Fatigue test method and system for mortise and tenon joint

Abstract

The invention discloses a fatigue test method and system for a tenon-and-mortise joint, which are used for the fatigue test of the tenon-and-mortise joint of a tested piece, the fatigue test is carried out by applying a tension-compression cyclic load through a fatigue testing machine, the fatigue testing machine adopts a constant load for cyclic loading, and when the tenon-and-mortise joint has an obvious opening or is pulled out, the tenon-and-mortise joint is pulled out. When the load of the fatigue testing machine is lower than the set constant load, the loading is automatically stopped, and the cycle index at the moment is regarded as the fatigue life of the tested piece at the set load amplitude; testing the deflection angle of the fatigue critical point of the tested piece at the set load amplitude, calculating to obtain the pulling strength of the fatigue critical point, and testing the residual pulling strength of the tested piece; and according to the critical anti-pulling strength and the residual anti-pulling strength, the fatigue of the mortise and tenon joint is judged, and whether the mortise and tenon joint is fatigued or not is obtained. According to the method, furniture fatigue is considered from the perspective of nodes, the fatigue performance of the nodes can be quantitatively represented, meanwhile, the loading mode and conditions are optimized, test materials are saved, and the test cost is reduced.

Description

Technical Field

[0001] The invention relates to the field of fatigue testing of wooden product structures, and in particular to a fatigue testing method and system for mortise and tenon joints. Background Art

[0002] Mortise and tenon joints are a common connection method in structural engineering. In the field of wood product design and manufacturing, fatigue is one of the important considerations. Taking wooden furniture as an example, the mortise and tenon joint is its most critical part. It not only bears the functions of support and connection, but also directly affects the stability and durability of the entire furniture. Furniture fatigue usually manifests as loosening and damage of mortise and tenon joints, rather than node fracture caused by high-intensity loads. In actual use, furniture mortise and tenon joints are subjected to repeated forces and vibrations, which can cause loose connections at the nodes and thus affect the stability of the furniture. However, current research on the evolution of fatigue loosening of mortise and tenon joints is relatively limited.

[0003] Existing research mainly focuses on the testing and analysis of overall furniture and furniture components [Reference 1: ECKELMAN C, HAVIAROVAE. Performance tests of school chairs constructed with round mortise and tenonjoints[J]. Forest Products Journal, 2006, 56(3): 51-57.].

[0004] At the same time, in the traditional furniture design process, the fatigue life of furniture products is usually obtained by fatigue testing a certain amount of test pieces. Although it is a practical method to directly test the fatigue performance of the entire furniture from the perspective of engineering design, it also requires a lot of time and cost. Therefore, in the field of furniture engineering and design, it is necessary to find a convenient and cost-effective method to test the fatigue life of furniture.

[0005] Fatigue testing methods are key factors in conducting experimental tests and determining the reliability of research results and conclusions. There are two main aspects of testing methods for furniture fatigue performance: standards and specifications, and methods proposed in published studies. At present, many countries recognize the importance of furniture fatigue testing and have formulated testing standards and specifications. Comparing these standards, it is found that they all use test equipment driven by pneumatic systems, and the main difference lies in the type of test load and load amplitude. Some standards use constant cyclic loads [Reference 2: Beijing Wood Industry Research Institute, Shanghai Furniture Research Institute. Furniture mechanical properties test: Part 3 Strength and durability of chairs and stools: GB / T10357.3[S]. Beijing: China Standards Press, 2013. Reference 3: Beijing Wood Industry Research Institute, Shanghai Furniture Research Institute. Furniture mechanical properties test Part 1: Strength and durability of tables: GB / T10357.1[S]. Beijing: China Standards Press, 2013.].

