A test sample and tool for testing the z-direction fatigue performance of a layered composite material

Abstract

The present application relates to the technical field of material testing, in particular to a sample and tool for testing Z-direction fatigue performance of laminated composite material, the sample is axisymmetric dumbbell-shaped, comprising a middle test section and two end holding ends, and the bonding interface is located in the test section; the diameter of the test section is 5-10 mm, and the diameter of the holding end is greater than or equal to 2 times the diameter of the test section; the thickness of the holding end is not less than 5 mm, and the axial distance from the inner side end face to the bonding interface is not less than 3 mm, so that the interface is ensured to be in a uniform stress area; the transition area is smoothly connected by a circular arc with a radius of greater than or equal to 2 mm. The present application can accurately and repeatedly characterize the Z-direction interface fatigue performance on a conventional fatigue testing machine, and solves the problem that the traditional composite material joint sample cannot test the real joint interface performance.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and in particular to a specimen and tooling for testing the Z-axis fatigue properties of layered composite materials. Background Technology

[0002] With the rapid development of the shipbuilding industry, single-metal hull structural materials are no longer sufficient to meet the design requirements of high-speed ships. To reduce weight, lower the center of gravity, improve stability, and increase speed, the use of lightweight alloy (titanium, aluminum) structures for the superstructure or certain components has become a major trend in modern shipbuilding. Because lightweight alloys such as titanium and aluminum have very low solubility with steel, and they form various embrittled intermetallic phases when fused together, traditional fusion welding methods cannot be used for connection. In the past, the connection between the superstructure and the main hull was achieved through riveting or mechanical joining. In recent years, transition joints made of aluminum-steel or titanium-steel explosively welded composite plates (layered metal composite materials) have emerged, achieving the connection between aluminum alloys and steel through welding. Due to its advantages such as simplified construction processes, this connection method has gradually replaced traditional connection methods and gained widespread application.

[0003] Common types of transition joints used in application are shown below. Figure 1 As shown, the main performance characteristics are those in the thickness direction (Z-direction). Therefore, evaluating the Z-direction performance of the bonding interface of composite materials is crucial, and relevant metal composite material products and test methods have relatively clear specifications for the mechanical properties of the bonding interface. For example, CB 20091 "Specification for Aluminum Alloy-Aluminum-Steel Composite Transition Joints" specifies the Z-direction pull-out strength of the product; GB / T 6396 "Test Methods for Mechanical and Technological Properties of Composite Steel Plates" specifies the method for testing the Z-direction static strength through bond testing. However, in actual ship service, a high frequency of cracking has occurred at the transition joint area, such as... Figure 2 As shown, the root cause of this phenomenon is that the structure in this part is subjected to cyclic fatigue stress during the operation of the hull, which causes cracking.

[0004] The structural dimensions of dissimilar metal composite structures in ships are often designed based on the Z-direction tensile static strength of the transition joints. Generally, the transition joints are designed to withstand loads greater than the strength of the connecting plates and welds on both sides, and the transition joints are not considered weak points in terms of stress. However, even when static strength design is met, the structures still experience a high frequency of cracking during actual service, indicating that relying solely on the static strength of the joints for structural design is insufficient to meet operational requirements. Due to the fatigue loads generated during ship operation, fatigue design methods must be employed to ensure the structure meets fatigue stress conditions.

[0005] Because transition joints are typically made of metal composite plates, and the Z-direction (thickness direction) dimension of these plates is relatively small, there are currently very few fatigue testing methods for the thickness direction of composite plates used in transition joints. Relevant standards, such as: 1) The US Navy standard MIL-24445A specifies a fatigue test method for aluminum-steel composite transition joints. This involves welding aluminum and steel fins to both ends of the aluminum-steel composite material to form a structural component, and then conducting a fatigue test under a specified stress. This test method typically results in failure at the aluminum base material or weld toes at both ends of the structural component. This method is a component fatigue test and cannot determine the true fatigue limit or fatigue life of the transition joint, thus providing no effective data for structural design. 2) In recent years, some foreign scholars have designed a fatigue test method for the Z-direction performance of transition joints, processing the composite plate into a shape such as... Figure 4 The cup-shaped sample is then designed, and a corresponding fixture is designed to install the sample inside the fixture (e.g., ...). Figure 5 As shown in the figure, a fatigue loading test with Z-axis force was then carried out on a fatigue testing machine, ultimately causing the failure location of the transition joint to be at the joint interface, and the fatigue strength of the joint interface was measured. There is relatively little domestic research on this aspect of fatigue testing.

