Tensile and Compressive Test Fixture for Bolt-Connected Thin-Walled Plate Parts and Fatigue Test Method

Abstract

The present invention provides a tension-compression test fixture and a fatigue test method for bolt-connected thin-walled plate members. The tension-compression test fixture includes upper and lower clamping arms installed on a tension-torsion fatigue testing machine. The two clamping arms have the same structure and are arranged oppositely in an upper and lower staggered manner. Each clamping arm respectively includes a cross beam, a fastening slider, and a clamping rod. The upper three-jaw chuck of the tension-torsion fatigue testing machine clamps the clamping rod provided on the upper clamping arm; the lower three-jaw chuck of the tension-torsion fatigue testing machine clamps the clamping rod provided on the lower clamping arm. The test fixture provided by the present invention can effectively clamp bolt-connected thin-walled plate members of different specifications, making it difficult for the bolt-connected thin-walled plate members to slip, and ensuring that the bolt-connected thin-walled plate members undergo fatigue fracture in the connection weak area. The fatigue test method provided by the present invention can accurately obtain the load-life curve, and then predict the fatigue life of the specimen to ensure the service safety of the bolt-connected thin-walled plate members, and its simulation effect of the test is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of tensile and compressive test devices, and particularly relates to a tensile and compressive test device and test method for thin-walled metal plates, and more particularly to a tensile and compressive test fixture and fatigue test method for bolt-connected thin-walled plates. Background Art

[0002] To meet the lightweight requirements, nowadays, suspension devices such as rail vehicles and automobiles often use the method of bolt-connecting thin-walled plates to connect and fasten related components. This connection form mainly bears tensile and compressive loads. The fatigue fracture of bolt-connected thin-walled plates is characterized by concealment, suddenness, instantaneity, difficulty in monitoring and prevention. Once fatigue fracture occurs, it may cause serious safety accidents.

[0003] There are many factors affecting the fatigue performance of bolt-connected thin-walled plates and they show a coupling effect with each other, resulting in a very complex stress state and various failure modes. It is very difficult to accurately obtain its stress state by using the traditional nominal stress method and finite element simulation method. Moreover, the crack initiation position is in a closed space and cannot be directly measured. In addition, it is also very difficult to apply tensile and compressive loads to bolt-connected thin-walled plates. Not only problems such as difficult clamping, easy slipping, and easy deformation need to be overcome, but also the bolt clamping force needs to be collected in real time to ensure that the bolt-connected thin-walled plates fatigue fracture in the connection weak area. Due to these technical problems not being solved yet, there is an urgent need for a tensile and compressive fatigue test fixture and fatigue test method for bolt-connected thin-walled plates. Summary of the Invention

[0004] The first object of the present invention is to provide a tensile and compressive test fixture and fatigue test method for bolt-connected thin-walled plates. The tensile and compressive test fixture includes upper and lower clamping arms installed on a tensile-torsional fatigue testing machine. The structures of the two clamping arms are the same and they are relatively arranged in an upper and lower staggered manner. Each clamping arm respectively includes a cross beam, a fastening slider, and a clamping rod. The upper three-jaw chuck of the tensile-torsional fatigue testing machine clamps the clamping rod arranged on the upper clamping arm; the lower three-jaw chuck of the tensile-torsional fatigue testing machine clamps the clamping rod arranged on the lower clamping arm. The test fixture proposed by the present invention can effectively clamp bolt-connected thin-walled plates of different specifications, making the bolt-connected thin-walled plates not easy to slip, and can ensure that the bolt-connected thin-walled plates fatigue fracture in the connection weak area. The fatigue test method proposed by the present invention can accurately obtain the load-life curve, and then predict the fatigue life of the specimen to ensure the service safety of the bolt-connected thin-walled plates, and its test simulation effect is good.

[0005] The technical problems of the present invention are solved by adopting the following technical solutions:

[0006] A tensile and compressive test fixture for bolt - connecting thin - walled plate parts, comprising a pair of clamping arms installed on a torsional fatigue testing machine. The pair of clamping arms refers to the upper and lower clamping arms. The structures of the two clamping arms are the same and they are arranged relatively in an upper - lower staggered manner. Each clamping arm respectively includes a cross - beam, fastening sliders, and clamping rods. The upper three - jaw chuck of the torsional fatigue testing machine clamps the clamping rod arranged on the upper clamping arm; the lower three - jaw chuck of the torsional fatigue testing machine clamps the clamping rod arranged on the lower clamping arm.

[0007] The clamping rod is fixedly connected to the cross - beam. There are two fastening sliders, and both of the two fastening sliders are connected to the left and right sides of the end of the cross - beam far from the clamping rod. The cross - beam and the two fastening sliders form a portal - shaped structure.

[0008] On each fastening slider, a fastening groove and a number of threaded through - holes are provided. A set screw is threadedly connected in the threaded through - hole. The fastening groove is opened on the opposite side of the two fastening sliders and penetrates the front and rear sides of the fastening slider. The threaded through - hole is opened at the end of the fastening slider far from the cross - beam and communicates with the fastening groove.

[0009] A tensile and compressive test specimen assembly is connected between the upper and lower clamping arms. The tensile and compressive test specimen assembly includes a connecting bolt and a gasket, a pressure sensor, a cap - shaped clamped part, a strip - shaped clamped part, and a connecting nut that are sequentially sleeved on the connecting bolt. Through - holes adapted to the connecting bolt are opened at the central parts of the strip - shaped clamped part, the cap - shaped clamped part, the gasket, and the pressure sensor. After the gasket, the pressure sensor, the cap - shaped clamped part, and the strip - shaped clamped part are sequentially sleeved on the connecting bolt, the cap - shaped clamped part and the strip - shaped clamped part overlap each other to form a cross - shape.

