WO2023109454A1

WO2023109454A1 - Variable-temperature fatigue test device

Info

Publication number: WO2023109454A1
Application number: PCT/CN2022/133972
Authority: WO
Inventors: 尹海山; 仇星文; 行祺程; 郝国强; 晋琦
Original assignee: 青岛科技大学
Priority date: 2021-12-16
Filing date: 2022-11-24
Publication date: 2023-06-22
Also published as: CN114608938A

Abstract

A variable-temperature fatigue test device, relating to the technical field of rubber fatigue testing. A main structure of the device comprises sliding rails (2), an adjusting arm (3), an upper loading shaft (4), a lower loading shaft (5), a clamp (6) and a thermal insulation box (7), wherein the adjusting arm (3) is provided on the sliding rails (2), the adjusting arm (3) is connected to the upper loading shaft (4), the clamp (6) is arranged between the upper loading shaft (4) and the lower loading shaft (5) having a force sensor, the thermal insulation box (7) is provided on an outer side of the clamp (6), the thermal insulation box (7) is internally provided with an infrared heating tube (11) and an imaging mechanism (9), the thermal insulation box (7) is connected to a liquid nitrogen tank (22), a test piece is heated by means of the infrared heating tube (11), and the thermal insulation box (7) is cooled by means of the liquid nitrogen tank (22) to simulate a low-temperature environment, so that an actual working environment of a rubber product is simulated, and a variable-temperature fatigue test under a complex stress state is performed; and the device has a simple and reliable structure, and can record a fatigue process in real time.

Description

A variable temperature fatigue test device

Technical field:

The invention belongs to the technical field of rubber fatigue testing, and relates to a variable temperature fatigue test device, which can perform variable temperature fatigue tests under complex stress states.

Background technique:

As one of the three major polymer materials, rubber plays an indispensable role in aerospace, production and life. Due to the excellent superelastic properties of rubber, its products are often used in harsh environments, resulting in increasingly serious fatigue damage problems of rubber products. , so it is very important to study the fatigue damage mechanism of rubber to improve its service life and safety.

Rubber fatigue testing machine is mainly used to test the physical properties of raw materials, finished products, and semi-finished products. It can be used for tensile testing, compressive testing, and bending testing to obtain elongation, elongation, stress, and strain. The test results and test data can be equipped with different fixtures and accessories to realize the fatigue performance of rubber test pieces of different shapes, and can be connected to the computer to control the machine.

The fixture of the rubber fatigue testing machine in the prior art is a bolt clamping the rubber test piece, often occurs during the test process due to the phenomenon of the test piece sliding due to the loosening of the screw, making the test result inaccurate; and the general test piece is 2mm thick For the dumbbell-shaped test piece, the strain during the test is the strain of the gauge length. However, the general-purpose test piece will inevitably be deformed, and the strain of the gauge length will change accordingly, which will cause errors in the test results. By designing vulcanization with different thicknesses Such errors can be avoided by using molds to obtain new rubber test pieces. Rubber products are usually subject to complex stresses during work, and rubber fatigue testing machines in the prior art can only achieve uniaxial loading in tension or compression. By designing diabolo-shaped rubber columns, fatigue tests under multi-axial loading conditions can be realized. Chinese patent 201910137101.6 discloses a tensile-compression-bending composite fatigue test fixture for round bar specimens, including an upper chuck, an upper load-bearing frame, an upper adapter, a lower adapter, a lower load-bearing frame, a lower chuck, and an adjustment screw ;The middle part of the upper load-bearing frame and the lower load-bearing frame is a cavity, and the lower part is a load-bearing tooth with grooves; the upper part of the upper adapter and the lower adapter is a rectangular block, and the lower part is a cylinder with threaded holes; the upper chuck It is connected with the upper load-bearing frame through threads, and the lower chuck is connected with the lower load-bearing frame through threads; the upper adapter is located in the bottom groove of the upper load-bearing frame, and the lower adapter is located in the bottom groove of the lower load-bearing frame; the round bar test The parts are respectively connected to the upper adapter and the lower adapter through threads; there are two screw holes on the left and right sides of the upper load-bearing frame and the lower load-bearing frame respectively, and the round bar test can be changed by controlling the screw-in depth of the adjustment screws on both sides. The relative position between the center line of the fatigue machine and the axial load of the fatigue machine. When the center line of the round bar test piece does not coincide with the axial load of the fatigue machine, the round bar test piece will bear additional bending loads in addition to the uniaxial load; it can be Fatigue tests with torsion angles, however, are not suitable for fatigue tests on rubber specimens.