[0006] Other standards use the stepped cyclic load proposed by Eckelman [Reference 4: ECKELMAN C A. The use of performance tests and quality assurance programs in the selection of library chairs [J]. Library Technology Reports, 1982, 18 (5): 483-571.] [Reference 5: General Services Administration. Upholstered furniture test method: FNAE80-214A [S]. Washington: Furniture Commodity Center, 1998.], and the tested pieces in all these standards are the furniture as a whole, not the joints. Although some relevant test standards have been developed for furniture fatigue and durability testing, there are few standards or specifications to follow when it comes to the cyclic load performance of furniture joints. Summary of the invention

[0007] Purpose of the invention: In order to solve the problem of characterizing the fatigue performance of mortise and tenon joints, the present invention provides a fatigue testing method for mortise and tenon joints.

[0008] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0009] A fatigue test method for a mortise and tenon joint is used for fatigue testing of a mortise and tenon joint of a test piece, wherein the test piece comprises a mortise hole test piece and a tenon test piece, wherein the mortise hole test piece and the tenon test piece are fixedly connected with each other through a mortise and tenon structure, and the tenon test piece is provided with a tenon end through groove, comprising the following steps:

[0010] Step 1, fixing the mortise hole specimen on a workbench, and fixing the tenon specimen to a fatigue testing machine via a tenon end through groove.

[0011] Step 2, applying a tension-compression cycle load to perform fatigue testing using a fatigue testing machine, wherein the applied tension-compression cycle load includes a vertical upward load F x and vertical downward load -F x Stop loading when the mortise and tenon joints begin to open or pull out.

[0012] Step 3: The fatigue testing machine uses a constant load cycle to load. When the mortise and tenon joints are obviously opened or pulled out, the fatigue testing machine load is lower than the set constant load F. x The loading stops automatically. The number of cycles at this time is regarded as the number of cycles of the tested piece at the load amplitude F. x Fatigue life N Fx .

[0013] Step 4: Take the pull-out strength of the tested piece as an indicator to evaluate its fatigue performance, and use the measured fatigue life as a reference to test the tested piece under load amplitude F. x The deflection angle β at the fatigue critical point x , calculate the critical pull-out strength F at the fatigue critical point c .

[0014] Step 5: Determine the residual pull-out strength F of the test piece h and fatigue life N Fx The residual tensile strength F of the tested piece is measured by the relationship between h .

[0015] Step 6: According to the critical pull-out strength F c and residual tensile strength F h The fatigue of the mortise and tenon joint is judged to determine whether fatigue occurs in the mortise and tenon joint.

[0016] Preferably: in step 6, according to the critical pull-out strength F c and residual tensile strength F h The method for determining fatigue of mortise and tenon joints comprises the following steps:

[0017] Step 61, when the load amplitude is F x , the number of cycles is N FX If the residual tensile strength F hGreater than the tensile strength F of the fatigue critical point c , the test piece is not fatigued.

[0018]

[0019] Among them, F h Represents the residual tensile strength, F c represents the tensile strength at the fatigue critical point, g and i represent the fitting parameters obtained by fitting a small amount of test data, and N Fx Indicates that the load amplitude is F x The number of cycles, F x represents the load amplitude, β x Indicates that the load amplitude is F x The deflection angle of the fatigue critical point.

[0020] Step 62, if the residual tensile strength F h Less than the tensile strength F of the fatigue critical point c , then the test piece will fatigue.

[0021]

[0022] Among them, F h Represents the residual tensile strength, F c represents the tensile strength at the fatigue critical point, g and i represent the fitting parameters obtained by fitting a small amount of test data, and N Fx Indicates that the load amplitude is F x The number of cycles, F x represents the load amplitude, β x Indicates that the load amplitude is F x The deflection angle of the fatigue critical point.

[0023] Preferably: In step 3, the load amplitude F is obtained by the relationship between the load amplitude and the fatigue life. x Fatigue life N Fx , the relationship between load amplitude and fatigue life is obtained by fitting the test data:

[0024] N Fx =k(a+br Fx ), F x ≤S m ,k=1;

[0025] Among them, N Fx Indicates that the load amplitude F x The fatigue life at this time, k represents the coefficient related to the fatigue life, a, b, r all represent the fitting parameters obtained by fitting, F x Indicates the load amplitude, S m Indicates the ultimate strength under cyclic loading.

