阅读说明：本技术 电磁加载新型中应变率冲击拉伸测试系统及其试验方法 (Electromagnetic loading novel medium strain rate impact tensile test system and test method thereof ) 是由 曹增强 曹跃杰 张铭豪 李想 袁昕宇 杜蒙 王晓荷 于 2021-06-28 设计创作，主要内容包括：本发明公开了一种电磁加载新型中应变率冲击拉伸测试系统及其试验方法,涉及实验力学测量技术领域,其技术方案要点是包括加载杆、应力波放大器、次级线圈、放电线圈、夹持装置和压力传感器,其特征是：压力传感器通过连接件与夹持装置的一侧固定连接,加载杆、应力波放大器、次级线圈和放电线圈位于夹持装置远离压力传感器的一侧,效果是通过设置前夹头和后夹头,前夹头和后夹头的内部均设有夹持块,利用夹持块将测试试件夹紧,可以有效避免高速加载过程中出现的试件滑脱。本发明利用电磁感应原理将电能最终转化为冲击动能,从而实现了在可控范围内对金属材料和复合材料及其连接结构在中应变率(1～500/s)下的有效测量。(The invention discloses a novel electromagnetic loading medium strain rate impact tensile test system and a test method thereof, relating to the technical field of experimental mechanics measurement, and the key point of the technical scheme is that the system comprises a loading rod, a stress wave amplifier, a secondary coil, a discharge coil, a clamping device and a pressure sensor, and is characterized in that: pressure sensor passes through connecting piece and clamping device's one side fixed connection, and load bar, stress wave amplifier, secondary coil and discharge coil are located clamping device and keep away from one side of pressure sensor, and the effect is through chuck and back chuck before setting up, and the inside of preceding chuck and back chuck all is equipped with the grip block, utilizes the grip block to press from both sides the test piece tightly, can effectively avoid the test piece slippage that appears at high-speed loading in-process. The invention utilizes the electromagnetic induction principle to finally convert electric energy into impact kinetic energy, thereby realizing the effective measurement of metal materials, composite materials and connecting structures thereof in a controllable range under the medium strain rate (1-500/s).)

1. The utility model provides a novel well strain rate impact tensile test system of electromagnetic loading, includes load bar (2), stress wave amplifier (3), secondary coil (4), discharge coil (5), clamping device (7) and pressure sensor (10), characterized by: the pressure sensor (10) is fixedly connected with one side of the clamping device (7) through a connecting piece, the loading rod (2), the stress wave amplifier (3), the secondary coil (4) and the discharge coil (5) are positioned on one side, far away from the pressure sensor (10), of the clamping device (7), the loading rod (2), the stress wave amplifier (3), the secondary coil (4) and the discharge coil (5) are sequentially arranged and connected together, and one side, close to the clamping device (7), of the discharge coil (5) is connected with the clamping device (7) through a bolt;

clamping device (7) include preceding chuck (12) and back chuck (13), and preceding chuck (12) and back chuck (13) are door font structure, both sides all are equipped with grip block (14) around preceding chuck (12) and back chuck (13) inner chamber, the both sides at preceding chuck (12) and back chuck (13) door clip position all seted up the screw hole, grip block (14) and preceding chuck (12) and back chuck (13) chuck position complex inclined plane seted up the counter bore, and the position of counter bore corresponds with the position of screw hole.

2. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 1, wherein: protective frames (15) are additionally arranged on the peripheries of the front chuck (12) and the rear chuck (13).

3. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 2, wherein: one side of the loading rod (2) departing from the stress wave amplifier (3) is provided with a damper (1), the loading rod (2) is not in contact with the damper (1), the damper (1) is of a cylindrical structure, and plasticine or foam is filled in the damper (1).

4. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 1, wherein: the material of the loading rod (2) and the coil support (6) is stainless steel.

5. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 1, wherein: discharge coil (5) are circular through-hole structure, and the center of discharge coil (5) is equipped with sharp slide bearing, clearance fit between discharge coil (5) and loading pole (2), one side that discharge coil (5) are close to coil support (6) is equipped with the plastic base, and pass through first bolted connection between plastic base and coil support (6), coil support (6) are connected through the loading pole with preceding chuck (12) in clamping device (7), and pass through second bolted connection between loading pole (2) and preceding chuck (12).

6. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 1, wherein: the secondary coil (4) is of a round cake-shaped structure.

7. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 3, wherein: the connecting piece includes fixed connection pole (8), fixed connection pole (8) are connected through fixed bolster (9) and pressure sensor (10), and one side and clamping device (7) fixed connection of fixed bolster (9) are kept away from in fixed connection pole (8), the bottom of fixed bolster (9) is equipped with load test platform (11), fixed bolster (9) are the structure of falling T shape of symmetry, and both ends that fixed bolster (9) are close to load test platform (11) one side all are equipped with the muscle that adds, add and be connected through the accessory between muscle and load test platform (11).

8. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 7, wherein: the accessory comprises a third bolt, a thread groove for assembling the third bolt is formed in the upper surfaces of the fixing support (9) and the loading test bed (11), and the third bolt is assembled inside the thread groove.

9. The electromagnetically-loaded novel intermediate strain rate impact tensile test system of claim 7, wherein: the damper (1) and the coil support (6) are located at the top of the loading test bed (11), and the damper (1), the coil support (6) and the loading test bed (11) are fixed through fourth bolts.

10. A novel electromagnetic loading medium strain rate impact tensile test method is characterized by comprising the following steps: the method comprises the following steps:

s1, mounting test pieces: fixing a test piece by using a clamping device (7), then respectively connecting a cable, a strain acquisition data wire and a pressure acquisition data wire, and adjusting the target position of the high-speed camera;

s2, setting a charging voltage parameter: carrying out mechanical test by using equipment;

s3, charging and acquisition trigger: inputting a target charging voltage value, charging the equipment, and controlling a trigger key for high-speed shooting, pressure acquisition and strain acquisition after charging is finished;

s4, discharge loading: pressing down a discharge switch button immediately after pressing down each data acquisition trigger key to complete one-time quick loading and acquire each required data;

and S5, data processing.

Technical Field

The invention relates to the technical field of experimental mechanics measurement, in particular to a novel electromagnetic loading medium strain rate impact tensile test system and a test method thereof.

Background

Strain rate is an important parameter for the performance research in the field of modern material mechanics. In general, a medium strain rate range refers to loading conditions between 1/s and 500/s, with less than 1/s generally referred to as quasi-static loading, also referred to as low strain rate loading, and greater than 500/s referred to as high strain rate loading. At present, the low strain rate is mainly tested by a material tensile testing machine and is also the most common method for testing the mechanical property of the material, and the high strain rate is mainly tested by a separated Hopkinson bar for high-speed performance.

The anti-collision characteristic of the structure needs to be fully considered in the initial design and the service process of modern aircrafts, high-speed trains and high-performance sports cars, which has important significance on passenger safety and the service life of the structure. Particularly, for the fuselage and wing structures of modern airplanes, bird collisions, hailstones, emergency crash and the like occur frequently, which requires that the airplane needs to effectively test and analyze the performance of relevant materials and structures thereof under impact load at the beginning of design. Titanium alloy, aluminum alloy and novel composite materials which are used in a large amount on the current aircraft all show certain strain rate effect in different degrees. The medium strain rate is precisely one loading condition experienced under high speed vehicle impact loads. The high-speed tensile testing machine can realize the test of medium and low strain rate, but mainly performs the test in a relatively uniform loading mode. The Hopkinson bar test device can only realize the impact test of high strain rate, and can not be used for the dynamic performance test of a conventional connecting structural member due to the limitation of the structure size, so that the Hopkinson bar test device is mainly applied to the research of basic mechanical properties at present.

