A fixture structure for testing mechanical properties of cross-lap joints of plates

Abstract

The present invention discloses a fixture structure for testing the mechanical properties of cross-lap joints of plates, and relates to the field of industrial manufacturing technology. The fixture structure of the present invention is composed of a first fixture and a second fixture; the first fixture and the second fixture both include an adapter, an angle plate and a U-shaped block, the inner pin at the bottom end of the adapter is connected with the angle plate, and a U-shaped block is arranged on the outer side of the bottom of the angle plate, wherein one of the U-shaped blocks is composed of an upper U-shaped block ‑A and an upper U-shaped block ‑B, and the upper U-shaped block ‑B is arranged at the bottom end of the upper U-shaped block ‑A, and a pressure block is arranged at the bottom end of one of the U-shaped blocks ‑B. The present invention adopts a split design, and the contact surfaces of the fixture and the sample, and the fixture and the thickness compensation sheet are processed with anti-slip teeth, and the thickness compensation sheet is installed between the split fixtures and does not directly contact the sample, thereby increasing the friction force, and the U-shaped pressure block with side walls is adopted, which can effectively prevent the sample from rotating during the test process containing shear force.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial manufacturing, and in particular relates to a fixture structure used for mechanical property testing of a cross-lap joint of a plate. Background Art

[0002] In the automotive, aerospace and other manufacturing industries, there are a variety of processes to choose from for connecting plates: resistance spot welding, laser welding, stir friction welding, bolt connection, pull riveting, hot melt self-tapping, self-piercing riveting, adhesive bonding, etc.; since each method has its advantages and limitations, they are more or less used in specific occasions. The relevant evaluation indicators include joint coefficient, joint assembly and design, joint strength and stiffness, joint fracture mode, cost-effectiveness (equipment cost, production efficiency, etc.); therefore, it is usually necessary to use experimental methods to test and evaluate the mechanical properties of the joint such as strength, stiffness, energy absorption performance, joint coefficient, etc. under different working conditions, so as to provide a basic reference for the selection of connection process type, formulation of material matching combination scheme, and setting of process parameters, and design different matching fixtures according to different experimental conditions. There are many problems in the existing cross lap joint test, and we have proposed improvement methods to address these problems. Summary of the invention

[0003] The object of the present invention is to provide a fixture structure for testing the mechanical properties of a cross-lap joint of a plate material, so as to solve the problems raised in the above-mentioned background technology.

[0004] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0005] The invention relates to a fixture structure for testing the mechanical properties of a cross-lap joint of a plate.

[0006] The clamp structure consists of a first clamp and a second clamp;

[0007] The first clamp and the second clamp both include an adapter, an angle plate and a U-shaped block. The inner pin at the bottom end of the adapter is connected to the angle plate, and the outer side of the bottom of the angle plate is provided with a U-shaped block.

[0008] Furthermore, one of the U-shaped blocks consists of an upper U-shaped block-A and an upper U-shaped block-B, and the upper U-shaped block-B is arranged at the bottom end of the upper U-shaped block-A.

[0009] Furthermore, a pressing block is provided at the bottom end of one of the U-shaped blocks-B.

[0010] Furthermore, the other U-shaped block is composed of a lower U-shaped block-A and a lower U-shaped block-B, and the lower U-shaped block-B is arranged at the bottom end of the lower U-shaped block-A.

[0011] Furthermore, a U-shaped pressing block is provided at the bottom end of the other U-shaped block-B.

[0012] Furthermore, a rectangular groove is provided inside one end of the upper U-shaped block-A and the lower U-shaped block-A.

[0013] Furthermore, observation windows are provided on the inner sides of the upper U-shaped block-A and the lower U-shaped block-A.

[0014] Furthermore, thickness compensation sheets are installed between the upper U-shaped block-A and the upper U-shaped block-B, and between the lower U-shaped block-A and the lower U-shaped block-B.

[0015] Furthermore, through holes are opened inside the two sides of the U-shaped pressing block, bolts are arranged inside the through holes, and the U-shaped pressing block is connected to the lower U-shaped block-A through bolts.