[0010] Further, the strip - shaped clamped part has a linear structure, and the cap - shaped clamped part is bent from a linear thin - walled plate part into a "concave" - shaped structure with high ends and a low middle. The connecting nut is used to press the strip - shaped clamped part, the cap - shaped clamped part, and the pressure sensor tightly on the connecting bolt with a set pre - tightening force; the two ends of the cap - shaped clamped part are respectively inserted and pressed into the fastening grooves opened on the two fastening sliders of the upper clamping arm; the two ends of the strip - shaped clamped part are respectively inserted and pressed into the fastening grooves opened on the two fastening sliders of the lower clamping arm.

[0011] Preferably, the cross - beam and the two fastening sliders are detachably connected. A plurality of chutes penetrating the upper and lower surfaces of the cross - beam are opened on the cross - beam. Positioning bolts are used to pass through the chutes to connect and fix the fastening sliders on the cross - beam. The chute is a strip - shaped groove, and a positioning bolt is inserted into each chute.

[0012] More preferably, the chute is a stepped counterbore groove with a larger upper part and a smaller lower part, and the bolt head of the positioning bolt can sink into the chute; a number of threaded through - holes are evenly opened on the wall of the fastening groove, and a set screw is screwed into each threaded through - hole. The number of threaded through - holes and set screws is set according to the length of the fastening groove.

[0013] Further, two fastening sliders are slidably connected to the left and right sides of the beam at the end far from the clamping rod. At the connection between the beam and the fastening slider, there are also provided an induction groove and a sliding table in sliding fit. The cross-sectional shapes of the induction groove and the sliding table are rectangular, trapezoidal or dovetail-shaped, and the sliding directions of the induction groove and the sliding groove are the same. When the distance between the two fastening sliders on the beam slides to an appropriate distance, a positioning bolt is used to pass through the sliding groove to connect and fix the fastening slider to the beam.

[0014] Furthermore, a controller and a portable dynamic acquisition instrument are also provided, and the controller, the portable dynamic acquisition instrument and the pressure sensor are electrically connected;

[0015] The induction groove is arranged on the beam, and the sliding table is arranged on the fastening slider; or, the induction groove is arranged on the fastening slider, and the sliding table is arranged on the beam.

[0016] A fatigue test method for bolt-connected thin-walled plate parts proposed by the present invention uses the above-mentioned tensile and compressive test fixture for bolt-connected thin-walled plate parts for testing, and includes the following steps:

[0017] Step S100: The thin-walled plate part to be tested is made into a strip-shaped clamped part and a cap-shaped clamped part. A gasket, a pressure sensor, a cap-shaped clamped part and a strip-shaped clamped part are sequentially sleeved on the connecting bolt, and the cap-shaped clamped part and the strip-shaped clamped part overlap each other in a cross shape. A connecting nut is used to press the strip-shaped clamped part, the cap-shaped clamped part and the pressure sensor on the connecting bolt with a set pre-tightening force to form a tensile and compressive test piece assembly;

[0018] Step S200: Adjust the distance between the two fastening sliders through the sliding groove to be adapted to the tensile and compressive test piece assembly, and then press and fix the fastening slider on the beam through the positioning bolt; install the tensile and compressive test piece assembly on the upper and lower clamping arms, and insert and press the two ends of the cap-shaped clamped part into the fastening grooves opened on the two fastening sliders on the upper clamping arm respectively through the set screws; insert and press the two ends of the strip-shaped clamped part into the fastening grooves opened on the two fastening sliders on the lower clamping arm respectively.

[0019] Step S300: Adjust the distance between the upper three-jaw chuck and the lower three-jaw chuck of the tensile and torsional fatigue testing machine so that the upper three-jaw chuck of the tensile and torsional fatigue testing machine clamps the clamping rod arranged on the upper clamping arm; make the lower three-jaw chuck of the tensile and torsional fatigue testing machine clamp the clamping rod arranged on the lower clamping arm; electrically connect the pressure sensor with the portable dynamic acquisition instrument and the controller.

[0020] Step S400: Turn on the tension-torsion fatigue testing machine, apply tensile and compressive loads to the upper and lower clamping rods in a sine wave pattern. Select connection bolts of various specifications to pass through the corresponding strip-shaped clamped parts and cap-shaped clamped parts respectively. Different specifications of connection bolts correspond to different pre-tightening forces. Divide the specimens formed by passing each specification of connection bolt through the strip-shaped clamped part and the cap-shaped clamped part into multiple test groups. The amplitudes of the tensile and compressive loads borne by each test group are different. Each test group includes multiple specimens of the same specification and conducts tensile and compressive load tests respectively. When the strip-shaped clamped part or the cap-shaped clamped part in the specimen breaks, the number of vibrations of the tension-torsion fatigue testing machine is used as the fatigue life of the specimen, and the fatigue life is collected and statistically analyzed by a dynamic data collector. The clamping force applied by the connection nut to the strip-shaped clamped part and the cap-shaped clamped part is collected by a pressure sensor. Record the fatigue life and clamping force when each specimen in each test group breaks.

