CN111426555B - Tensile fixture and experimental method for split Hopkinson pull rod thin sheet test piece - Google Patents

Tensile fixture and experimental method for split Hopkinson pull rod thin sheet test piece Download PDF

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Publication number
CN111426555B
CN111426555B CN202010290323.4A CN202010290323A CN111426555B CN 111426555 B CN111426555 B CN 111426555B CN 202010290323 A CN202010290323 A CN 202010290323A CN 111426555 B CN111426555 B CN 111426555B
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clamp
test piece
rod
positioning
test
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CN111426555A (en
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敬霖
冯超
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Southwest Jiaotong University
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Southwest Jiaotong University
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/02Details
    • G01N3/04Chucks
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/30Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight
    • G01N3/307Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight generated by a compressed or tensile-stressed spring; generated by pneumatic or hydraulic means
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0001Type of application of the stress
    • G01N2203/001Impulsive
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/026Specifications of the specimen
    • G01N2203/0262Shape of the specimen
    • G01N2203/0268Dumb-bell specimens
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/04Chucks, fixtures, jaws, holders or anvils
    • G01N2203/0429Chucks, fixtures, jaws, holders or anvils using adhesive bond; Gluing
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/06Indicating or recording means; Sensing means
    • G01N2203/067Parameter measured for estimating the property
    • G01N2203/0682Spatial dimension, e.g. length, area, angle

Abstract

The invention discloses a tensile clamp of a split type Hopkinson pull rod thin sheet test piece and an experimental method, wherein the tensile clamp comprises a main clamp body and an auxiliary clamp body, the main clamp body is provided with a fixed block and a positioning lug on a semicircular section, a positioning clamping groove is formed between the fixed block and the positioning lug, the main clamp body is provided with a placing groove for placing a test piece on the semicircular section, a positioning cylinder is arranged in the placing groove, the auxiliary clamp body is provided with a positioning groove matched with the positioning lug on the semicircular section, a protrusion of the auxiliary clamp body on the positioning groove is a positioning clamping block, the positioning clamping block is matched with the positioning clamping groove, and the auxiliary clamp body is provided with a positioning blind hole matched with the positioning cylinder on the semicircular section. The invention effectively solves the problem of the slippage of the sheet test piece in the test process, ensures the fastening stability of the clamp and the test piece, ensures the waveform propagation integrity in the test process, avoids the interference to stress waves and effectively improves the precision of test data.

Description

Tensile fixture and experimental method for split Hopkinson pull rod thin sheet test piece
Technical Field
The invention relates to the technical field of research of material mechanics, experimental mechanics and the like, in particular to a tensile clamp and an experimental method for a split Hopkinson pull rod thin sheet test piece.
Background
The dynamic mechanical property research of the material under high strain rate has important academic and engineering values in the fields of aerospace, rail traffic, automobiles, ships, national defense engineering and the like. Accurate acquisition of the mechanical response of materials in a wide strain rate range, especially the mechanical response of materials at medium and high strain rates, has become a research focus and difficulty. At present, the commonly used material dynamic mechanical property testing equipment mainly comprises a high-speed material testing machine (10) of a servo hydraulic control system0~103s-1) Drop hammer tester (10)1~103s-1) And a split Hopkinson bar (10)2~104s-1) And the like. The split hopkinson bar (compression bar and tension bar) experimental technique is considered as the most main and reliable experimental method for researching the mechanical properties of materials under high strain rate, and comprises two basic assumptions: 1) one-dimensional stress wave assumption: assuming that stress waves transmitted in the impact rod, the incident rod, the transmission rod and the test piece are linear elastic waves, and any cross sections of the impact rod, the incident rod, the transmission rod and the test piece are always kept as a plane in the transmission process; 2) stress uniformity assumption: it is assumed that the stress and strain in the test piece are evenly distributed along the length during the entire loading process. The stress-strain relation of the test piece can be obtained through a one-dimensional stress wave propagation theory.
The Split Hopkinson Tension Bar (SHTB) system consists essentially of three parts: the pull rod comprises a bracket part, a pull rod main body part and a data acquisition part. Wherein the bracket part is mainly used for supporting and fixing the pull rod part and ensuring the level of the pull rod. The main body part of the pull rod comprises a buffer absorber, a single wave transmission rod, a loading joint, an impact tube (commonly called a bullet), a gun barrel, an incident rod, a transmission rod and a corresponding air pressure device. The data acquisition system consists of a strain gauge adhered to the rod, a Wheatstone bridge (strain gauge wiring bridge box), an ultra-dynamic strain gauge and a high-speed acquisition system. The split Hopkinson pull rod consists of a striker rod, an incident rod, a transmission rod and an energy absorption system, wherein the striker rod, the incident rod, the transmission rod and the energy absorption system are made of materials with the same performance and outer diameter. When the impact rod impacts the incident rod coaxially, an approximate compression square wave is generated on the incident rod, the elastic compression wave is transmitted to the interface of the incident rod and the test piece, one part of the elastic compression wave is transmitted to the test piece, and the other part of the elastic compression wave is reflected back to the incident rod in the form of tensile wave to form a reflection strain wave. When the compression wave entering the test piece reaches the interface of the test piece and the transmission rod, a small part of the compression wave returns to the test piece and is reflected back and forth in the test piece to achieve stress balance, and the other part of the compression wave is transmitted to the transmission rod to form transmission strain wave.
