CN110646281A

CN110646281A - Tensile testing machine suitable for low cycle fatigue test

Info

Publication number: CN110646281A
Application number: CN201910850066.2A
Authority: CN
Inventors: 湛永钟; 吴泊良; 杨文超
Original assignee: Guangxi University
Current assignee: Guangxi University
Priority date: 2019-09-10
Filing date: 2019-09-10
Publication date: 2020-01-03
Anticipated expiration: 2039-09-10
Also published as: CN110646281B

Abstract

The invention discloses a tensile testing machine, in particular to a tensile testing machine suitable for low cycle fatigue tests, which comprises a frame and a spring tension cylinder, wherein a swinging universal floating joint is fixedly arranged at the top of the frame and is coaxially connected with a tension sensor; the first group of clamping mechanisms are coaxially connected with the spring tension cylinder, the second group of clamping mechanisms are connected with the swinging universal floating joint, and a corrosion system is arranged between the two groups of clamping mechanisms; the ball screw lifter is arranged at the bottom of the rack and is coaxially connected with the spring tension cylinder; the servo driving motor is arranged at the bottom of the rack and is in transmission connection with the ball screw lifter; and the servo motor control assembly is respectively connected with the swinging universal floating joint and the servo driving motor. The invention has simple structure, low manufacturing cost and stable tension-time curve.

Description

Tensile testing machine suitable for low cycle fatigue test

Technical Field

The invention relates to a tensile testing machine, in particular to a tensile testing machine suitable for a low-cycle fatigue test.

Background

The tensile testing machine is the most commonly used equipment for testing basic mechanical performance parameters of the material, such as yield strength, tensile strength, elongation, elastic modulus and the like. It can be divided into two types, gear (or screw) and hydraulic drive. The gear drive control system is simple, the stretching speed is usually within the range of 0.001-500 mm/min, and the gear drive control system is suitable for quasi-static stretching. The hydraulic drive control system is more complex, the operation cost is higher, but the stretching speed range is larger, and the application range is wider. The general stretcher generally adopts a vertical structure, has a large volume, and needs to design a specific stretching test device according to test conditions and requirements on some in-situ test occasions.

A horizontal small-sized drawing machine is a common in-situ tensile testing machine, and is generally powered by a servo motor, and after speed change, a sliding seat which is arranged on a linear guide rail and clamps a sample is driven by a ball screw to realize tensile displacement feeding. However, due to the influence of the rigidity of the rack, the displacement of the sliding seat cannot truly reflect the deformation of the sample, the rigidity of the rack is not corrected, the requirement of the method A (namely a strain rate control method) of B/T228.1-2010 is difficult to meet, and the requirement of the method A cannot be met on testing machines of most domestic manufacturers due to the difficulty in correcting the rigidity of the rack.

In addition, due to the problem of frame stiffness correction and the problem of the PID control technology level, it is difficult to ensure that the tension-time is in a stable linear relationship by using the B/T228.1-2010 method B (i.e., the stress rate control method). The low-cycle stress fatigue test, particularly the low-cycle stress corrosion fatigue test, has strict requirements on tension-time, so that many common tensile testing machines do not meet the use requirements. Although some high-end tensile testing machines (e.g., Instron universal materials testing machines) can meet the requirements of low cycle (below 1 Hz) corrosion fatigue testing, the cost of using these devices is high. The test time of a single sample for the low-cycle corrosion fatigue test is as long as 1 week, and in some cases, even one or two months, the test cost is a factor which has to be considered.

Disclosure of Invention

The invention aims to provide a tensile testing machine suitable for low-cycle fatigue tests, aiming at the defects of the prior art.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

a tensile testing machine suitable for low cycle fatigue tests comprises a frame, wherein a swinging universal floating joint is fixedly arranged at the top of the frame; a spring tension drum; the two groups of clamping mechanisms comprise a first group of clamping mechanisms and a second group of clamping mechanisms; the first group of clamping mechanisms are coaxially connected with the spring tension cylinder, and the second group of clamping mechanisms are connected with the swinging universal floating joint; an etching system mounted between the first and second sets of clamping mechanisms; the ball screw lifter is arranged at the bottom of the rack and is coaxially connected with the spring tension cylinder; the servo driving motor is arranged at the bottom of the rack and is in transmission connection with the ball screw lifter; and the servo motor control assembly is respectively connected with the swinging universal floating joint and the servo driving motor.

The working mode of the invention is as follows:

the servo driving motor is used as a power source, and the ball screw lifter is used as a stretching power source;

the two ends of the sample are correspondingly and fixedly connected with the clamping mechanisms, namely the lower end of the sample is fixedly connected with the first group of clamping mechanisms, and the upper end of the sample is fixedly connected with the second clamping mechanism;

the power supply is switched on, the servo motor control assembly and the servo drive motor are electrified, and then the low-cycle fatigue tensile test can be carried out;

the servo motor control assembly controls the servo driving motor to start, the servo driving motor drives the ball screw lifter to work, the ball screw lifter drives the spring tension cylinder to work, and the spring tension cylinder realizes low-cycle tensile fatigue test on the sample fixedly connected with the first group of clamping mechanisms

The servo motor control assembly can control the tensile testing machine of the invention to continuously stretch at a constant speed and also can stretch at variable speed. And the steel wire can be repeatedly and circularly stretched according to a set tension-time curve in a certain tension interval to perform a fatigue test.

In the test process, the servo motor control assembly can display the numerical value of the tensile force and record various test data.

As a further improvement of the invention, the servo motor control assembly comprises a tension sensor, a servo driver, a tension display controller and a PLC, wherein the tension sensor is positioned on the top surface of the rack and is coaxially connected with the swinging universal floating joint; the servo driver is connected with the servo driving motor; the tension display controller is connected with the tension sensor; the PLC is respectively and correspondingly electrically connected with the servo driver and the tension display controller.