[0021] Step S500: According to the fatigue life data and clamping force data of the number of vibrations when each specimen breaks collected in Step S400, draw a typical clamping force decay curve. The typical clamping force decay curve takes the clamping force as the vertical coordinate and the number of vibrations of the fatigue life as the horizontal coordinate.

[0022] Step S600: Take the load amplitude F a as the vertical coordinate and the fatigue life N as the horizontal coordinate. Based on the least squares method, fit the data points in a double logarithmic coordinate system and draw the F a -N curve.

[0023] Step S700: Apply the two-fold life scatter band method to evaluate the quality of F a -N. If the data points fall within the two-fold life scatter band, it is considered that the correlation of the load-life (F a -N) prediction curve is strong, otherwise it is considered that the correlation is weak.

[0024] Further, in Step S400, the various specifications of connection bolts include connection bolts of specifications M6, M8, M10, and M12. Among them, the pre-tightening force corresponding to the connection bolt of specification M6 is 4 kN; the pre-tightening force corresponding to the connection bolt of specification M8 is 5 kN; the pre-tightening force corresponding to the connection bolt of specification M10 is 5.8 kN; the pre-tightening force corresponding to the connection bolt of specification M12 is 6.6 kN.

[0025] Furthermore, in Step S600, the F a -N curve is obtained from the following equation:

[0026] log(F a ) = klog(N) + b

[0027] In the formula: k is the slope of the F a -N curve, and b is the Fa -Intercept of the N curve;

[0028] After subjecting multiple sets of tensile-compressive specimen assemblies to tensile-compressive fatigue tests, the obtained F a -N curves are fitted, and the fitted data is compared with the calculation results of the equation log(F a ) = klog(N) + b respectively to obtain the square of the correlation coefficient of the F a -N curve equation.

[0029] In the above fatigue test method for bolt-connected thin-walled plate parts, in step S700, if the square of the correlation coefficient of the F a -N curve equation is greater than 0.8, it indicates a good correlation between the load amplitude F a and the fatigue life N; if it is lower than 0.8, it indicates a poor correlation.

[0030] The beneficial effects of the present invention adopting the above technical solutions are as follows:

[0031] A tensile-compressive test fixture for bolt-connected thin-walled plate parts proposed by the present invention clamps the clamped part through the set screws uniformly arranged in the fastening groove, making the clamped part not easy to displace during the test; by using the method of the sliding groove and the positioning bolt to connect the fastening slider and the cross beam, it can be applied to the tests of various different specifications of clamped parts.

[0032] Through the production of the hat-shaped clamped part and the setting of the relative positions of the two fixtures, a cross-shaped gap is left between the four fastening sliders of the two clamping arms, which is convenient for realizing the steps of first adjusting the distance between the cross beam and the fastening slider during installation, then clamping the clamped part with the fastening groove, and finally tightening the connecting bolts, ensuring convenient test operation and easy installation.

[0033] The test fixture proposed by the present invention can effectively clamp bolt-connected thin-walled plate parts of different specifications for testing, making the bolt-connected thin-walled plate parts not easy to slip, and ensuring that the bolt-connected thin-walled plate parts have fatigue fractures in the connection weak areas. The fatigue test method proposed by the present invention can accurately obtain the load-life (F a -N) curve of bolt-connected thin-walled plate parts, and then predict the fatigue life of the specimen to ensure the service safety of bolt-connected thin-walled plate parts. The simulation effect of the test is good. It can accurately predict the fatigue life of bolt-connected thin-walled plate parts, form a complete set of bolt-connected thin-walled plate part life prediction methods, and can be used to guide the operation and maintenance monitoring of bolt-connected thin-walled plate parts such as rail vehicles and automobiles, so as to improve the vehicle load-bearing performance and ensure safe operation. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of a tensile-compressive fixture for thin-walled bolt connections of the present invention;

[0035] Figure 2 Schematic structural diagram of the bar-shaped clamped part connected to the tension-compression test piece assembly and the second clamping arm;

[0036] Figure 3 Schematic structural diagram of the hat-shaped clamped part connected to the tension-compression test piece assembly and the first clamping arm;

[0037] Figure 4 Schematic structural diagram of the fastening slider;

[0038] Figure 5 Schematic structural diagram of the connection between the fastening slider and the cross beam;

[0039] Figure 6 Schematic structural diagram of the cross beam;

[0040] Figure 7 Schematic structural diagram of the connection between the tension-compression test piece assembly and the clamped part;

[0041] Figure 8 Typical clamping force decay curve of thin-walled bolt connection under tension-compression load in Test Example 1;

[0042] Figure 9 F of bolt connection of each test object group under tension-compression load in Test Example 1 a -N curve.

[0043] Reference numerals: 1-cross beam, 2-fastening slider, 21-fastening groove, 22-sliding table, 23-positioning bolt, 24-set screw, 3-chute, 4-tension-compression test piece assembly, 41-bar-shaped clamped part, 42-hat-shaped clamped part, 43-connecting bolt, 44-gasket, 45-pressure sensor, 5-clamping rod, 6-inducing groove. Detailed implementation manners

[0044] The following further describes the detailed implementation manners of the present invention with reference to the accompanying drawings:

[0045] Embodiment

[0046] As Figures 1-7 shown, the present invention provides a tension-compression test fixture for bolt connection of thin-walled plates, including a pair of clamping arms installed on a torsional fatigue testing machine. The pair of clamping arms refers to the upper and lower clamping arms. The structures of the two clamping arms are the same and are arranged relatively in an up-and-down staggered manner. As Figure 1 shown, each clamping arm respectively includes a cross beam 1, a fastening slider 2, and a clamping rod 5.

