CN113281165A - Limit test fixture and method for high-strength steel plate fracture in complex tension-compression path - Google Patents
Limit test fixture and method for high-strength steel plate fracture in complex tension-compression path Download PDFInfo
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- CN113281165A CN113281165A CN202110738003.5A CN202110738003A CN113281165A CN 113281165 A CN113281165 A CN 113281165A CN 202110738003 A CN202110738003 A CN 202110738003A CN 113281165 A CN113281165 A CN 113281165A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/04—Chucks
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
- G01N3/066—Special adaptations of indicating or recording means with electrical indicating or recording means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0001—Type of application of the stress
- G01N2203/0003—Steady
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0017—Tensile
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/0617—Electrical or magnetic indicating, recording or sensing means
Abstract
The invention provides a limit test fixture and a limit test method for fracture of a high-strength steel plate in a complex tension-compression path. The middle part of apron is equipped with the lug of type of protruding, and the microcephaly end of lug is equipped with broach and shoulder pad respectively, and the major part end of lug is equipped with countersunk head bolt through-hole, and the middle part of backplate is equipped with the recess of type of protruding, and the microcephaly end of recess is equipped with broach and shoulder pad respectively, and the major part end of recess is equipped with countersunk head bolt through-hole and screw adapter in proper order. The countersunk head bolt through hole of the cover plate is fixedly connected with the countersunk head bolt through hole of the back plate through a head screw, the first end of the socket head cap screw penetrates through the powerful spring to be connected with the gasket, the second end of the socket head cap screw penetrates through the cover plate and the back plate in sequence to be fixedly connected with the nut, and the electrode plate is positioned in the groove of the back plate. According to the method, the fracture behavior data of the high-strength steel under the complex path can be obtained, and further the damage and instability fracture behavior can be accurately predicted.
Description
Technical Field
The invention relates to the technical field of plate forming test equipment, in particular to a limit test fixture and a limit test method for fracture of a high-strength steel plate in a complex tension-compression path.
Background
In the field of plate forming, the plasticity index and the fracture index of metal are particularly important performance indexes, and how to accurately acquire plasticity and fracture data under various paths is an important basis for formulating a forming process. The sheet material has low compression ratio due to the bending instability phenomenon in the compression test, and the change rule of stress and strain cannot be fully and accurately obtained; the fracture of metal is also influenced by various factors such as metal loading path and strain ratio, and how to accurately acquire fracture data to predict damage and fracture behavior of metal is also a challenge for scientists. Particularly, with the development of light weight of automobiles, most stamping parts of automobiles are made of plates, but high-strength steel has high strength and poor plasticity, requires larger deformation force, and is very easy to generate damage fracture and instability fracture. However, damage and fracture behaviors are highly related to deformation and loading history of the material, and the influence of the deformation history cannot be considered when the traditional method for predicting the plate performance based on the FLD (flash mapping) diagram is used, so that the test of fracture behavior data of the material under a complex path is urgently needed, and the accurate prediction of the damage and unstable fracture behaviors of the high-strength steel is realized. The traditional DIC-based test method is mainly used for testing the fracture strain of the material, but the common instability-preventing clamp is inconvenient for testing optical data and cannot provide large clamping force for the plate, and the instability-preventing heavy-load clamp capable of testing damage behaviors based on electricity is provided by the invention.