Rubber is a temperature-sensitive material, and its mechanical properties will show great differences at different temperatures. Therefore, finding the relationship between temperature and mechanical properties is an important step in the study of its fatigue damage mechanism.

At present, the rubber fatigue testing machine with variable temperature function only changes the ambient temperature of the space where the rubber test piece is located, and then heats the rubber test piece through convective heat exchange. However, most of the rubber products work in a state where their own temperature is relatively high, and the ambient temperature will not be too high, which is far from the actual situation. A small self-controlled temperature fatigue testing machine disclosed in Chinese patent 201710906844.6 includes a test frame and a cylinder installed inside the test frame, a heating furnace, a low-temperature constant temperature bath, a heat-insulating flange, an upper stroke switch, a temperature sensor, and a lower stroke Switches, programmable controllers, three-position five-way solenoid valves, transmission rods, and touch rods; the test frame is a rectangular parallelepiped frame; The reserved opening that runs through the transmission rod is filled with coolant inside; the heating furnace is set above the low-temperature constant temperature bath, and an inlet and an outlet for penetrating the transmission rod are respectively formed on the top surface and the middle of the bottom surface, and the low-temperature constant temperature bath. The openings correspond to the inlet and outlet positions on the heating furnace; one end of the cylinder block on the cylinder is fixed on the top surface of the test frame, the piston rod is located at the lower end, and an air inlet and outlet are formed at the upper and lower ends respectively; the heat insulation flange There is a threaded hole in the center, and two heat-insulating flanges placed in opposite positions are threadedly connected with the lower end of the piston rod and the upper end of the transmission rod through the threaded holes, and the lower end of the transmission rod is used to fix the test piece; above the upper travel switch and the lower travel switch The lower corresponding methods are respectively set on the side of the test frame between the lower end of the cylinder block and the top surface of the electric heating furnace; the temperature sensor is set on the electric heating furnace; the touch rod is set horizontally, one end is fixed on the lower part of the piston rod, and the other end When moving up and down with the piston rod, it can be in contact with the bottom surface of the upper limit switch and the top surface of the lower limit switch; the three-position five-way solenoid valve is set on one side of the cylinder and connected to the air intake pipeline and the air inlet and outlet of the cylinder body Between; the programmable controller is set on the side of the test frame, with a touch screen, and is electrically connected with the heating furnace, the upper travel switch, the temperature sensor, the lower travel switch and the three-position five-way solenoid valve; The furnace realizes ambient heating, and the low-temperature constant temperature bath realizes the low-temperature environment. The two processes are carried out in two devices respectively, which is inconvenient and has a small temperature control range, which cannot meet the actual application conditions.

At the same time, the current general-purpose rubber fatigue testing machine cannot realize the real-time tracking of the crack generation during the test process. The average crack growth rate can only be converted by dividing the crack length by time, and it is impossible to know in which temperature range the crack grows in a fatigue test. The fastest. A rubber fatigue tensile test bench disclosed in Chinese patent 201811432574.0 is composed of three parts: an actuator, a data acquisition system and a control system. Rod, lead screw, slide table base, coupling, servo motor; the left fixture is installed on the force sensor through the fixing bracket and bolts, and the force sensor is installed on the sensor installation column of the overall fixed frame through the bolt; the right fixture is installed on the sensor through the bolt Installed on the sliding table, the middle of the sliding table is processed with a threaded hole, and there is a light hole on both sides of the threaded hole; the sliding table is installed on the support rod and the screw, when the screw rotates, the sliding table can drive the right fixture to move left and right. The screw is connected with the rotating shaft of the servo motor through a coupling; the servo motor is installed on the base of the slide table through its own mounting hole; the base of the slide table is fixed on the overall fixed frame by bolts; the control system includes a data acquisition card, a computer , human-computer interaction interface, PLC control system; the control system controls the speed and direction of the servo motor through the PLC control system, and then controls the left clamp and the right clamp to load the rubber sample; the data acquisition system includes power supply, ART Data acquisition card, circuit amplifier, the circuit amplifier is connected to the force sensor, the ART data acquisition card is connected to the USB through the communication interface; every 2mm crack is observed through the scale, the stop button is pressed and the number of cycles is recorded, and its existence measurement method It is inconvenient and requires the experimenter to observe and track in real time.