The specific working mode of the servo motor control assembly is as follows:

the sample transmits the tensile force to the universal floating joint of swing, tension sensor measures the tensile force that the universal floating joint of swing received, tension sensor converts the tensile force behind the signal of telecommunication, and carry the signal of telecommunication to the tension display controller, show corresponding tensile force value on the tension display controller, at some specific tensile force value (like tensile force upper limit and lower limit value) output control signal, the tension display controller is with signal transfer PLC, PLC is according to the signal of conveying to servo driver transfer control command, servo driver is according to the rotation of control command control servo drive motor. The servo driving motor drives the ball screw lifter to work, the ball screw lifter drives the spring tension cylinder to work, and the spring tension cylinder drives the sample to stretch.

The PLC program controls the servo drive motor through the servo driver to realize continuous uniform speed or variable speed, and the ball screw lifter in transmission connection with the servo drive motor further realizes corresponding continuous uniform speed stretching or variable speed stretching; moreover, the PLC controls the servo drive motor through the servo driver, and then the servo drive motor drives the ball screw lifter to perform reciprocating circular stretching in a certain tension interval; therefore, the tensile fatigue test of the sample under the action of different tensile forces is realized. Thus, the sample's draw rate was controlled by the PLC.

The tension sensor outputs signals to the tension display controller, the tension display controller can display tension values and also can set certain specific tension values (such as upper tension limit and lower tension limit) to output control signals, the tension display controller is connected with the PLC, the PLC controls the servo driver, and the servo driver is connected with the servo motor. The motion of the servo motor can be controlled through PLC programming, so that stress-time curves of the sample, such as triangular waves, T-shaped waves, sin curves and the like, are controlled, and the aim of fatigue tensile test is fulfilled. If the tension display controller and the PLC transmit signals between 10-100 KN of tension to realize a tension-time T-shaped wave control mode: when the pulling force is equal to or lower than 10KN, a signal is transmitted to the PLC by the pulling force display controller; and when the pull force is higher than or equal to 100KN, the pull force display controller transmits another corresponding signal to the PLC. The PLC sends start/stop commands to the servo driver according to the two signals. And when the tensile force is lower than 10KN, the device runs in the positive direction, stops for 30 seconds after the tensile force is pulled up to 10KN, and then starts to run in the positive direction again. Stopping for 30 seconds after reaching 100KN, then running reversely, stopping for 30 seconds when reducing to 10KN, and then running forwards; thereby realizing the operation back between 10KN and 100 KN. The velocity profile side is controlled by a PLC and a servo driver. The periodic tension-time curve control of triangular waves, sin waves and the like can also be realized through PLC programming.

The PLC that this scheme used can use domestic simple and easy PLC, and domestic simple and easy PLC replaces can realize pulling force-time T shape ripples, triangle ripples control, nevertheless will realize sin ripples control then needs the more comprehensive PLC of function. The PLC used in the scheme and the action control of each device connected with the PLC belong to mature single chip microcomputer technology, can be easily purchased from the market, and can be used after simple debugging.

As a further improvement of the invention, the servo driving motor comprises a speed reducer and a servo motor, the speed reducer and the servo motor are both fixedly arranged at the bottom of the rack, and the servo motor is in transmission connection with the speed reducer; the speed reducer is in transmission connection with the ball screw lifter; the servo motor drives the speed reducer to rotate, and the speed reducer drives the screw rolling rod lifter to work.

As a modification of the present invention, the tensile testing machine of the present invention further includes an etching system, which is installed between the first and second sets of clamping mechanisms. The corrosion system provides a corrosive environment for the specimens used for the tensile test. The corrosion system comprises a container and a solution, wherein the container is used for placing the solution, and the solution can be a mixed solution of Cl- (chloride ion) and acetic acid. The test data are collected by an experimental method of an electrochemical workstation.

As a further improvement of the invention, the spring tension cylinder comprises a pull cylinder, a nut joint and a telescopic member, one end of the telescopic member is accommodated in the pull cylinder, and the other end of the telescopic member extends out of the pull cylinder and is fixedly connected with the nut joint.

The spring tension cylinder is coaxially connected with a main shaft of the ball screw lifter, and the telescopic component extends or contracts in the tension cylinder under the driving action of the ball screw lifter. When the telescopic component is in extension, the telescopic component has downward tension on the pull cylinder, the pull cylinder has downward tension on a clamping mechanism connected with the pull cylinder, and the clamping mechanism is connected with one end of a sample, so that the clamping mechanism has downward tension on the sample, and the tensile test of the sample is realized.

As a further improvement of the invention, the telescopic component comprises an upper pressure plate, an elastic element group, a pull cylinder sealing plate and a pull rod, wherein the pull rod sequentially penetrates through the pull cylinder sealing plate and the elastic element group and then is fixedly connected with the upper pressure plate through threads; the pull cylinder sealing plate is fixedly connected with the pull cylinder, and the pull cylinder sealing plate is fixedly connected with the pull cylinder. The pull cylinder sealing plate is connected with the pull cylinder for further limitation, and the pull cylinder is prevented from being separated from the pull cylinder in the sliding process.

As a further improvement of the invention, the elastic element group is a belleville spring group, and comprises an even number of belleville springs, 4, 6 or 8 pieces of belleville springs can be selected, and the like. The elastic element group can be selected according to the size and the deformation of the tensile sample; the sample is small, the required tension is small, and involution combination can be adopted; the sample is large, and the required tension is large, and the superposition combination can be adopted. The deformation of the sample is large, more spring combinations are used, and under the same tension, the deformation of the spring group is increased to offset the influence of the deformation of the workpiece on the elastic tension. The end surfaces of the belleville springs are flat and can be compactly stacked and installed; the small deformation high bearing capacity, the space saving, and the ideal loading characteristic can be obtained through different matching combinations.