Heretofore, the prior art has documented a series of common anti-destabilizing clamping devices: two high-rigidity flat plates are adopted, the test piece is elastically clamped to avoid compression instability, the device cannot perform a compression test and a tension-compression cycle test with large deformation, and meanwhile, the influence of the friction force between the flat plates and the test piece on the test cannot be ignored; a can realize the continuous tension-compression test, the pressure is exerted to the sample through the nonstandard section in this apparatus in the form of frictional force, is not suitable for the material with high yield strength of high-strength steel class; the utility model provides a clamping device of sheet metal compression experiment, the nonstandard section of sample is cliied through two splint, and the middle part uses two clamp splice to pass through resilient means and presss from both sides tight sample, but this device unbalanced arrangement's gravity can not guarantee the big compressive capacity of expectation. Meanwhile, the devices have the defects of complex structure, inconvenience in damage and fracture detection of the steel plate and the like. Therefore, a heavy-load fixture which can realize a complex tension-compression path and sensitively detect damage behaviors is urgently needed to ensure the test precision.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a limit test fixture and a limit test method for the breakage of a high-strength steel plate in a complex tension-compression path, which are used for detecting the voltage change of a sample in a test based on the damage behavior of electrical test, detecting the internal microcrack of the sample through pressure difference fluctuation, overcoming the defect that the existing damage test technology is only observed from the outside of the sample, identifying the damage and the breakage behavior of the steel plate with high precision, obtaining the breakage behavior data of the high-strength steel in the complex path and further realizing the accurate prediction of the damage and the unstable breakage behavior.
The invention provides a limit test fixture for fracture of a high-strength steel plate in a complex tension-compression path, which comprises a cover plate, a back plate, a strong spring, a gasket, an inner hexagon screw, a nut, an inner hexagon screw through hole, a countersunk head screw, a threaded hole, a shoulder pad, comb teeth, an electrode plate, a lead, a groove, a bump and a threaded adapter. The cover plate comprises an upper cover plate and a lower cover plate, the upper cover plate and the lower cover plate are identical in appearance structure, a convex block in a shape like a Chinese character 'tu' is arranged in the middle of the cover plate, a small head end of the convex block is respectively provided with a first comb tooth, a second comb tooth and a shoulder pad, a large head end of the convex block is provided with a countersunk head bolt through hole, two sides of the small head end of the convex block are respectively provided with a first hexagon socket head bolt through hole and a second hexagon socket head bolt through hole, the back plate comprises an upper back plate and a lower back plate, the upper back plate and the lower back plate are identical in appearance structure, a groove in a shape like a Chinese character 'tu' is arranged in the middle of the back plate, the small head end of the groove is respectively provided with a first comb tooth, a second comb tooth and a shoulder pad, two sides of the small head end of the groove are respectively provided with a first hexagon socket head bolt through hole, and a threaded hole is formed in the middle of the back plate groove. The screw adapter and the press fixed connection of backplate, the countersunk head bolt through-hole of apron pass through countersunk screw with the countersunk head bolt through-hole fixed connection of backplate, the first end of socket cap screw passes powerful spring with the gasket is connected, the second end of socket cap screw passes in proper order the apron with the backplate with nut fixed connection, the electrode slice is located inside the recess of backplate, the first end of wire with the first end of electrode slice is connected, the second end of wire passes the screw hole stretches out the outside of backplate.
Preferably, the socket head cap screw, the washer, the strong spring, and the nut constitute an elastic assembly.
Preferably, the axes of the socket head cap screw, the washer, the strong spring and the nut are on the same straight line.
Preferably, the number of the upper cover plate, the lower cover plate, the upper back plate and the lower back plate is equal, and the size of the convex block of the cover plate is smaller than that of the concave groove of the back plate.
The invention provides a second aspect of the invention, which provides a limit test method for the fracture of the high-strength steel plate in the complex tension-compression path by using the test fixture, and the specific operation steps are as follows:
s1, respectively attaching high polymer material polytetrafluoroethylene (PTFE insulation material for short) to the side faces of the shoulder pads, the first comb teeth and the second comb teeth of the upper back plate, the lower back plate, the upper cover plate and the lower cover plate, wherein the PTFE insulation material is symmetrically distributed on the two sides of the upper back plate and the lower back plate and the two sides of the upper cover plate and the lower cover plate, and simultaneously testing whether a clamp consisting of the upper back plate, the lower back plate, the upper cover plate and the lower cover plate is insulated;
s2, connecting the threaded adapters of the upper back plate and the lower back plate on a press machine through threads, enabling the comb teeth of the upper back plate and the lower back plate to be in cross contact, and adjusting the cross height of the comb teeth of the upper back plate and the lower back plate according to the length of a sample;
s3, placing the positive electrode plate and the negative electrode plate into the grooves of the upper back plate and the lower back plate respectively, connecting the second ends of the leads connected with the positive electrode plate and the negative electrode plate respectively to corresponding detectors, and detecting whether signals output by equipment are stable or not;
s4, lubricating the sample by using a PTFE insulating material, adjusting an upper chuck and a lower chuck of the testing machine, positioning a sample gauge length section, namely the sample gauge length section for measuring the partial length of the sample with the strain or length change of the sample at a comb tooth end, and placing the sample into a back plate groove;
s5, fixedly connecting the upper cover plate and the upper back plate, and fixedly connecting the lower cover plate and the lower back plate by using the elastic components and the countersunk screws, and adjusting the clamping force of the cover plate and the back plate by using the elastic components;
and S6, respectively introducing current to the positive electrode plate and the negative electrode plate through leads, and starting to perform the test.