Based on the problem that the rubber fatigue test in the prior art cannot truly reflect the complex stress and strain suffered by rubber products, a device that can perform high and low temperature tests on rubber specimens and track crack growth in real time is provided. At the same time, it can Provides a firmer grip on rubber test pieces.

Invention content:

The purpose of the present invention is to overcome the shortcomings of the prior art, and seek to design a variable temperature fatigue test device, which can realize rubber fatigue tests in different temperature ranges, and can record crack growth in real time.

The main structure of a variable temperature fatigue test device involved in the present invention includes a slide rail, an adjustment arm, an upper loading shaft, a lower loading shaft, a fixture and an incubator; A clamp is arranged between the loading shaft and the lower loading shaft with the force sensor, and an incubator is arranged outside the clamp.

The two mutually parallel sliding rails involved in the present invention are arranged on both sides of the base with universal wheels, the lower loading shaft is arranged on the base, the door of the incubator is inlaid with heat-insulating glass, and the inside is provided with an imaging mechanism and The infrared temperature measuring probe has an infrared heating tube on the inner wall, through holes on the top and bottom, and connection holes on the side.

When the variable temperature fatigue test device involved in the present invention is used, the variable temperature fatigue test device is connected to the hydraulic power system and the monitoring system respectively. The hydraulic power system can provide three loading modes: sine wave, triangular wave and square wave. The nitrogen tank is connected, and the low-temperature environment is simulated by feeding liquid nitrogen. The imaging mechanism is connected to the computer through the data acquisition system and the data conversion system. The principle of monitoring the crack extension length, real-time monitoring of the crack extension, the computer controls the imaging mechanism to take pictures when the crack increases by 1mm and uploads to the computer, the computer records the number of cycles and working time, and the infrared temperature measuring probe is connected to the computer through the data conversion system. Monitor the temperature of the test piece in real time, store the temperature change curve of the test piece, connect the infrared heating tube to the computer through the data acquisition system and data conversion system to control the heating temperature of the infrared heating tube, and inlay and fix the test piece on the fixture , load the test piece, the monitoring system records the fatigue process in real time, and feeds back to the computer every time the crack expands by 1mm, and stores the cycle number, running time and temperature at this time. When the test piece breaks, the force sensor monitors the force value The computer stops the test in time, records the number of cycles at this time, and saves the data curves of stress and strain throughout the test process.

The material of the test pieces involved in the present invention is rubber, including dumbbell-shaped test pieces of different thicknesses, diabolo-shaped test pieces and tear test pieces: the length of section A of the dumbbell-shaped test piece is 100mm, the length of section B is 25mm, and the length of section C is 25mm. The length is 20mm, the length of the G section is 80mm, the thickness D of the gauge length part C follows the national standard, which is 2mm, and the thickness of the upper and lower ends is changed from 2mm to 5mm, so as to ensure that only the gauge length part C is deformed during the test to avoid the overall deformation The strain measurement is inaccurate, and the upper and lower ends are cuboid columns; the radius of the thinnest part of the middle cylinder of the diabolo-type test piece is 5.85mm, the side length of the two ends of the cuboid column is 30mm, and the thickness is 15mm; the length of the tear test piece is 140mm, the height is 10mm, the thickness of the middle part is 2mm, and the size of the cuboid columns at both ends is the same as the size of the cuboid columns at both ends of the dumbbell-shaped specimen.

Compared with the prior art, the present invention is equipped with two kinds of fixtures and three kinds of test pieces, and an incubator is set outside the fixture, and an infrared heating tube and an imaging mechanism are arranged inside the incubator, and are connected with a liquid nitrogen tank. The heating tube heats the test piece, and the liquid nitrogen tank cools the incubator to simulate the low temperature environment, thereby simulating the working environment of the actual rubber product, and conducts variable temperature fatigue tests under complex stress states, including tensile tests with torsion angles in the range of -50 to 99°C Tension-compression fatigue test; its structure is simple, the principle is scientific and reliable, and the fatigue process can be recorded in real time, which can avoid the error caused by loose clamping of the specimen and make the strain measurement more accurate.