[0006] Publication No.: CN208833611U A composite material fatigue specimen includes a long strip-shaped specimen body. The specimen body comprises a first clamping part, a measuring part, and a second clamping part connected in sequence. Both the first and second clamping parts are cuboid structures. The measuring part has a rectangular or square cross-section along the direction perpendicular to the length of the specimen body. The measuring part has a third upper side, a third lower side, a third front side, and a third rear side. The third upper side, third lower side, third front side, and third rear side are all concave arc-shaped surfaces. However, the specimen length in this technical solution is relatively large, making it difficult to use for fatigue testing in the thickness direction of layered metal composite materials.

[0007] Therefore, there is an urgent need to propose a new type of specimen and tooling to solve the problem that traditional composite joint specimens cannot test the true joint interface performance. Summary of the Invention

[0008] In view of this, the present invention aims to provide a specimen and tooling for testing the Z-axis fatigue performance of layered composite materials, thereby solving the problem that traditional composite material joint specimens cannot test the true joint interface performance.

[0009] The primary reason for designing fatigue specimens in the thickness direction for layered composite materials used as transition joints is that the materials typically used for transition connections are relatively thin, with actual ship applications generally having a thickness of 20–40 mm. The challenges of conducting Z-axis fatigue performance tests on materials of this thickness are as follows:

[0010] 1) There are no existing standards that can be directly applied, and there are no directly applicable methods in the available information;

[0011] 2) Insufficient testing methods: For example, GB / 5313-2010 "Thickness Direction Properties of Steel Plates" specifies the test method for thickness direction tensile testing, but lacks a fatigue test method. The tensile specimen specifications state that specimens can be directly machined (with sufficient thickness) or extended portions can be added at both ends, with friction welding generally used for adding the extended portions. For composite plates used as transition joints, directly machining the specimen results in insufficient thickness; if welding is used at both ends, the layered interface of the transition joint is sensitive to heat input, and the welding heat source will significantly affect the interface of the layered composite material, making it impossible to test the true joint interface performance.

[0012] Addressing the urgent needs of my country's shipbuilding industry, this invention, considering the actual operating conditions of transition joints, proposes a fatigue specimen type and matching tooling for Z-axis fatigue performance testing of layered metal composite plates. Using the specimen and tooling described herein on a fatigue testing machine, the Z-axis fatigue performance of the bonding interface of the layered composite material can be tested using axial force control. This provides the true fatigue strength of the transition joint material for related structural designs, supports fatigue design, and improves equipment reliability.

[0013] The technical solution of this invention is implemented as follows:

[0014] One object of the present invention is to disclose a specimen for testing the Z-axis fatigue properties of layered composite materials. The specimen is axisymmetric dumbbell-shaped and includes a test section in the middle and two clamping ends located at both ends of the test section.

[0015] Wherein, at least one bonding interface of the layered metal composite material is located within the test section;

[0016] The cross-sectional area of ​​the test section is smaller than the cross-sectional area of ​​the clamping end, so that stress is concentrated in the test section under axial tensile load;

[0017] The clamping end includes a multi-layer clamping end and a base layer clamping end, both of which have a thickness of not less than a preset minimum value, to ensure that failure occurs preferentially at the bonding interface rather than the clamping end during fatigue loading.

[0018] Sufficient straight-line distance is provided between the interface and the adjacent transition region to avoid interference of geometric discontinuities in the transition region on the interface fatigue behavior.

[0019] The transition region uses a smooth curved surface to connect the test section and the clamping end to reduce stress concentration in the non-interface area.

[0020] Furthermore, the total length T of the sample satisfies: 40mm ≥ T ≥ 20mm.

[0021] Furthermore, the test segment is cylindrical, and the diameter φB of the test segment satisfies: 5mm≤φB≤10mm; the clamping end is cylindrical, and the diameter φA of the clamping end satisfies: φA≥2φB.

[0022] Furthermore, the thickness T1 of the multilayer clamping end and the thickness T2 of the base layer clamping end are both not less than 5 mm.

[0023] Furthermore, the thickness T1 of the multilayer clamping end is determined according to the following formula: ;

[0024] Where T1 is the thickness of the multilayer clamping end, in mm;

[0025] L6 is the groove width of the tooling, in mm;

[0026] τ1 is the shear strength of the multilayer material, in mm;

[0027] Rm is the bonding strength of the interface, in MPa;

[0028] ΦB is the diameter of the test section, in mm.