[0026] Preferably: the formula for the pull-out strength at the fatigue critical point in step 4 is as follows: c

[0027] F c <F mw ;

[0028] Among them, F c Indicates the tensile strength at the fatigue critical point, F x represents the load amplitude, β x Indicates that the load amplitude is F x The deflection angle of the fatigue critical point, F mw Indicates the ultimate pull-out strength.

[0029] Preferred: Residual pull-out strength F in step 5 h and fatigue life N Fx The relationship between them is as follows:

[0030]

[0031] Among them, F h represents the residual tensile strength, g and i represent the fitting parameters obtained by fitting a small amount of test data, and N Fx Indicates that the load amplitude is F x The number of cycles.

[0032] Preferably: In step 4, it is necessary to measure the change in the pull-out strength of the mortise and tenon joint of the test piece before fatigue failure, and perform fatigue testing on the test piece. At this time, the number of cycles of the fatigue test should be lower than the fatigue life N Fx .

[0033] Preferred: Test the test piece at load amplitude F x The deflection angle β at the fatigue critical point x Method: The deflection angle of the fatigue critical point is the deflection angle before the test piece shows obvious fatigue opening or failure. The test is carried out using a mechanical testing machine and the load is controlled. The load direction is vertically downward, and the deflection angle β of the fatigue critical point is measured. x .

[0034] Preferably, during the fatigue test, the test piece is preloaded.

[0035] Another object of the present invention is to provide a fatigue testing system for mortise and tenon joints, which is used to implement the fatigue testing method for mortise and tenon joints, and includes a concave fixture, a conversion joint, a vise fixture, a fatigue testing machine, a pull-out strength determination unit, a residual pull-out strength determination unit, and a fatigue determination unit. The concave fixture is used to fix the mortise hole specimen on a workbench, the concave fixture and the conversion joint are fixed to each other, the vise fixture is used to fix to the tenon end through-slot by a fixing bolt, and the conversion joint is used to be fixedly connected to the fatigue testing machine.

[0036] The fatigue testing machine is used to apply a tension-compression cycle load to perform fatigue testing, wherein the applied tension-compression cycle load includes a vertical upward load F x and vertical downward load -F x Stop loading when the mortise and tenon joints begin to open or pull out.

[0037] The pull-out strength determination unit is used to test the load amplitude F of the tested piece. x The deflection angle β at the fatigue critical point x , calculate the tensile strength F at the fatigue critical point c .

[0038] The residual tensile strength determination unit is used to determine the residual tensile strength of the tested piece by comparing it with the fatigue life N Fx The residual tensile strength F of the tested piece is measured by the relationship between h .

[0039] The fatigue judgment unit is used to determine the critical pull-out strength F c and residual tensile strength F h The fatigue of the mortise and tenon joint is judged to determine whether fatigue occurs in the mortise and tenon joint.

[0040] Another object of the present invention is to provide a computer system, comprising a memory and a processor, wherein the memory is used to store computer programs / instructions, and the processor is used to execute the computer programs / instructions to implement the fatigue testing method for mortise and tenon joints.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention takes the actual use of furniture as the starting point, focuses the fatigue of furniture on the nodes, and tests it through a fatigue testing machine. The fatigue life of the tested piece can be output by the fatigue testing machine, the pull-out strength of the tested piece can be output by the mechanical testing machine, and the judgment criteria of the mortise and tenon nodes are obtained by comparison; at the same time, the tested piece is not limited to the T-shaped elliptical tenon used in the present invention, and other forms of mortise and tenon nodes are also applicable. This fatigue testing method and judgment criteria for mortise and tenon nodes saves test materials, reduces testing costs, improves fatigue testing efficiency to a certain extent, can more comprehensively reflect the furniture fatigue process, and provides a deeper understanding and data support for the design and manufacture of mortise and tenon furniture nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the installation structure of the tested piece of the present invention;