Description of drawings:

Fig. 1 is a schematic diagram of the principle of the main structure of the present invention.

Fig. 2 is a front view of an incubator related to the present invention.

Fig. 3 is a perspective view of an incubator according to the present invention.

Fig. 4 is a schematic diagram of the main body structure of the first clamp involved in the present invention.

Fig. 5 is a schematic diagram of a partial structure of the first clamp involved in the present invention.

Fig. 6 is a schematic diagram of the main body structure of the second clamp involved in the present invention.

Fig. 7 is a schematic diagram of a partial structure of the second clamp involved in the present invention.

FIG. 8 is a schematic diagram of the main structure of the imaging mechanism involved in the present invention.

Fig. 9 is a schematic diagram of the main structure of the dumbbell-shaped test piece involved in the present invention.

Fig. 10 is a side view of a dumbbell-shaped test piece according to the present invention.

Fig. 11 is a schematic diagram of the main structure of the diabolo-type test piece involved in the present invention.

Fig. 12 is a schematic diagram of the dimensions of the tear test piece involved in the present invention.

Fig. 13 is a schematic diagram of the main structure of the tear test piece involved in the present invention.

Fig. 14 is a schematic diagram of the use state of the present invention.

Fig. 15 is a schematic diagram of the finite element simulation results of the strain energy density of the tear test piece without pre-cracks involved in the present invention.

Detailed ways:

The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings.

Example 1:

The main structure of a variable temperature fatigue test device involved in this embodiment includes a base 1, a slide rail 2, an adjustment arm 3, an upper loading shaft 4, a lower loading shaft 5, a fixture 6, an incubator 7, an insulating glass 8, and an imaging mechanism 9. Infrared temperature measuring probe 10, infrared heating tube 11, through hole 12 and connection hole 13; slide rails 2 are arranged on both sides of base 1 with universal wheels, and adjustment arm 3 is arranged on slide rail 2 to adjust The arm 3 is connected to the upper loading shaft 4, the base 1 is provided with a lower loading shaft 5 with a force sensor, a clamp 6 is provided between the upper loading shaft 4 and the lower loading shaft 5, and an incubator 7 is provided on the outside of the clamp 6 for heat preservation. The door of the box 7 is inlaid with heat-insulating glass 8 with a rectangular structure, an imaging mechanism 9 and an infrared temperature measuring probe 10 are arranged inside, an infrared heating tube 11 is arranged on the inner wall, through holes 12 are opened on the top and bottom, and through holes 12 are opened on the side. Connecting hole 13 is arranged.

The clamp 6 involved in this embodiment includes two structures. The main structure of the first clamp 6 includes a guide rail 101, a No. 1 upper clamp 102, a No. 1 lower clamp 103, a No. 1 front clamp 104, a No. 1 rear clamp 105, Cylindrical slots 106 and bolt holes 107; the upper ends of the two parallel guide rails 101 are provided with a No. 1 upper clamp 102, and the lower end is provided with a No. 1 lower clamp 103. The structure of the No. 1 upper clamp 102 and the No. 1 lower clamp 103 are the same, and the surfaces are uniform. A No. 1 front clamping block 104 and a No. 1 rear clamping block 105 are provided. Both ends of the No. 1 front clamping block 104 are provided with cylindrical grooves 106, and several bolt holes 107 are provided at equal intervals in the middle; The main structure includes the No. 2 upper clamp 201, the upper guide rail 202, the No. 2 lower clamp 203, the lower guide rail 204, the No. 2 front clamp block 205, the No. 2 rear clamp block 206 and the circular hole 207; the No. 2 upper clamp of the circular structure 201 is provided with an upper guide rail 202, and the No. 2 lower clamp 203 of circular structure is provided with a lower guide rail 204. The upper guide rail 202 is connected with the lower guide rail 204. The structure of the No. 2 upper clamp 201 and the No. 2 lower clamp 203 are the same, and the surfaces are uniform. A No. 2 front clamping block 205 and a No. 2 rear clamping block 206 with a flange are provided, and a circular hole 207 is opened between the No. 2 front clamping block 205 and the No. 2 rear clamping block 206 .