Compared with the prior art, the invention has the following advantages:
1. according to the invention, according to electrical tests, microcracks in a test sample are detected through pressure difference, the damage and the fracture behavior of a steel plate are identified at high precision, the fracture behavior data of high-strength steel under a complex path can be obtained, and the accurate prediction of the damage and the unstable fracture behavior is further realized; the two ends of the sample are insulated and then connected with the constant-current power supply, the metal pins are led out, voltage change is detected in a test, and the defect that the existing damage test technology is observed from the outside of the sample is overcome.
2. According to the invention, through the cross fit of the comb teeth between the upper cover plate and the lower cover plate and the cross fit of the comb teeth between the upper back plate and the lower back plate, the sample gauge length section is always positioned at the cross fit section of the comb teeth in the whole compression process, and the sample is subjected to lateral force, so that the phenomenon of compression instability of the sample can be effectively avoided within a longer compression distance. In addition, the space between the comb teeth can be used as a strain measuring hole.
3. The cover plate is fixed on the back plate through the countersunk head screw, and the back plate is connected to the press machine through the screw thread. So set up, the gravity transfer of anchor clamps is for the press, no longer floats on the sample, and the device is connected stably. The stretching and compressing integration can be realized, and various complex stretching and compressing paths can be realized.
Drawings
FIG. 1 is a schematic overall structure diagram of the ultimate test fixture and method for the fracture of a high-strength steel plate in a complex tension-compression path according to the invention;
FIG. 2 is a partial detailed view of the upper part of the clamp used in the limit test clamp and method for the fracture of the high-strength steel plate in the complex tension-compression path according to the present invention;
FIG. 3 is a schematic diagram of the upper back plate and the lower back plate matching in the limit test fixture and method for the fracture of the high-strength steel plate in the complex tension-compression path according to the invention;
FIG. 4 is a schematic diagram of a plate sample used in the limit test fixture and method for fracture of a high-strength steel plate in a complex tension-compression path according to the present invention;
FIG. 5 is a schematic diagram of the upper cover plate and the lower cover plate matching in the limit test fixture and method for the fracture of the high-strength steel plate in the complex tension-compression path according to the invention;
FIG. 6 is a schematic view of an upper back plate with electrodes for a limit test fixture and a method for breaking a high-strength steel plate in a complex tension-compression path according to the present invention;
FIG. 7 is a schematic diagram of electrode plates and wires in the limit test fixture and method for fracture of a high-strength steel plate in a complex tension-compression path according to the invention;
FIG. 8 is a rear view of the overall structure of the extreme limit test fixture and method for high strength steel plate fracture in a complex tension-compression path according to the present invention;
FIG. 9 is a drawing and pressing cycle true stress-strain curve and damage signal detection of a Q235 steel plate in the limit test fixture and method for fracture of a high-strength steel plate in a complex drawing and pressing path according to the invention;
FIG. 10 is a diagram illustrating stress-strain curves and damage signal detection of a DP980 steel plate under three different strain tension-compression paths in the limit test fixture and method for breaking of a high-strength steel plate in a complex tension-compression path according to the present invention;
FIG. 11 is a flow chart of a method of the limit test fixture and the method for the fracture of the high-strength steel plate in a complex tension-compression path.