[0029] Furthermore, the distance T3 from the interface to the adjacent transition region is not less than 1 mm.

[0030] Furthermore, the transition region is a circular arc transition segment with a radius of not less than 2mm.

[0031] Furthermore, the surface roughness Ra of the test section and transition area is no greater than 0.2 μm, and the surface roughness Ra of the outer end face of the clamping end is no greater than 0.8 μm.

[0032] Another object of the present invention discloses a fixture for testing the Z-axis fatigue properties of layered composite materials, used to fix the specimen for testing the Z-axis fatigue properties of layered composite materials as described in any of the above claims, wherein the fixture is a pair and is made of high-strength alloy structural steel;

[0033] Each tooling includes an upper connecting section and a lower clamping section;

[0034] The connecting section is equipped with a connection structure that matches the fatigue testing machine;

[0035] The clamping section has a rectangular cavity along the axial direction for embedding the clamping end of the sample. The width of the rectangular cavity is equal to the thickness of the corresponding clamping end, the depth is not less than the diameter of the clamping end, and the height is not less than the diameter of the test section.

[0036] Furthermore, the high-strength alloy structural steel is 42CrMo or 40CrNiMo.

[0037] Compared with existing technologies, the specimen and tooling for testing the Z-axis fatigue properties of layered composite materials of the present invention have the following advantages:

[0038] 1. This invention designs an axisymmetric dumbbell-shaped specimen with a central test section and two end clamping sections, ensuring that the bonding interface is located within the test section and transitions smoothly to the arc transition zone. This allows the maximum alternating stress under axial fatigue load to be precisely concentrated at the Z-axis bonding interface, effectively suppressing non-target failures in the base material or geometrically abrupt areas. Combined with the design that the thickness of the cladding / base layer clamping ends is ≥5 mm, the clamping strength is guaranteed. Thus, the Z-axis fatigue performance of the layered metal composite material interface itself can be obtained truthfully and reliably, solving the problem that traditional joint specimens cannot test the true performance of the joint interface.

[0039] 2. The tooling of this invention is integrally machined from high-strength alloy structural steel such as 42CrMo. Its clamping section has a rectangular cavity that precisely matches the thickness (T1 / T2) of the sample clamping end, realizing coaxial embedding of the sample and pure axial force transmission. The entire test only requires embedding the sample into the tooling and installing it on a conventional hydraulic servo fatigue testing machine. All operations are completed at room temperature and pressure. The tooling structure is simple, low in cost, and has a long service life. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0041] Figure 1 A schematic diagram of the structural configuration of an aluminum-steel joint.

[0042] Figure 2 This is a diagram showing the cracking of an aluminum-steel joint.

[0043] Figure 3 This is a schematic diagram of the composite panel orientation;

[0044] Figure 4 Background technology sample size and structure diagram;

[0045] Figure 5 Here is a structural diagram of the background technology test device;

[0046] Figure 6 This is a schematic diagram of the Z-axis fatigue test specimen of the composite plate of the present invention;

[0047] Figure 7 This is a schematic diagram of the surface accuracy of the composite plate fatigue specimen in the Z-axis direction according to the present invention.

[0048] Figure 8 This is a schematic diagram of the Z-axis fatigue test fixture structure of the composite plate of the present invention.

[0049] Figure 9 This is a cross-sectional view (AA) of the composite plate Z-axis fatigue specimen tooling structure of the present invention.

[0050] Figure 10 This is a schematic diagram of the installation of the composite plate fatigue test specimen in the Z direction according to the present invention;

[0051] Figure 11 This is a sample diagram of Example 1;

[0052] Figure 12 This is a sample diagram of the steel-nickel-titanium fatigue specimen from Example 1.

[0053] Figure 13 This is a drawing showing the dimensions and specifications of the fatigue specimen tooling for Example 1.

[0054] Figure 14 This is a cross-sectional view (AA) of the fatigue specimen tooling structure in Example 1.

[0055] Figure 15 This is a fatigue test diagram;

[0056] Figure 16 This is a diagram of a fatigue test specimen.

[0057] Explanation of reference numerals in the attached figures

[0058] 1. Sample; 101. Test section; 102. Clamping end; 1021. Multilayer clamping end; 1022. Base layer clamping end; 103. Bonding interface; 2. Tooling; 201. Connecting section; 202. Clamping section; 3. Fatigue testing machine. Detailed Implementation

[0059] To make the technical means and objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below with reference to specific illustrations.