The main structure of the imaging mechanism 9 involved in this embodiment includes a CCD industrial high-speed camera 91, an imaging aperture plate 92, a backlight 93 and a light source 94; the CCD industrial high-speed camera 91 and the infrared temperature measuring probe 10 are all embedded in the inner wall of the incubator 7 , the surface is covered with heat insulating material of transparent material to prevent the CCD industrial high-speed camera 91 and the infrared temperature measuring probe 10 from being damaged due to temperature changes. 6 diagonally above.

The upper loading shaft 4 and the lower loading shaft 5 involved in this embodiment are respectively flange-connected to the fixture 6; the No. 1 upper fixture 102, the No. 1 lower fixture 103 and the No. 1 front clamping block 104 are bolted to the No. 1 rear clamping block 105 respectively. Type connection; No. 2 upper clamp 201, No. 2 lower clamp 203 and No. 2 front clamp 205 are respectively connected with No. 2 rear clamp 206 by bolts.

The base 1 involved in this embodiment can be moved, so that the test can be carried out in different places; the adjustment arm 3 can slide up and down along the slide rail 2; Embed in the cylindrical groove 106, fix the dumbbell-shaped test piece by bolts and clamp the dumbbell-shaped test piece back and forth, prevent the No. 1 front clamping block 104 and the No. 1 rear clamping block 105 from moving up and down, and ensure the fixing of the dumbbell-shaped test piece by the first clamp 6 It will not be too tight. During the test, the No. 1 lower fixture 103 reciprocates, and the guide rail 101 is coated with lubricating oil, which can reduce the friction between the guide rail 101 and the No. 1 upper fixture 102 and the No. 1 lower fixture 103; the second fixture 6 For multi-axial fatigue test, by adjusting the position of the lower rail 204 on the No. There is lubricating oil to reduce friction; the through hole 12 is the channel for the upper loading shaft 4 and the lower loading shaft 5 to enter and exit the incubator 7; the diameter of the guide rail 101 is 8mm, and it is used to fix the No. 1 upper clamp 102 and the No. 1 lower clamp 103 , and ensure that the No. 1 lower fixture 103 will not be twisted to avoid test errors; the diameter of the upper guide rail 202 and the lower guide rail 204 is 8mm, which are used to fix the No. 2 upper fixture 201 and the No. 2 lower fixture 203 respectively.

When the variable temperature fatigue test device involved in this embodiment is used, the variable temperature fatigue test device is connected to the hydraulic power system 20 and the monitoring system 21 respectively. The hydraulic power system 20 can provide three loading modes: sine wave, triangular wave and square wave. The connection hole 13 connects the incubator 7 with the liquid nitrogen tank 22, and adopts the method of feeding liquid nitrogen to simulate a low-temperature environment. The imaging mechanism 9 is connected to the computer through the data acquisition system and the data conversion system, and the light source 94 provides light to break the test piece. The gray level of the crack is different from that of the unbroken part. According to the principle of gray scale, the crack extension length is monitored, and the crack extension is monitored in real time. The computer controls the CCD industrial high-speed camera 91 to take pictures when the crack increases by 1mm and upload it to the computer. The computer records the number of cycles and work. Time, connect the infrared temperature measuring probe 10 with the computer through the data conversion system to monitor the temperature of the test piece in real time, store the temperature change curve of the test piece, connect the infrared heating tube 11 to the computer through the data acquisition system and the data conversion system, and Control the heating temperature of the infrared heating tube 11, insert the test piece 23 between the No. 1 upper fixture 102 and the No. 1 lower fixture 103 or between the No. 2 upper fixture 201 and the No. 2 lower fixture 203. 104 is fixed with the No. 1 rear clamp 105 or the No. 2 front clamp 205 is fixed with the No. 2 rear clamp 206, and the specimen 23 is loaded, and the monitoring system 21 records the fatigue process in real time, and feeds back to the Computer, and store the number of cycles, running time and temperature at this time. When the specimen breaks, the force sensor detects a sudden change in the force value, and the computer stops the test in time, and records the number of cycles at this time, and saves the stress and strain of the entire test process. item data graph.