As a further improvement of the invention, the upper pressure plate is provided with a shock-absorbing member. The shock absorbing member may be rubber or a spring. The direct rigid contact between the upper pressure plate and the top of the pull cylinder can be avoided, so that noise is easily generated, and the equipment is easily damaged.

As a further improvement of the invention, a height-adjusting cylinder is arranged between the upper pressure plate and the elastic element group. The height-adjusting cylinder can enable the length of the pull rod in the pull cylinder to be lengthened, and the distance between the pull rod and the ball screw lifter is shortened, so that the integral downward moving distance of the pull rod is shortened in the tensile test. The height-adjusting cylinder can also improve the coaxiality between the pull rod and the pull cylinder.

As a further improvement of the present invention, the clamping mechanism includes,

an ER collet;

an insulating nut inserted into the ER collet;

the insulating washer is attached to the insulating nut;

the ER collet chuck is used for supporting the insulating washer and attaching the insulating washer to the insulating nut; and

and the chuck nut is sleeved on the ER collet chuck and is fixedly connected with the ER collet chuck through threads.

When the clamping mechanism clamps the sample, the sample and the clamping mechanism have high coaxiality, and the accuracy of data obtained by a tensile test is ensured.

As a further improvement of the invention, the clamping mechanism is fixedly connected with the swinging universal floating joint through a connecting screw rod in a threaded manner. The connecting screw rod is used as the intermediate connection between the clamping mechanism and the swinging universal floating joint, so that the clamping mechanism can be conveniently installed on the swinging universal floating joint, and meanwhile, the equipment can be conveniently disassembled after the tensile test is finished.

As a further improvement of the invention, the two ends of the connecting screw rod are provided with thread sections, and the middle of the connecting screw rod is provided with a fixing nut. The nut that connecting screw middle part was equipped with can conveniently be connected connecting screw swivelling joint in swing universal joint of floating. The connecting screw rod is in threaded connection with the clamping mechanism and the swinging universal floating joint, and the obtained connecting structure is stable and the threaded connection has a self-locking function. The stability of the connecting structure is greatly improved.

As a further improvement of the invention, the frame comprises a top part, a bottom part and a vertical column, and the vertical column is installed between the top part and the bottom part. The frame is the unified installation of other parts, provides the supporting role for these parts.

Compared with the prior art, the invention has the substantive characteristics and the progress that:

1. the tensile testing machine is suitable for low-cycle corrosion fatigue tests, and has the advantages of simple structure, low manufacturing cost and stable tensile force-time curve.

2. The servo motor is connected with the servo driver, the tension sensor is connected with the tension display controller, and the servo driver and the tension display controller are respectively and correspondingly electrically connected with the PLC; during operation, the tensile force that the tensile force sensor measured the sample and received, and the tensile force sensor signal is through the conversion back, shows on pulling force display controller, sends PLC to simultaneously, PLC control servo motor's operation. The PLC can control the stretcher to continuously stretch at a constant speed and can also stretch at variable speed. And the steel can be repeatedly and circularly stretched in a certain tension interval to carry out a corrosion fatigue test. The stretching rate is controlled by a PLC. Thereby making the pull-time curve stable and controllable.

3. The invention adopts the ball screw lifter, and can accurately control and adjust the lifting or propelling height.

4. The invention adopts the spring tension cylinder which comprises the telescopic component and the pull cylinder, the telescopic component is accommodated in the pull cylinder, the telescopic component stretches and slides in the pull cylinder, the damping part is arranged at one end of the telescopic component, which is positioned at the pull cylinder, and the elastic component group is arranged at the other end of the telescopic component, so that the telescopic component has a buffering effect when contacting with the two ends of the pull cylinder when sliding in the pull cylinder, thereby avoiding direct rigid connection, playing a role of protecting equipment and prolonging the service life of the equipment.

5. The invention adopts a clamping mechanism which comprises an ER chuck; an insulating nut inserted into the ER collet; the insulating washer is attached to the insulating nut; the ER collet chuck is used for supporting the insulating washer and attaching the insulating washer to the insulating nut; and the chuck nut is sleeved on the ER collet chuck and is fixedly connected with the ER collet chuck through threads. When the clamping mechanism clamps the sample, the sample and the clamping mechanism have high coaxiality, and the accuracy of data obtained by a tensile test is ensured.

Drawings

In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.

FIG. 1 is a schematic structural diagram of a tensile testing machine suitable for low cycle corrosion fatigue testing according to the present invention;

FIG. 2 is a schematic perspective view of the present invention;

FIG. 3 is a schematic perspective view of the frame;

FIG. 4 is a schematic cross-sectional view of the spring tension drum;

FIG. 5 is an exploded view of the spring pull cartridge;

FIG. 6 is an exploded view of the telescoping member;

FIG. 7 is a schematic view of the assembly structure of the telescopic member;

FIG. 8 is a schematic structural view of the upper and lower press plates;

FIG. 9 is an exploded view of the clamping mechanism;

FIG. 10 is an exploded view of the connection between the clamping mechanism, the connecting screw, and the swinging gimbal floating joint;

FIG. 11 is a schematic view showing a connection structure of a clamping mechanism, a sample, a swinging universal floating joint and a connecting screw;

FIG. 12 is a schematic view of the structure of a sample

FIG. 13 is a schematic cross-sectional view of the connection between the oscillating gimbal floating joint, the connecting screw, the clamping mechanism and the test specimen;

FIG. 14 is a schematic structural view of an unmounted elastic element group;

FIG. 15 is a schematic structural view of an elastic element set with 4 disc springs;

FIG. 16 is a schematic view of the structure of the elastic element set with 6 disc-shaped springs;

FIG. 17 is a schematic diagram of the structure of signal transmission of the servo motor control assembly;

FIG. 18 is a schematic diagram of the relationship between the draw force and the feed stroke of the stretcher;

