controlling boundary conditions and improving the reliability of test results at the girder's cut-off end.

[0066] Specifically, in one embodiment of this application, the test piece is a composite material wall panel test piece, including a skin 6, at least one stringer 7 with a cut-off end, and a frame 5 with through holes corresponding to the stringer. The frame 5, skin 6, and stringer 7 are connected as one unit. The stringer 7 has a T-shaped, L-shaped, or Ω-shaped configuration. The frame 5 has a self-symmetrical shape and is formed by combining two L-shaped members or two C-shaped members.

[0067] This embodiment integrates the skin, a single stringer with a cut-off end, and a frame with corresponding through holes into a single composite material panel test specimen structure. This allows the load to be transferred from the skin to the stringer according to the actual engineering path, forming a real stress concentration at the cut-off end. By limiting the stringer configuration to T-shaped, L-shaped, or Ω-shaped, the test specimen can cover typical stiffening forms commonly found in aerospace structures, improving the applicability of the testing method. At the same time, the frame adopts a self-symmetrical structure formed by combining two L-shaped members or two C-shaped members. While ensuring the frame's own stiffness and stability, it avoids the introduction of additional bending or eccentric effects due to the asymmetry of the frame configuration. This overcomes the defects in existing tests where the failure location shifts due to excessive structural simplification or asymmetrical stress, achieving the technical effect of making the overall stress state of the test specimen closer to the actual structure and making the stringer cut-off end the main control failure area.

[0068] Specifically, in one embodiment of this application, the geometric dimensions of the test piece satisfy the following conditions: in the test structure of the terminal scenario in which the test piece is applied, the width of the test piece is not less than the minimum stringer spacing in the test structure, the length of the test piece is between 1.25 times and 2 times the adjacent frame spacing, and the distance between the stringer 7 and the clamp of the testing machine 4 is less than one-fifth of the frame spacing, the stringer spacing is the adjacent spacing width between adjacent stringers, and the frame spacing is the distance between adjacent frames 5.

[0069] This embodiment quantitatively defines the geometric dimensional relationships of the test specimen's width, length, and the relative position of the stringer's cut-off end to the fixture. By ensuring that the test specimen's width is not less than the minimum stringer spacing in the actual structure, excessive influence of the lateral free edge on the target stringer's stress is avoided. Simultaneously, the test specimen's length is controlled between 1.25 and 2 times the adjacent frame spacing, ensuring that the frame's constraint on the skin and stringer forms an effective boundary without introducing unnecessary overall deformation due to excessive length. Furthermore, by limiting the distance between the stringer's cut-off end and the testing machine fixture to less than one-fifth of the frame spacing, the direct influence of the fixture end on the cut-off end area is reduced. This overcomes the shortcomings of existing technologies where arbitrary test specimen dimensions and significant fixture interference lead to failure location shifts or distorted load-bearing capacity assessments. The result is a technical effect where the stringer's cut-off end becomes the main control stress and failure area in the test, and the test results are comparable and representative of engineering.

[0070] Specifically, in one embodiment of this application, the lateral support assembly includes a connecting plate 1, an L-shaped base 2, and a sliding support 3. The L-shaped base 2 is used to connect the testing machine 4. Both ends of the connecting plate 1 are connected to the L-shaped base 2, and the connecting plate 1 is provided on both sides of the test piece. The sliding support 3 is provided on one side of the test piece through the connecting plate 1, and the other side of the test piece is provided with a stringer 7 and a frame 5.

[0071] One side of the test piece is supported by the sliding support 3, and the other side of the test piece is supported on the connecting plate 1 by the frame 5. The position where the sliding support 3 abuts against the test piece and the position where the frame 5 connects to the test piece are respectively set at corresponding positions on both sides of the test piece, so that the abutting forces of the sliding support 3 and the frame 5 on both sides of the test piece cancel each other out.

[0072] This embodiment utilizes a lateral support assembly consisting of a connecting plate, an L-shaped base, and a sliding support. By fixing the L-shaped base to the testing machine, the lateral support assembly obtains a stable installation reference. The connecting plates on both sides of the test piece serve as force transmission and installation carriers. On one side, the sliding support abuts against the test piece to form lateral support, while on the other side, the frame abuts against the connecting plate to achieve corresponding constraint. Simultaneously, the positions of the sliding support abutting against the test piece and the frame connecting to the test piece are arranged correspondingly on both sides of the test piece, so that the lateral constraint forces on both sides cancel each other out in spatial position and direction of action. This overcomes the defects of asymmetrical lateral support forces and easy overall displacement or additional bending of the test piece in the prior art. It achieves the technical effect of effectively limiting the out-of-plane displacement of the test piece, stabilizing the test boundary conditions, and improving the reliability of test results without affecting the free deformation in the loading direction.