[0016] The present invention has the following beneficial effects:

[0017] The present invention adopts a split design so that the contact surfaces between the fixture and the sample, and between the fixture and the thickness compensation sheet are processed with anti-slip teeth. The thickness compensation sheet is installed between the split fixtures and does not directly contact the sample, thereby improving the friction force. The U-shaped pressure block with side walls is used to effectively prevent the sample from rotating during the test process involving shear force. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0019] Figure 1 A schematic diagram of a force bearing structure for testing the mechanical properties of a cross-lap joint of a plate according to the present invention;

[0020] Figure 2 It is a schematic diagram of the force of a joint used for mechanical performance testing of a cross lap joint of a plate under different working conditions according to the present invention;

[0021] Figure 3 It is a force diagram of a cross-lap specimen used for mechanical property testing of a cross-lap joint of a plate according to the present invention;

[0022] Figure 4 The present invention is a first method for testing the mechanical properties of a cross-lap joint of a plate Cross specimen fixture developed by JK;

[0023] Figure 5 The second method for testing the mechanical properties of a cross-lap joint of a plate according to the present invention Developed a matching fixture for cross-lap specimens;

[0024] Figure 6 It is a schematic diagram of the installation of a cross shear test specimen for testing the mechanical properties of a cross lap joint of a plate according to the present invention;

[0025] Figure 7 It is a schematic diagram of the effect of thinning of the right side plate of a cross lap joint specimen used for mechanical property testing of a cross lap joint of plates on joint installation in the present invention;

[0026] Figure 8 It is a schematic diagram of the effect of thickening of the right side plate of a cross-lap specimen on the installation of the joint for testing the mechanical properties of a cross-lap joint of a plate according to the present invention;

[0027] Fig. 9 It is a schematic diagram of the rotation phenomenon of the sample clamping area in a shear test of a cross-lap specimen used for mechanical property testing of a cross-lap joint of a plate according to the present invention;

[0028] Fig.10 A schematic diagram of a cross shear test for testing the mechanical properties of a cross lap joint of a plate according to the present invention;

[0029] Fig.11 It is a schematic diagram of the split design of the fixture used for the mechanical property test of the cross lap joint of the plate and the installation of the thickness compensation sheet of the present invention;

[0030] Fig.12 It is a schematic diagram of the cross specimen orientation definition for testing the mechanical properties of a cross lap joint of a plate according to the present invention;

[0031] Fig.13 This is a three-view drawing of a fixture for testing the mechanical properties of a cross-lap joint of a plate according to the present invention;

[0032] Fig.14 This is an axonometric diagram of the upper part of a fixture for testing the mechanical properties of a cross-lap joint of a plate according to the present invention;

[0033] Fig.15 The present invention is an axonometric view of the lower half of a fixture used for testing the mechanical properties of a cross lap joint of a plate. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] See also Figure 1-Figure 10 Shown is the prior art and technical analysis of the present invention, which are as follows:

[0036] like Figure 1 As shown in the figure, peeling, lap shear and cross tension tests are commonly used to test the mechanical properties of welded, adhesively bonded and mechanically connected joints. The stress conditions of the three test joints are as follows: Figure 1 As shown, however, the above three lap joint methods cannot fully represent the mechanical behavior of the joint under actual working conditions;

[0037] In addition, in order to perform numerical simulation analysis on the joint structure, it is usually necessary to conduct additional joint mechanical property tests under more different working conditions as the test basis for calibrating or verifying the empirical joint numerical model. These additional test conditions include shear and tension-shear combination under different combination scale factors, such as Figure 2 As shown;

[0038] Some scholars use cross lap joints and matching fixtures to perform tensile, shear and combined tensile and shear loading tests on the joints (referred to as the cross method). The force diagram of the joint is as follows: Figure 3 As shown in the figure, the fixture structure can be divided into two types: one is to adjust the installation position of the fixture on the angle plate to achieve tension, shear and combined tension and shear tests under four different proportional factors on the joint, such as Figure 4 As shown; the other is a set of fixtures corresponding to the joint loading test under one working condition, such as Figure 5 As shown in (c), (e), and (f), the three sets of fixtures correspond to the tensile, shear, and 45° tension-shear combined loading tests of the joint respectively;