[0044] Figure 2 Force analysis diagram for determining fatigue of mortise and tenon joints;

[0045] Among them, 1-mortise specimen, 2-tenon specimen, 3-tenon end through slot, 4-fixing bolt, 5-concave clamp, 6-conversion joint, 7-vice clamp. DETAILED DESCRIPTION

[0046] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0047] A fatigue test method for mortise and tenon joints is used for fatigue testing of mortise and tenon joints of a test piece, such as Figure 1 As shown, the node form is derived from the force analysis and structural decomposition of wooden furniture, including T-type nodes and L-type nodes. The height of the mortise position is greater than or equal to the length of the tenon specimen. The mortise and tenon joints use through tenons and non-through tenons. The tenon shapes include elliptical, square, and circular. No adhesive is used at the connection between the tenon specimen and the mortise and tenon hole specimen. The tested piece used in this embodiment is a T-type node, and the tested piece includes a tenon hole specimen 1 and a tenon specimen 2. The tenon hole specimen 1 and the tenon specimen 2 are fixedly connected by a mortise and tenon structure. The tenon specimen 2 is provided with a tenon end through groove 3. The shape of the tenon end through groove 3 is U-shaped, square, or circular. The position of the groove is determined according to the test situation. The following steps are included:

[0048] Step 1, fixing the mortise hole specimen 1 on a workbench, and fixing the tenon specimen 2 to a fatigue testing machine via the tenon end through groove 3.

[0049] like Figure 1As shown, one end of the mortise specimen is fixed on the workbench by a vise clamp 7, one end of the tenon specimen is inserted into the mortise, and the other end of the tenon specimen is provided with a through groove 3 for installing a concave clamp 5. There is a circular through hole at each end of the concave clamp for installing a fixing bolt 4. The top of the concave clamp is connected to one end of the conversion interface 6, and the other end of the conversion joint is connected to the fatigue testing machine.

[0050] Take the chair as an example to analyze the stress at the connection between the chair legs, seat and backrest:

[0051] When the seat back is under horizontal load, the chair legs and the chair back are connected by mortise and tenon joints. When the tenon is subjected to horizontal force, static friction will be generated between the tenon and the tenon hole to resist the external horizontal force. The friction is related to its contact surface and positive pressure. The greater the positive pressure, the rougher the contact surface and the greater the friction. When the tensile force exceeds the maximum static friction, the tenon will be pulled out; as the load continues to load, the tenon and the side wall of the tenon hole are squeezed, generating friction and normal stress on both sides. When the load further increases until the yield load is reached, the connection stiffness of the tenon and tenon joint reaches the maximum. After that, the tenon is squeezed by the tenon hole, and the two sides are deformed under pressure. The width of the tenon becomes narrower. According to the interaction of forces, the groove inside the tenon hole is squeezed and expanded by the tenon, the slippage increases, and the node stiffness decreases sharply. If the load continues to load, the tenon will be pulled out due to excessive slippage, resulting in structural damage. Therefore, this embodiment considers the fatigue of furniture from the perspective of nodes, optimizes the loading mode and conditions, saves test materials, reduces test costs, improves fatigue test efficiency to a certain extent, and provides a new way to analyze and evaluate the fatigue performance of mortise and tenon joints.

[0052] The tree species used in the embodiment is beech (Fagus orientalis), the wood is stored in a wood processing laboratory until it reaches an air-dried state, and the tested pieces are processed using CNC equipment, and the interference is determined according to the test objectives and the load range of the testing machine.

[0053] Step 2, applying a tension-compression cycle load to perform fatigue testing using a fatigue testing machine, wherein the applied tension-compression cycle load includes a vertical upward load F x and vertical downward load -F x Stop loading when the mortise and tenon joints begin to open or pull out.