The main reference numbers:
the structure comprises an upper cover plate 1, an upper back plate 2, a lower back plate 3, a lower cover plate 4, a powerful spring 5, a gasket 6, an inner hexagonal screw 7, a nut 8, a first inner hexagonal bolt through hole 9, a second inner hexagonal bolt through hole 10, a countersunk head bolt through hole 11, a threaded hole 12, a shoulder pad 13, first comb teeth 14, second comb teeth 15, an electrode plate 16, a lead 17, a groove 18, a convex block 19, a threaded adapter 20 and a countersunk head screw 21.
Detailed Description
The technical contents, structural features, attained objects and effects of the present invention are explained in detail below with reference to the accompanying drawings.
A limit test fixture for fracture of a high-strength steel plate in a complex tension-compression path comprises a cover plate, a back plate, a strong spring 5, a gasket 6, a socket head cap screw 7, a nut 8, a socket head cap screw through hole, a countersunk head screw through hole 11, a countersunk head screw 21, a threaded hole 12, a shoulder pad 13, comb teeth, an electrode plate 16, a lead 17, a groove 18, a bump 19 and a threaded adapter 20, wherein the high-strength steel plate is shown in figure 1 and figure 8.
As shown in fig. 5, the cover plate includes an upper cover plate 1 and a lower cover plate 4, the upper cover plate 1 and the lower cover plate 4 have the same shape and are rectangular, a convex-shaped projection 19 is disposed in the middle of the cover plate, and is convenient for positioning and matching with the back plate during installation, first comb teeth 14, second comb teeth 15 and a shoulder pad 13 are disposed at the small end of the projection 19, a countersunk bolt through hole 11 is disposed at the large end of the projection 19, and a first hexagon socket head cap bolt through hole 9 and a second hexagon socket head cap bolt through hole 10 are disposed at two sides of the small end of the projection 19. The first comb teeth 14 and the second comb teeth 15 of the shoulder pad 13 arranged on the cover plate are used for matching the upper cover plate 1 with the lower cover plate 4.
As shown in fig. 3, the back plate comprises an upper back plate 2 and a lower back plate 3, the upper back plate 2 and the lower back plate 3 have the same appearance structure and are both rectangular, a concave groove 18 in a shape like a Chinese character 'tu' is arranged in the middle of the back plate and is used for placing a sample and an electrode plate 16, the concave groove 18 in the back plate is in transition with a round angle or an inclined plane to prevent stress concentration, the small head end of the concave groove 18 is respectively provided with a first comb tooth 14, a second comb tooth 15 and a shoulder pad 13, and two sides of the small head end of the concave groove 18 are respectively provided with a first hexagon socket head cap screw through hole 9 and a second hexagon socket head cap screw through hole 10 for installing an elastic component; the big end of the groove 18 is sequentially provided with a countersunk bolt through hole 11 and a threaded adapter 20, and the countersunk bolt through hole 11 is used for fixing a cover plate; the middle part of backplate recess 18 is equipped with screw hole 12 for go up backplate 1 and lower backplate 4 cooperation use, in compression or tensile test, when the sample deflection is too big, the card can't take out in recess 18, and this hole screw in screw of accessible is ejecting with the sample. The first comb teeth 14 and the second comb teeth 15 are always in a matched state in the compression process, sufficient lateral force of the sample is provided to prevent the sample from bending and instability, and the shoulder pads 13 play a certain guiding role.
The threaded adapter 20 of the back plate is fixedly connected with the press, and the countersunk head bolt through hole 11 of the cover plate is fixedly connected with the countersunk head bolt through hole 11 of the back plate through a countersunk head screw 21. The first end of the socket head cap screw 7 penetrates through the strong spring 5 to be connected with the gasket 6, the second end of the socket head cap screw 7 penetrates through the cover plate and the back plate in sequence to be fixedly connected with the nut 8, as shown in fig. 2, the strong spring 5, the cover plate and the back plate are all in a movable state, and the clamping force of the cover plate and the back plate is properly adjusted according to actual conditions.