The pulse electromagnetic force loading technology based on the RLC discharge circuit has the advantages of safety, controllability, high-speed loading, adjustable amplitude and the like, and is widely applied and popularized in the military industry. For an electromagnetic loading test device, the invention patent with the patent number of 201710399113.7 provides a mechanical connection joint high-speed impact test device based on electromagnetic loading and a test method, and the method utilizes the electromagnetic loading principle and can realize the dynamic loading test of 0-50 m/s theoretically by controlling capacitance and voltage. The problem of clamping is not solved at the test piece centre gripping position among the device, adopts the bolt to carry out fenestrate connected mode and is similar to the connection of many nails structure, and in dynamic loading process, the near connecting hole at chuck position can undertake certain impact load, reduces the accuracy of test result.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a novel electromagnetic loading medium strain rate impact tensile test system with a stable clamping device and a quick test method thereof.

In order to achieve the purpose, the invention provides the following technical scheme: a novel electromagnetic loading medium strain rate impact tensile test system comprises a loading rod, a stress wave amplifier, a secondary coil, a discharge coil, a clamping device and a pressure sensor, wherein the pressure sensor is fixedly connected with one side of the clamping device through a connecting piece;

the clamping device comprises a front chuck and a rear chuck, the front chuck and the rear chuck are in a door-shaped structure, clamping blocks are arranged on the front side and the rear side of an inner cavity of the front chuck and the rear chuck, threaded holes are formed in the two sides of a door-shaped clamping position of the front chuck and the two sides of a door-shaped clamping position of the rear chuck, counterbores are formed in inclined planes of the clamping blocks, which are matched with the front chuck and the rear chuck, and the positions of the counterbores correspond to the positions of the threaded holes.

Preferably, the periphery of the front chuck and the periphery of the rear chuck are provided with protective frames.

Preferably, a damper is arranged on one side, away from the stress wave amplifier, of the loading rod, the loading rod is not in contact with the damper, the damper is of a cylindrical structure, and plasticine or foam is filled in the damper.

Preferably, the material of the loading rod and the coil support is stainless steel.

Preferably, the discharge coil is circular through-hole structure, and the center of discharge coil is equipped with sharp slide bearing, clearance fit between discharge coil and the loading pole, and one side that discharge coil is close to the coil support is equipped with the plastic base, and passes through first bolted connection between plastic base and the coil support, passes through second bolted connection between loading pole and the preceding chuck.

Preferably, the secondary coil is of a pancake-like structure.

Preferably, the connecting piece includes fixed connection rod, and fixed connection rod passes through the fixed bolster and pressure sensor connects, and one side and the clamping device fixed connection that the fixed bolster was kept away from to fixed connection rod, and the bottom of fixed bolster is equipped with the load test platform, and the fixed bolster is the inverted T shape structure of symmetry, and the both ends that the fixed bolster is close to load test platform one side all are equipped with the muscle, are connected through the accessory between muscle and the load test platform.

Preferably, the fitting comprises a third bolt, threaded grooves for assembling the third bolt are formed in the upper surfaces of the fixing support and the loading test bed, and the third bolt is assembled inside the threaded grooves.

Preferably, the damper and the coil support are located at the top of the loading test bed, and the damper, the coil support and the loading test bed are fixed through fourth bolts.

A novel electromagnetic loading medium strain rate impact tensile test method comprises the following steps:

s1, mounting test pieces: fixing a test piece by using a clamping device, then respectively connecting a cable, a strain acquisition data line and a pressure acquisition data line, and adjusting the target position of the high-speed camera;

s2, setting a charging voltage parameter: carrying out mechanical test by using equipment;

s3, charging and acquisition trigger: inputting a target charging voltage value, charging the equipment, and controlling a trigger key for high-speed shooting, pressure acquisition and strain acquisition after charging is finished;

s4, discharge loading: pressing down a discharge switch button immediately after pressing down each data acquisition trigger key to complete one-time quick loading and acquire each required data;

and S5, data processing.

Compared with the prior art, the invention has the following beneficial effects:

1. through chuck and back chuck before setting up, the inside of preceding chuck and back chuck all is equipped with the grip block, utilizes the grip block to press from both sides the test piece tight, places the fifth bolt in the counter bore of seting up on the grip block this moment, and the screw hole that the fifth bolt was seted up on chuck and the back chuck through preceding chuck presss from both sides tightly the sample, prevents that the test piece from sliding to appear in the high-speed loading process to guarantee the accuracy of test result reliable.