[0054] During the fatigue test, the test pieces under the same working conditions are regarded as the same test pieces. Before the fatigue test, the mechanical testing machine is first used to test the pull-out strength. The force loading direction is vertically upward. The mechanical testing machine uses the displacement control method to load. The loading rate is 5mm / min. The loading is stopped until the tenon specimen is completely pulled out. The pull-out strength limit F of the mortise and tenon joint of the test piece is mwThe output of the mechanical testing machine, in N, is taken after multiple tests and the average value is used as the reference value for the pull-out strength of the specimens in the same batch.

[0055] Before the fatigue test, the tenon and the mortise specimens were assembled to form a T-shaped mortise and tenon joint. One end of the mortise specimen 1 was fixed on the workbench of the fatigue testing machine using a vise clamp 7, and the end of the tenon specimen with the through slot 3 was fixed on the concave clamp 5 and connected to the fatigue testing machine. Then, a tension and compression cyclic load (vertical upward load F x , and the vertical downward load -F x ), the load size is controlled by the air pressure of the fatigue testing machine, and the loading is stopped when the mortise and tenon joint opens or is pulled out; through fatigue testing, the ultimate strength S of the tested piece under cyclic load is recorded m (Cyclic Load Limit) and the load amplitude is F x The number of cycles or fatigue life N Fx .

[0056] The ultimate strength S of the tested piece under cyclic load m (Cyclic load limit) is low cycle fatigue, the load amplitude is F x Fatigue life N Fx It is high cycle fatigue. During the fatigue test, the test piece is preloaded. By applying a certain initial load, the node is in a preloaded state to simulate the stress conditions in actual use. The initial load should not be too large, preferably 20N-50N, and the loading frequency can be selected.

[0057] Step 3: The fatigue testing machine uses a constant load cycle to load. When the mortise and tenon joints are obviously opened or pulled out, the fatigue testing machine load is lower than the set constant load F. x The loading stops automatically. The number of cycles at this time is regarded as the number of cycles of the tested piece at the load amplitude F. x Fatigue life N Fx .

[0058] In step 3, the relationship between load amplitude and fatigue life is used to obtain the load amplitude F x Fatigue life N Fx , the relationship between load amplitude and fatigue life is obtained by fitting the test data:

[0059] N Fx =k(a+br Fx ), F x ≤S m ,k=1;

[0060] Among them, N Fx Indicates that the load amplitude F x The fatigue life at this time, k represents the coefficient related to the fatigue life, a, b, r all represent the fitting parameters obtained by fitting, Fx Indicates the load amplitude, S m Indicates the ultimate strength under cyclic loading.

[0061] Step 4: Take the pull-out strength of the tested piece as an indicator to evaluate its fatigue performance, and use the measured fatigue life as a reference to test the tested piece under load amplitude F. x The deflection angle β at the fatigue critical point x , that is, the deflection angle before the test piece shows obvious fatigue opening or failure. The test is carried out using a mechanical testing machine and the load is controlled. The load direction is vertically downward, and the deflection angle β at the fatigue critical point is measured. x , calculate the tensile strength F at the fatigue critical point c .

[0062] The formula for the pull-out strength at the fatigue critical point is as follows:

[0063] F c <F mw ;

[0064] Among them, F c Indicates the tensile strength at the fatigue critical point, F x represents the load amplitude, β x Deflection angle representing the fatigue critical point, F mw Indicates the ultimate pull-out strength.

[0065] In the embodiment, it is necessary to measure the change in the pull-out strength of the mortise and tenon joint of the tested piece before fatigue failure, and perform fatigue testing on the tested piece. At this time, the number of cycles of the fatigue test should be lower than the fatigue life N Fx .