[0047] The upper three-jaw chuck of the torsional fatigue testing machine clamps the clamping rod 5 provided on the upper clamping arm; the lower three-jaw chuck of the torsional fatigue testing machine clamps the clamping rod 5 provided on the lower clamping arm.

[0048] Taking the upper clamping arm as an example, the specific structure of the clamping arm will be described below.

[0049] The clamping rod 5 is fixedly connected to the center of the upper surface of the cross beam 1, and the clamping rod 5 is perpendicular to the upper surface of the cross beam 1. There are two fastening sliders 2, and the two fastening sliders 2 are both connected to the lower surface of the cross beam 1 and are respectively arranged on the left and right sides of the lower surface of the cross beam 1. The cross beam 1 and the two fastening sliders 2 form a portal structure. The cross beam 1 and the two fastening sliders 2 are detachably connected. Specifically, a plurality of chutes 3 penetrating the upper and lower surfaces of the cross beam 1 are opened on the cross beam 1, and positioning bolts 23 are used to pass through the chutes 3 to connect and fix the fastening sliders 2 to the cross beam 1. The chute 3 is a strip-shaped groove, and the chute 3 is preferably a stepped counterbore groove with a larger upper part and a smaller lower part, so that the bolt head of the positioning bolt 23 can be sunk into the chute 3. In this embodiment, four chutes 3 and four positioning bolts 23 are provided on each cross beam 1.

[0050] A fastening groove 21 and a number of threaded through holes are opened on each fastening slider 2, and set screws 24 are threadedly connected in the threaded through holes. As Figures 1 to 4 shown, the fastening groove 21 is opened on one side of the two fastening sliders 2 facing each other, and penetrates the front and rear sides of the fastening slider 2. The threaded through holes are opened at one end of the fastening slider 2 away from the cross beam 1 and extend into the fastening groove 21. That is: one end of the threaded through hole communicates with the fastening groove 21, and the other end communicates with the end face of the fastening slider 2 away from the cross beam 1.

[0051] As Figures 1 to 3 shown, a tension-compression specimen assembly 4 is connected between the upper and lower clamping arms.

[0052] As Figure 7 shown, the tension-compression specimen assembly 4 includes a connecting bolt 43 and a gasket 44, a pressure sensor 45, a cap-shaped clamped part 42, a strip-shaped clamped part 41 and a connecting nut sequentially sleeved on the connecting bolt 43. Through holes adapted to the connecting bolt 43 are opened in the central parts of the strip-shaped clamped part 41, the cap-shaped clamped part 42, the gasket 44 and the pressure sensor 45. When the gasket 44, the pressure sensor 45, the cap-shaped clamped part 42 and the strip-shaped clamped part 41 are sequentially sleeved on the connecting bolt 43, the cap-shaped clamped part 42 and the strip-shaped clamped part 41 overlap each other to form a cross shape. In this embodiment, the strip-shaped clamped part 41 has a linear structure, and the cap-shaped clamped part 42 is formed by bending a linear thin-walled plate into a "concave" shape with higher ends and a lower middle part. Specifically, the middle part of the linear thin-walled plate can be pressed into a trapezoid. Through holes adapted to the connecting bolt 43 are opened in the middle parts of the strip-shaped clamped part 41 and the cap-shaped clamped part 42. A connecting nut is used to press the strip-shaped clamped part 41, the cap-shaped clamped part 42 and the pressure sensor 45 against the connecting bolt 43 with a set pre-tightening force.

[0053] AsFigures 1 to 3 As shown, the two ends of the hat-shaped clamped part 42 are respectively inserted and pressed into the fastening grooves 21 opened on the two fastening sliders 2 of the upper clamping arm; the two ends of the strip-shaped clamped part 41 are respectively inserted and pressed into the fastening grooves 21 opened on the two fastening sliders 2 of the lower clamping arm. To make the pressing performance more reliable, a number of threaded through holes are evenly opened on the groove wall of the fastening groove 21, and a set screw 24 is screwed into each threaded through hole. The number of threaded through holes and set screws 24 is set according to the length of the fastening groove 21. In this embodiment, fourteen threaded through holes are opened on each fastening slider 2. Of course, other numbers of threaded through holes can also be opened, such as ten to eighteen.

[0054] In addition, to expand the range of test samples that this fixture can test, the distance between the two fastening sliders 2 connected to the cross beam 1 can also be set to be adjustable. The two fastening sliders 2 are slidably connected to the lower surface of the cross beam 1. Specifically, at the connection between the cross beam 1 and the fastening slider 2, there are also an induction groove 6 and a sliding table 22 that are slidably matched. For example, the induction groove 6 is arranged on the cross beam 1, and the sliding table 22 is arranged on the fastening slider 2; of course, the induction groove 6 can also be arranged on the fastening slider 2, and the sliding table 22 is arranged on the cross beam 1. The cross-sectional shapes of the induction groove 6 and the sliding table 22 can be rectangular, trapezoidal or dovetail-shaped. The slidable direction of the induction groove 6 is the same as that of the sliding groove 3. When the distance between the two fastening sliders 2 on the cross beam 1 slides to an appropriate distance, a positioning bolt 23 is used to pass through the sliding groove 3 to connect and fix the fastening slider 2 to the cross beam 1.