2. The invention utilizes the electromagnetic induction principle to finally convert the pulse electromagnetic energy of the RLC discharge circuit into the impact kinetic energy of material testing, thereby realizing the effective measurement of metal materials and composite materials under the conditions of medium and high strain rate (1-500/s) in a controllable range, and filling the gap between a high-speed tensile testing machine and a Hopkinson bar loading test at home and abroad.

3. The device has the characteristics of low cost, simple operation, high test precision, good repeatability, stable and reliable structure and the like.

4. The invention is also suitable for relevant measurement in the field of impact dynamics, can realize impact performance test of different connecting joints and panel structures under medium strain rate, and can ensure the consistency of measured data and results under real service environment.

Drawings

FIG. 1 is a plan view of an electromagnetic force loading test platform according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a three-dimensional structure of a loading experiment platform according to an embodiment of the present invention;

FIG. 3 is a schematic three-dimensional structure diagram of a clamping device according to an embodiment of the present invention;

FIG. 4 is a schematic view of a clamping block of the clamping device according to the embodiment of the present invention;

FIG. 5 is a schematic diagram of a three-dimensional structure of a power control cabinet of a strain rate testing system in electromagnetic loading according to an embodiment of the present invention;

FIG. 6 is a pulse electromagnetic force curve of a strain rate testing system under electromagnetic loading at different voltages according to an embodiment of the present invention;

FIG. 7 is an actual tensile loading electromagnetic force curve of a strain rate testing system under electromagnetic loading at different voltages according to an embodiment of the present invention;

FIG. 8 is an electromagnetic loading tensile failure mechanical response curve of 2024 aluminum alloy of an embodiment of the present invention at different strain rates.

1. A damper; 2. a loading rod; 3. a stress wave amplifier; 4. a secondary coil; 5. a discharge coil; 6. a coil support; 7. a clamping device; 8. a fixed connecting rod; 9. fixing a bracket; 10. a pressure sensor; 11. loading the test bed; 12. a front chuck; 13. a rear chuck; 14. a clamping block; 15. a protective frame; 16. a power cabinet switch; 17. a power cabinet control screen; 18. a charge button; 19. a discharge button; 20. an emergency switch.

Detailed Description

An embodiment of a novel electromagnetic loading medium strain rate impact tensile test system according to the present invention is further described with reference to fig. 1 to 8.

Referring to fig. 1, 3 and 4, a novel electromagnetic loading medium strain rate impact tensile test system comprises a loading rod 2, a stress wave amplifier 3, a secondary coil 4, a discharge coil 5, a clamping device 7 and a pressure sensor 10, wherein the pressure sensor 10 is fixedly connected with one side of the clamping device 7 through a connecting piece, the loading rod 2, the stress wave amplifier 3, the secondary coil 4 and the discharge coil 5 are positioned on one side of the clamping device 7 away from the pressure sensor 10, the loading rod 2, the stress wave amplifier 3, the secondary coil 4 and the discharge coil 5 are sequentially arranged and connected together, and one side of the discharge coil 5 close to the clamping device 7 is connected with the clamping device 7 through a bolt;

the clamping device 7 comprises a front chuck 12 and a rear chuck 13, the front chuck 12 and the rear chuck 13 are in a door-shaped structure, clamping blocks 14 are arranged on the front side and the rear side of the inner cavities of the front chuck 12 and the rear chuck 13, threaded holes are formed in the two sides of the door-shaped clamping part of the front chuck 12 and the rear chuck 13, countersunk holes are formed in the inclined surfaces of the clamping blocks 14, matched with the chuck parts of the front chuck 12 and the rear chuck 13, and the positions of the countersunk holes correspond to the positions of the threaded holes. The stress wave amplifier 3 is of a conical structure and is used for amplifying stress, before testing, a test piece is placed in the front chuck 12 and the rear chuck 13 and is clamped by the clamping block 14, at the moment, a fifth bolt is placed in a counter bore formed in the clamping block 14, and the fifth bolt passes through threaded holes formed in the front chuck 12 and the rear chuck 13 to ensure that the test piece is clamped. In addition, the clamping block 14 surface knurling line strengthens the frictional force between clamping block 14 and the tensile test piece to guarantee that the test piece is fixed more firmly by clamping block 14, can not appear sliding in the loading process.