In the process of researching the dynamic mechanical properties of materials by using the split Hopkinson pull rod, the contact surface of a test piece and an experimental rod needs to bear tensile stress, and a thread method is a common connection method. The thread method is to make the test piece into a dumbbell-shaped revolving body, process external threads at two ends of the test piece, and connect the test piece with the split Hopkinson pull rod through threads. However, the thickness of some original plates of test materials is not enough, the diameter required by the split Hopkinson pull rod threaded connection cannot be achieved, the test materials cannot be processed into cylindrical test pieces with the diameter meeting the requirements, and only the test materials can be processed into sheet-shaped test pieces. For such a sheet-like test piece, a gluing method is generally used. The gluing method is to use high-strength glue to tightly connect the clamping end of the plate-shaped test piece with the incident rod and the transmission rod of the split Hopkinson pull rod. The data obtained by the method has high precision, but the test period is long, the test piece and the rod piece are adhered independently in each test, and the disassembly and the cleaning are not good after the test. Although the screw thread method improves the test efficiency, the obtained data precision is lower than that of the glue method, and many materials are difficult to process into screw thread test pieces in the engineering, so the screw thread method is not suitable for engineering application. Therefore, for a sheet-like specimen, a jig is often used to connect the specimen and the rod.
In the dynamic tensile test process using the jig for connecting the sheet-like test piece and the rod member, the following problems must be considered: 1) stress concentration between the loading rod and the test piece must be minimized; 2) the mismatching of wave impedance is avoided as much as possible between the loading rod and the test piece so as to reduce the weakening of effective pulse load caused by the reflection of stress wave and further facilitate waveform analysis; 3) the tensile load is preferably transmitted to the test piece by the loading rod through only one shearing loading area, so that the situation that the tension fails due to the fact that the load is transmitted in multiple ways or too many interference clutter is generated to influence waveform acquisition and analysis is avoided as much as possible; 4) the area over which shear loads are transmitted should be as large as possible, otherwise shear failure is likely to occur. In consideration of the problems, the sheet test piece test fixture of the split Hopkinson pull rod is designed.
The first prior art is as follows: patent number cn201520417815.x discloses a dynamic tensile test anchor clamps (as shown in fig. 1-4), including the main anchor clamps body 1, clamping piece 2 and screw thread mounting fixture 3, wherein, the one end trompil of the main anchor clamps body 1, the inner wall in hole sets gradually internal thread and interior conical surface from outside to inside, the one end periphery of screw thread mounting fixture 3 is provided with the external screw thread with main anchor clamps body 1 internal thread matched with, screw thread mounting fixture 3 opens along the axle center has the centre bore that supplies lath test piece 4 to pass, and open the one end in stretching into the main anchor clamps body 1 and have the taper hole coaxial with the centre bore and the minimum aperture is greater than the centre bore, two symmetrical clamping pieces are configured and are used for pressing from both sides lath test piece 4, the appearance at clamping piece 2 both ends respectively with the interior conical surface of main anchor clamps body 1 and the taper hole shape cooperation of screw.
Structural assembly of the first technique: the main clamp body 1 is connected with the configured Hopkinson pull rod through threads, and the two symmetrical clamping pieces 2 clamp the strip-shaped test piece 4 and are attached to the inner hole conical surface of the main clamp body 1; the conical surface of the thread fixing clamp 3 is attached to the clamping piece 2, and the external thread of the thread fixing clamp is matched with the internal thread of the main clamp body 1 to achieve the purpose of fixing.
Experimental procedure for technique one: before the experiment, the material to be tested is cut into a strip-shaped test piece 4 with a certain width, the size of the test piece is smaller than the size of a central hole of the thread fixing clamp 3, the two symmetrical clamping pieces 2 are clamped tightly and then placed into the main clamp body 1, the main clamp body 1 is assembled on the pull rod through conical surface matching, the thread fixing clamp 3 is screwed into the main clamp body 1, the conical surface of the conical hole in the thread fixing clamp 3 is matched with the conical surface of the clamping piece 2, the test piece is fixed and is guaranteed not to slip, and the high strain rate experiment is completed through dynamic stretching.
The first prior art has the following disadvantages: for the dynamic tensile experiment clamp, a complex connection mode is adopted, a conical surface with higher processing requirements is involved, and the required main clamp body, the clamping piece and the thread fixing clamp still have more gaps after the assembly is completed, so that the clamp is not tightly matched, the propagation of stress waves is interfered, and the test effect is influenced.
The second prior art is: patent number CN201510793051.9 discloses a clamping device and an experimental method for a split type hopkinson pull rod test piece (as shown in fig. 4-8, in the figure, 1 is a buffer absorber, 2 is a single wave transmission rod, 3 is a loading rod head, 4 is a striking rod, 5 is a strain gauge, 6 is an incident rod, 7 is a clamping device, 8 is a test piece, 9 is a transmission rod, 10 is a joint, 11 is a clamping part, 12 is a blind hole, 13 is a pressing block, 14 is a base, 15 is a groove, 16 is a screw hole, and 17 is a screw); the clamping part comprises a pressing block and a base, the pressing block is buckled above the base, the base and the joint are fixed into a whole, the upper surface of the base is provided with a groove, the structure of the groove is flat, the groove main body is square, the end part of the groove is horn-shaped, the pressing block is of a hexahedral structure, the upper surface and the lower surface of the groove are parallel, the pressing block is provided with screw holes all around, the screw holes are formed in the corresponding positions of the base and the pressing block, and the pressing block is fixedly connected with the base.
Experimental operation of technique two: adjusting the levelness and the coaxiality of the incident rod and the transmission rod, and checking whether the strain gauge is attached; tightly screwing the adapter with the experimental rod through the thread seal tape; checking the levelness and coaxiality of the incident rod and the transmission rod again; loading the test piece into the groove; fixing the pressing block and the base together by using a screw; opening the strain gauge and opening the data acquisition system; carrying out a high strain rate dynamic tensile test; unscrewing the nut, and taking out the test piece; and repeating the steps.