FIG. 19 is a schematic diagram showing the square difference of the three measured tensile values without the elastic element set;

FIG. 20 is a graph showing the relationship between the tension and the feeding stroke obtained by loading and unloading the elastic element set provided with 4 disc springs

FIG. 21 is a graph showing the loading and unloading of a set of resilient elements having 6 belleville springs installed;

FIG. 22 is a graphical representation of the results of a linear fit of the tension curve for three mounting modes;

FIG. 23 is a graphical representation of the 882N-8820N low cycle tensile corrosion fatigue test open circuit potential versus time curve;

element names and serial numbers in the drawings: the device comprises a frame 1, a bottom 101, a vertical column 102, a top 103, a ball screw lifter 2, a servo motor 3, a spring tension cylinder 4, a nut joint 401, a pull rod 402, a pull cylinder sealing plate 403, an elastic element group 404, a lower pressing plate 405, an heightening cylinder 406, an upper pressing plate 407, a nut 408, a shock absorption piece 409, a pull cylinder 410, a clamping mechanism 5, a chuck nut 501, an ER collet chuck 502, an insulating washer 503, an insulating nut 504, an ER collet 505, a swinging universal floating joint 6, a tension sensor 7, an erosion body 8, a connecting screw rod 9, a sample 10, a sheath 11, a screw rod joint 12, a speed reducer 13 and a screw rod 14.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and therefore are only examples, and the protection scope of the present invention is not limited thereby.

Example 1:

referring to fig. 1 to 17, a first embodiment of the present invention: a tensile testing machine suitable for low cycle fatigue tests comprises a rack 1, a swinging universal floating joint 6 is fixedly arranged at the top of the rack 1, two groups of clamping mechanisms 5, a first group of clamping mechanisms 51 are coaxially connected with the top of a spring tension cylinder 4, the bottom of the spring tension cylinder 4 is coaxially and fixedly connected with a ball screw lifter 2, and the ball screw lifter 2 is in transmission connection with a servo driving motor; the second group of clamping mechanisms 52 is connected with the swinging universal floating joint 6; the servo motor control assembly is respectively and correspondingly electrically connected with the swinging universal floating joint 6 and the servo driving motor; the ball screw lifter 2 and the servo driving motor are both arranged at the bottom of the frame 1.

As shown in figure 1, the servo driving motor comprises a servo motor 3 and a speed reducer 13, the servo motor 3 and the speed reducer 13 are both fixedly installed on the bottom of the frame 1, the servo motor 3 is in transmission connection with the speed reducer 13, and the speed reducer 13 is in transmission connection with the ball screw lifter 2. The servo motor 3 drives the speed reducer 13, and the speed reducer 13 drives the ball screw lifter 2 to work.

The servo motor control assembly comprises a tension sensor 7, a servo driver, a tension display controller and a PLC (programmable logic controller), wherein the tension sensor 7 is positioned on the top surface of the rack 1 and is coaxially connected with the swinging universal floating joint 6; the servo driver is connected with the servo motor 3; the tension display controller is connected with the tension sensor 7; and the PLC is respectively and correspondingly electrically connected with the servo driver and the tension display controller. The tension sensor 7 is used for measuring the tension transmitted by the swinging universal floating joint 6, and further obtaining the tension condition of the sample in the fatigue tensile test.

As shown in fig. 1 and 2, a sheath 11 is disposed at a connection position of the first group of clamping mechanisms 51 and the spring tension drum 4, the sheath 11 wraps the first group of clamping mechanisms 51 therein, and meanwhile, the sheath 11 is fixedly connected with the spring tension drum 4.

As shown in fig. 1 and 2, a main shaft of the ball screw elevator 2 is a screw 14, a screw joint 12 is disposed on an upper end surface of the screw 14, and the screw joint 12 is used for facilitating connection and fixation between the ball screw elevator 2 and the spring tension cylinder 4.

As shown in fig. 4 and 5, the spring pulling cylinder 4 includes a pulling cylinder 410, a nut joint 401, and a telescopic member, one end of the telescopic member is received in the pulling cylinder 410, and the other end of the telescopic member extends out of the pulling cylinder 410 and is fixedly connected to the nut joint 401.

The nut block 401 is connected in alignment with the screw block 12 on the ball screw elevator 2. So that the telescopic member fixedly connected to the nut runner 401 is coaxial with the screw 14 of the ball screw elevator 2.

The nut joint 401 and the screw rod joint 12 are provided with aligned connecting through holes, the number of the through holes can be 4, 6 or 8, and the through holes are uniformly distributed according to the circumference, and the nut joint 401 and the screw rod joint 12 are fixedly connected through a screw rod penetrating through the through holes.

As shown in fig. 5 to 7, the telescopic member includes a pull rod 402, an upper pressing plate 407, an elastic element group 404 and a pull cylinder sealing plate 403, wherein the pull rod 402 sequentially penetrates through the pull cylinder sealing plate 403 and the elastic element group 404 and then is fixedly connected with the upper pressing plate 407 through a screw thread. The elastic element group can play a role in buffering the pull rod, and can have deformation amount due to the elastic element group, so that the influence of workpiece deformation on elastic tension is counteracted.

The number of springs and the method of stacking the springs in the set 404 may be selected based on the size and amount of deflection of the tensile specimen. The sample 10 is small, the required tension is small, the involutory combination can be adopted, the sample 10 is large, and the superposition combination can be adopted when the required tension is large. The deformation of the sample 10 is large, more spring combinations are used, and the deformation of the spring group is increased under the same tension to offset the influence of the deformation of the workpiece on the elastic tension.

The elastic element set 404 is a set of belleville springs, and preferably includes 4 belleville springs. The end surfaces of the belleville springs are flat and can be compactly stacked and installed; small deformation, high bearing capacity and space saving; when the extrusion is carried out by external force, the stress is concentrated; and can also assist in adjusting the pull rod 402 to be coaxial with the pull cylinder 410.