Referring to fig. 3, a protective frame 15 is additionally arranged on the periphery of each of the front chuck 12 and the rear chuck 13. The protective frame 15 is provided to ensure that the front chuck 12 and the rear chuck 13 of the door-shaped structure are not deformed by the abutting action of the fifth bolt during the clamping process.

Referring to fig. 1 and 2, a damper 1 is arranged on one side, away from a stress wave amplifier 3, of a loading rod 2, the loading rod 2 is not in contact with the damper 1, the damper 1 is of a cylindrical structure, and plasticine or foam is filled in the damper 1. The damper 1 is filled with plasticine or foam, and is used for effectively buffering the impact of the loading rod 2 after the test piece is failed in stretching and for safety protection of the loading test bed 11 and the test process.

Referring to fig. 1 and 2, the material of the loading rod 2 and the coil support 6 is stainless steel. The purpose is mainly to prevent the magnetization phenomenon caused by electromagnetic induction, and cast iron and common carbon steel are easy to generate a local reverse magnetic field due to magnetization, so that the back of the coil support 6 is cracked.

See fig. 1 and 2, discharge coil 5 is circular through-hole structure, and the center of discharge coil 5 is equipped with sharp slide bearing, clearance fit between discharge coil 5 and the loading pole 2, and one side that discharge coil 5 is close to coil support 6 is equipped with the plastic base, and passes through first bolted connection between plastic base and the coil support 6, passes through second bolted connection between loading pole 2 and the preceding chuck 12. The copper strips are drawn out along central symmetry left and right sides, correspond with bearing frame both sides fluting position, make things convenient for the connection of cable, simultaneously in order to use safety, draw out end copper strips position and need twine high-pressure insulating tape earlier, twine ordinary insulating tape again, in order to improve loading process centering uniformity, the central connecting hole cooperates with stainless steel loading rod 2 through installation straight line slide bearing, carry out certain lubrication protection to the bearing inner wall simultaneously, be convenient for reduce loading process sliding resistance, discharge coil 5 adopts the copper strips of wide size thickness more than T2 level to twine back pouring resin solidification's mode processing more than 1.5mm, in order to increase electric conductivity and magnetic flux, discharge coil 5 base adopts high strength resistant crashworthiness plastics to process, the connected mode that utilizes first bolt and second bolt connects, make the device can connect stably.

Referring to fig. 1 and 2, the secondary coil 4 is of a pancake-like configuration. The secondary coil 4 functions as an induction coil for a discoid structure.

See fig. 1 and 2, the connecting piece includes fixed connecting rod 8, fixed connecting rod 8 passes through fixed bolster 9 and pressure sensor 10 and connects, and one side and clamping device 7 fixed connection that fixed connecting rod 8 kept away from fixed bolster 9, and the bottom of fixed bolster 9 is equipped with load test bench 11, and fixed bolster 9 is the inverted T structure of symmetry, and the both ends that fixed bolster 9 is close to load test bench 11 one side all are equipped with the muscle that adds, add the muscle and be connected through the accessory between the load test bench 11. One side of the fixed support 9 close to the fixed connecting rod 8 is provided with a boss, the fixed connecting rod 8 is installed in the boss, and the purpose is to prevent the fixed connecting rod 8 from swinging up and down in a free state to influence the consistency of the loading process.