The second prior art has the following disadvantages: for the clamping device and the experimental method for the split Hopkinson pull rod test piece, the test piece is clamped and connected in a physical loading mode by using the pressing block and the screw, and the defects that the joint section changes greatly and stress wave propagation is interfered exist. In addition, threaded connection easily appears the thread clearance, and in the dynamic tensile test in-process, the clamping state of test piece is stable inadequately because of the thread clearance leads to between briquetting and the base easily.
The prior art is three: patent number CN107941606A discloses a split type hopkinson pull rod test fixture, (as shown in fig. 9-13), which comprises a main fixture body, an auxiliary fixture body and a lock nut, wherein the main fixture body is a special-shaped cylinder structure with a cut at one end, a threaded rod in threaded connection with an incident rod and a transmission rod of a test device is arranged at the end of the cylinder, and an external thread matched with the lock nut is arranged at the end of the cut; the section of the main clamp body cylinder is as follows: a notch is formed by intersecting an axial tangent line of the central line of the end part of the external thread with a radial tangent line at one third of the cylinder, a groove for placing a test piece is arranged on the horizontal plane of the kerf, and a positioning blind hole matched with the positioning cylinder at the end part of the auxiliary clamp body is arranged on the vertical end surface of the kerf; the auxiliary clamp body is of a semi-cylindrical structure, one end of the auxiliary clamp body is provided with a positioning cylinder matched with the positioning blind hole on the vertical end face of the main clamp body, and the other end of the auxiliary clamp body is provided with an external thread matched with the locking nut; the horizontal plane of the semi-cylinder is provided with a groove consistent with the main clamp body, and the locking nut is of a circular ring structure with internal threads.
Test operation of technique three: adjusting the levelness and the coaxiality of the incident rod and the transmission rod, and checking whether the strain gauge is attached; placing a test piece 4 in grooves of the main clamp body 1 and the auxiliary clamp body 2, and locking and fixing the main clamp body 1, the auxiliary clamp body 2 and the test piece 4 through a locking nut 3 after the test piece 4 is placed; the main clamp body 1 is connected with a Hopkinson pull rod piece through a threaded rod; checking the levelness and coaxiality of the incident rod and the transmission rod again; opening the strain gauge and opening the data acquisition system; carrying out a high strain rate dynamic tensile test; and repeating the steps.
The third prior art has the following disadvantages: for the split Hopkinson pull rod test fixture, the main fixture body and the auxiliary fixture body are connected through the threaded connection method, but gaps are easy to occur due to threaded matching, and the main fixture body and the auxiliary fixture body are easy to loosen in the high strain rate tensile test process, so that signal jitter is caused.
The prior art is four: patent No. CN 206876480U discloses a detachable dynamic tensile test fixture (as shown in fig. 14-19, in the figure, 1-main fixture body, 2-auxiliary fixture body, 3-thread fixing fixture, 4-reinforcing sheet, 5-test piece, 6-groove, 7-cylinder structure, 8-semi-cone structure), which comprises main fixture body 1, auxiliary fixture body 2, reinforcing sheet 3 and thread fixing fixture 4. The main clamp body 1 is L-shaped, one end of a short edge of the L shape is a cylindrical structure 7, a circular blind hole is formed in the cylindrical structure 7, an internal thread matched with the Hopkinson pull rod is arranged in the blind hole, the end face of the cylindrical structure 7 is a fillet, and four grooves (namely four sides) are uniformly distributed on the outer side wall of the end face, so that the assembly is convenient; one end of the long side of the L shape is a half flat-head conical structure 8, the outer side wall of the end part of the half flat-head conical structure 8 is provided with an external thread, the central plane of the inner side is longitudinally provided with a groove 6, the main body of the groove 6 is a rectangular flat structure, the end part is horn-shaped, and the depth of the horn-shaped structure at the end part of the groove 6 is gradually reduced from the bottom of the half flat-head conical structure to the end part for placing a test piece; and an arc chamfer is arranged at the joint of the groove 6 of the main clamp body 1 and the cylindrical structure 7. The shape and the structure of the auxiliary clamp body 2 are completely the same as the half-truncated-cone structure 8 of the main clamp body 1, the shape of the groove 6 of the auxiliary clamp body 2 is the same as the shape of the groove 6 of the main clamp body 1, and the shapes of the groove 6 and the reinforcing sheet 3 are matched; the main clamp body 1 and the auxiliary clamp body 2 are matched to form a complete truncated cone structure, the outer diameter of the conical bottom of the truncated cone structure is matched with the outer diameter of the cylindrical structure 7 of the main clamp body 1, and the center of the truncated cone structure is provided with a groove 6. The shape of the reinforcing piece 3 is matched with the shape of the groove 6 of the main clamp body 1 and the auxiliary clamp body 2, the reinforcing piece is a cuboid with an inclined plane, and the length of the reinforcing piece 3 is smaller than that of the groove 6; during operation, the test piece 5 is adhered to the outer side of the test piece 5 by glue, the upper side and the lower side of the test piece 5 are respectively adhered with a reinforcing sheet, and one reinforcing sheet is placed in the groove 6. The thread fixing clamp 4 is of a hexagonal structure, a central through hole is formed in the thread fixing clamp, and internal threads matched with the threads of the outer side walls of the main clamp body and the auxiliary clamp body are formed in the inner side wall of the central through hole.