The upper pressure plate 407 is provided with a damping member 409, and the damping member 409 can be damping rubber or a spring; the shock absorbing member 409 prevents a direct rigid connection between the upper press plate 407 and the pull cup 410. The shock absorbing member 409 has a buffering function, and when the pull rod 402 pushes the telescopic member to slide upwards along the inner side of the pull cylinder 410, the top surface of the telescopic member is contacted with the inner top surface of the pull cylinder 410 through the shock absorbing member 409, so that the buffering function is achieved. The pull cylinder 410 can be protected in the test process, when the test sample 10 is broken, the pull cylinder 410 falls downwards, the shock absorption piece 409 contacts with the inner top surface of the pull cylinder 410 firstly when falling to the top surface of the telescopic component, and the upward buffering acting force on the pull cylinder 410 is avoided, so that the pull cylinder 410 is prevented from directly colliding with the nut 408, and the protection effect on the equipment is realized.

A height-adjusting cylinder 406 is arranged between the upper pressure plate 407 and the elastic element group 404. The height-adjusting cylinder 406 can prolong the length of the pull rod 402 inside the pull cylinder 410 and shorten the length of the pull rod 402 outside the pull cylinder 410, thereby reducing the pull-down displacement of the pull rod 402. The height-adjustable barrel 406 also improves the stability of the pull rod 402 in the pull barrel 410 and improves the coaxiality of the pull rod 402 and the pull barrel 410.

A lower pressing plate 407 may be installed between the height-adjusting cylinder 406 and the elastic element group 404. The lower pressing plate 407 is in pressing contact with the elastic element group 404, so that the stress balance in the stretching process of the pull rod 402 can be improved.

As shown in fig. 8, a circular boss is provided on each of the side surfaces of the upper platen 407 and the lower platen 405, and the circular boss is connected with the height-adjusting cylinder 406 in a matching manner. The height-adjusting cylinder 406 can be positioned in a limited manner.

As shown in fig. 9 to 10, the clamping mechanism 5 includes an ER cartridge 505, an insulating nut 504, an insulating washer 503, an ER collet 502, and a cartridge nut 501, the insulating nut 504 being inserted into the ER cartridge 505; the insulating washer 503 is attached to the insulating nut 504; ER collet 502 bears against insulating washer 503, which fits over insulating nut 504, and ER collet 502 is also inserted into ER collet 505; the chuck nut 501 is sleeved on the ER collet chuck 502 and is fixedly connected with the ER chuck 505 in a threaded manner.

The ER collet chuck 502 is formed by reaming a standard collet chuck, during installation, an insulating washer 503 and an insulating nut 504 are placed in a counter bore of an ER collet 505, the shape of the counter bore corresponds to that of the ER collet chuck 502, the ER collet chuck 502 is used for supporting the insulating washer 503, the collet nut 501 and the ER collet 505 are fixedly connected in a threaded mode, then a sample 10 is screwed into the insulating nut 504 and then stretched, and the sample 10 is ensured to be insulated from the rack 1 during an electrochemical corrosion test. The swinging universal floating joint 6 plays a role in automatically aligning the sample 10 with the pulling direction. The existing testing machine generally adopts wedge block clamping, threaded connection, hanging pin connection, half block clamping and other modes, and the modes determine that the test sample is difficult to insulate from the machine body in the stress corrosion test.

As shown in fig. 10, the connecting screw 9 has threaded sections at both ends and a fixing nut in the middle. The nut can conveniently rotate one end of the connecting screw rod 9 to enter the swinging universal floating joint 6; or the connecting screw 9 is rotated into the ER collet 505 of the clamping mechanism 5.

As shown in fig. 3, the frame 1 includes a top part 103, a bottom part 101 and a pillar 102, and the pillar 102 is installed between the top part 103 and the bottom part 101. There is no cross beam common to conventional stretching machines. The top 103 and the upright 102, and the bottom 101 and the upright 102 are connected by screws. In order to ensure the accuracy of the

upright posts

102, 4 upright posts 102 are processed simultaneously after being spot-welded together, so that the end faces are parallel and uniform in height. When assembled, the top 103 and bottom 101 portions are parallel to each other.

On the premise of meeting the use precision requirement, the cost is saved through structural design, machining and assembly process optimization. The frame 1 is formed by four equal-height upright columns 102 supporting a top 103 and a bottom 101, and positioning grooves of the equal-height upright columns 102 are formed in the top 103 and the bottom 101. The top 103 is used for installing equal-height upright post 102 positioning grooves and tension sensor 7 positioning pin holes, the bottom 101 is used for installing equal-height upright post 102 positioning grooves and ball screw lifter 2 positioning holes, and the equal-height upright post 102 positioning grooves and the ball screw lifter 2 positioning holes are machined in one-time clamping of a numerical control machining center, so that the accuracy of the installation positions of all main parts is guaranteed. The equal-column 102 is processed by linear cutting, so that two end faces are parallel and vertical to the axis. During assembly, the equal-height upright posts 102 are inserted into the positioning grooves at the top 103 and the bottom 101 and then fixed by screws. The boss at the bottom of the ball screw lifter 2 is sleeved into the positioning hole in the middle of the lower bottom plate, and the tension sensor 7 is positioned by the pin and then screwed down by the screw. By these methods, parallelism of the top 103 and bottom 101, and coaxiality of the ball screw lifter 2 and the center of the tension sensor 7 are ensured.

When the sample 10 is subjected to the tensile fatigue test, both ends of the sample 10 are respectively fixedly attached to the first group clamp mechanism 51 and the second group clamp mechanism 52.

The swing universal floating joint 6 and the second group of clamping mechanisms 52, the second group of clamping mechanisms 52 and the test sample 10, the test sample 10 and the first group of clamping mechanisms 51, the first group of clamping mechanisms 51 and the spring tension cylinder 4, the spring tension cylinder 4 and the ball screw lifter 2 are coaxially connected.