[0073] Specifically, in one embodiment of this application, a strain measuring device is arranged on the skin 6 and / or stringer of the test piece, and strain data is collected synchronously during loading for quantitative analysis of the failure process at the cut-off end of the stringer 7.

[0074] To address the problem that relying solely on load-displacement curves is insufficient to accurately reflect the local damage evolution and failure initiation process at the girder's cut-off end, this embodiment employs a technique of arranging strain measurement devices on the skin and / or key stress areas of the girder of the test specimen. During unidirectional loading, strain data at each measurement point is collected synchronously, enabling a correlation between strain changes near the girder's cut-off end and load and displacement responses. This allows for quantitative characterization of the damage initiation, propagation, and eventual failure process at the cut-off end. By rationally selecting the location of strain measurement points close to the girder's cut-off end, the flange-skin interface, or stress concentration areas, response distortion caused by improper measurement point placement can be effectively avoided. This overcomes the shortcomings of existing technologies that only obtain overall load-bearing capacity but struggle to analyze local failure mechanisms, achieving the technical effect of improving failure determination accuracy and data analysis depth.

[0075] Specifically, in one embodiment of this application, a composite material wall panel test piece with framed stringer end includes: a skin, a composite material wall panel with stringer end, and a frame;

[0076] The skin is rectangular;

[0077] A stringer with a cut-off end is arranged along the 0° fiber direction of the skin, and the frame has through holes for the stringer, which are connected to the wall panel composed of the skin and the stringer by fasteners.

[0078] The end of the stringer is located near the through hole of the stringer frame. The stringer can be configured in T-shape, L-shape, or Ω-shape.

[0079] The frame configuration can consist of two L-shaped or two C-shaped structures. To ensure the stability of the frame, it should be a symmetrical structure.

[0080] The minimum width of the test specimen takes into account the minimum stringer spacing width in the measured structure, which is the minimum value of the adjacent spacing width between multiple stringers in the measured structure.

[0081] The minimum length of the test specimen shall not be less than 1.25 times the frame spacing and not more than 2 times the frame spacing;

[0082] The distance between the end of the stringer and the clamp should be less than one-fifth of the frame spacing;

[0083] In structural measurement, frame spacing refers to the distance between adjacent frames.

[0084] Test specimen fixture: Support component I on the side in contact with the frame is made of nylon, which can ensure that the frame slides under tension and prevents out-of-plane deformation of the frame;

[0085] Test method: Strain gauges are arranged on the wall panel, and the test specimen is placed on the testing machine with the fixture installed. The rollers on both sides of the fixture and the frame baffle are fixed with bolts. The strain gauges and the strain recorder are connected by wires. The strain recorder can obtain strain data. Tensile load is applied by the testing machine until the test specimen fails. The failure location of the test specimen basically occurs at the end of the stringer.

[0086] Data analysis and comparison were performed using the finite element method:

[0087] The simulation results using the technical solution of this application are as follows: Figure 3 , Figure 4 Compared with existing technologies Figure 5 , Figure 6 This application is more in line with actual engineering practice; the technical solution adopted in this application... Figure 7 , Figure 8 ;

[0088] When the thickness of the skin and stringers is 3mm, the frame thickness is 1.8mm, and the tensile yield strength of the aluminum alloy material is 420MPa;

[0089] The proposed solution is as follows: the tensile failure load of the framed and skinned lateral support fixture test specimen is 137.4 KN, and the displacement is 2.528 mm.

[0090] Existing technical test scheme: The tensile failure load of the test specimen with frameless and skinned lateral support fixture is 126.6KN, and the displacement is 3.083mm;

[0091] The test specimen design scheme of this application is as follows: a test specimen with three long stringers, and the out-of-plane deformation tensile failure load of the frame is 406.5KN and the displacement is 2.493mm.

[0092] The technical effects of this application are as follows:

[0093] The design scheme of the composite material wall panel test piece with framed stringer end is simple and versatile. It reflects the failure location and failure load of the stringer end wall panel under unidirectional load in actual application, and effectively achieves the purpose of integrity analysis and verification of the stringer end wall panel.

[0094] 2. The test fixture device is easy to operate and effectively limits the out-of-plane deformation of the stringer end and the frame, avoiding the risk of the test piece being damaged at the fixture end. The lateral support avoids the phenomenon of overly conservative test results caused by the absence of fixtures.

[0095] 3. The test method for the test specimen is simple and convenient. The use of a general-purpose universal testing machine can accurately obtain the failure load of the end wall of the stringer, which greatly reduces the test cost.

[0096] In summary, this invention aims to address the problems in existing mechanical testing of reinforced composite panels, such as the lack of dedicated testing methods for the critical weak point of the girder termination, unclear test boundary conditions, and significant deviations between the results and the actual structural load-bearing capacity. To address the technical challenge of girder termination near the frame and the tendency for delamination under unidirectional in-plane loads, making accurate assessment of its load-bearing performance difficult, this invention proposes a unidirectional load testing method for the girder termination with lateral support.