[0039] The current shortcomings of the cross method test are explained below using the cross shear test as an example:

[0040] (1) shows a schematic diagram of a tensile testing machine. Generally speaking, the lower chuck of the tensile testing machine is fixed on the base, and the upper chuck is installed on the crossbeam of the testing machine. The crossbeam of the testing machine can only move up and down, and the clamping center of the testing machine (i.e., the load center line) is always kept in a straight line during the entire test process. Figure 3), first fix one side of the sample to the lower part of the fixture, then fix the other side to the upper part of the fixture, and then install the round rod adapter of the lower part of the fixture into the lower clamp of the testing machine. At this time, the movement of the entire fixture is restricted (not fully constrained), and the position of the clamp can only be adjusted by adjusting the position of the crossbeam on the testing machine to achieve the clamping and fixing of the upper part of the fixture. From the above installation process, it can be found that when the total thickness of the cross specimen changes, the left and right relative positions of the upper part of the fixture will also change. The following is combined with Figure 7 , Figure 8 The reasons for this phenomenon are explained in detail (the fixture and chuck are assumed to be rigid bodies);

[0041] When the total thickness of the sample becomes thinner ( Figure 7 (Assuming that the thickness of the right plate is thinner), the specimen is still installed. After the installation process is completed, it can be found that the position of the round rod adapter on the upper part of the fixture has shifted to the right relative to the load centerline. If the round rod adapter is still forcibly installed into the test machine chuck at this time, a tensile load beyond the test expectation will be applied to the joint. Especially for joints with lower strength, plastic deformation will occur in the joint, significantly reducing the accuracy of the test results;

[0042] When the total thickness of the sample becomes thicker ( Figure 8 (Assuming that the thickness of the plate on the right side is thicker), similar to the above process, after the installation process is completed, it can be found that the position of the round rod adapter on the upper part of the fixture has shifted to the left relative to the load centerline. If the round rod adapter is still forcibly installed into the test machine chuck at this time, an unexpected compression load will be applied to the joint. For joints with lower strength, it will also cause initial damage to the joint, significantly reducing the accuracy of the test results.

[0043] In fact, any cross joint test involving shear force will have the above problems, but the test methods proposed in the existing literature do not take into account the installation problems caused by the change of specimen thickness;

[0044] (2) During the shear test, the cross-lap specimen rotates, as shown in Figure 10. The force analysis of the cause of this phenomenon is as follows: when the upper plate moves upward, the upper plate is subjected to the support force F1 of the rivet; the force analysis of the right clamping area is carried out separately, and the cross section has an internal force F1′ with the same magnitude and direction as F1, and the surface of the clamping area is subjected to the resultant force F μ The resultant torque M generated by the friction force μ ; When F1′ and F μ The torque generated is greater than M μWhen the joint strength is high (i.e., when the joint strength is high, such as adhesive joints, adhesive riveted composite joints, etc.), the clamping area on the right side of the specimen rotates counterclockwise relative to the fixture during the test; the analysis of the clamping area on the left side of the specimen is similar to the above process. When the shear test is performed on the high-strength joint, the clamping area on the left side will rotate clockwise relative to the fixture;

[0045] From the above analysis, it can be seen that when the joint is subjected to a shear force test, the imbalance of the moment is the root cause of the difference between the final deformation mode of the joint and the test expectation. Increasing the friction between the specimen and the fixture can effectively suppress the occurrence of the rotation phenomenon.

[0046] See also Figure 11-Figure 15 As shown, the present invention is a fixture structure for testing the mechanical properties of cross-lap joints of plates.

[0047] against Figure 1 — Fig.10 The present invention provides the following solutions to the existing technical problems:

[0048] (1) Install thickness compensation sheet: During the design stage of the fixture, the design should be based on the maximum clamping thickness of the specimen. During the test, if the joint specimen is less than the maximum clamping thickness, adding a thickness compensation sheet of corresponding thickness can avoid installation problems caused by changes in specimen thickness.