As shown in fig. 6 and 7, the electrical test system includes signal receiving devices such as electrode pads 16, wires 17, and associated voltage amplifiers. The electrode plate 16 is located inside the groove 18 of the back plate, and the electrode plate 16 is tightly matched with the groove 18 of the back plate and used for applying voltage to the sample. The first end of wire 17 and the first end of electrode slice 16 are connected, and the second end of wire 17 passes screw hole 12 and stretches out the outside of backplate, and wire 17 connects signal receiving equipment to whether the test sample produces the damage in the test process, and the record relevant signal, the damage and the rupture condition of sample under the complicated route are discerned from this.
Specifically, the socket head cap screw 7, the washer 6, the strong spring 5, and the nut 8 constitute an elastic assembly.
Further, in order to make the elastic component function better, the axes of the socket head cap screw 7, the gasket 6, the strong spring 5 and the nut 8 are in the same straight line.
As shown in fig. 2, the number of the upper cover plate 1, the lower cover plate 4, the upper back plate 2 and the lower back plate 3 is equal, in a preferred embodiment of the present invention, the height of the protrusion 19 of the cover plate is about 6mm, the depth of the groove 18 of the back plate is about 7mm, and the shape and size of the protrusion 19 of the cover plate are smaller than the size of the groove 18 of the back plate.
In the clamp, the tensile force (or the pressure) of the test piece is not provided by the friction force between the test piece and the back plate and the cover plate, but the tensile force (or the pressure) is directly applied through the matching with the groove of the back plate, and meanwhile, the clamp does not float on the test piece any more. Therefore, the fixture has the advantages that the gravity or the friction force of the fixture does not interfere with the experiment any more, the overall structure is compact, the fixture is small and exquisite, the fixture is suitable for the fracture limit test of the plate with high yield strength under a complex tension-compression path, and meanwhile, the situation that other fixtures are not suitable for high-strength steel materials due to insufficient friction force can be avoided. In addition, the deformation part of the sample is fully lubricated, and the condition that the friction force between the gauge length section and the comb teeth influences the accuracy of the experiment can not occur.
The whole clamping device is fixed on the press machine through threaded connection, so that the stretching and compressing integration can be realized, a clamp does not need to be replaced midway, the continuous stretching and compressing test can be carried out to measure the Bauschinger effect, and various complex stretching and compressing paths are realized.
The upper cover plate 1, the lower cover plate 4, the upper back plate 2 and the lower back plate 3 in the clamp are respectively provided with a shoulder pad 13 beside the comb teeth, and the upper cover plate, the lower cover plate, the upper back plate 2 and the lower back plate 3 are arranged in a staggered manner from top to bottom and can play a certain positioning and guiding role.
This anchor clamps pass through spring unit and press from both sides the sample tight in the middle of apron and backplate, and the elasticity of adjustment powerful spring 5 can change clamping-force, and uses the spring centre gripping mode economy and simply effective, avoids pneumatic or hydraulic device equipment huge, uses complicacy.
The upper back plate 1 and the lower back plate 4 of the clamp are internally provided with threaded holes 12, and the clamp is used for two functions: firstly, in a compression or tensile test, when the sample is too large in deformation and is clamped in the back plate groove 18 and cannot be taken out, the sample can be ejected out through the hole by using a screw; secondly, the lead of the positive electrode and the negative electrode is led out through the threaded hole 12, the crack state of the sample can be sensitively reflected, and the lead is used for detecting the damage and the fracture condition of metal in different plastic behaviors, so that the accurate prediction of the damage and the unstable fracture behavior of the high-strength steel is realized.