Assembly steps of the fourth technique: strengthen piece 4 with gluing in test piece 5 one side, main anchor clamps bodies 1 and the supporting pull rod pass through circular blind hole female connection, main anchor clamps bodies 1 and vice anchor clamps bodies 2 through the recess 6 fixed test piece 5 at center, thread tightening anchor clamps 3 through the internal thread on the taper hole with main anchor clamps bodies 1, vice anchor clamps on 2 the external screw-thread fit.
Experimental procedure for technique four: before the test, a material to be tested is cut into a strip-shaped test piece 5, the width of the test piece needs to be matched with the grooves 6 of the main clamp body 1 and the auxiliary clamp body 2, two reinforcing pieces 4 are adhered to two side faces of the test piece 5 through glue, the test piece 5 is placed into the groove 6 of the main clamp body 1, then the groove of the auxiliary clamp body 2 is attached to the test piece 5, the thread fixing clamp 3 is screwed into the main clamp body 1 and the auxiliary clamp body 2, the conical surface of the inner conical hole of the thread fixing clamp 3 is matched with the conical surfaces of the main clamp body 1 and the auxiliary clamp body 2, the test piece is fixed to ensure that the test piece cannot slip, finally the main clamp body 1 is assembled on the pull rod through the inner threads matched with the pull rod, and as shown in figure 1.5.6, a high strain rate test is completed through dynamic stretching.
The fourth prior art has the following disadvantages: for the above-mentioned dismantled and assembled dynamic tensile test anchor clamps, though adopt sticky and thread tightening's mode to guarantee that the slippage can not take place for the test piece, the connected mode is comparatively complicated, and is higher to the machining precision requirement of reinforcing piece, and thread tightening anchor clamps still have more clearance after the assembly is accomplished, and the propagation of interference stress wave influences experimental effect.
Disclosure of Invention
The invention aims to overcome the defects of the related technology, provides the dynamic tensile test fixture for the split Hopkinson pull rod sheet test piece, which has the advantages of simple structure, convenience in assembly and low processing requirement, effectively solves the problem of sheet test piece slippage in the test process, ensures the stability of fastening the fixture and the test piece, ensures the waveform propagation integrity in the test process, avoids the interference on stress waves, and effectively improves the test data precision.
The purpose of the invention is realized by the following technical scheme:
tensile anchor clamps of disconnect-type hopkinson pull rod thin slice test piece includes:
the main clamp body is semi-cylindrical, a fixing block and a positioning lug are arranged on a semi-circular section of the main clamp body, a positioning clamping groove is formed between the fixing block and the positioning lug, a placing groove for placing a test piece is formed in the semi-circular section of the main clamp body, the placing groove comprises a cuboid part and a chamfering part, the chamfering part penetrates through one end, far away from the fixing block, of the main clamp body, and a positioning cylinder is arranged in the center of the cuboid part of the placing groove;
the auxiliary clamp body is semi-cylindrical, the auxiliary clamp body is provided with a positioning groove matched with the positioning lug on a semi-circular tangent plane, the protrusion of the auxiliary clamp body at the positioning groove is a positioning fixture block, the positioning fixture block is matched with the positioning groove, and the auxiliary clamp body is provided with a positioning blind hole matched with the positioning cylinder on the semi-circular tangent plane.
Furthermore, the main clamp body and the auxiliary clamp body are matched to form a complete cylinder structure.
Further, after the fixing block and the positioning lug are installed, the cross section of the main clamp body is F-shaped.
Furthermore, a cylindrical threaded rod connected with an incident rod and a transmission rod of the test device is arranged on one side face, far away from the positioning bump, of the fixing block.
Further, the diameter of the cylindrical threaded rod is the same as the diameter of the internal thread of the rod piece of the test device, and the thread specification is M10.
Further, the diameter of a cylindrical structure formed by matching the main clamp body and the auxiliary clamp body is consistent with the diameter of an incident rod and the diameter of a transmission rod of the Hopkinson pull rod, and the diameters of the cylindrical structure and the transmission rod are both 19 mm; the consistency between the clamp structure and the incident rod and the consistency between the clamp structure and the transmission rod of the test device are better, the interference on stress wave propagation is reduced, and the test effect is improved.
Furthermore, a connecting cylinder is arranged between the cylindrical threaded rod and the fixed block, one end of the connecting cylinder is fixedly connected with the cylindrical threaded rod, the other end of the connecting cylinder is fixedly connected with the fixed block, the height of the connecting cylinder is 2mm, and the diameter of the cylinder structure is 7 mm.
Furthermore, the test piece is a sheet dumbbell-shaped test piece, and a positioning round hole matched with the positioning cylinder is formed in the center of the clamping end of the test piece.
Further, the thickness of the test piece and the depth of the placing groove are both 2 mm.
Further, after the main clamp body and the auxiliary clamp body are assembled, a distance of 1mm is reserved between the top surface of the positioning cylinder and the bottom surface of the positioning blind hole; therefore, the problem that the positioning cylinder in the main clamp groove and the positioning blind hole of the auxiliary clamp are not matched with each other due to the machining precision problem can be solved.
The experimental operation method of the tensile clamp comprises the following steps:
1) checking whether the strain gauges are attached or not, wherein the strain gauges are respectively arranged on the incident rod and the transmission rod; adjusting the levelness and coaxiality of the incident rod and the transmission rod to ensure that the rod pieces are kept horizontal and coaxial; and checking whether the power supply is safe or not, and connecting the ground wire.