[0049] (2) Split fixture design: Although the use of a thickness compensation sheet can solve the installation problem caused by the change in specimen thickness, there is also the problem of the installation position of the thickness compensation sheet; according to the analysis in the previous article, when a joint with high strength is tested with shear force, the imbalance of the torque will cause the specimen to rotate, and increasing the friction between the specimen and the fixture is an effective means to suppress this phenomenon. According to the friction formula: (here is the friction coefficient, is the normal pressure, and is the friction force), increasing the friction coefficient and normal pressure are two ways to increase friction:

[0050] ⅰ. Increase the positive pressure, such as using high-strength bolts and applying a large pre-tightening force;

[0051] ⅱ. Increase the friction coefficient between the contact surface of the specimen, thickness compensation sheet and fixture, such as processing anti-slip teeth on the contact surface of the fixture and thickness compensation sheet;

[0052] However, when the thickness of the thickness compensation sheet is small, it is difficult to directly process anti-skid teeth on its surface. If the thickness compensation sheet with a smooth surface is placed directly between the fixture and the sample, the maximum friction force that can be provided between the thickness compensation sheet and the sample will be significantly smaller than the maximum friction force that can be provided between the fixture with anti-skid teeth and the sample when the thickness compensation sheet is not installed, increasing the risk of rotation in the sample clamping area. Therefore, the fixture adopts a split design, and the contact surfaces between the fixture and the sample, and between the fixture and the thickness compensation sheet are processed with anti-skid teeth. The thickness compensation sheet is installed between the split fixtures and does not directly contact the sample, thereby increasing the friction; Fig.11 The split structure of the fixture, the processing position of the anti-slip teeth and the installation position of the thickness compensation sheet are demonstrated.

[0053] (3) Using a lower U-shaped pressure block with side walls: In order to facilitate the description of the role of the pressure block with side walls, the length direction (long side) of the plate is defined as the longitudinal direction, the width direction is the transverse direction, and the thickness direction is the normal direction (both the upper and lower plates are defined using the local coordinate system). Fig.12 The definition of sheet orientation is further explained. Fig.14 , Fig.15 The upper clamp without side walls and the lower U-shaped clamp with side walls are shown in the figure. In the cross shear test, the rotation tendency of the clamping area only occurs on the plate moving in the transverse direction (the plate on the other side is used as the reference origin, that is, the relative static state). If a clamp without side walls is used, it can only constrain the normal translation of the plate and the rotation around the longitudinal and transverse directions. The rotation tendency of the plate around the normal direction is balanced by friction. If a U-shaped clamp with side walls is used, the rotation of the plate around the normal direction can be further constrained, thereby obtaining a joint failure mode closer to the pure shear condition.

[0054] The above is a specific structural design scheme of the clamp, and is described in detail with reference to the accompanying drawings;

[0055] like Figure 11-Figure 15 The present invention designs a fixture structure for testing the mechanical properties of a cross lap joint of a plate, which consists of a first fixture and a second fixture, and the first fixture and the second fixture are connected by a rectangular groove with an external hexagonal bolt, and the rectangular groove prevents the bolt from rotating during tightening, wherein:

[0056] The first fixture is composed of an adapter, an angle plate, a U-shaped block, a thickness compensation sheet and a pressing block;

[0057] The inner pin at the bottom of the adapter is connected to an angle disk, which can change the position of the adapter on the outside of the angle disk and position the adapter through the pin. By adjusting the installation position of the adapter, the specimen can be subjected to tensile, shear and 5 different proportions of tension-shear combination tests. A U-shaped block is set on the outside of the bottom of the angle disk.

[0058] The U-shaped block is composed of an upper U-shaped block-A and an upper U-shaped block-B. The upper U-shaped block-B is arranged at the bottom end of the upper U-shaped block-A. A pressing block is arranged at the bottom end of the upper U-shaped block-B. A rectangular groove is provided inside one end of the upper U-shaped block-A. An observation window is provided inside the upper U-shaped block-A for visual monitoring of the joint loading test process.