On the other hand, the invention discloses a limit test method for the fracture of a high-strength steel plate in a complex tension-compression path, which comprises the following steps as shown in fig. 11:
s1, respectively attaching high polymer material polytetrafluoroethylene (PTFE for short, interlayer sliding is easily generated) to the side faces of the upper back plate 1, the lower back plate 4, the shoulder pads 13 of the upper cover plate 2 and the lower cover plate 3, the first comb teeth 14 and the second comb teeth 15, so that the friction coefficient is very low (0.04-0.05). under high load, the friction coefficient is reduced to 0.016. in the friction process, a transfer film is formed on the dual surface in a very short time, so that the friction pair is converted into the friction inside the PTFE, and the PTFE insulation material has good chemical stability and thermal stability and is an insulation material, and is respectively and symmetrically distributed on the two sides of the upper back plate 1 and the lower back plate 4, and the upper cover plate 2 and the lower cover plate 3;
s2, connecting the threaded adapters 20 of the upper back plate 1 and the lower back plate 4 on a press machine through threads, enabling the comb teeth of the upper back plate 1 and the lower back plate 4 to be in cross contact, and adjusting the cross height of the comb teeth of the upper back plate 1 and the lower back plate 4 according to the length of a sample;
s3, respectively placing the positive electrode plate and the negative electrode plate in the grooves 18 of the upper back plate 1 and the lower back plate 4, respectively connecting the second ends of the leads 17 respectively connected with the positive electrode plate and the negative electrode plate to corresponding detectors, and simultaneously detecting whether signals output by equipment are stable;
s4, lubricating the sample by using a PTFE insulating material, adjusting an upper chuck and a lower chuck of the testing machine, and enabling a sample gauge length section (the length of a sample part for measuring the strain or the length change of the sample) to be positioned at the comb tooth end as shown in figure 4, and placing the sample into the groove 18 of the back plate;
s5, fixedly connecting the upper cover plate 2 with the upper back plate 1, and fixedly connecting the lower cover plate 3 with the lower back plate 4 by using the elastic components and the countersunk screws 21, and adjusting the clamping force of the cover plate and the back plate by using the elastic components;
and S6, respectively introducing current to the positive electrode plate and the negative electrode plate through the lead 17, and starting to perform the test.
The limit test fixture and method for the fracture of the high-strength steel plate in the complex tension-compression path according to the invention are further described with reference to the following embodiments:
example 1:
s1, respectively attaching high polymer material polytetrafluoroethylene (PTFE insulation material for short) to the side faces of the upper back plate 1, the lower back plate 4, the shoulder pads 13 of the upper cover plate 2 and the lower cover plate 3, the first comb teeth 14 and the second comb teeth 15, wherein the PTFE insulation material is respectively and symmetrically distributed on two sides of the upper back plate 1 and the lower back plate 4, the upper cover plate 2 and the lower cover plate 3, the surfaces in mutual contact are only attached to one side face, whether a clamp composed of the upper back plate 1, the lower back plate 4, the upper cover plate 2 and the lower cover plate 3 is insulated or not is tested, and whether a clamp composed of the upper back plate 1, the lower back plate 4, the upper cover plate 2 and the lower cover plate 3 is insulated or not is tested;
s2, connecting the threaded adapters 20 of the upper back plate 1 and the lower back plate 4 on a press machine through threads, enabling the comb teeth of the upper back plate 1 and the lower back plate 4 to be in cross contact, and adjusting the cross height of the comb teeth of the upper back plate 1 and the lower back plate 4 according to the length of a sample of the Q235 steel plate;
s3, respectively placing the positive electrode plate and the negative electrode plate in the grooves 18 of the upper back plate 1 and the lower back plate 4, respectively connecting the second ends of the leads 17 respectively connected with the positive electrode plate and the negative electrode plate to corresponding detectors, and simultaneously detecting whether signals output by equipment are stable;
s4, lubricating the sample by using PTFE insulating material, adjusting an upper chuck and a lower chuck of the testing machine, and enabling the sample gauge length of the Q235 steel plate to be as shown in figure 4, wherein the partial length L0 of the sample for measuring the strain or length change of the sample is positioned at the comb tooth end, and the sample of the Q235 steel plate is placed in the groove 18 of the back plate;
s5, fixedly connecting the upper cover plate 2 with the upper back plate 1, and fixedly connecting the lower cover plate 3 with the lower back plate 4 by using the elastic components and the countersunk screws 21, and adjusting the clamping force of the cover plate and the back plate by using the elastic components;
s6, as shown in fig. 8, currents are respectively supplied to the positive electrode sheet and the negative electrode sheet through the lead 17 internally connected to the electrode sheet 16, and the test is started, and the experimental data shown in fig. 9 can be obtained.