[0066] N Fx =k(a+br Fx ), F x ≤S m ,0<k<1

[0067] Step 5: Test the residual tensile strength F of the test piece again. h (i.e., the pull-out strength of the tested piece when it has not reached the fatigue life after a certain number of fatigue loadings), and the residual pull-out strength F of the tested piece is obtained by fitting h With load amplitude F x , number of cycles N Fx When used, the residual pull-out strength F of the tested piece h and fatigue life N Fx The residual tensile strength F of the tested piece is measured by the relationship between h .

[0068] Residual tensile strength Fh and fatigue life N Fx The relationship between them is as follows:

[0069]

[0070] Among them, F h represents the residual tensile strength, g and i represent the fitting parameters obtained by fitting the test data, and N Fx Indicates that the load amplitude is F x The number of cycles.

[0071] Step 6: According to the pull-out strength F c and residual tensile strength F h The fatigue of the mortise and tenon joint is judged to determine whether fatigue occurs in the mortise and tenon joint.

[0072] According to the pull-out strength F c and residual tensile strength F h Methods for determining fatigue of mortise and tenon joints, such as Figure 2 As shown, the following steps are included:

[0073] Step 61, when the load amplitude is F x , the number of cycles is N FX If the residual tensile strength F h Greater than the tensile strength F of the fatigue critical point c , the test piece is not fatigued.

[0074]

[0075] Among them, F h Represents the residual tensile strength, F c represents the tensile strength at the fatigue critical point, g and i represent the fitting parameters obtained by fitting the test data, and N Fx Indicates that the load amplitude is F x The number of cycles, F x represents the load amplitude, β x The deflection angle representing the fatigue critical point.

[0076] Step 62, if the residual tensile strength F h Less than the tensile strength F of the fatigue critical point c , then the test piece will fatigue.

[0077]

[0078] Among them, F h Represents the residual tensile strength, F c represents the tensile strength at the fatigue critical point, g and i represent the fitting parameters obtained by fitting the test data, and N FxIndicates that the load amplitude is F x The number of cycles, F x represents the load amplitude, β x The deflection angle representing the fatigue critical point.

[0079] In another embodiment, a fatigue test system for mortise and tenon joints is provided, which is used to implement the fatigue test method for mortise and tenon joints, and includes a concave fixture 5, a conversion joint 6, a vise fixture 7, a fatigue testing machine, a pull-out strength determination unit, a residual pull-out strength determination unit, and a fatigue determination unit. The concave fixture 5 is used to fix the mortise hole specimen 1 on a workbench, the top of the concave fixture 5 and the conversion joint 6 are fixed to each other, and there is a through hole at each end of the bottom of the concave fixture 5 for installing a fixing bolt. The part where the bolt passes through the groove is a threadless connecting rod, and the bolt diameter should be equal to the diameter of the concave fixture through hole. The vise fixture 7 is used to fix with the tenon end through groove 3 through the fixing bolt 4, and the conversion joint 6 is used to be fixedly connected with the fatigue testing machine.

[0080] The fatigue testing machine is used to apply a tension-compression cycle load to perform fatigue testing, wherein the applied tension-compression cycle load includes a vertical upward load F x and vertical downward load -F x Stop loading when the mortise and tenon joints begin to open or pull out.

[0081] The pull-out strength determination unit is used to test the load amplitude F of the tested piece. x The deflection angle β at the fatigue critical point x , calculate the tensile strength F at the fatigue critical point c .

[0082] The residual pull-out strength determination unit is used to determine the residual pull-out strength F of the tested piece. h and fatigue life N Fx The residual tensile strength F of the tested piece is measured by the relationship between h .

[0083] The fatigue judgment unit is used to determine the critical pull-out strength F c and residual tensile strength F h The fatigue of the mortise and tenon joint is judged to determine whether fatigue occurs in the mortise and tenon joint.

[0084] In another embodiment, a computer system is provided, comprising a memory and a processor, wherein the memory is used to store a computer program / instruction, and the processor is used to execute the computer program / instruction to implement the fatigue testing method of the mortise and tenon joint.