2) The clamp is connected with a rod piece of the test equipment through a cylindrical threaded rod, and in order to ensure that the clamp and the rod piece can be tightly connected and eliminate waveform clutter caused by threaded connection, the threaded connection is fastened by thread seal tape coupling.
3) And the levelness and the coaxiality of the incident rod and the transmission rod are checked again, so that errors caused by the raw material belt are avoided.
4) Placing a test piece into the placing groove, and matching a positioning round hole of the test piece with the positioning cylinder; after the test piece is placed in the placing groove, high-strength glue is coated on the upper surface of the test piece, and the main clamp body, the auxiliary clamp body and the test piece are adhered together; after the main clamp body and the auxiliary clamp body are assembled, a cylindrical structure with the same diameter as the rod piece of the test equipment is formed.
5) The levelness and the coaxiality of the incident rod, the transmission rod and the clamp are checked, and the rod piece and the clamp are ensured to be horizontal and coaxial.
6) And (3) poking an impact rod of the test equipment into a gun barrel of the Hopkinson pull rod, and opening the strain gauge, the data acquisition system and the data acquisition software.
7) And checking whether the split Hopkinson pull rod system is ready again. And opening an inflation valve, and inflating the air cylinder until the pressure required by the test is reached.
8) And clicking a data acquisition button of data acquisition software, pulling a switch of a pull rod system to a launching position, launching a striking rod, and carrying out a high strain rate dynamic tensile test to research the influence of different strain rates on the dynamic tensile mechanical property of the material.
The invention has the beneficial effects that:
compared with the prior art, the clamp is simple and convenient to assemble, the processing requirement is low, the test piece is not in threaded connection with the clamp, thread gaps for interfering stress wave propagation do not exist, the problem that the clamp is not matched and fastened due to the thread gaps is solved, the integrity of the waveform in the propagation process can be ensured, the positioning cylinder on the main clamp body is matched with the positioning blind hole on the auxiliary clamp body, the test piece is clamped in the middle, the test piece can be prevented from slipping, and the clamp is fastened with the test piece. In addition, the threaded connection between the clamp and the test equipment rod piece is filled with thread gaps by using the raw material belt, so that wave form clutter can be avoided.
Compared with the prior art II, the positioning cylinder on the main clamp body is matched with the positioning blind hole on the auxiliary clamp body to clamp the test piece in the middle, so that the test piece can be prevented from slipping, the main clamp body and the auxiliary clamp body of the clamp are not in threaded connection, and no thread gap is generated, so that the clamp has a stable clamping state on the test piece in a high-strain-rate stretching process, the clamp cannot loosen the fastening of the test piece due to the thread gap, the stress surface of the test piece in the stretching direction changes slightly, the stress wave shape is complete in the propagation process, and the obtained data precision is high.
Compared with the third prior art, the main clamp body and the auxiliary clamp body are simple and stable to assemble and are connected without threads, the problem that gaps are prone to occur between thread matching is solved, the positioning cylinder is matched with the round hole and the positioning blind hole of the clamping end of the test piece, the test piece can be prevented from slipping in a high-strain-rate experiment, the stress state of the test piece in the experiment process is stable, and the stress wave waveform is complete. In addition, the threaded connection between the clamp and the test equipment rod piece is filled with thread gaps by using the raw material belt, so that wave form clutter can be avoided.
Compared with the prior art, the clamp is simple and stable in connection mode, the clamps are in thread-free connection, the processing requirement is low, thread gaps cannot occur, the problem that the clamps are not matched and fastened due to the thread gaps in the high-strain-rate stretching process cannot occur, the integrity of waveforms in the transmission process can be ensured, the positioning cylinders are matched with the positioning blind holes, the test piece is clamped in the middle, the test piece can be prevented from slipping, and the fastening between the test piece and the clamps is ensured. Only when the test piece is assembled, the upper surface of the test piece is coated with glue, and no glue is applied to the groove, so that the clamp and the test piece are fastened, and the inconvenience in loading and unloading the test piece caused by two-side glue application is avoided. In addition, the threaded connection between the clamp and the test equipment rod piece is filled with thread gaps by using the raw material belt, so that wave form clutter can be avoided.
Drawings
FIG. 1 is a schematic diagram of a dynamic tensile test fixture according to the first prior art;
FIG. 2 is a schematic perspective view of a main fixture of a first prior art dynamic tensile test fixture;
FIG. 3 is a schematic perspective view of a clamping piece of a first prior art dynamic tensile test fixture;
FIG. 4 is a schematic perspective view of a screw fastening fixture of a dynamic tensile test fixture according to the first prior art;
FIG. 5 is a diagram illustrating the state of use of a Hopkinson bar of the second prior art;
FIG. 6 is a schematic structural diagram of a second clamping device of the prior art;
FIG. 7 is a top view of FIG. 6 with the press block and bolt removed;
FIG. 8 is a right side view of FIG. 6;
FIG. 9 is a sectional view of a prior art clamp assembly;
FIG. 10 is a schematic structural diagram of a third prior art main clamp;
FIG. 11 is a schematic structural view of a third prior art sub-clamp;
FIG. 12 is a schematic structural view of a locking nut of the prior art III;
FIG. 13 is a schematic illustration of a sample of prior art three;
FIG. 14 is a schematic structural view in general section of a prior art four;
FIG. 15 is a perspective view of a master clamp of the prior art four;
FIG. 16 is a perspective view of a prior art sub-clamp;
FIG. 17 is a perspective view of a prior art four thread mounting fixture;
FIG. 18 is a perspective view of a prior art reinforcing sheet;
FIG. 19 is a schematic view of an assembled structure of a prior art four;
FIG. 20 is a cross-sectional view of an assembled configuration of a stretch clip provided in accordance with the present invention;
fig. 21 is a schematic structural view of a main clamp body of the stretching clamp provided by the present invention;
fig. 22 is a schematic structural view of a sub-clamp body of the stretching clamp provided by the present invention;
FIG. 23 is a schematic structural diagram of a sheet-like test piece matched with the tensile fixture provided by the invention;
fig. 24 is an assembly view of the tension clamp provided by the present invention.