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] like Figures 1-16As shown, traditional joint specimen 1 or plate specimen 1 cannot effectively concentrate cyclic load on the bonding interface 1023, and is easily affected by the strength of the base material, geometric changes or clamping eccentricity, resulting in the inability to obtain true fatigue data of the interface.

[0062] To accurately measure the fatigue performance of layered metal composite materials at the interface 1023 in the thickness direction (Z-direction), and to solve the technical problems of uncontrollable stress distribution, failure location deviation from the interface, and large dispersion of test results in existing testing methods, this invention provides a specimen 1 and a fixture 2. Through the coordinated design of geometric configuration and clamping system, it achieves accurate and repeatable testing of the interface fatigue behavior in the Z-direction.

[0063] Specifically, specimen 1 adopts an axisymmetric dumbbell-shaped structure, including a central test section 101 and two clamping ends 102 located at its two ends, wherein at least one bonding interface 1023 of the layered metal composite material is confined within the test section 101. This specimen 1 utilizes the stress concentration effect generated by abrupt changes in cross-sectional area, causing the maximum alternating stress under axial tensile load to preferentially act on the target interface region, thereby guiding fatigue crack initiation and propagation at the interface, preventing premature failure in non-target areas, and ensuring that the test results accurately reflect the interface performance. Preferably, the non-target region can be the base material or the weld toe.

[0064] Preferably, the cross-sectional shapes of the test segment 101 and the clamping end 102 can be any geometric shape, including but not limited to square, rectangle, ellipse, polygon, or combinations thereof. As long as the minimum cross-sectional area of ​​the test segment 101 in the direction perpendicular to the loading axis is less than the minimum cross-sectional area of ​​the clamping end 102, the technical effect of confining the high-stress area to the region where the bonding interface 1023 is located can be achieved. Preferably, to ensure the uniformity and symmetry of stress distribution, the test segment 101 and the clamping end 102 adopt the same type of cross-sectional shape, such as both being circular or both being square, and the cross-sectional centers are coaxial.

[0065] Furthermore, to balance stress concentration and fabrication feasibility, the test section 101 is preferably cylindrical, with its diameter φB controlled within the range of 5 mm to 10 mm; the clamping end 102 is also cylindrical, with a diameter φA satisfying φA ≥ 2φB, for example, φA = 12–20 mm. This proportional relationship ensures a significant stress gradient within the test section 101 while retaining sufficient clamping area. The total length T of the specimen 1 is preferably 20 mm to 40 mm to accommodate the clamp spacing of a conventional fatigue testing machine 3.

[0066] To ensure the structural integrity and testing validity of specimen 1 during fatigue testing, this invention proposes clear design criteria for the axial thickness of the clamping ends 102 on both sides. The clamping ends 102 include a multi-layer clamping end 10211102T1 and a base clamping end 10222102T2. Both the multi-layer clamping end 10211102T1 and the base clamping end 10222102T2 need to have sufficient thickness to provide adequate clamping support area, preventing failure under high-cycle cyclic loading, i.e., clamping ends 102 peeling off or slipping from the specimen 1 body, thereby ensuring stable load transfer to the test section 101.

[0067] In addition, to ensure that the bonding interface 1023 of the layered metal composite material is completely located within the straight segment with uniform stress and to avoid it being disturbed by stress due to proximity to the geometric transition zone, the axial distance from the inner end face of the clamping end 102, i.e. the side facing the test segment 101, to the bonding interface 1023 is not less than 3 mm.

[0068] Specifically, the thickness T1 of the multilayer clamping end 10211102 can be determined according to the material properties using the formula:

[0069] ...(1)

[0070] From equation (1), we can obtain: ;

[0071] In the formula: T1 is the thickness of the multilayer clamping end 10211102, in mm;

[0072] L6 is the groove width of tooling 2, in mm;

[0073] τ1 is the shear strength of the multilayer material, in mm;

[0074] Rm is the bonding strength of the interface, in MPa;

[0075] ΦB is the diameter of test section 101, in mm.

[0076] Furthermore, both the thicknesses T1 and T2 are not less than 5 mm to provide sufficient structural strength.

