Low-strength automobile sheet strain fatigue test device and method

Abstract

The invention relates to the technical field of material fatigue testing, in particular to a low-strength automobile sheet strain fatigue testing device and method. The device comprises an upper clamp, an anti-buckling device and a lower clamp, the anti-buckling device is formed by attaching a first anti-buckling plate and a second anti-buckling plate together, and the middle of the automobile sheet sample is clamped between the first anti-buckling plate and the second anti-buckling plate; the inner sides of the buckling-restrained plate I and the buckling-restrained plate II are respectively provided with a row of cylindrical roller pins, and the cylindrical roller pins are in rolling contact with the automobile sheet sample; sliding friction between the buckling-restrained device and the automobile sheet sample is converted into rolling friction, so that the influence of friction force on a test result is reduced; the thin metal sheet is adhered to the side surface of the automobile sheet sample, so that an invalid sample broken at the knife edge of the extensometer is avoided, and various indexes of strain fatigue of the automobile sheet are correctly represented.

Description

Technical Field

[0001] The present invention relates to the technical field of material fatigue testing, and particularly to a strain fatigue test device and method for low-strength automotive thin plates. Background Art

[0002] As known from the knowledge of mechanics of materials, slender rods or strip-shaped objects are extremely prone to compression buckling when loaded along the length direction. Due to the large length-to-thickness ratio and length-to-width ratio of automotive thin plate specimens, they are extremely prone to buckling failure during the compression process. Therefore, an anti-buckling device needs to be installed during the strain fatigue test. When installing the fatigue specimen, due to the gap between the anti-buckling device and the testing machine fixture, a small section of the clamping section of the specimen will be exposed and unconstrained. The unconstrained part is in a plane strain state, and it is extremely easy for thin plate materials with a thickness less than 1 mm to bend at this place, resulting in invalid tests.

[0003] In addition, after installing the anti-buckling device, friction will be generated between the thin plate specimen and the anti-buckling device, affecting the test results. To reduce the influence of friction on the test results, the commonly used method at present is to place a polytetrafluoroethylene plate between the specimen and the anti-buckling plate. During the cyclic strain loading process, the friction between the two is sliding friction, and the sliding friction coefficient is usually larger than the rolling friction coefficient. At the same time, for low-strength automotive thin plates with a thickness less than 1 mm, the specimen is prone to fracture at the contact between the extensometer knife edge and the specimen side, resulting in invalid test results.

[0004] Therefore, how to avoid the instability of the thin plate during compression, reduce the influence of friction on the test results, and prevent fractures at the extensometer knife edge is crucial for obtaining accurate cyclic stress-strain curves and various performance indicators under the strain conditions of the thin plate. Summary of the Invention

[0005] The present invention provides a strain fatigue test device and method for low-strength automotive thin plates. Cylindrical roller needles are installed on the inner sides of the anti-buckling plate 1 and the anti-buckling plate 2 to convert the sliding friction between them and the automotive thin plate specimen into rolling friction, so as to reduce the influence of friction on the test results. A thin metal sheet is pasted on the side of the automotive thin plate specimen to avoid invalid specimens that break at the extensometer knife edge, thereby correctly characterizing various strain fatigue indicators of the automotive thin plate.

[0006] To achieve the above object, the present invention is realized by adopting the following technical solutions:

[0007] A low-intensity strain fatigue test device for automotive thin plates, comprising an upper fixture, an anti-buckling device and a lower fixture; both the upper fixture and the lower fixture are of a split structure in the middle. The anti-buckling device is composed of an anti-buckling plate one and an anti-buckling plate two which are attached together. Both the anti-buckling plate one and the anti-buckling plate two are "I"-shaped plates, and their shapes and sizes are the same; the middle part of the automotive thin plate specimen is clamped between the anti-buckling plate one and the anti-buckling plate two; the upper end of the automotive thin plate specimen extends into the middle gap of the upper fixture, and the lower end of the automotive thin plate specimen extends into the middle gap of the lower fixture; the anti-buckling plate one and the anti-buckling plate two are detachably connected; a row of cylindrical roller needles are respectively arranged on the inner sides of the anti-buckling plate one and the anti-buckling plate two, and are in rolling contact with the automotive thin plate specimen.