[0085] The present invention takes the actual use of furniture as a starting point, focuses the fatigue of furniture on the nodes, and tests it through a fatigue testing machine. The fatigue life of the tested piece can be output through the fatigue testing machine, the pull-out strength of the tested piece can be output through the mechanical testing machine, and the judgment criterion of the mortise and tenon node is obtained through comparison; at the same time, the tested piece is not limited to the T-shaped elliptical tenon used in the present invention, and other forms of mortise and tenon nodes are also applicable.

[0086] The present invention quantitatively characterizes the fatigue performance of nodes through fatigue testing. The present invention considers furniture fatigue from the perspective of nodes, optimizes loading modes and conditions, saves test materials, reduces test costs, improves fatigue test efficiency to a certain extent, and provides a new approach to the analysis and evaluation of fatigue performance of mortise and tenon joints.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fatigue test method for a mortise and tenon joint, used for fatigue testing of a mortise and tenon joint of a test piece, wherein the test piece comprises a mortise hole test piece (1) and a tenon test piece (2), wherein the mortise hole test piece (1) and the tenon test piece (2) are fixedly connected via a mortise and tenon structure, and the tenon test piece (2) is provided with a tenon end through groove (3), characterized in that: The following steps are involved: Step 1, fixing the mortise hole specimen (1) on a workbench, and the tenon specimen (2) is fixedly connected to a fatigue testing machine via a tenon end through groove (3); Step 2, applying a tension-compression cycle load to perform fatigue testing using a fatigue testing machine, wherein the applied tension-compression cycle load includes a vertical upward load F x and vertical downward load -F x ; Stop loading when the mortise and tenon joint opens or is pulled out; Step 3: The fatigue testing machine uses a constant load cycle to load. When the mortise and tenon joints are obviously opened or pulled out, the fatigue testing machine load is lower than the set constant load F. x The loading stops automatically. The number of cycles at this time is regarded as the number of cycles of the tested piece at the load amplitude F. x Fatigue life N Fx ; Step 4: Take the pull-out strength of the tested piece as an indicator to evaluate its fatigue performance, and use the measured fatigue life as a reference to test the tested piece under load amplitude F. x The deflection angle β at the fatigue critical point x , calculate the critical pull-out strength F at the fatigue critical point c ; Step 5: Determine the residual pull-out strength F of the test piece h and fatigue life N Fx The relationship between the residual tensile strength F of the tested piece is measured. h ; Step 6: According to the critical pull-out strength F c and residual tensile strength F h The fatigue of the mortise and tenon joint is judged to determine whether fatigue occurs in the mortise and tenon joint.

2. The fatigue testing method of mortise and tenon joints according to claim 1, characterized in that: In step 6, according to the critical pull-out strength F c and residual tensile strength F h The method for determining fatigue of mortise and tenon joints comprises the following steps: Step 61, when the load amplitude is F x , the number of cycles is N FX If the residual tensile strength F h Greater than the tensile strength F of the fatigue critical point c , then the tested piece is not fatigued; Among them, F h Represents the residual tensile strength, F c represents the tensile strength at the fatigue critical point, g and i represent the fitting parameters obtained by fitting a small amount of test data, and N Fx Indicates that the load amplitude is F x The number of cycles, F x represents the load amplitude, β x Indicates that the load amplitude is F x The deflection angle of the fatigue critical point; Step 62, if the residual tensile strength F h Less than the tensile strength F of the fatigue critical point c , then the tested piece will be fatigued; Among them, F h Represents the residual tensile strength, F c represents the tensile strength at the fatigue critical point, g and i represent the fitting parameters obtained by fitting a small amount of test data, and N Fx Indicates that the load amplitude is F x The number of cycles, F x represents the load amplitude, β x Indicates that the load amplitude is F x The deflection angle of the fatigue critical point.