[0077] This setup, through dual constraints, prevents shear tearing of the strata under high-cycle fatigue, forces the failure mode to be confined to the bonding interface 1023, ensures the mechanical stability of sample 1 during fatigue loading, and ensures that the bonding interface 1023 is in an ideal uniform stress field, significantly improving the accuracy and repeatability of the Z-axis fatigue performance test results.

[0078] To eliminate the disturbance of the stress field caused by geometric discontinuities, the distance T4 from interface 1023 to the adjacent arc transition section is not less than 1 mm, ensuring that the interface is located within a straight segment with uniform stress distribution. The radius of the arc transition section is preferably not less than 2 mm to smoothly connect the test section 101 and the clamping end 102, significantly reducing the local stress concentration factor. Simultaneously, the surface roughness Ra of the test section 101 and the transition area is controlled to be no greater than 0.2 μm, and the surface roughness Ra of the outer end face of the clamping end 102 is no greater than 0.8 μm, reducing non-interface cracks caused by surface defects and ensuring good fit with the fixture 2.

[0079] To achieve pure axial force transmission and suppress eccentric loading, this invention designs a pair of high-rigidity fixtures 2, integrally machined from high-strength alloy structural steel such as 42CrMo or 40CrNiMo. Each fixture 2 includes an upper threaded connecting section 201 and a lower clamping section 202. The clamping section 202 has a rectangular cavity along the axial direction, with its width L9 precisely equal to the thickness of the corresponding clamping end 102, i.e., L9 = T1 or T2, depth L5 not less than φA, and height L6 not less than φB. This embedded structure makes the sample 1 and the fixture 2 form a coaxial force-bearing system, effectively eliminating bending and shear components, ensuring that the load is strictly applied to the interface along the Z-direction, and significantly improving test repeatability and data reliability.

[0080] The entire testing process of this invention requires only conventional immersion cleaning, turning, and a standard hydraulic servo fatigue testing machine 3. It eliminates the need for vacuum, plasma, electrochemical deposition, or complex alignment devices. All operations can be completed under normal temperature and pressure conditions and low temperature (≤80°C). Sample preparation is simple, and the tooling 2 has a simple structure, low cost, and long service life, allowing for direct integration into existing aluminum alloy or composite material surface treatment and mechanical testing production lines. Practical verification shows that the Z-axis fatigue SN curves obtained using the method of this invention exhibit low dispersion and clear interface failure modes, successfully solving the industry bottleneck of "inaccurate and incomparable" Z-axis fatigue performance of high-strength layered metal composite materials. This provides crucial basic data support for the fatigue-resistant design of major equipment such as ships, nuclear power plants, and rail transportation.

[0081] Example 1

[0082] Taking titanium-nickel-steel composite material used as a transition joint for dissimilar metal connections as an example, we illustrate its Z-axis fatigue performance test.

[0083] The original composite plate thickness of the titanium-nickel-steel joint is 8+2+16mm, and the material combination is titanium (TA1) + nickel (N7) + steel (Grade B steel). It is prepared by explosive welding and includes two bonding interfaces: a 1023 interface and a nickel-steel interface. The steps are as follows:

[0084] 1. Sample 1 of an 8+2+16mm steel-nickel-titanium composite material was processed as follows. Figure 11 The dimensions shown are as indicated.

[0085] 2. For example Figures 11-12 As shown, the total thickness of sample 1 is T=26mm; the diameter φB of test section 101 is selected as 10mm, the diameter φA of clamping section is selected as 20mm, and T1 is the thickness of the cladding end 102 of the cladding layer (titanium layer) calculated according to formula 1.

[0086] Rm is the lower limit of the interfacial strength of titanium-nickel-steel, which is 196 MPa; L6 is the mounting size of tooling 2, which is 12 mm; τ1 is the shear strength of TA1 pure titanium, which is 0.7 times the tensile strength index, 240 MPa × 0.7 = 168 MPa; Substituting the values ​​into the formula, we can calculate that T1 ≥ 2.43 mm. Considering the safety factor and processing applicability, we choose 5 mm.

[0087] T2 represents the thickness of the steel layer clamping end 102, which is the same as T1. The transition section is 2mm at both ends, the length of test section 101 is T3 (12mm), and T4 (1mm). Both the titanium-nickel interface and the steel-nickel interface are located in the weakest stress areas of test section 101.

[0088] 3. Made of 42CrMo alloy steel, as shown in the figure. Figures 13-14 Tooling 2, process two pieces.