List of numbers in the figures of the invention: 1-main clamp body, 2-auxiliary clamp body, 3-sheet sample, 4-test equipment rod piece, 5-cylindrical threaded rod, 6-positioning clamping groove, 7-positioning lug, 8-placing groove, 9-positioning cylinder, 10-positioning clamping block, 11-positioning groove, 12-positioning blind hole and 13-positioning round hole.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
Referring to fig. 20-24, the invention provides a dynamic tensile test fixture for a split hopkinson pull rod sheet test piece, which has the advantages of simple structure, convenience in assembly and low processing requirement, effectively solves the problem of sheet test piece slippage in the test process, ensures the stability of fastening the fixture and the test piece, ensures the waveform propagation integrity in the test process, avoids interference on stress waves, and effectively improves the test data precision.
The tensile clamp of the split Hopkinson pull rod thin sheet test piece comprises two main clamp bodies 1 and an auxiliary clamp body 2; the main clamp body 1 is in a semi-cylindrical shape, a fixing block (not marked in the figure) and a positioning bump 7 are arranged on a semi-circular section of the main clamp body 1, a positioning clamping groove 6 is formed between the fixing block and the positioning bump 7, a placing groove 8 for placing a sheet-shaped test piece 3 is formed in the semi-circular section of the main clamp body 1, the placing groove 8 comprises a cuboid part and a chamfering part, the chamfering part penetrates through one end, far away from the fixing block, of the main clamp body 1, and a positioning cylinder 9 is arranged at the center of the cuboid part of the placing groove 8; the auxiliary clamp body 2 is in a semi-cylindrical shape, the auxiliary clamp body 2 is provided with a positioning groove 11 matched with the positioning lug 7 on a semi-circular tangent plane, the protrusion of the auxiliary clamp body 2 at the positioning groove 11 is a positioning fixture block 10, the positioning fixture block 10 is matched with the positioning fixture groove 6, and the auxiliary clamp body 2 is provided with a positioning blind hole 12 matched with the positioning cylinder 9 on the semi-circular tangent plane.
The positioning cylinder 9 on the main clamp body 1 and the positioning blind hole 12 on the auxiliary clamp body 2 are mutually matched and connected; specifically, the positioning round holes 13 and the positioning blind holes 12 on the positioning cylinder 9 and the sheet-shaped test piece 3 are matched with each other, so that the test piece 3 can be prevented from slipping in a high-strain-rate tensile test, and the fastening degree of the clamp and the test piece 3 is ensured. The positioning mode has no thread clearance possibly generated by the thread positioning mode, and the integrity of the waveform in the propagation process can be ensured to be better.
In some examples, it is within the scope of the present invention to replace the mating positioning projections and positioning recesses between the main clamp body 1 and the auxiliary clamp body 2 with positioning cylinders and positioning blind holes.
In some examples, it is also within the scope of the present invention to replace the positioning cylinders 9 and the positioning blind holes 12 used for positioning the main chuck body 1, the sub-chuck body 2, and the sheet-like test piece 3 in the present chuck with a plurality of positioning cylinders 9 and positioning blind holes 12, or to change the positions of the positioning cylinders 9 and the positioning blind holes 12 (i.e., to provide the positioning cylinders 9 on the sub-chuck body 2 and the positioning blind holes 12 on the main chuck body 1).
In some examples, the main clamp body 1 and the auxiliary clamp body 2 are matched to form a complete cylinder structure; after the fixing block and the positioning lug 7 are installed, the section of the main clamp body 1 is F-shaped.
In some examples, the fixing block is provided with a cylindrical threaded rod 5 connected with an incident rod and a transmission rod of the test device on one side far away from the positioning lug 7; preferably, the fixing block is cylindrical and is positioned at one end of the main clamp body 1, and the fixing block and the main clamp body 1 are of an integral structure; specifically, a cylindrical threaded rod 5 is installed at the center of the fixing block, and the central axis of the cylindrical threaded rod 5 coincides with the semicircular central axis of the main clamp body 1.
In some examples, the diameter of the cylindrical threaded rod 5 is the same as the diameter of the internal thread of the trial rod 4, with a thread gauge of M10; the diameter of a cylindrical structure formed by matching the main clamp body 1 and the auxiliary clamp body 2 is consistent with the diameters of an incident rod and a transmission rod of the Hopkinson pull rod, and the diameters of the incident rod and the transmission rod are 19 mm; the consistency between the clamp structure and the incident rod and the consistency between the clamp structure and the transmission rod of the test device are better, the interference on stress wave propagation is reduced, and the test effect is improved.
In some examples, a connecting cylinder (not labeled in the figures) is arranged between the cylindrical threaded rod 5 and the fixing block, one end of the connecting cylinder is fixedly connected with the cylindrical threaded rod 5, the other end of the connecting cylinder is fixedly connected with the fixing block, the height of the connecting cylinder is 2mm, and the diameter of the cylindrical structure is 7 mm.
In some examples, the test piece 3 is a sheet dumbbell-shaped test piece, and a positioning round hole 13 matched with the positioning cylinder 9 is formed in the center of the clamping end of the test piece 3; the thickness of the test piece 3 and the depth of the placing groove 8 are both 2 mm.