If the second clamping mechanism 52 is not coaxial with the first clamping mechanism 51, the test data distortion can be caused by the bending moment generated by the test sample 10, the main shaft of the tension sensor 7 is coaxial with the main shaft of the ball screw lifter 2, and in addition, the second clamping mechanism 52 is provided with the swinging universal floating joint 6 which is coaxially connected with the main shaft of the tension sensor 7, so that the condition that the main shaft of the tension sensor 7 and the main shaft of the ball screw lifter 2 are not coaxial is avoided.

The specific test working mode is as follows:

the power supply is switched on, and the servo motor control assembly and the servo drive motor are electrified; starting a servo motor control assembly, wherein a tension sensor 7 in the servo motor control assembly measures the tension of a swinging universal floating joint 6, a measurement signal is converted into an electric signal and then is transmitted to a tension display controller, the tension display controller displays a tension value and simultaneously transmits the signal to a PLC (programmable logic controller), the PLC sends a control command to a servo driver after signal processing, the servo driver regulates and controls the servo motor 3 to rotate according to the control command, then the servo motor 3 regulates and controls a speed reducer 13, and the speed reducer 13 drives a ball screw lifter 2 to work according to the command. When the ball screw lifter 2 works, the main shaft can move up and down, so that the spring tension cylinder 4 is driven to move up and down, and the spring tension cylinder 4 stretches the sample 10; the tensile force is measured by the tensile force sensor 7, so that the tensile fatigue test of the sample 10 can be accurately monitored.

After the test is finished: the PLC sends a command to the servo driver, the servo driver controls the servo motor 3 to reversely drive the speed reducer 13, the speed reducer 13 reversely drives the ball screw lifter 2, the ball screw lifter 2 drives the spring tension cylinder 4 to contract upwards, and the tensile state of the sample 10 is relieved.

The PLC can control the tensile testing machine of the invention to continuously stretch at a constant speed and also can perform variable-speed stretching. And the tensile fatigue test can be carried out by performing reciprocating cyclic stretching according to a set tensile force-time curve in a certain tensile force interval.

Example 2:

in addition to example 1, the number of the disc springs in the elastic element group was changed to 6 by modifying the elastic element group in the extensible member.

Example 3:

as shown in fig. 2, in addition to embodiment 2, the tensile testing machine of the present invention is additionally provided with an etching system 8, and the etching system 8 is installed between the first group of clamping mechanisms 51 and the second group of clamping mechanisms 52. Corrosion system 8 enables the specimen 10 to perform a corrosion fatigue tensile test.

During a corrosion fatigue test, the sample 10 penetrates through the corrosion system 8, the corrosion system 8 comprises a container and a corrosion solution, the corrosion solution is placed in the container, and the corrosion solution can be a mixed solution of Cl- (chloride ions) and acetic acid; when the sample 10 penetrates through the corrosion system 8, the middle part of the sample is soaked in the corrosion solution in the corrosion system 8, and the two ends of the sample 10 are hermetically connected with the corrosion system 8, so that the corrosion solution can be effectively prevented from leaking from the connection part. Meanwhile, the sample 10 is partially soaked in the corrosion system 8 to generate stress corrosion under the action of the tensile force of the spring tension cylinder 4. So that the test piece 10 can perform the corrosion fatigue test.

The sample 10 was tested for corrosion fatigue by an electrochemical workstation (CHI660E, beijing, waukee) for open circuit potential.

Example 4:

in addition to embodiment 1, the number of the disc springs in the elastic element group was changed to 0 by modifying the elastic element group in the telescopic member. This was used as a control group.

Test and results

1.1 test specimens

As shown in FIG. 12, the material was Q235B (Shandong Steel Co., Ltd.), and the yield strength and tensile strength of the material were 285MPa and 430MPa, respectively. The sample target was 6.35mm in diameter and 15mm in length. And the round bar is linearly cut out from a steel plate with the thickness of 20mm along the rolling direction and then processed. The surface of the target is polished to be bright by 3000-mesh abrasive paper, cleaned by acetone and dried for later use. Other parts (except threads) are sprayed with high-temperature-resistant corrosion-resistant antirust paint (800 ℃ high-temperature-resistant self-spraying paint, GOOT company), dried and packaged by a PVDF heat-shrinkable tube.

1.2 test methods

Two sets of tests were performed, the first set of test specimens was not immersed in the corrosive solution and was exposed to air. The second set of tests soaked the test specimens in an ethanol solution with Cl- (chloride ion) and acetic acid concentration 5 times higher than the national standard for ethanol of the denatured fuel GB 18350-2013. The highest tensile force for both tests did not exceed 8624N (880kgf), at which point the specimen stress did not reach the yield point.

The first set of experiments tested three cases, respectively, in which no belleville spring was installed in the spring tension drum (i.e., corresponding to example 4 of the present invention, as shown in fig. 14), 4 belleville springs were stacked two by two and then mounted in opposition (i.e., corresponding to example 1 of the present invention, as shown in fig. 15), and 6 belleville springs were mounted in opposition (i.e., corresponding to example 2 of the present invention, as shown in fig. 16), the belleville spring specification was 180102/90 x 46 x 3.5.

During the test, the tension is firstly increased to be near the maximum tension 7840N, the tension stays for 5 minutes, then the reverse rotation is carried out until the tension is reduced to about 100N, the tension value is recorded, then the reverse rotation is carried out, the pulse number with a certain value is operated, the tension is increased by a certain value, the stay is carried out, and the tension value is recorded after the reading of the tension sensor 7 is stable.

Then, the next pulse number is continued to be run. When the tension rises above 7840N, the process is stopped, reversed again, the tension is lowered, and the cycle is averaged three times.