[0008] A small column one is arranged on the outer side of the middle part of the anti-buckling plate one, and a small column two is arranged on the outer side of the middle part of the anti-buckling plate two. During the test, the extensometer rubber band is connected through the small column one and the small column two.

[0009] Hard material plates are pasted at the gauge positions on both sides of the automotive thin plate specimen corresponding to the extensometer knife edges. A thin metal sheet is pasted at the extensometer knife edge on one side of the automotive thin plate specimen, and the length of the thin metal sheet is 1 - 3 mm.

[0010] The thin metal sheet is a copper sheet, and its thickness is similar to or the same as the thickness of the automotive thin plate specimen.

[0011] The anti-buckling device is connected to the upper fixture and the lower fixture through mortise and tenon structures; the height gap at the mortise and tenon connection structure is 2 - 5 mm; the horizontal gap is 0.5 - 1 mm.

[0012] The anti-buckling plate one is composed of a transverse plate one, a middle vertical plate one and a tenon head one. Two transverse plates one and the middle vertical plate one form an "I"-shaped structure. A number of tenon heads one are respectively arranged at the top and bottom of the "I"-shaped structure, and a mortise one is formed between two adjacent tenon heads one; the anti-buckling plate two is composed of a transverse plate two, a middle vertical plate two and a tenon head two. Two transverse plates two and the middle vertical plate two form an "I"-shaped structure. A number of tenon heads two are respectively arranged at the top and bottom of the "I"-shaped structure, and a mortise two is formed between two adjacent tenon heads two; the widths of the middle vertical plate one and the middle vertical plate two are smaller than the width of the test section of the automotive thin plate specimen, and the difference is 2 - 4 mm; the lengths of the middle vertical plate one and the middle vertical plate two are greater than the length of the test section of the automotive thin plate specimen, and the difference is 1 - 3 mm.

[0013] The diameter of the cylindrical roller needle ≤ 1.5 mm, and the spacing of the cylindrical roller needle grooves ≤ 3 mm.

[0014] A low-intensity strain fatigue test method for automotive thin plates, comprising the following steps:

[0015] 1) Measure the width W of the clamping section of the automotive thin plate specimen and the width W' of the anti-buckling plate 1. Taking the axis of symmetry of the anti-buckling plate 1 as the axis of symmetry and one outer side of the anti-buckling plate 1 as the reference plane, draw 2 parallel lines M. The distance between the 2 parallel lines M is the width W of the automotive thin plate specimen, and the distance between the reference plane and the proximal line M is (W' - W) / 2;

[0016] 2) Horizontally place the anti-buckling plate 1 and place the cylindrical roller needles in the cylindrical roller needle groove 1 of the anti-buckling plate 1;

[0017] 3) Align one side of the automotive thin plate specimen with a straight line M and place it on top of the cylindrical roller needles;

[0018] 4) Horizontally place the anti-buckling plate 2, paste double-sided tape in the cylindrical roller needle groove 2, with the double-sided tape not exceeding the range of the cylindrical roller needle groove 2, and then stick the cylindrical roller needles in the cylindrical roller needle groove 2 through the double-sided tape;

[0019] 5) Place the side of the anti-buckling plate 2 with the cylindrical roller needles downwards on top of the automotive thin plate specimen; use a torque wrench to connect the fastening screws of the anti-buckling plate 1 and the anti-buckling plate 2, and adjust the fastening force of the fastening screws according to the preset parameters based on the thickness and strength of the automotive thin plate specimen;

[0020] 6) Install the extensometer, clamp the automotive thin plate specimen, ensuring that the vertical clearances between the upper fixture and the anti-buckling device and between the lower fixture and the anti-buckling device are both 2 - 5 mm; and the horizontal clearances are both 0.5 - 1 mm;

[0021] 7) Conduct a friction elimination test and a tensile elastic modulus inspection test. After the tensile elastic modulus inspection test passes, conduct the test in accordance with GB / T 26077 - 2021 "Test Method for Axial Strain Control of Fatigue Test of Metal Thin Sheets".