[0097] This method designs a framed test specimen of a long girder end panel, clearly defining the specimen's width, length, and the relative positional relationship between the girder end and the clamps. This makes the test structure geometrically and stress-wise closer to engineering reality. Simultaneously, lateral support clamps are installed on both sides of the frame, allowing the frame to slide dynamically in the loading direction while effectively restricting it in the out-of-plane direction. This avoids loading eccentricity and non-target failures caused by unconstrained or insufficiently constrained conditions. This technical solution can accurately obtain the failure load, displacement level, and failure mode of the long girder end while ensuring the simplicity and versatility of the test device. It provides a reliable basis for the integrity analysis and design verification of stiffened panel structures, significantly reduces test costs, and has good engineering application value.

[0098] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A test method for the unidirectional load on the end of a laterally supported stringer, used to test the load-bearing capacity of a stiffened wall panel with a frame (5) and a stringer (7), characterized in that, Includes the following steps: A support member I is installed on the testing machine (4) to laterally constrain the frame (5) on the test piece, so that the test piece is unconstrained along the loading direction and the support member I, and the test piece is rigidly constrained in the horizontal direction perpendicular to the loading direction; On the other side of the test specimen, a support member II is provided to laterally constrain the test specimen, so that the test specimen is unconstrained along the loading direction and the support member II, and the test specimen is rigidly constrained in the horizontal direction perpendicular to the loading direction; Apply a unidirectional in-plane load to the test specimen until the specimen fails; Obtain the corresponding load, displacement, and / or strain data.

2. The test method for the laterally supported stringer end under unidirectional load as described in claim 1, characterized in that, The lateral support assembly includes support component I and support component II; support component I and support component II are respectively disposed on both sides of the test specimen, and the contact forces of support component I and support component II on the test specimen cancel each other out.

3. The test method for the laterally supported stringer end under unidirectional load as described in claim 1, characterized in that, Support I, support II and test specimen are in surface contact. The frame (5) is provided with a clearance groove for the stringer (7) and the test specimen is allowed to move relative to each other along the load direction.

4. The test method for the laterally supported stringer end under unidirectional load as described in claim 1, characterized in that, Support member I is in surface contact with frame (5) and restricts the outward displacement of the contact surface of frame (5). Frame (5) and support member I form a sliding pair along the load direction.

5. The test method for the laterally supported stringer end under unidirectional load as described in claim 1, characterized in that, The test piece is a composite material wall panel test piece, including a skin (6), at least one stringer (7) with a cut-off end, and a frame (5) with through holes corresponding to the stringer. The frame (5), skin (6), and stringer (7) are connected as one unit.

6. The test method for the laterally supported stringer end under unidirectional load as described in claim 1, characterized in that, The configuration of the stringer (7) is T-shaped, L-shaped or Ω-shaped.

7. The test method for the laterally supported stringer end under unidirectional load as described in claim 1, characterized in that, The frame (5) is symmetrically arranged and is formed by combining two L-shaped components or two C-shaped components.

8. A test method for the laterally supported stringer end under unidirectional load as described in any one of claims 1-7, characterized in that, The geometric dimensions of the test piece meet the following conditions: in the test structure of the terminal scenario in which the test piece is applied, the width of the test piece is not less than the minimum stringer spacing in the test structure, the length of the test piece is between 1.25 times and 2 times the adjacent frame spacing, and the distance between the stringer (7) and the clamp of the test machine (4) is less than one-fifth of the frame spacing. The stringer spacing is the adjacent spacing width between adjacent stringers, and the frame spacing is the distance between adjacent frames (5).

9. A test method for the unidirectional load on the cut-off end of a laterally supported stringer as described in any one of claims 1-7, characterized in that, The lateral support assembly includes a connecting plate (1), an L-shaped base (2), and a sliding support (3). The L-shaped base (2) is used to connect the testing machine (4). The two ends of the connecting plate (1) are connected to the L-shaped base (2), and the connecting plate (1) is provided on both sides of the test piece. The sliding support (3) is provided on one side of the test piece through the connecting plate (1), and the other side of the test piece is provided with a stringer (7) and a frame (5). One side of the test piece is supported by the sliding support (3), and the other side of the test piece is supported on the connecting plate (1) by the frame (5).

10. A test method for the laterally supported stringer end under unidirectional load as described in any one of claims 1-7, characterized in that, The sliding support (3) abuts against the test piece and the frame (5) connects to the test piece, respectively, at corresponding positions on both sides of the test piece, so that the abutting forces of the sliding support (3) and the frame (5) on both sides of the test piece are canceled out. Strain measurement devices are arranged on the skin (6) and / or stringer of the test piece, and strain data are collected synchronously during loading for quantitative analysis of the failure process at the cut-off end of the stringer (7).

Images