The second group used the installation as shown in fig. 16 (i.e. corresponding to example 3 of the present invention) in which a sample 10 was immersed in an etching solution using an etching system 8 and repeatedly and cyclically stretched at a tensile force of 882N-8820N while testing the open circuit potential using an electrochemical workstation (CHI660E, beijing china).

1.3 results

First set of test results:

example 4: as shown in fig. 14, in other words, no spring is installed in the tension cylinder, the tension of the ball screw lifter 2 reaches 8431N (below the stress yield point) every time the ball screw lifter is fed by 0.125mm, the stroke is normalized, and the relationship between the obtained tension and the feeding stroke is shown in fig. 18.

As can be seen from FIG. 18, the loading curve deviates significantly from the unloading curve, and the maximum difference between the loading and unloading tension at the same stroke position is 876N (6107N-5231N). During loading, under 1739N, the load rises more slowly, and the load and the stroke are obviously not in a linear relation; above 1739N, the load rises sharply, with a substantially linear relationship to stroke. When unloading, the load descending speed from the highest point of the load to 5231N is higher than that of the middle and rear sections, and the linear relation is not formed. In the middle of the unloading, the load stroke is linear, but after the load is reduced to 1234N, the load reduction rate is obviously reduced, and after the load is reduced to 355N, the load reduction is slow, and the curve is flattened. The squared difference of the three measurements is shown in FIG. 19, which is a maximum of 62761, indicating that the measured tension is very unstable.

Example 1: the curve of the relationship between the tension and the feed stroke obtained by loading and unloading is shown in fig. 20 by adopting the mode that 4 belleville springs are overlapped in pairs and then oppositely installed as shown in fig. 15. The loading and unloading are each 0.156mm in feed steps. During loading, when the tensile force reaches 123N, the load rising rate is basically stable, the load and the stroke are approximately in a linear relation, and after 15 times of feeding, 8265N is reached. During unloading, the tension rapidly drops to 7141N from the highest point and then steadily drops, the load dropping speed begins to drop after 760N is reached, and the load curve levels off after 123N is reached. The loading curve and the unloading curve have larger deviation, and the loading and unloading maximum tension at the same stroke position is 534N (6369N-5835N). The maximum value of the square difference of the three measured tensile forces is 1948, which shows that the measured tensile force is also relatively unstable.

Example 2: with 6 belleville springs mounted in opposition as shown in fig. 16, the loading and unloading of this mounting is plotted as shown in fig. 21. The feed pitch was 0.625 mm. As can be seen in fig. 21, the load and unload curves are relatively close, with a difference between the maximum pull force for loading and unloading of only 133N (5572N-5439N) at the same stroke position. When the tension reaches 313N during loading, the load rising rate is basically stable, and the load and the stroke are approximately linear until 8265N is reached after 15 times of feeding. During unloading, the tension falls stably, and after the tension reaches the position near 313N, the load falling rate begins to fall and slowly falls to the position near 0. The loading curve and the unloading curve are curved downward, similar to the belleville spring load-displacement curve. The maximum value of the square difference of the tensile force obtained by three times of measurement is 242, and most of the tensile force is less than 100, which shows that the actually measured tensile force has higher reproduction rate and is more stable.

The results of linear fitting of the tension curves obtained by the three embodiments are shown in fig. 22, in example 4, the spring-loaded curve F >1024N is not installed, and the approximately linear relationship begins to be obtained, but the unloading linear relationship is not obvious. Example 1 when F >511N, the loading curve begins to approach a linear relationship, but the segment of the unloading curve from the loading end point to the first stagnation point deviates significantly from the linear relationship. And example 2 starts with F313, the curve can be fitted with a straight line, whether loaded or unloaded. From the corrosion fatigue test point of view, a stable near-linear loading and unloading curve is more than ideal. Thus, example 2 is preferred.

The second set of test results:

example 3: the test results are shown in fig. 23, and fig. 23 is an open circuit potential-time curve measured by an electrochemical workstation in an in-situ tensile corrosion fatigue test performed by using the stretcher of the present invention. As can be seen from the figure, the open circuit potential varies periodically with the tension. In the first cycle, the tension dropped from 8820N to 882N for 95 seconds, and the potential increased by 7.95 mV. Stay at 882N for 120 seconds, the potential continues to rise by 7.36 mV. The pulling force gradually rises from 882N to 8820N, the time is 95 seconds, the potential firstly continuously rises to reach the first peak value of 91.36mV, the pulling force reaches about 3840N, and the potential begins to fall. The potential drop speed is accelerated along with the increase of the tensile force. During the process of staying for 120 seconds after the tension reaches 8820N, the potential firstly continues to rapidly decrease, then the speed is gradually reduced, and after about 50 seconds, the potential begins to slowly increase again.

The tensile testing machine suitable for the low cycle fatigue test is characterized in that the disk spring is adopted in the spring tension cylinder 4 as a deformation buffer, so that the stability of tension output is greatly improved. Due to the influence of the stiffness of the tester itself, a displacement error occurs during stretching. In addition, the jitter caused by the servo system, and the creep, vibration, etc. generated by the mechanical kinematic pair may cause displacement deviation. Assuming that the total displacement error such as the rigidity correction error, the servo jitter, the kinematic pair displacement error and the like of the testing machine is delta LM, if the total displacement error is directly acted on a sample, the tension error is

ΔF＝E×A×ΔL/L_C.......................(1)

In the formula, E is the elastic modulus of the sample, and E is approximately equal to 210GPa for steel; a is the sectional area of the sample; Δ L is the sample extension error, L_CIs the parallel length of the sample. Since Δ L is Δ LM, the tension error is large even if the displacement error is small. The universal material testing machine introduces the rigidity of the testing machine to correct when calculating the displacement of the cross beam in order to control the stress or the displacement rate. The calculation formula of the beam displacement after the rigidity correction is given by GB/T228.1-2010 is as follows:

wherein, V is the displacement rate of the beam; e.g. of the type_Lc-the strain rate of the sample; m-the slope on the stress-elongation curve at a given time; s₀-the original cross-sectional area of the sample; c_M-the stiffness of the tester; l is_C-the parallel length of the specimen. In reality, the rigidity of the testing machine is a function of F and is not a constant, so that the rigidity of the machine tool cannot be measured accurately easily. Although the pull-time curve control of a testing machine can be made very good using modern technology (e.g., PID technology, closed loop servo systems, etc.), the cost of developing and commissioning such a system for a particular testing machine is still prohibitive.