[0022] The process of presetting parameters when adjusting the fastening force of the fastening screws is as follows: Conduct a tensile elastic modulus inspection test before the start of the test, repeatedly apply cyclic forces to the automotive thin plate specimen within the elastic range, measure the tensile elastic modulus of the automotive thin plate specimen after installing the anti-buckling plate device, ensuring that the deviation value of the measured value of the tensile elastic modulus from the elastic modulus does not exceed ±5%; determine the set value of the fastening force of the fastening screws within this range.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1) Install cylindrical roller needles on the inner sides of the anti-buckling plate 1 and the anti-buckling plate 2, converting the sliding friction between them and the automotive thin plate specimen into rolling friction to reduce the influence of friction force on the test results;

[0025] 2) Paste a thin metal sheet on the side of the automotive sheet specimen to avoid invalid specimens that break at the knife edge of the extensometer, thereby correctly characterizing the strain fatigue indicators of the automotive sheet;

[0026] 3) Adopt a mortise and tenon structure connection between the fixture and the anti-buckling plate to "narrow the width" of the unconstrained part of the clamping section of the automotive sheet specimen, and avoid the bending failure of the automotive sheet specimen caused by the plane strain state. Description of the Drawings

[0027] Figure 1 is the front view of a low-strength automotive sheet strain fatigue test device according to the present invention.

[0028] Figure 2 is Figure 1 the side view of.

[0029] Figure 3 is the front view of the first anti-buckling plate according to the present invention.

[0030] Figure 4 is Figure 3 the B-B view in.

[0031] Figure 5 is the front view of the second anti-buckling plate according to the present invention.

[0032] Figure 6 is Figure 5 the side view of.

[0033] Figure 7 is the front view of the upper fixture according to the present invention.

[0034] Figure 8 is the front view of the lower fixture according to the present invention.

[0035] Figure 9 is the front view of the specimen according to the present invention.

[0036] In the figure: 1 - upper fixture; 11 - upper fixture tenon; 12 - upper fixture mortise; 2 - fastening screw; 3 - cylindrical roller; 4 - automotive sheet specimen; 41 - clamping section; 42 - test section; 5 - first anti-buckling plate; 51 - first tenon; 52 - first mortise; 53 - first middle vertical plate; 54 - first cylindrical roller groove; 55 - first small column; 6 - second anti-buckling plate; 61 - second tenon; 62 - second mortise; 63 - second middle vertical plate; 64 - second cylindrical roller groove; 65 - second small column; 7 - lower fixture; 71 - lower fixture tenon; 72 - lower fixture mortise. Detailed Embodiments

[0037] The following further describes the detailed embodiments of the present invention with reference to the drawings:

[0038] Such as Figure 1 、Figure 2 As shown in the figure, a low-intensity strain fatigue test device for automotive thin plates according to the present invention includes an upper fixture 1, an anti-buckling device, and a lower fixture 7; both the upper fixture 1 and the lower fixture 7 are of a split structure in the middle. The anti-buckling device is composed of an anti-buckling plate 1 5 and an anti-buckling plate 2 6 that are fitted together. Both the anti-buckling plate 1 5 and the anti-buckling plate 2 6 are "I"-shaped plates, and their shapes and dimensions are the same; the middle part of the automotive thin plate specimen 4 is clamped between the anti-buckling plate 1 5 and the anti-buckling plate 2 6; the upper end of the automotive thin plate specimen 4 extends into the middle gap of the upper fixture 1, and the lower end of the automotive thin plate specimen 4 extends into the middle gap of the lower fixture 7; the anti-buckling plate 1 5 and the anti-buckling plate 2 6 are detachably connected; a row of cylindrical roller needles 3 are respectively arranged on the inner sides of the anti-buckling plate 1 5 and the anti-buckling plate 2 6 (as Figure 2 shown), and rollingly contact with the automotive thin plate specimen 4.

[0039] A small column 1 55 is arranged on the outer side of the middle part of the anti-buckling plate 1 5, and a small column 2 65 is arranged on the outer side of the middle part of the anti-buckling plate 2 6. During the test, an extensometer rubber band is connected through the small column 1 55 and the small column 2 65.

[0040] A thin metal sheet is pasted at the extensometer knife edge on one side of the automotive thin plate specimen 4, and the length of the thin metal sheet is 1 to 3 mm.

[0041] The thin metal sheet is a copper sheet, and its thickness is similar to or the same as the thickness of the automotive thin plate specimen 4.

[0042] The anti-buckling device is connected to the upper fixture 1 and the lower fixture 7 through a mortise and tenon structure; the heightwise gap at the mortise and tenon connection structure is 2 to 5 mm; the horizontal gap is 0.5 to 1 mm.