Example 2:

When the variable temperature fatigue test device involved in this embodiment is used, the test piece is heated to the set temperature through the infrared heating tube 11 or after the liquid nitrogen tank 22 is passed into the liquid nitrogen to cool down to the set temperature, at 10-100% The test is carried out under the conditions of strain rate and temperature from -50 to 120°C; the imaging mechanism 9 automatically takes pictures every time a 1mm crack occurs in the test piece according to the gray scale principle, and the monitoring system 21 automatically records the cycle number and working time at this time; the test piece breaks When the force sensor measures the stiffness of the test piece as 0, the computer records the number of cycles and working time at this time, and saves the stress-strain curve of the test process, and according to the formula:

Calculate the crack growth rate, where l is the crack length and N is the number of cycles.

For dumbbell and diabolo specimens:

The strain of the specimen is the same as the displacement of the specimen, and the load under the required strain is measured by the force sensor, and then the stress is calculated by the formula: σ=F/A, where F is the tensile or compressive load, and A is the cross-section of the specimen area;

Then calculate the strain energy density by the formula: dW _SED = σdε, where W _SED is the strain energy density, σ is the stress on the specimen, and ε is the strain of the specimen.

According to the formula: N _f = K(P) ^d , the fatigue life of the rubber is calculated using the strain energy density as the fatigue damage parameter, where Nf is the fatigue life, K, d are the parameters of the rubber material, what are the specific parameters, P is the fatigue damage parameter, The correlation coefficient r ² is used to indicate the closeness of the prediction to the actual result, and the closer the r ² is to 1, the better the prediction effect is.

For tearing specimens to measure tear energy:

Before the test, a crack with a length of 15-20mm is preset at both ends or in the middle of the tearing specimen. During the test, the crack propagation is divided into four stages:

Phase 1:

Phase 2:

Phase 3:

Phase 4:

Among them, da/dN represents the crack growth rate, T ₀ is the threshold tear energy, T _c is the critical tear energy, T _t is the turning tear energy, r is the crack growth rate, and A, B, F are the rubber material fatigue constants , obtained by fitting the measured crack growth rate and tear energy data.

Stage 1 means that the crack does not expand, and the life is infinite; stage 4 means that the crack growth rate is infinite, ignore stage 1 and stage 4, and only consider stage 2 and stage 3.

The measurement of tear energy is the key. Since the tear test piece is a plane tensile style, the tear energy can be calculated by the formula: T=Wh, where W is the strain energy density without pre-cracks, and h is the tear test specimen. The initial height of the part, the calculation formula of strain energy is:

The strain energy density of the tearing specimen without pre-cracks is obtained by finite element simulation, as shown in Figure 15, the strain energy density under different strains can be substituted into the formula: T=Wh to obtain the tear energy.

The dumbbell-shaped test piece, diabolo-shaped test piece and tear test piece involved in this embodiment are prepared from 10g, 35g and 15g of unvulcanized rubber respectively; the installation method of the dumbbell-shaped test piece and the tear test piece is as follows: The upper clamp 102 and the No. 1 lower clamp 103 are bolted to the upper loading shaft 4 and the lower loading shaft 5 respectively, insert one end of the dumbbell-shaped test piece or the tear test piece into the cylindrical groove 106, and install the No. 1 front clamping block 104 , using bolts to connect the No. 1 front clamping block 104 and the No. 1 rear clamping block 105; the installation method of the diabolo-shaped specimen is similar to that of the dumbbell-shaped specimen. The position on the fixture 203 is sufficient; after the first fixture 6 clamps the dumbbell-shaped specimen, the distance between the No. Finally, the distance between the No. 1 upper clamp 102 and the No. 1 lower clamp 103 is 10mm; when the dumbbell-shaped specimen and the tear specimen are tested, the prestress value measured by the force sensor is 200N; the second clamp 6 After tightening the diabolo-type specimen, the distance between No. 2 upper fixture 201 and No. 2 lower fixture 203 is 60mm. When the diabolo-type specimen is tested, the prestress value measured by the force sensor is 0N.