The stretcher solves the problem of displacement-tension curve error by additionally arranging the spring in the spring tension cylinder 4. Suppose that at a certain position, the total error of the displacement of the ball screw of the testing machine is Δ LM, and at this time, the total error of the position scale is equal to two parts of the error of the extension length of the sample and the error of the deformation of the spring:

ΔLM＝ΔLS+Δh.......................(3)

in the formula, Delta LS is the extension length error of the sample piece; Δ h is the deformation error of the spring. If the stiffness of the spring is much less than that of the sample, Δ LS < < Δ h, and the pull error Δ F will be small as can be seen from equation 1. Comparing fig. 19 and 20, it can be seen that the square difference of the three measured tensile forces is large before the spring is installed, and the improvement is large after the spring is installed. Whereas the stiffness of the spring of fig. 21 is 1/6 of fig. 20, the maximum squared difference also falls to the level of 1/8. Therefore, the influence of the displacement error on the stress of the sample can be obviously reduced by the deformation of the spring.

Therefore, the invention takes the spring tension cylinder as the stretching main shaft and installs the spring in the stretching main shaft, thereby being capable of offsetting the stress fluctuation caused by the displacement error of the stretching main shaft, the lower the rigidity of the spring is, the better the offsetting effect is, the more stable the corresponding relation between the stress and the nominal displacement of the stretching main shaft is, and the smaller the statistical square difference is. The invention also realizes the stretching of a stress rate control mode through the controller, 6 disc springs are oppositely overlapped, and the stress-displacement or stress-time curve is close to the linear relation.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. The utility model provides a tensile testing machine suitable for low cycle fatigue test which characterized in that: comprises the steps of (a) preparing a mixture of a plurality of raw materials,

a machine frame (1),

the swing universal floating joint (6) is fixedly arranged at the top of the rack (1);

a spring tension drum (4);

two sets of clamping mechanisms (5) comprising a first set of clamping mechanisms (51) and a second set of clamping mechanisms (52); the first group of clamping mechanisms (51) are coaxially connected with the spring tension cylinder (4), and the second group of clamping mechanisms (52) are coaxially connected with the swinging universal floating joint (6);

the ball screw lifter (2) is arranged at the bottom of the rack (1) and is coaxially connected with the spring tension cylinder (4);

the servo driving motor is arranged at the bottom of the rack (1) and is in transmission connection with the ball screw lifter (2); and

and the servo motor control assembly is respectively connected with the swinging universal floating joint (6) and the servo driving motor.

2. The tensile testing machine suitable for low cycle fatigue testing according to claim 1, wherein: the servo motor control assembly comprises a servo motor control assembly,

the tension sensor (7) is positioned on the top surface of the rack (1) and is coaxially connected with the swinging universal floating joint (6);

the servo driver is connected with the servo driving motor;

the tension display controller is connected with the tension sensor (7); and

and the PLC is respectively and correspondingly electrically connected with the servo driver and the tension display controller.

3. The tensile testing machine suitable for low cycle fatigue testing according to claim 1, wherein: further comprising an etching system (8), the etching system (8) being mounted between the first set of clamping means (51) and the second set of clamping means (52).

4. The tensile testing machine suitable for low cycle fatigue testing according to claim 1, wherein: the spring tension cylinder (4) comprises a cylinder body,

a pull cup (410);

a nut fitting (401); and

one end of the telescopic component is accommodated in the pull cylinder (410), and the other end of the telescopic component extends out of the pull cylinder (410) and is fixedly connected with the nut joint (401).

5. The tensile testing machine suitable for low cycle fatigue testing according to claim 4, wherein: the telescopic member comprises a telescopic member and a telescopic component,

an upper platen (407);

an elastic element group (404);

a pull cylinder closing plate (403); and

the pull rod (402) sequentially penetrates through the pull cylinder sealing plate (403) and the elastic element group (404) and then is fixedly connected with the upper pressure plate (407) in a threaded manner;

the pull cylinder closing plate (403) is fixedly connected with the pull cylinder (410).

6. The tensile testing machine suitable for low cycle fatigue testing of claim 5, wherein: the elastic element group (404) is a butterfly spring group and comprises an even number of butterfly springs.

7. The tensile testing machine suitable for low cycle fatigue testing of claim 5, wherein: the upper pressure plate (407) is provided with a damping member (409).

8. The tensile testing machine suitable for low cycle fatigue testing according to claim 5 or 7, wherein: a height-adjusting cylinder (406) is arranged between the upper pressure plate (407) and the elastic element group (404).

9. The tensile testing machine suitable for low cycle fatigue testing according to claim 1, wherein: the clamping mechanism (5) comprises a clamping mechanism,

an ER collet (505);

an insulating nut (504) inserted into the ER cartridge (505);

an insulating washer (503) attached to the insulating nut (504);

an ER collet chuck (502) supporting the insulating washer (503) to be attached to the insulating nut (504); and

and the chuck nut (501) is sleeved on the ER collet chuck (502) and is fixedly connected with the ER chuck (505) in a threaded manner.

10. The tensile testing machine suitable for low cycle fatigue testing according to claim 1 or 9, characterized in that: and the clamping mechanism (5) is fixedly connected with the swinging universal floating joint (6) through a connecting screw rod (9) in a threaded manner.