[0043] As Figure 3 , Figure 4 shown, the anti-buckling plate 1 5 is composed of a transverse plate 1, a middle vertical plate 1 53, and a tenon 1 51. Two transverse plates 1 and the middle vertical plate 1 53 form an "I"-shaped structure. A number of tenons 1 51 are respectively arranged at the top and bottom of the "I"-shaped structure, and a mortise 1 52 is formed between two adjacent tenons 1 51; as Figure 5 , Figure 6 shown, the anti-buckling plate 2 6 is composed of a transverse plate 2, a middle vertical plate 2 63, and a tenon 2 61. Two transverse plates 2 and the middle vertical plate 2 63 form an "I"-shaped structure. A number of tenons 2 61 are respectively arranged at the top and bottom of the "I"-shaped structure, and a mortise 2 62 is formed between two adjacent tenons 2 61; the widths of the middle vertical plate 1 53 and the middle vertical plate 2 63 are smaller than the width of the test section 42 of the automotive thin plate specimen 4, and the difference is 2 to 4 mm; the lengths of the middle vertical plate 1 53 and the middle vertical plate 2 63 are greater than the length of the test section 42 of the automotive thin plate specimen 4, and the difference is 1 to 3 mm.

[0044] The diameter of the cylindrical needle roller 3 ≤ 1.5 mm, and the spacing of the cylindrical needle roller grooves (including the first cylindrical needle roller groove 54 and the second cylindrical needle roller groove 64) ≤ 3 mm.

[0045] A low-intensity strain fatigue test method for automotive thin sheets according to the present invention includes the following steps:

[0046] 1) Measure the width W of the clamping section 41 of the automotive thin sheet specimen 4 and the width W' of the first anti-buckling plate 5. Taking the central axis of the first anti-buckling plate 5 as the axis of symmetry and one outer side of the first anti-buckling plate 5 as the reference plane, draw two parallel lines M. The distance between the two parallel lines M is the width W of the automotive thin sheet specimen 4, and the distance between the reference plane and the proximal line M is (W' - W) / 2;

[0047] 2) Horizontally place the first anti-buckling plate 5 and place the cylindrical needle roller 3 in the first cylindrical needle roller groove 54 of the first anti-buckling plate 5;

[0048] 3) Align one side of the automotive thin sheet specimen 4 with a straight line M and place it on top of the cylindrical needle roller 3;

[0049] 4) Horizontally place the second anti-buckling plate 6, paste double-sided tape in the second cylindrical needle roller groove 64, and the double-sided tape does not exceed the range of the second cylindrical needle roller groove 64. Then stick the cylindrical needle roller 3 in the second cylindrical needle roller groove 64 through the double-sided tape;

[0050] 5) Place the side of the second anti-buckling plate 6 with the cylindrical needle roller 3 facing down on top of the automotive thin sheet specimen 4; use a torque wrench to connect the fastening screws 2 of the first anti-buckling plate 5 and the second anti-buckling plate 6, and adjust the fastening force of the fastening screws 2 according to the thickness and strength of the automotive thin sheet specimen 4 and the preset parameters;

[0051] 6) Install an extensometer, clamp the automotive thin sheet specimen 4, and ensure that the vertical clearances between the upper fixture 1 and the anti-buckling device, and between the lower fixture 7 and the anti-buckling device are both 2 - 5 mm; the horizontal clearances are both 0.5 - 1 mm;

[0052] 7) Conduct a friction elimination test and a tensile elastic modulus inspection test. After the tensile elastic modulus inspection test passes, conduct the test according to GB / T 26077-2021 "Test Method for Axial Strain Control of Fatigue Test of Metal Thin Sheets".

[0053] The process of presetting parameters when adjusting the fastening force of the fastening screw 2 is as follows: Conduct a tensile elastic modulus inspection test before the start of the test. Repeatedly apply cyclic forces to the automotive thin sheet specimen 4 within the elastic range, measure the tensile elastic modulus of the material after installing the anti-buckling plate device, and ensure that the deviation value of the measured value of the tensile elastic modulus from the elastic modulus does not exceed ±5%; determine the set value of the fastening force of the fastening screw 2 within this range.