Referring to fig. 1 and 2, the fitting comprises a third bolt, the upper surfaces of the fixing support 9 and the loading test bed 11 are both provided with thread grooves for assembling the third bolt, and the third bolt is assembled inside the thread grooves. The loading test bed 11 adopts an integral flat plate structure, the surface is subjected to smooth rust-proof treatment, the bottom plate of the fixed support 9 and the upper surface of the loading test bed 11 adopt a bolt connection mode, for preventing looseness, a bolt adopts a threaded hole connection mode, and meanwhile, the lower bottom surface of the loading test bed 11 is screwed up by adopting a high-strength nut.

Referring to fig. 1 and 2, the damper 1 and the coil support 6 are both located at the top of the loading test bed 11, and the damper 1, the coil support 6 and the loading test bed 11 are all fixed through fourth bolts.

A novel electromagnetic loading medium strain rate impact tensile test method comprises the following steps:

s1, mounting test pieces: fixing the test piece by using a clamping device 7, then respectively connecting a cable, a strain acquisition data line and a pressure acquisition data line, and adjusting the target position of the high-speed camera; before this, the measuring device needs to be installed, during installation, the loading rod 2 is sequentially connected with the stress wave amplifier 3, the secondary coil 4 and the discharge coil 5, wherein the stress wave amplifier 3, the secondary coil 4 and the discharge coil 5 are tightly attached, then the loading rod is connected with the front chuck 12 through the second bolt, then the fixed connecting rod 8 is used for tightly attaching and connecting with the pressure sensor 10 through the fixed support 9, finally the rear chuck 13 is fixed, when a test sample is installed, the test sample is fixed through the clamping device 7, after the test sample is firmly fixed, a cable corresponding to the outlet end of the discharge coil 5 and a data line and a pressure acquisition data line for strain acquisition of the set position of the test sample are respectively connected, the structural stability and the centering consistency in the loading process are checked, and the position of the high-speed camera is adjusted.

S2, setting a charging voltage parameter: carrying out mechanical test by using equipment; and (3) calculating voltage parameters to be loaded according to the following formulas (1), (2) and (3), then opening a system control power supply, checking a power supply system and various data acquisition systems, and ensuring that all the components are normal and then are ready for mechanical testing.

S3, charging and acquisition trigger: inputting a target charging voltage value, charging the equipment, and controlling a trigger key for high-speed shooting, pressure acquisition and strain acquisition after charging is finished; the method comprises the steps of firstly turning on a power cabinet switch 16, starting the equipment, then inputting a set target charging voltage value on a power cabinet control screen 17, then pressing a charging button switch 18, and respectively pressing trigger keys for controlling high-speed shooting, pressure acquisition and strain acquisition on a computer after a green indicator lamp is turned on after charging is finished.

S4, discharge loading: pressing down a discharge switch button immediately after pressing down each data acquisition trigger key to complete one-time quick loading and acquire each required data;

and S5, data processing. And calculating the actual strain rate and stress-strain mechanical response in the loading process according to the recording result of the relevant instrument, summarizing and analyzing the failure change behavior in the loading process, and writing a relevant test report and an academic paper.

In S2, equations (1), (2), and (3) are required to calculate the voltage parameter to be loaded, and the maximum loading speed calculation equation of the test piece in the loading process is as follows:

wherein, V_maxFor maximum rate of loading, M is the amplification factor of the stress amplifier 3, K is the constant for the RLC discharge loop process, U0 loads the process discharge voltage, ρ is the density of the stainless steel load bar 2, and S is the circular area of 4 of the secondary coil.

The pulse electromagnetic force loading process is actually the loading of a half-sine stress wave, the energy of the pulse electromagnetic force loading process is the result of the combined action of peak force and pulse width, and the calculation formula of the pulse width is as follows:

wherein, T is the pulse width value of electromagnetic loading, L refers to the inductance of the RLC discharge circuit, C is the capacity of the power cabinet capacitor bank, and R is the equivalent resistance of the whole discharge circuit, and can be directly measured by a universal meter.

The strain rate is the change of the material strain per unit time and can be calculated by the following formula:

wherein epsilon^*To the strain rate, L₀The original length of the gauge length of the test piece, L the length of the test piece after stretching, and V the effective speed of the loading process.

The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.