3. The fatigue testing method of mortise and tenon joints according to claim 2, characterized in that: In step 3, the relationship between load amplitude and fatigue life is used to obtain the load amplitude F x Fatigue life N Fx , the relationship between load amplitude and fatigue life is obtained by fitting the test data: N Fx =k(a+br Fx ),F x ≤S m ,k=1; Among them, N Fx Indicates that the load amplitude F x The fatigue life at this time, k represents the coefficient related to the fatigue life, a, b, r all represent the fitting parameters obtained by fitting, F x Indicates the load amplitude, S m Indicates the ultimate strength under cyclic loading.

4. The fatigue testing method of mortise and tenon joints according to claim 3, characterized in that: The formula for the pull-out strength at the fatigue critical point in step 4 is as follows: Among them, F c Indicates the tensile strength at the fatigue critical point, F x represents the load amplitude, β x Indicates that the load amplitude is F x The deflection angle of the fatigue critical point, F mw Indicates the ultimate pull-out strength.

5. The fatigue testing method of mortise and tenon joints according to claim 4, characterized in that: Residual pull-out strength F in step 5 h and fatigue life N Fx The relationship between is obtained by fitting the experimental data: Among them, F h represents the residual tensile strength, g and i represent the fitting parameters obtained by fitting, and N Fx Indicates that the load amplitude F x Fatigue life at .

6. The fatigue testing method of mortise and tenon joints according to claim 5, characterized in that: In step 4, it is necessary to measure the change in the pull-out strength of the mortise and tenon joint of the test piece before fatigue failure, and perform fatigue testing on the test piece. At this time, the number of cycles of the fatigue test should be lower than the fatigue life N Fx .

7. The fatigue testing method of mortise and tenon joints according to claim 6, characterized in that: Test the test piece at load amplitude F x The deflection angle β at the fatigue critical point x Method: The deflection angle of the fatigue critical point is the deflection angle before the test piece shows obvious fatigue opening or failure. The test is carried out using a mechanical testing machine and the load is controlled. The load direction is vertically downward, and the deflection angle β of the fatigue critical point is measured. x .

8. The fatigue testing method of mortise and tenon joints according to claim 7, characterized in that: During fatigue testing, the test piece is preloaded.

9. A fatigue testing system for mortise and tenon joints, characterized in that: A fatigue test method for a mortise and tenon joint as claimed in any one of claims 1 to 8, comprising a concave fixture (5), a conversion joint (6), a vise fixture (7), a fatigue testing machine, a pull-out strength determination unit, a residual pull-out strength determination unit, and a fatigue determination unit; the concave fixture (5) is used to fix the mortise hole specimen (1) on a workbench, the concave fixture (5) and the conversion joint (6) are fixed to each other, the vise fixture (7) is used to fix to the tenon end through groove (3) via a fixing bolt (4), and the conversion joint (6) is used to be fixedly connected to the fatigue testing machine; The fatigue testing machine is used to apply a tension-compression cycle load to perform fatigue testing, wherein the applied tension-compression cycle load includes a vertical upward load F x and vertical downward load -F x ; Stop loading when the mortise and tenon joint opens or is pulled out; The pull-out strength determination unit is used to test the load amplitude F of the tested piece. x The deflection angle β at the fatigue critical point x , calculate the tensile strength F at the fatigue critical point c ; The residual pull-out strength determination unit is used to determine the residual pull-out strength F of the tested piece. h and fatigue life N Fx The residual tensile strength F of the tested piece is measured by the relationship between h ; The fatigue judgment unit is used to determine the critical pull-out strength F c and residual tensile strength F h The fatigue of the mortise and tenon joint is judged to determine whether fatigue occurs in the mortise and tenon joint.

10. A computer system, characterized in that: It comprises a memory and a processor, wherein the memory is used to store computer programs / instructions; and the processor is used to execute the computer programs / instructions to implement the fatigue testing method for mortise and tenon joints as described in any one of claims 1-8.

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