[0054] AsFigure 9 As shown in the figure, the strain fatigue specimen of automotive sheet (hereinafter referred to as the automotive sheet specimen 4) is composed of a clamping section 41 and a test section 42. The clamping section 41 is the thicker part at both ends of the automotive sheet specimen 4, and the part in the middle of the automotive sheet specimen 4 is the test section 42.

[0055] The specimen width is one of the parameters that directly affect the fatigue test results. The principle for width selection is to ensure that all points on the specimen are in a uniaxial stress state. When the thickness t and elastic modulus E of the specimen remain unchanged, the width W or the parallel length Lc of the test section should be made as large as possible. However, when the width of the specimen is greater than six times the thickness, a transverse moment will be generated at the center of the specimen, and a plane strain state will occur. The specimen in the plane strain state is subjected to a triaxial tensile stress, and at this time the material will become brittle and the specimen is extremely easy to break.

[0056] To avoid specimen fracture in the clamping section, it is generally required that the width W of the clamping section ≥ 2w (w is the width of the test section), that is, the width W of the specimen clamping section cannot be too small. However, when installing the fatigue specimen, there will inevitably be a gap between the anti-buckling device and the upper fixture and the lower fixture, that is, a small section of the clamping section of the specimen will be exposed and not constrained. The present invention assumes that the exposed clamping section is equivalent to the test section of the specimen. On this premise, the "test width" of the exposed clamping section should be reduced as much as possible to avoid being in a plane strain state due to being too wide here, and then buckling resulting in test failure.

[0057] The present invention adopts the design idea of the mortise and tenon structure. n straight grooves are respectively cut on the upper fixture 1 and the lower fixture 7 of the conventional testing machine (the number of straight grooves depends on the width W of the clamping section), forming an upper fixture tenon 11 and an upper fixture mortise 12 (as Figure 7 shown), and a lower fixture tenon 71 and a lower fixture mortise 72 (as Figure 8 shown); the anti-buckling device is connected to the upper fixture 1 and the lower fixture 7 through mortise and tenon joints respectively. In this way, the width W of the exposed clamping section 41 is evenly divided into (2n + 1) segments, which is equivalent to reducing the "test width" here, avoiding the exposed part of the clamping section being in a plane strain state, and preventing the automotive sheet specimen 4 from bending at this place and causing test failure.

[0058] When performing the strain fatigue test, there is friction between the anti-buckling device and the specimen. To reduce the influence of the friction on the test results, the present invention places cylindrical roller needles 3 on the upper and lower surfaces of the automotive sheet specimen 4 respectively, changing the friction between the anti-buckling plate device and the automotive sheet specimen 4 from the conventional sliding friction to rolling friction, effectively reducing the friction force.

[0059] In order to install the cylindrical roller 3, double-sided adhesive is pasted in the cylindrical roller groove II 64 of the anti-buckling plate II 6 which is above the automotive sheet specimen 4 during the installation of the automotive sheet specimen 4. The four sides of the double-sided adhesive should be within the cylindrical roller groove II 64, and then the cylindrical roller 3 is pasted in the cylindrical roller groove II 64 to prevent the cylindrical roller 3 from falling off when installing the anti-buckling plate II 6.

[0060] In the present invention, when installing the automotive sheet specimen 4, the smaller the gap between the upper fixture 1, the lower fixture 7 and the anti-buckling plate device, the better, so as to reduce the exposed length of the clamping section 41 and improve the test stiffness at this place.

[0061] When installing the automotive sheet specimen 4 in the present invention, first draw two straight lines M parallel to the outer side surface of the anti-buckling plate I 5 ( Figure 3 the A surface in the middle). The distance between the two parallel lines M is the width W of the automotive sheet specimen 4, and the distance from the A surface to the proximal line M is (W′ - W) / 2. When installing the automotive sheet specimen 4, one of its side edges is aligned with the straight line M, thus ensuring the centering of the specimen clamping. The widths of the middle vertical plate I 53 and the middle vertical plate II 63 are W", which is smaller than the width w of the test section 42 of the automotive sheet specimen 4.

[0062] In order to prevent the automotive sheet specimen 4 from breaking at the extensometer knife edge, the present invention selects a thin metal sheet (such as a copper sheet) with a thickness basically the same as that of the automotive sheet specimen 4, with a length of 1 - 3 mm, and pastes it at the gauge length of the automotive sheet specimen 4 with glue. The test can be started after the glue is cured.