Fig. 9 is a stress-strain curve drawn under a path of loading, unloading and reloading of the Q235 steel plate under the clamping of the clamp, and a detected voltage change curve, and it can be known from the graph that the test data can be stably output by loading in a tension-compression cycle, and the damage change of the sample can be sensitively reflected, so that the accurate prediction of fracture instability can be realized.
Example 2:
s1, respectively attaching high polymer material polytetrafluoroethylene (PTFE for short) to the side faces of the upper back plate 1, the lower back plate 4, the shoulder pads 13 of the upper cover plate 2 and the lower cover plate 3, the first comb teeth 14 and the second comb teeth 15, wherein PTFE insulating materials are respectively and symmetrically distributed on the two sides of the upper back plate 1 and the lower back plate 4 and the upper cover plate 2 and the lower cover plate 3, the surfaces in mutual contact are only attached to one side face, and whether a clamp composed of the upper back plate 1, the lower back plate 4, the upper cover plate 2 and the lower cover plate 3 is insulated or not is tested;
s2, connecting the threaded adapters 20 of the upper back plate 1 and the lower back plate 4 to a press machine through threads, enabling the comb teeth of the upper back plate 1 and the lower back plate 4 to be in cross contact, and adjusting the cross height of the comb teeth of the upper back plate 1 and the lower back plate 4 according to the length of a test sample of the DP600 steel plate;
s3, respectively placing the positive electrode plate and the negative electrode plate in the grooves 18 of the upper back plate 1 and the lower back plate 4, respectively connecting the second ends of the leads 17 respectively connected with the positive electrode plate and the negative electrode plate to corresponding detectors, and simultaneously detecting whether signals output by equipment are stable;
s4, lubricating the sample by using PTFE insulating material, adjusting an upper chuck and a lower chuck of the testing machine, and enabling a sample gauge length section (the length of a sample part for measuring the strain or the length change of the sample) of the DP980 steel plate to be positioned at a comb tooth end as shown in figure 4, and placing the sample of the DP980 steel plate into a groove 18 of a back plate;
s5, fixedly connecting the upper cover plate 2 with the upper back plate 1, and fixedly connecting the lower cover plate 3 with the lower back plate 4 by using the elastic components and the countersunk screws 21, and adjusting the clamping force of the cover plate and the back plate by using the elastic components;
s6, as shown in fig. 8, the positive electrode sheet and the negative electrode sheet are respectively supplied with current through the lead 17, and the test is started, and the experimental data is plotted as shown in fig. 10.
Fig. 10 is stress strain data obtained for DP980 steel at 5% strain, 10% strain, and 20% strain, respectively (where the 5% strain was followed by the press-then-pull (CT) and pull-then-press (TC) experiments, respectively), and voltage data at break-to-break under single pull. It can be concluded that: the clamp can obtain stable experimental data under any path, and the damage detection device can sensitively reflect the damage initiation of the material.
The results of the embodiments 1 and 2 show that the cover plate and the back plate are mutually matched in the test process, and the comb teeth are in a cross state all the time, so that the buckling generated in the compression process can be effectively avoided. Various cyclic loading paths such as loading, unloading and reverse loading can be stably carried out. In addition, after the electrode plate is placed in the clamp and the detection device is connected, the damage and fracture behaviors of various complex paths can be identified through the change of the pressure difference of the positive electrode and the negative electrode.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope defined by the claims of the present invention.