In some examples, after the main clamp body 1 and the auxiliary clamp body 2 are assembled, the distance between the top surface of the positioning cylinder 9 and the bottom surface of the positioning blind hole 12 is 1 mm; therefore, the problem that the positioning cylinder 9 on the main clamp body 1 and the positioning blind hole 12 on the auxiliary clamp body 2 are not matched with each other due to the problem of machining precision can be avoided.
In some examples, the thread gap at the threaded connection of the cylindrical threaded rod 5 and the rod 4 is filled with a raw material tape, eliminating wave noise caused by the threaded connection.
The structure of the present clamp is assembled (as shown in fig. 24):
1) the main clamp body 1 is connected with the testing equipment rod piece 4 through a cylindrical threaded rod 5 in a threaded connection mode, and thread gaps at threaded connection positions are filled with raw material belts to eliminate waveform clutter.
2) Placing the sheet-shaped test piece 3 into the placing groove 8 of the main clamp body 1, and matching the positioning round hole 13 of the test piece 3 with the positioning cylinder 9;
3) cooperate the positioning fixture block 10 of the vice anchor clamps body 2 with the positioning groove 6 of the main anchor clamps body 1, the positioning groove and 11 of the vice anchor clamps body 2 cooperate with the positioning lug 7 of the main anchor clamps body 1, the location blind hole 12 of the vice anchor clamps body 2 cooperates with the location cylinder 9 of the main anchor clamps body 1, make the main anchor clamps body 1 cooperate into a complete cylinder structure with the vice anchor clamps body 2, the diameter of cylinder structure is the same with the diameter of test equipment member 4, it is better to ensure the uniformity of this anchor clamps and test equipment member 4, reduce the interference to stress wave propagation, and the test effect is improved.
The experimental operation method of the clamp comprises the following steps:
1) checking whether the strain gauges are attached or not, wherein the strain gauges are respectively arranged on the incident rod and the transmission rod; adjusting the levelness and coaxiality of the incident rod and the transmission rod to ensure that the rod pieces 4 are kept horizontal and coaxial; and checking whether the power supply is safe or not, and connecting the ground wire.
2) The clamp is connected with a rod piece 4 of the test equipment through a cylindrical threaded rod 5, and in order to ensure that the clamp and the rod piece 4 can be tightly connected and eliminate waveform clutter caused by threaded connection, the threaded connection is tightly fastened by thread tape coupling.
3) And the levelness and the coaxiality of the incident rod and the transmission rod are checked again, so that errors caused by the raw material belt are avoided.
4) Placing the test piece 3 into the placing groove 8, and matching the positioning round hole 13 of the test piece 3 with the positioning cylinder 9; after the test piece 3 is placed in the placing groove 8, high-strength glue is coated on the upper surface of the test piece, and the main clamp body 1, the auxiliary clamp body 2 and the test piece 3 are adhered together; after the main clamp body 1 and the auxiliary clamp body 2 are assembled, a cylindrical structure with the same diameter as the rod 4 of the test device is formed.
5) The horizontality and coaxiality of the incident rod, the transmission rod and the clamp are checked, and the rod piece 4 and the clamp are ensured to be horizontal and coaxial.
6) And (3) poking an impact rod of the test equipment into a gun barrel of the Hopkinson pull rod, and opening the strain gauge, the data acquisition system and the data acquisition software.
7) And checking whether the split Hopkinson pull rod system is ready again. And opening an inflation valve, and inflating the air cylinder until the pressure required by the test is reached.
8) And clicking a data acquisition button of data acquisition software, pulling a switch of a pull rod system to a launching position, launching a striking rod, carrying out a high strain rate dynamic tensile test, and researching the influence of different strain rates on the dynamic tensile mechanical property of the material.
Compared with the prior art, the clamp is simple and convenient to assemble, the processing requirement is low, the test piece 3 is not in threaded connection with the clamp, thread gaps for interfering stress wave propagation do not exist, the problem that the clamp is not matched and fastened due to the thread gaps is solved, the integrity of waveforms in the propagation process can be ensured, the positioning cylinder 9 on the main clamp body 1 is matched with the positioning blind hole 12 on the auxiliary clamp body 2, the test piece 3 is clamped in the middle, the test piece can be prevented from slipping, and the clamp is fastened between the test piece 3 and the clamp. In addition, the threaded connection between the clamp and the test equipment rod piece is filled with thread gaps by using the raw material belt, so that wave form clutter can be avoided.
Compared with the prior art II, the positioning cylinder 9 on the main clamp body 1 and the positioning blind hole 12 on the auxiliary clamp body 2 are matched with each other to clamp the test piece 3 in the middle, so that the test piece can be prevented from slipping, and the main clamp body and the auxiliary clamp body of the clamp are not in threaded connection and cannot generate thread gaps, so that the clamp has a stable clamping state on the test piece in a high-strain-rate stretching process, the clamp cannot loosen the fastening of the test piece due to the thread gaps, the stress surface of the test piece in the stretching direction changes slightly, the stress wave waveform is complete in the propagation process, and the obtained data precision is high.
Compared with the prior art III, the main clamp body 1 and the auxiliary clamp body 2 are simple and stable to assemble and are connected without threads, the problem that gaps are prone to appearing between thread matching is solved, the positioning cylinder 9 is matched with the positioning round hole 13 and the positioning blind hole 12 of the clamping end of the test piece 3, the test piece 3 can be prevented from slipping in a high-strain-rate experiment, the stress state of the test piece 3 in the experiment process is stable, and the stress wave waveform is complete. In addition, the threaded connection between the clamp and the test equipment rod piece is filled with thread gaps by using the raw material belt, so that wave form clutter can be avoided.