[0063] The specific details and requirements of the automotive sheet strain fatigue test device described in the present invention are as follows:

[0064] Threaded holes are drilled in the anti-buckling plate I 5, and counterbores are drilled in the anti-buckling plate II 6 to facilitate the connection of the two through the fastening screw 2; in addition, their sizes and shapes are exactly the same; the sizes and shapes of the upper fixture 1 and the lower fixture 7 are exactly the same.

[0065] The vertical clearance at the mortise and tenon joint of the upper fixture 1, the lower fixture 7 and the anti-buckling device should be greater than 2 mm to avoid collision during the tensile and compressive fatigue test; at the same time, the clamping strength should be ensured, so the vertical clearance at the mortise and tenon joint is preferably between 2 - 5 mm.

[0066] The horizontal clearance at the mortise and tenon joint of the upper fixture 1, the lower fixture 7 and the anti-buckling device is between 0.5 - 1 mm, which is convenient for installation and also ensures the reliability of the connection.

[0067] The width of the middle vertical plate 53 of the buckling restraining plate 1 5 and the middle vertical plate 63 of the buckling restraining plate 2 6 should be slightly smaller than the width w of the test section of the automotive sheet specimen 4, and the preferred width is 2 - 4 mm; at the same time, the length L1 of the middle vertical plate 53 and the middle vertical plate 63 should be greater than the length L2 of the test section 42 of the automotive sheet specimen 4, and the preferred length is 1 - 3 mm. This can ensure that the test section 42 of the automotive sheet specimen 4 is not completely constrained, thus reflecting the real test process and test results.

[0068] In the present invention, a number of cylindrical needle grooves 54 are milled on the inner side of the middle vertical plate 53 of the buckling restraining plate 1 5, and a number of cylindrical needle grooves 64 are milled on the inner side of the middle vertical plate 63 of the buckling restraining plate 2 6 for placing the cylindrical needles 3; the diameters of the cylindrical needle grooves 54 and the cylindrical needle grooves 64 are the same as the diameter of the cylindrical needles 3. The diameter of the cylindrical needles 3 is preferably not greater than 1.5 mm, and the spacing of the cylindrical needles 3 is preferably not more than 3 mm.

[0069] In the present invention, a small column 55 is welded on the outer side of the middle vertical plate 53 of the buckling restraining plate 1 5, and a small column 65 is welded on the outer side of the middle vertical plate 63 of the buckling restraining plate 2 6 for connecting the extensometer rubber band.

[0070] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A low-intensity strain fatigue test device for automotive thin plates, comprising an upper fixture, an anti-buckling device and a lower fixture; both the upper fixture and the lower fixture are of a split structure in the middle. The anti-buckling device is composed of an anti-buckling plate one and an anti-buckling plate two that are fitted together. Both the anti-buckling plate one and the anti-buckling plate two are "I"-shaped plates, and their shapes and sizes are the same. The middle part of the automotive thin plate specimen is clamped between the anti-buckling plate one and the anti-buckling plate two. The upper end of the automotive thin plate specimen extends into the middle gap of the upper fixture, and the lower end of the automotive thin plate specimen extends into the middle gap of the lower fixture. The anti-buckling plate one and the anti-buckling plate two are detachably connected; characterized in that, On the inner sides of the buckling restraint plate 1 and the buckling restraint plate 2, a row of cylindrical roller needles are respectively arranged, which are in rolling contact with the automotive thin plate specimen.

2. The low-intensity automotive sheet strain fatigue test device according to claim 1, wherein On the outer side of the middle part of the buckling restraint plate 1, a small column 1 is arranged, and on the outer side of the middle part of the buckling restraint plate 2, a small column 2 is arranged. During the test, the extensometer rubber band is connected through the small column 1 and the small column 2.

3. The low-intensity automotive sheet strain fatigue test device according to claim 1, characterized in that, A thin metal sheet is pasted at the extensometer knife edge on one side of the automotive thin plate specimen, and the length of the thin metal sheet is 1 - 3 mm.

4. A low-intensity automotive sheet strain fatigue test device according to claim 3, characterized in that, The thin metal sheet is a copper plate, and its thickness is similar to or the same as the thickness of the automotive thin plate specimen.