[0089] 4. Install fatigue specimen 1 and its matching fixture 2 onto the fatigue testing machine 3, as follows: Figure 11 As shown, fatigue tests were then conducted.

[0090] 5. Different fatigue test conditions can be set according to the test requirements. For example, (1) a tensile load of 196 MPa (the lower limit of the tensile strength index of the interface of the titanium-steel composite plate is 196 MPa) is set, the axial force control method is adopted, the stress ratio is 0, and the frequency is 80-100 Hz. The test results show that the specimen 1 failed after the 452,300th test. The specimen 1 after failure is shown in the figure. Figure 16 As shown.

[0091] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A specimen for testing the Z-axis fatigue properties of layered composite materials, characterized in that, The sample (1) is axially symmetric dumbbell-shaped, including a test section (101) in the middle and two clamping ends (102) located at both ends of the test section (101). Wherein, at least one bonding interface (103) of the layered metal composite material is located within the test section (101); The cross-sectional area of ​​the test segment (101) is smaller than that of the clamping end (102) so that stress is concentrated in the test segment (101) under axial tensile load. The clamping end (102) includes a multi-layer clamping end (1021) and a base clamping end (1022), both of which have a thickness of not less than a preset minimum value, so as to ensure that failure occurs preferentially at the bonding interface (103) rather than the clamping end (102) during fatigue loading. Sufficient straight-line distance is provided between the bonding interface (103) and the adjacent transition region to avoid the interference of geometric discontinuity of the transition region on the interface fatigue behavior; The transition region uses a smooth curved surface to connect the test section (101) and the clamping end (102) to reduce stress concentration in the non-interface region.

2. The specimen for testing the Z-axis fatigue properties of layered composite materials according to claim 1, characterized in that, The total length T of the sample (1) satisfies: 40mm ≥ T ≥ 20mm.

3. The specimen for testing the Z-axis fatigue properties of layered composite materials according to claim 1, characterized in that, The test segment (101) is cylindrical, and the diameter φB of the test segment (101) satisfies: 5mm≤φB≤10mm; the clamping end (102) is cylindrical, and the diameter φA of the clamping end (102) satisfies: φA≥2φB.

4. The specimen for testing the Z-axis fatigue properties of layered composite materials according to claim 1, characterized in that, The thickness T1 of the multilayer clamping end (1021) and the thickness T2 of the base clamping end (1022) are both not less than 5 mm.

5. The specimen for testing the Z-axis fatigue properties of layered composite materials according to claim 1, characterized in that, The thickness T1 of the multilayer clamping end (1021) is determined according to the following formula: ; Where T1 is the thickness of the multilayer clamping end (1021), in mm; L6 is the groove width of tooling (2), in mm; τ1 is the shear strength of the multilayer material, in mm; Rm is the bonding strength of the interface, in MPa; ΦB is the diameter of the test segment (101), in mm.

6. The specimen for testing the Z-axis fatigue properties of layered composite materials according to claim 1, characterized in that, The distance T3 from the bonding interface (103) to the adjacent transition region is not less than 1 mm.

7. The specimen for testing the Z-axis fatigue properties of layered composite materials according to claim 1, characterized in that, The transition area is a circular arc transition section with a radius of not less than 2mm.

8. The specimen for testing the Z-axis fatigue properties of layered composite materials according to claim 1, characterized in that, The surface roughness Ra of the test section (101) and the transition area is no greater than 0.2 μm, and the surface roughness Ra of the outer end face of the clamping end (102) is no greater than 0.8 μm.

9. A tooling for testing the Z-axis fatigue properties of layered composite materials, characterized in that, The tooling (2) is used to fix the specimen for testing the Z-axis fatigue properties of the layered composite material according to any one of claims 1 to 8, and the tooling (2) is a pair made of high-strength alloy structural steel; Each tooling (2) includes an upper connecting section (201) and a lower clamping section (202); The connecting section (201) is provided with a connecting structure that matches the fatigue testing machine (3); The clamping section (202) has a rectangular cavity along the axial direction for inserting the clamping end (102) of the sample (1). The width of the rectangular cavity is equal to the thickness of the corresponding clamping end (102), the depth is not less than the diameter of the clamping end (102), and the height is not less than the diameter of the test section (101).

10. The tooling for testing the Z-axis fatigue properties of layered composite materials according to claim 9, characterized in that, The high-strength alloy structural steel is 42CrMo or 40CrNiMo.

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