[0055] Furthermore, a controller and a portable dynamic data collector are also provided. The controller, the portable dynamic data collector and the pressure sensor 45 are electrically connected. The pressure sensor 45 transmits the collected data to the portable dynamic data collector for screening and recording, and then transmits it to the controller for calculation and analysis.

[0056] On the other hand, the present invention also provides a fatigue test method for bolt-connected thin-walled plate parts. The tensile and compressive test fixture for bolt-connected thin-walled plate parts proposed in the above-mentioned embodiment of the present application is used for the test. The fatigue test method specifically includes the following steps:

[0057] Step S100: Fabricate the thin-walled plate to be tested into a strip-shaped clamped part 41 and a hat-shaped clamped part 42. The strip-shaped clamped part 41 has a linear structure, and the hat-shaped clamped part 42 is formed by bending a linear plate into a "concave" shape with both ends high and the middle low. Through holes adapted to the connecting bolts 43 are provided at the central parts of both the strip-shaped clamped part 41 and the hat-shaped clamped part 42. The gasket 44, the pressure sensor 45, the hat-shaped clamped part 42, and the strip-shaped clamped part 41 are successively sleeved on the connecting bolt 43, and the hat-shaped clamped part 42 and the strip-shaped clamped part 41 overlap each other to form a cross shape. Use a connecting nut to press the strip-shaped clamped part 41, the hat-shaped clamped part 42, and the pressure sensor 45 onto the connecting bolt 43 with a set pre-tightening force to form a tension-compression test piece assembly 4;

[0058] Step S200: Adjust the distance between the two fastening sliders 2 through the chute 3 to make it adapted to the tension-compression test piece assembly 4, and then press and fix the fastening slider 2 on the cross beam 1 through the positioning bolt 23; Install the tension-compression test piece assembly 4 on the upper and lower clamping arms. Insert and press the two ends of the hat-shaped clamped part 42 into the fastening grooves 21 provided on the two fastening sliders 2 of the upper clamping arm through the set screws 24 respectively; Insert and press the two ends of the strip-shaped clamped part 41 into the fastening grooves 21 provided on the two fastening sliders 2 of the lower clamping arm respectively;

[0059] Step S300: Adjust the distance between the upper three-jaw chuck and the lower three-jaw chuck of the tension-torsion fatigue testing machine so that the upper three-jaw chuck of the tension-torsion fatigue testing machine clamps the clamping rod 5 provided on the upper clamping arm; Make the lower three-jaw chuck of the tension-torsion fatigue testing machine clamp the clamping rod 5 provided on the lower clamping arm; Electrically connect the pressure sensor 45 to a portable dynamic data collector and a controller;

[0060] Step S400: Start the tension-torsion fatigue testing machine, apply tension-compression loads to the upper and lower clamping rods 5 in a sine wave pattern. Select various specifications of connecting bolts 43 to pass through the corresponding strip-shaped clamped part 41 and hat-shaped clamped part 42 respectively. Different specifications of connecting bolts correspond to different pre-tightening forces; Divide the test pieces formed by passing each specification of connecting bolt 43 through the strip-shaped clamped part 41 and the hat-shaped clamped part 42 into multiple test groups. The amplitude of the tension-compression loads borne by each test group is different. Each test group includes multiple test pieces of the same specification and conducts tension-compression load tests respectively. When the strip-shaped clamped part 41 or the hat-shaped clamped part 42 in the test piece breaks, the number of vibrations of the tension-torsion fatigue testing machine is used as the fatigue life of the test piece. The fatigue life is collected and statistically analyzed by the dynamic data collector; The clamping force applied by the connecting nut to the strip-shaped clamped part 41 and the hat-shaped clamped part 42 is collected through the pressure sensor 45; Record the fatigue life and the clamping force when each test piece in each test group breaks;

[0061] Step S500: According to the fatigue life data and clamping force data of the vibration times at the fracture of each specimen collected in Step S400, plot a typical clamping force decay curve, where the typical clamping force decay curve has the clamping force as the ordinate and the vibration times of the fatigue life as the abscissa;

[0062] Step S600: With the load amplitude F a as the ordinate and the fatigue life N as the abscissa, fit the data points based on the least squares method in a double logarithmic coordinate system and plot the F a -N curve. The F a -N curve is obtained from the following equation:

[0063] log(F a ) = klog(N) + b

[0064] where: k is the slope of the F a -N curve, and b is the intercept of the F a -N curve;

[0065] Step S700: Apply the double life scatter band method to evaluate the quality of F a -N. If the data points fall within the double life scatter band, it is considered that the correlation of the load-life (F a -N) prediction curve is strong, otherwise it is considered that the correlation is weak.

[0066] Furthermore, in Step S400, the various specifications of connecting bolts include connecting bolts with specifications of M6, M8, M10, and M12; among them, the pre-tightening force F P corresponding to the M6 connecting bolt is 4 kN; the pre-tightening force F P corresponding to the M8 connecting bolt is 5 kN; the pre-tightening force F P corresponding to the M10 connecting bolt is 5.8 kN; the pre-tightening force F P corresponding to the M12 connecting bolt is 6.6 kN;

[0067] Furthermore, in Step S700, if the square of the correlation coefficient (R a ) of the F 2 -N curve equation is greater than 0.8, it indicates that the correlation between the load amplitude F a and the fatigue life N is good; if it is lower than 0.8, it indicates that the correlation is not good.