Claims

A variable temperature fatigue test device is characterized in that the main structure includes a slide rail, an adjustment arm, an upper loading shaft, a lower loading shaft, a fixture and an incubator; A clamp is arranged between the loading shaft and the lower loading shaft with the force sensor, and an incubator is arranged outside the clamp.
The variable temperature fatigue test device according to claim 1, characterized in that two mutually parallel slide rails are arranged on both sides of the base with universal wheels, the lower loading shaft is arranged on the base, and on the door of the incubator Inlaid with heat-insulating glass, with an imaging mechanism and an infrared temperature measuring probe inside, an infrared heating tube on the inner wall, through holes on the top and bottom, and connecting holes on the side.
The variable temperature fatigue test device according to claim 1 or 2, wherein the fixture includes two structures, the main structure of the first fixture includes guide rails, No. 1 upper fixture, No. 1 lower fixture, No. 1 front clamping block, The No. 1 rear clamping block, cylindrical groove and bolt hole; the upper end of the two parallel guide rails is provided with a No. 1 upper clamp, and the lower end is provided with a No. 1 lower clamp. The structure of the No. There is a No. 1 front clamping block and a No. 1 rear clamping block. Both ends of the No. 1 front clamping block are provided with cylindrical grooves, and several bolt holes are equally spaced in the middle; the main structure of the second type of clamp includes the No. 2 upper clamp , upper guide rail, No. 2 lower clamp, lower guide rail, No. 2 front clamp block, No. 2 rear clamp block and circular hole; No. 2 upper clamp with circular structure is provided with an upper guide rail, and No. 2 lower clamp with circular structure There is a lower guide rail on the top, and the upper guide rail is connected with the lower guide rail. The structure of the No. 2 upper fixture and the No. 2 lower fixture is the same. The surface is equipped with a No. 2 front clamp block and a No. 2 rear clamp block with a flange. A circular hole is provided between the front clamp block and the No. 2 rear clamp block.
The variable temperature fatigue test device according to claim 3, wherein the main structure of the imaging mechanism includes a CCD industrial high-speed camera, an imaging aperture plate, a backlight and a light source; the CCD industrial high-speed camera and the infrared temperature measuring probe are all embedded in the incubator In the inner wall, the surface is covered with transparent heat insulation material to prevent the CCD industrial high-speed camera and infrared temperature measurement probe from being damaged due to temperature changes. The imaging orifice plate and the backlight are respectively arranged in front and rear of the fixture, and the light source is arranged obliquely above the fixture .
The variable temperature fatigue test device according to claim 3, wherein the upper loading shaft and the lower loading shaft are flange-connected to the fixtures respectively; the No. 1 upper fixture, the No. 1 lower fixture and the No. The rear clamping block is connected by bolts; the No. 2 upper clamp, the No. 2 lower clamp and the No. 2 front clamping block are respectively bolted to the No. 2 rear clamping block.
The variable temperature fatigue test device according to claim 3, wherein the base can move; the adjusting arm can slide up and down along the slide rail; the first fixture is used for uniaxial tensile test, and the cylindrical boundary of the dumbbell-shaped test piece is embedded In the cylindrical groove, the dumbbell-shaped specimen is fixed by bolts and clamped back and forth to prevent the No. 1 front clamp and the No. 1 rear clamp from moving up and down. During the test, the No. 1 lower clamp reciprocates, and the guide rail is coated with lubricating oil. ; The second kind of fixture is used for multi-axis fatigue test. By adjusting the position of the lower guide rail on the No. 2 lower fixture, the tension-compression fatigue test under different torsion angles is realized. Coated with lubricating oil; the through hole is the channel for the upper loading shaft and the lower loading shaft to enter and exit the incubator; the diameter of the guide rail is 8mm, which is used to fix the No. 1 upper clamp and the No. 1 lower clamp, and ensure that the No. 1 lower clamp will not twist ; The diameter of the upper guide rail and the lower guide rail is 8mm, which are used to fix the No. 2 upper fixture and the No. 2 lower fixture respectively.
According to the variable temperature fatigue test device according to claim 1 or 2, it is characterized in that, when in use, the variable temperature fatigue test device is connected to the hydraulic power system and the monitoring system respectively, and the hydraulic power system can provide three kinds of sine wave, triangular wave and square wave Loading method, connect the incubator to the liquid nitrogen tank, simulate the low temperature environment by feeding liquid nitrogen, connect the imaging mechanism to the computer through the data acquisition system and data conversion system, and under the action of light, the fractured and unbroken parts of the specimen According to the gray scale principle, the crack extension length is monitored, and the crack extension is monitored in real time. The computer controls the imaging