Claims (5)
1. A limit test fixture for high-strength steel plate fracture in a complex tension-compression path comprises a cover plate, a back plate, a strong spring, a gasket, a socket head cap screw, a nut, a socket head cap screw through hole, a countersunk head screw, a threaded hole, a shoulder pad, comb teeth, an electrode plate, a lead, a groove, a bump and a threaded adapter,
the cover plate comprises an upper cover plate and a lower cover plate, the upper cover plate and the lower cover plate are identical in appearance structure, a convex block in a shape like a Chinese character 'tu' is arranged in the middle of the cover plate, a small head end of the convex block is respectively provided with a first comb tooth, a second comb tooth and a shoulder pad, a large head end of the convex block is provided with a countersunk head bolt through hole, two sides of the small head end of the convex block are respectively provided with a first hexagon socket head bolt through hole and a second hexagon socket head bolt through hole, the back plate comprises an upper back plate and a lower back plate, the upper back plate and the lower back plate are identical in appearance structure, a groove in a shape like a Chinese character 'tu' is arranged in the middle of the back plate, the small head end of the groove is respectively provided with a first comb tooth, a second comb tooth and a shoulder pad, two sides of the small head end of the groove are respectively provided with a first hexagon socket head bolt through hole and a second hexagon bolt through hole, the large head end of the groove is sequentially provided with a countersunk head bolt through hole and a threaded adapter, the middle part of the back plate groove is provided with a threaded hole;
the screw adapter and the press fixed connection of backplate, the countersunk head bolt through-hole of apron pass through countersunk screw with the countersunk head bolt through-hole fixed connection of backplate, the first end of socket cap screw passes powerful spring with the gasket is connected, the second end of socket cap screw passes in proper order the apron with the backplate with nut fixed connection, the electrode slice is located inside the recess of backplate, the first end of wire with the first end of electrode slice is connected, the second end of wire passes the screw hole stretches out the outside of backplate.
2. The limit test fixture for the breakage of a high-strength steel plate in a complex tension-compression path as claimed in claim 1, wherein the socket head cap screw, the gasket, the high-strength spring and the nut form an elastic assembly.
3. The limit test fixture for the breakage of the high-strength steel plate in the complex tension-compression path as claimed in claim 1 or 2, wherein the axes of the socket head cap screw, the gasket, the strong spring and the nut are on the same straight line.
4. The limit test fixture for the breakage of the high-strength steel plate in the complicated tension-compression path as claimed in claim 1, wherein the number of the upper cover plate, the lower cover plate, the upper back plate and the lower back plate is equal, and the size of the convex block of the cover plate is smaller than that of the concave groove of the back plate.
5. The limit test method for the breakage of a high-strength steel plate in a complex tension-compression path according to any one of claims 1 to 4, characterized by comprising the following steps:
s1, respectively pasting PTFE (polytetrafluoroethylene) insulating materials on the side faces of the shoulder pads, the first comb teeth and the second comb teeth of the upper back plate, the lower back plate, the upper cover plate and the lower cover plate, wherein the PTFE insulating materials are respectively and symmetrically distributed on the two sides of the upper back plate and the lower back plate, and the two sides of the upper cover plate and the lower cover plate, and simultaneously testing whether a clamp consisting of the upper back plate, the lower back plate, the upper cover plate and the lower cover plate is insulated;
s2, connecting the threaded adapters of the upper back plate and the lower back plate on a press machine through threads, enabling the comb teeth of the upper back plate and the lower back plate to be in cross contact, and adjusting the cross height of the comb teeth of the upper back plate and the lower back plate according to the length of a sample;
s3, placing the positive electrode plate and the negative electrode plate into the grooves of the upper back plate and the lower back plate respectively, connecting the second ends of the leads connected with the positive electrode plate and the negative electrode plate respectively to corresponding detectors, and detecting whether signals output by equipment are stable or not;
s4, lubricating the sample by using a PTFE (polytetrafluoroethylene) insulating material, adjusting an upper chuck and a lower chuck of the testing machine, enabling a sample gauge length section to be positioned at a comb tooth end, and placing the sample into a back plate groove;
s5, fixedly connecting the upper cover plate and the upper back plate, and fixedly connecting the lower cover plate and the lower back plate by using the elastic components and the countersunk screws, and adjusting the clamping force of the cover plate and the back plate by using the elastic components;
and S6, respectively introducing current to the positive electrode plate and the negative electrode plate through leads, and starting to perform the test.
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| CN202110738003.5A CN113281165B (en) | 2021-06-30 | 2021-06-30 | Limit test fixture and method for high-strength steel plate fracture in complex tension-compression path |
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| CN113281165B (en) | 2022-09-06 |
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