[0068] Test Example

[0069] Test Equipment: MTS 809 Pull-Torsion Fatigue Testing Machine

[0070] EVT-14T3-10T Pressure Sensor

[0071] DH5983 Portable Dynamic Data Collector

[0072] The test object of the PLC programmable controller: the tensile-compressive specimen assembly 4, and the specifications and quantities of the tensile-compressive specimen assembly are as follows:

[0073] 1. Tensile-compressive specimen assemblies with M6 connecting bolts, prepare three groups, with four to six pieces in each group;

[0074] 2. Tensile-compressive specimen assemblies with M8 connecting bolts, prepare three groups, with four to six pieces in each group;

[0075] 3. Tensile-compressive specimen assemblies with M10 connecting bolts, prepare four groups, with four to six pieces in each group;

[0076] 4. Tensile-compressive specimen assemblies with M12 connecting bolts, prepare four groups, with four to six pieces in each group;

[0077] For the above-mentioned tensile-compressive specimen assemblies, the thicknesses of the strip-shaped clamped part 41 and the cap-shaped clamped part 42 are both 2 mm;

[0078] The specific specifications of the tensile-compressive specimen assembly 4 to be tested are shown in Table 1:

[0079] Table 1 Specification Parameters of Tensile-Compressive Specimen Assembly

[0080]

[0081] Where: t1 is the plate thickness of the strip-shaped clamped part 41; t2 is the plate thickness of the cap-shaped clamped part 42.

[0082] The through-hole diameter of the clamped part refers to the aperture of the through-holes respectively opened at the central parts of the strip-shaped clamped part 41, the cap-shaped clamped part 42, the gasket 44 and the pressure sensor 45.

[0083] The pre-tightening force and load parameters of the tensile-compressive specimen assembly 4 for each group of tests are shown in Table 2:

[0084] Table 2 Pre-tightening Force and Load Parameters of Tensile-Compressive Specimen Assembly

[0085]

[0086]

[0087] According to steps S400 and S500 in the fatigue test method for bolt-connected thin-walled plate parts provided by the embodiment, fatigue life data of the vibration times when each specimen breaks and clamping force test data are collected, and a typical clamping force decay curve is plotted. Using the fracture of the strip-shaped clamped part 41 or the cap-shaped clamped part 42 in the specimen as the fatigue failure criterion, the vibration times of the tension-torsion fatigue testing machine are used as the fatigue life of the specimen. The typical clamping force decay curve has the clamping force as the ordinate and the vibration times of the fatigue life as the abscissa. The typical clamping force decay curves of each test object under tensile and compressive loads obtained through the test are as Figure 8 shown. It can be seen from Figure 8 that in the initial stage, the strip-shaped clamped part 41 and the cap-shaped clamped part 42 sleeved on the connecting bolt 43 are closely attached under the action of the tensile and compressive loads, and the clamping force of the connecting bolt 43 also rapidly increases under the action of the axial load. Then it is in a stable clamping state until the strip-shaped clamped part 41 or the cap-shaped clamped part 42 finally undergoes fatigue fracture.

[0088] According to steps S600 and S700 in the fatigue test method for bolt-connected thin-walled plate parts provided by the embodiment, an F a -N curve is plotted. The fatigue test results of all bolt connections under the tensile and compressive load modes are distinguished according to the specifications of the connecting bolts. With the load amplitude F a as the ordinate and the fatigue life N as the abscissa, the data points are fitted based on the least squares method in the double logarithmic coordinate system to obtain the F a -N curve under the tensile and compressive loads. The F a -N curves of each tensile and compressive specimen assembly under the tensile and compressive load tests are specifically as Figure 9 shown. The double-life dispersion band method is used to evaluate the quality of F a -N. If the data points fall within the double-life dispersion band, it is considered that the correlation of the load-life (F a -N) prediction curve is strong, otherwise it is considered that the correlation is weak.

[0089] As Figure 9 shown, all the data points of each test object under the tensile and compressive loads fall within the 2-fold life dispersion band, indicating that the correlation of the load-life (F a -N) prediction curve is strong.

[0090] Furthermore, according to step S700 in the fatigue test method for bolt-connected thin-walled plate parts provided by the embodiment, if the square of the correlation coefficient (R a ) of the F 2 -N curve equation is greater than 0.8, it indicates that the correlation between the load amplitude F a and the fatigue life N is good, and if it is lower than 0.8, it indicates that the correlation is not good.

[0091] After the four groups of tension-compression specimen assemblies in this test example were subjected to tension-compression fatigue tests, the obtained F a -N curves were fitted, and the fitted data were respectively compared with the calculation results of the curve equation log(F a ) = klog(N) + b, and the square of the correlation coefficient R a of the F 2 -N curve equation was obtained, as shown in Table 3 specifically:

[0092] Table 3 Correlation Coefficient of Curve Equation after Tension-Compression Fatigue Test of Each Group of Specimens

[0093] Type <![CDATA[F a -N curve]]> <![CDATA[R 2 > M6 <![CDATA[log(F a ) = -0.31364 log(N) + 4.9593]]> 0.9258 M8 <![CDATA[log(F a ) = -0.27206 log(N) + 4.7817]]> 0.9647 M10 <![CDATA[log(F a ) = -0.27016 log(N) + 4.8431]]> 0.9045 M12 <![CDATA[log(F a ) = -0.2815 log(N) + 4.9338]]> 0.9422

[0094] As shown in Table 3, the square of the correlation coefficient (R a ) of the F 2 -N curve equation of each group of specimens is greater than 0.9, indicating that the correlation between the load amplitude F a and the fatigue life N is good, proving that the tension-compression fatigue test method for bolt-connected thin-walled plate parts proposed in this application can accurately obtain the F a -N curve to predict the fatigue life of thin-walled bolt connection structures such as rail vehicles and automobiles under tension-compression loads.