Compared with the prior art, the clamp is simple and stable in connection mode, the clamps are in thread-free connection, the processing requirement is low, thread gaps cannot occur, the problem that the clamps are not matched and fastened due to the thread gaps in the high-strain-rate stretching process cannot occur, the integrity of waveforms in the transmission process can be ensured, the positioning cylinder 9 is matched with the positioning blind hole 13 to clamp the test piece 3 in the middle, the test piece 3 can be prevented from slipping, and the fastening between the test piece 3 and the clamps can be ensured. Only when the test piece is assembled, the upper surface of the test piece is coated with glue, and no glue is applied to the upper surface of the placing groove 8, so that the clamp and the test piece are fastened, and the inconvenience in loading and unloading the test piece caused by two-side glue coating is avoided. In addition, the threaded connection between the clamp and the test equipment rod piece is filled with thread gaps by using the raw material belt, so that wave form clutter can be avoided.
The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

1. Tensile anchor clamps of disconnect-type hopkinson pull rod thin slice test piece, its characterized in that includes:
the main clamp body is semi-cylindrical, a fixing block and a positioning lug are arranged on a semi-circular section of the main clamp body, a positioning clamping groove is formed between the fixing block and the positioning lug, a placing groove for placing a test piece is formed in the semi-circular section of the main clamp body, the placing groove comprises a cuboid part and a chamfering part, the chamfering part penetrates through one end, far away from the fixing block, of the main clamp body, and a positioning cylinder is arranged in the center of the cuboid part of the placing groove;
the auxiliary clamp body is semi-cylindrical, a positioning groove matched with the positioning lug is formed in the semi-circular section of the auxiliary clamp body, a protrusion of the auxiliary clamp body at the positioning groove is a positioning fixture block, the positioning fixture block is matched with the positioning clamp groove, and a positioning blind hole matched with the positioning cylinder is formed in the semi-circular section of the auxiliary clamp body; after the test piece is placed in the placing groove, high-strength glue is coated on the upper surface of the test piece, and the main clamp body, the auxiliary clamp body and the test piece are adhered together.
2. The tensile fixture of the split hopkinson pull rod thin sheet test piece of claim 1, wherein: the main clamp body with be a complete cylinder structure after the vice clamp body cooperatees, the diameter of cylinder structure keeps unanimous with the diameter of incident pole and the transmission pole of hopkinson pull rod, and its diameter is 19 mm.
3. The tensile fixture of the split hopkinson pull rod thin sheet test piece of claim 1, wherein: and a cylindrical threaded rod connected with an incident rod and a transmission rod of the test device is arranged on one side surface of the fixed block, which is far away from the positioning lug.
4. The tensile fixture of the split hopkinson pull rod thin sheet test piece of claim 3, wherein: the diameter of the cylindrical threaded rod is the same as the diameter of the internal threads of the incident rod and the transmission rod, and the thread specification is M10.
5. The tensile fixture of the split hopkinson pull rod thin sheet test piece of claim 1, wherein: the test piece is a sheet dumbbell-shaped test piece, and a positioning round hole matched with the positioning cylinder is formed in the center of the clamping end of the test piece.
6. The tensile fixture of the split hopkinson pull rod thin sheet test piece of claim 1, wherein: after the main clamp body and the auxiliary clamp body are assembled, the distance of 1mm exists between the top surface of the positioning cylinder and the bottom surface of the positioning blind hole, and the thickness of the test piece and the depth of the placing groove are both 2 mm.
7. The experimental operation method of the tensile jig of the split hopkinson tie bar sheet test piece according to any one of claims 1 to 6, characterized by comprising the steps of:
s1: checking whether the strain gauges are attached or not, wherein the strain gauges are respectively arranged on the incident rod and the transmission rod; adjusting the levelness and the coaxiality of the incident rod and the transmission rod to ensure that the incident rod and the transmission rod are kept horizontal and coaxial; checking whether the power supply is safe and connecting the ground wire;
s2: the clamp is connected with the incident rod and the transmission rod through the cylindrical threaded rod, and is tightly coupled and fastened by a thread connection part in order to ensure that the clamp can be tightly connected with the incident rod and the transmission rod and eliminate waveform clutter caused by thread connection;
s3: the levelness and the coaxiality of the incident rod and the transmission rod are checked again, so that errors caused by the raw material belt are avoided;
s4: placing a test piece into the placing groove, and matching a positioning round hole of the test piece with the positioning cylinder; after the test piece is placed in the placing groove, high-strength glue is coated on the upper surface of the test piece, and the main clamp body, the auxiliary clamp body and the test piece are adhered together; after the main clamp body and the auxiliary clamp body are assembled, a cylindrical structure with the same diameter as the incident rod and the transmission rod is formed;
s5: the levelness and the coaxiality of the incident rod, the transmission rod and the clamp are checked to ensure that the incident rod, the transmission rod and the clamp are horizontal and coaxial;
s6: inserting an impact rod of the test device into a gun barrel of the Hopkinson pull rod, and opening the strain gauge, the data acquisition system and the data acquisition software;
s7: checking whether the split Hopkinson pull rod system is ready again, starting an inflation valve, and inflating the air cylinder until the pressure required by the test is reached;
s8: and clicking a data acquisition button of data acquisition software, pulling a switch of a pull rod system to a launching position, launching a striking rod, and carrying out a high strain rate dynamic tensile test to research the influence of different strain rates on the dynamic tensile mechanical property of the material.
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