5. A low-intensity automotive sheet strain fatigue test device according to claim 1, characterized in that, The buckling restraint device is connected to the upper fixture and the lower fixture through mortise and tenon structures; the vertical clearance at the mortise and tenon connection structure is 2 - 5 mm; the horizontal clearance is 0.5 - 1 mm.

6. The low-intensity automotive sheet strain fatigue test device according to claim 1, wherein, The buckling restraint plate 1 is composed of a transverse plate 1, a middle vertical plate 1, and a tenon 1. Two transverse plates 1 and the middle vertical plate 1 form an I-shaped structure. A number of tenons 1 are respectively arranged at the top and bottom of the I-shaped structure, and a mortise 1 is formed between two adjacent tenons 1; the buckling restraint plate 2 is composed of a transverse plate 2, a middle vertical plate 2, and a tenon 2. Two transverse plates 2 and the middle vertical plate 2 form an I-shaped structure. A number of tenons 2 are respectively arranged at the top and bottom of the I-shaped structure, and a mortise 2 is formed between two adjacent tenons 2; the widths of the middle vertical plate 1 and the middle vertical plate 2 are smaller than the width of the test section of the automotive thin plate specimen, and the difference is 2 - 4 mm; the lengths of the middle vertical plate 1 and the middle vertical plate 2 are greater than the length of the test section of the automotive thin plate specimen, and the difference is 1 - 3 mm.

7. A low-intensity automotive sheet strain fatigue test device according to claim 1, characterized in that, The diameter of the cylindrical roller needle ≤ 1.5 mm, and the spacing of the cylindrical roller needle grooves ≤ 3 mm.

8. A strain fatigue test method for low-strength automotive thin sheets, which is implemented based on the low-strength automotive thin sheet strain fatigue test device described in any one of claims 1 to 7; characterized in that, It includes the following steps: 1) Measure the width W of the clamping section of the automotive thin plate specimen and the width W' of the buckling restraint plate 1. Taking the axis of symmetry of the buckling restraint plate 1 as the axis of symmetry and one outer side of the buckling restraint plate 1 as the reference surface, draw two parallel lines M. The distance between the two parallel lines M is the width W of the automotive thin plate specimen, and the distance between the reference surface and the proximal line M is (W' - W) / 2; 2) Horizontally place the buckling restraint plate 1 and place the cylindrical roller needles in the cylindrical roller needle grooves 1 of the buckling restraint plate 1; 3) Align one side edge of the automotive thin plate specimen with a straight line M and place it on the top of the cylindrical roller needles; 4) Horizontally place the buckling restraint plate 2, paste double-sided tape in the cylindrical roller needle groove 2, and the double-sided tape does not exceed the range of the cylindrical roller needle groove 2. Then stick the cylindrical roller needles in the cylindrical roller needle groove 2 through the double-sided tape; 5) Place the side of the buckling restraint plate 2 with the cylindrical roller needles downward on the top of the automotive thin plate specimen; use a torque wrench to connect the fastening screws of the buckling restraint plate 1 and the buckling restraint plate 2, and adjust the fastening force of the fastening screws according to the preset parameters according to the thickness and strength of the automotive thin plate specimen; 6) Install the extensometer, clamp the automotive thin plate specimen, and ensure that the vertical clearances between the upper fixture and the buckling restraint device and between the lower fixture and the buckling restraint device are both 2 - 5 mm; the horizontal clearances are both 0.5 - 1 mm; 7) Conduct a friction elimination test and a tensile elastic modulus inspection test. After the tensile elastic modulus inspection test passes, conduct the test according to GB / T 26077 - 2021 "Test Method for Axial Strain Control of Fatigue Test of Metal Thin Sheets".

9. The method for low-intensity strain fatigue test of automotive thin plates according to claim 8, characterized in that The process of presetting parameters when adjusting the fastening force of the fastening screw is as follows: Before the start of the test, a tensile elastic modulus inspection test is carried out. Within the elastic range, a cyclic force is repeatedly applied to the automotive sheet specimen, and the tensile elastic modulus of the material after installing the anti-buckling plate device is measured to ensure that the deviation value of the measured value of the tensile elastic modulus from the elastic modulus does not exceed ±5%; within this range, the set value of the fastening force of the fastening screw is determined.

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