[0095] Although the specific embodiments of the present invention have been described in detail with reference to the accompanying drawings, it should not be construed as a limitation on the protection scope of the present invention. Within the scope described in the claims, various modifications and deformations that can be made by those skilled in the art without creative labor still fall within the protection scope of this patent.

Claims

1. A tensile and compressive test fixture for bolt-connected thin-walled plate members, comprising a pair of clamping arms mounted on a tensile and torsional fatigue testing machine. The pair of clamping arms refers to the upper and lower clamping arms. The structures of the two clamping arms are the same and they are arranged relatively in an up-and-down staggered manner. It is characterized in that: Each clamping arm respectively includes a cross beam (1), a fastening slider (2) and a clamping rod (5). The upper three-jaw chuck of the tension-torsion fatigue testing machine clamps the clamping rod (5) provided on the upper clamping arm; the lower three-jaw chuck of the tension-torsion fatigue testing machine clamps the clamping rod (5) provided on the lower clamping arm. The clamping rod (5) is fixedly connected to the cross beam (1). There are two fastening sliders (2). Both of the two fastening sliders (2) are connected to the left and right sides of the end of the cross beam (1) far from the clamping rod (5). The cross beam (1) and the two fastening sliders (2) form a portal structure. A fastening groove (21) and a number of threaded through holes are formed in each fastening slider (2). A set screw (24) is threadedly connected in the threaded through hole. The fastening groove (21) is formed on the opposite side of the two fastening sliders (2) and penetrates the front and rear sides of the fastening slider (2). The threaded through hole is formed at the end of the fastening slider (2) far from the cross beam (1) and communicates with the fastening groove (21). A tension-compression specimen assembly (4) is connected between the upper and lower clamping arms. The tension-compression specimen assembly (4) includes a connecting bolt (43) and a gasket (44), a pressure sensor (45), a cap-shaped clamped part (42), a strip-shaped clamped part (41) and a connecting nut that are sequentially sleeved on the connecting bolt (43). Through holes adapted to the connecting bolt (43) are formed in the central parts of the strip-shaped clamped part (41), the cap-shaped clamped part (42), the gasket (44) and the pressure sensor (45). After the gasket (44), the pressure sensor (45), the cap-shaped clamped part (42) and the strip-shaped clamped part (41) are sequentially sleeved on the connecting bolt (43), the cap-shaped clamped part (42) and the strip-shaped clamped part (41) overlap each other in a cross shape. The strip-shaped clamped part (41) has a linear structure. The cap-shaped clamped part (42) is formed by bending a linear thin-walled plate into a "concave" shape with high ends and a low middle. The connecting nut is used to press the strip-shaped clamped part (41), the cap-shaped clamped part (42) and the pressure sensor (45) tightly on the connecting bolt (43) with a set pre-tightening force; the two ends of the cap-shaped clamped part (42) are respectively inserted and pressed into the fastening grooves (21) formed in the two fastening sliders (2) of the upper clamping arm; the two ends of the strip-shaped clamped part (41) are respectively inserted and pressed into the fastening grooves (21) formed in the two fastening sliders (2) of the lower clamping arm.

2. The tensile and compressive test fixture for bolt - connecting thin - walled plate parts according to claim 1, characterized in that: The cross beam (1) is detachably connected to the two fastening sliders (2). A plurality of chutes (3) penetrating the upper and lower surfaces of the cross beam (1) are formed in the cross beam (1). The positioning bolt (23) is used to pass through the chute (3) to connect and fix the fastening slider (2) to the cross beam (1). The chute (3) is a strip-shaped groove, and a positioning bolt (23) is inserted into each chute (3).

3. The tensile and compressive test fixture for bolt - connecting thin - walled plate parts according to claim 2, characterized in that: The chute (3) is a stepped counterbore groove with a larger upper part and a smaller lower part; a number of threaded through holes are evenly formed in the groove wall of the fastening groove (21), and a set screw (24) is screwed into each threaded through hole. The number of the threaded through holes and the set screws (24) is set according to the length of the fastening groove (21).

4. The tensile and compressive test fixture for bolt-connected thin-walled plate parts according to claim 2, characterized in that: Two fastening sliders (2) are slidably connected to the left and right sides of the end of the cross beam (1) far from the clamping rod (5). At the connection between the cross beam (1) and the fastening slider (2), there are also slidingly matched guiding grooves (6) and sliding platforms (22). The cross-sectional shapes of the guiding grooves (6) and the sliding platforms (22) are rectangular, trapezoidal or dovetail-shaped, and the sliding directions of the guiding grooves (6) and the sliding grooves (3) are the same. When the distance between the two fastening sliders (2) sliding on the cross beam (1) reaches an appropriate distance, a positioning bolt (23) is used to pass through the sliding groove (3) to connect and fix the fastening slider (2) to the cross beam (1).

5. The tensile and compressive test fixture for bolt-connected thin-walled plate parts according to claim 4, characterized in that: A controller and a portable dynamic collector are also provided, and the controller, the portable dynamic collector and the pressure sensor (45) are electrically connected; The guiding groove (6) is arranged on the cross beam (1), and the sliding platform (22) is arranged on the fastening slider (2); or, the guiding groove (6) is arranged on the fastening slider (2), and the sliding platform (22) is arranged on the cross beam (1).