mechanism to take pictures when the crack increases by 1mm and uploads it to the computer. The infrared temperature measuring probe is connected to the computer to monitor the temperature of the test piece in real time, store the temperature change curve of the test piece, and connect the infrared heating tube to the computer through the data acquisition system and data conversion system to control the heating temperature of the infrared heating tube. The test piece is inlaid and fixed on the fixture, the test piece is loaded, the monitoring system records the fatigue process in real time, and when the crack expands by 1mm, it is fed back to the computer, and the cycle number, running time and temperature at this time are stored, and the test piece breaks When the force sensor detects a sudden change in the force value, the computer stops the test, records the number of cycles at this time, and saves various data curves of stress and strain throughout the test process.
According to the variable temperature fatigue test device according to claim 4, it is characterized in that the variable temperature fatigue test device is connected with the hydraulic power system and the monitoring system respectively, and the hydraulic power system can provide three loading modes of sine wave, triangular wave and square wave. The hole connects the incubator with the liquid nitrogen tank, and the low temperature environment is simulated by introducing liquid nitrogen. The imaging mechanism is connected to the computer through the data acquisition system and the data conversion system. The gray scale is different. According to the gray scale principle, the length of the crack extension is monitored, and the crack expansion is monitored in real time. The computer controls the CCD industrial high-speed camera to take pictures when the crack increases by 1mm and uploads to the computer. The computer records the number of cycles and working time. Through the data conversion system The infrared temperature measuring probe is connected to the computer to monitor the temperature of the test piece in real time, store the temperature change curve of the test piece, and connect the infrared heating tube to the computer through the data acquisition system and data conversion system to control the heating temperature of the infrared heating tube. The specimen is embedded between the No. 1 upper fixture and the No. 1 lower fixture or between the No. 2 upper fixture and the No. 2 lower fixture, and the No. 1 front clamp and the No. 1 rear clamp are fixed by bolts or the No. The clamp block after the number is fixed, and the test piece is loaded. The monitoring system records the fatigue process in real time, and feeds back to the computer every time the crack expands by 1mm, and stores the number of cycles, running time and temperature at this time. When the test piece breaks, the force When the sensor detects a sudden change in the force value, the computer stops the test in time, records the number of cycles at this time, and saves various data curves of stress and strain throughout the test process.
The variable temperature fatigue test device according to claim 7 or 8, wherein the material of the test piece is rubber, including dumbbell-shaped test pieces of different thicknesses, diabolo-shaped test pieces and tear test pieces: The length of section A is 100mm, the length of section B is 25mm, the length of section C is 20mm, and the length of section G is 80mm. The end is a cuboid column; the radius of the thinnest part of the middle cylinder of the diabolo-type test piece is 5.85mm, the side length of the two ends of the cuboid column is 30mm, and the thickness is 15mm; the length of the tear test piece is 140mm, the height is 10mm, and the middle part The thickness is 2 mm, and the size of the two ends of the cuboid column is the same as that of the two ends of the dumbbell-shaped specimen.
The variable temperature fatigue test device according to claim 8, characterized in that, when in use, the test piece is heated to a set temperature by an infrared heating tube or cooled to a set temperature by feeding liquid nitrogen through a liquid nitrogen tank, and then after 10- The test is carried out at a strain rate of 100% and a temperature of -50 to 120°C; the imaging mechanism automatically takes pictures every time a 1mm crack occurs in the test piece according to the gray scale principle, and the monitoring system automatically records the number of cycles and working time at this time; the test piece When breaking, the force sensor measures the stiffness of the specimen as 0, and the computer records the number of cycles and working time at this time, and saves the stress-strain curve during the test to calculate the crack growth rate;

For dumbbell and diabolo specimens:

The strain of the specimen is the same as the displacement of the specimen, the load under the required strain is measured by the force sensor, the strain energy density is calculated after calculating the stress, and then the fatigue life of the rubber is calculated using the strain energy density as the fatigue damage parameter;

For tear test pieces:

Before the test, pre-set cracks with a length of 15-20 mm at both ends or in the middle of the tearing specimen, and calculate the tearing energy; the strain energy density of the tearing specimen without pre-cracking is obtained by finite element simulation. The tear energy is calculated from the strain energy density.