[0059] The thickness compensation sheet is assembled between the upper U-shaped block-A and the upper U-shaped block-B, and the specimen is assembled between the upper U-shaped block-B and the pressing block, and the specimen, the thickness compensation sheet, etc. are clamped by bolts;

[0060] Preferably, the contact surfaces between the fixture and the sample, and between the fixture and the thickness compensation sheet are processed with anti-slip teeth;

[0061] The second fixture is also composed of an adapter, an angle plate, a U-shaped block, a thickness compensation sheet and a U-shaped pressing block;

[0062] The inner pin at the bottom of the adapter is connected to an angle disk, which can change the position of the adapter on the outside of the angle disk and position the adapter through the pin. By adjusting the installation position of the adapter, the specimen can be subjected to tensile, shear and 5 different proportions of tension-shear combination tests. A U-shaped block is set on the outside of the bottom of the angle disk.

[0063] The U-shaped block is composed of a lower U-shaped block-A and a lower U-shaped block-B. The lower U-shaped block-B is arranged at the bottom end of the lower U-shaped block-A. A U-shaped pressing block is arranged at the bottom end of the lower U-shaped block-B. A rectangular groove is provided inside one end of the lower U-shaped block-A. An observation window is provided inside the lower U-shaped block-A for visual monitoring of the joint loading test process.

[0064] The thickness compensation sheet is assembled between the lower U-shaped block-A and the lower U-shaped block-B, and the specimen is assembled between the lower U-shaped block-B and the U-shaped pressing block, and the specimen, the thickness compensation sheet, etc. are clamped by bolts;

[0065] Furthermore, through holes are provided inside the two sides of the U-shaped pressing block, and bolts are provided inside the through holes, so that the U-shaped pressing block and the lower U-shaped block-A can be connected by bolts;

[0066] Preferably, the contact surfaces between the fixture and the sample, and between the fixture and the thickness compensation sheet are processed with anti-slip teeth;

[0067] A specific application of this embodiment is: taking the first clamp part as an example, the installation method for performing shear force tensile test on the cross-lap specimen is explained in detail: first, it is necessary to select a suitable thickness compensation sheet according to the thickness specification of the sheet material, and then stack and align the upper U-shaped block-A, thickness compensation sheet, upper U-shaped block-B, specimen, and pressure block in this order, and then clamp and tighten them with bolts. The installation method of the second clamp is the same as that of the first clamp, except that the side bolts under the pressure block need to be additionally installed, and then the upper and lower U-shaped blocks are installed as a whole together with the angle plate and the adapter on the tensile testing machine to perform the tensile test.

[0068] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0069] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the present invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A fixture structure for testing the mechanical properties of a cross-lap joint of a plate, characterized in that: The clamp structure consists of a first clamp and a second clamp; The first clamp and the second clamp both include an adapter, an angle plate and a U-shaped block, the inner pin at the bottom end of the adapter is connected to the angle plate, and the outer side of the bottom of the angle plate is provided with a U-shaped block; One of the U-shaped blocks is composed of an upper U-shaped block-A and an upper U-shaped block-B, and the upper U-shaped block-B is arranged at the bottom end of the upper U-shaped block-A; A pressing block is provided at the bottom end of one of the U-shaped blocks-B; The other U-shaped block is composed of a lower U-shaped block-A and a lower U-shaped block-B, and the lower U-shaped block-B is arranged at the bottom end of the lower U-shaped block-A; A U-shaped pressing block is provided at the bottom end of the other U-shaped block-B; Thickness compensation sheets are installed between the upper U-shaped block-A and the upper U-shaped block-B, and between the lower U-shaped block-A and the lower U-shaped block-B.

2. A fixture structure for testing mechanical properties of cross-lap joints of plates according to claim 1, characterized in that: A rectangular groove is formed inside one end of the upper U-shaped block-A and one end of the lower U-shaped block-A.

3. The fixture structure for testing the mechanical properties of a cross-lap joint of a plate material according to claim 1, characterized in that: Observation windows are provided on the inner sides of the upper U-shaped block-A and the lower U-shaped block-A.

4. The fixture structure for testing the mechanical properties of a cross-lap joint of a plate material according to claim 1, characterized in that: Through holes are provided inside the two sides of the U-shaped pressing block, bolts are arranged inside the through holes, and the U-shaped pressing block is connected to the lower U-shaped block-A through bolts.

Images