6. A fatigue test method for bolt-connected thin-walled plate parts, using the tensile and compressive test fixture for bolt-connected thin-walled plate parts according to any one of claims 1 to 5 for the test, including the following steps: Step S100: The thin-walled plate part to be tested is made into a strip-shaped clamped part (41) and a cap-shaped clamped part (42). The gasket (44), the pressure sensor (45), the cap-shaped clamped part (42) and the strip-shaped clamped part (41) are sequentially sleeved on the connecting bolt (43), and the cap-shaped clamped part (42) and the strip-shaped clamped part (41) overlap each other in a cross shape. A connecting nut is used to press the strip-shaped clamped part (41), the cap-shaped clamped part (42) and the pressure sensor (45) onto the connecting bolt (43) with a set pre-tightening force to form a tensile and compressive test piece assembly (4); Step S200: Adjust the distance between the two fastening sliders (2) through the sliding groove (3) to be adapted to the tensile and compressive test piece assembly (4), and then press and fix the fastening slider (2) on the cross beam (1) through the positioning bolt (23); Install the tensile and compressive test piece assembly (4) on the upper and lower clamping arms, and insert and press the two ends of the cap-shaped clamped part (42) into the fastening grooves (21) opened on the two fastening sliders (2) located on the upper clamping arm through the set screws (24); Insert and press the two ends of the strip-shaped clamped part (41) into the fastening grooves (21) opened on the two fastening sliders (2) located on the lower clamping arm; Step S300: Adjust the distance between the upper three-jaw chuck and the lower three-jaw chuck of the tensile and torsional fatigue testing machine, so that the upper three-jaw chuck of the tensile and torsional fatigue testing machine clamps the clamping rod (5) arranged on the upper clamping arm; Make the lower three-jaw chuck of the tensile and torsional fatigue testing machine clamp the clamping rod (5) arranged on the lower clamping arm; Electrically connect the pressure sensor (45) to the portable dynamic collector and the controller; Step S400: Turn on the tension-torsion fatigue testing machine, apply tensile and compressive loads to the upper and lower clamping bars (5) in a sine wave pattern. Select various specifications of connecting bolts (43) to pass through the corresponding strip-shaped clamped parts (41) and cap-shaped clamped parts (42) respectively. Different specifications of connecting bolts correspond to different pre-tightening forces. Divide the specimens formed by passing each specification of connecting bolt (43) through the strip-shaped clamped part (41) and the cap-shaped clamped part (42) into multiple test groups. The amplitudes of the tensile and compressive loads borne by each test group are different. Each test group includes multiple specimens of the same specification and conducts tensile and compressive load tests respectively. When the strip-shaped clamped part (41) or the cap-shaped clamped part (42) in the specimen fractures, the number of vibrations of the tension-torsion fatigue testing machine is used as the fatigue life of the specimen, and the fatigue life is collected and statistically analyzed by a dynamic data collector. The clamping force applied by the connecting nut to the strip-shaped clamped part (41) and the cap-shaped clamped part (42) is collected by a pressure sensor (45). Record the fatigue life and clamping force when each specimen in each test group fractures. Step S500: According to the fatigue life data and clamping force data of the number of vibrations when each specimen fractures collected in Step S400, draw a typical clamping force decay curve. The typical clamping force decay curve has the clamping force as the ordinate and the number of vibrations of the fatigue life as the abscissa. Step S600: Using the load amplitude F a as the ordinate and the fatigue life N as the abscissa, perform load-life fitting on the data points based on the least squares method in a double logarithmic coordinate system, and plot the F a -N curve; Step S700: Evaluate the advantages and disadvantages of F a -N using the double life scatter band method. If the data points fall within the double life scatter band, it is considered that the correlation of the load-life F a -N prediction curve is strong; otherwise, the correlation is considered weak.

7. The fatigue test method for bolt connecting thin-walled plate parts according to claim 6, characterized in that: In Step S400, the various specifications of connecting bolts include connecting bolts with specifications of M6, M8, M10, and M12. Among them, the pre-tightening force corresponding to the connecting bolt with a specification of M6 is 4 kN; the pre-tightening force corresponding to the connecting bolt with a specification of M8 is 5 kN; the pre-tightening force corresponding to the connecting bolt with a specification of M10 is 5.8 kN; the pre-tightening force corresponding to the connecting bolt with a specification of M12 is 6.6 kN.

8. The fatigue test method for bolt-connected thin-walled plate members according to claim 6, characterized in that: In step S600, the F a -N curve is obtained from the following equation: log(F a ) = k log(N) + b Where: k is the slope of the F a -N curve, and b is the intercept of the F a -N curve; After subjecting multiple sets of tensile-compressive specimen assemblies to tensile-compressive fatigue tests, the obtained F a -N curves are fitted, and the fitted data is compared with the calculation results of the equation log(F a ) = klog(N) + b respectively, to obtain the square of the correlation coefficient of the F a -N curve equation.

9. The fatigue test method for bolt connection of thin-walled plate members according to claim 8, characterized in that: In step S700, F a - If the square of the correlation coefficient of the N curve equation is greater than 0.8, it indicates that the correlation between the load amplitude F a and the fatigue life N is good; if it is lower than 0.8, it indicates that the correlation is poor.

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