CN114323949B - Normal loading thin plate micro-tensile test device and method - Google Patents
Normal loading thin plate micro-tensile test device and method Download PDFInfo
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- CN114323949B CN114323949B CN202111674524.5A CN202111674524A CN114323949B CN 114323949 B CN114323949 B CN 114323949B CN 202111674524 A CN202111674524 A CN 202111674524A CN 114323949 B CN114323949 B CN 114323949B
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Abstract
The invention provides a device and a method for a normal loading thin plate micro-tensile test, which solve the technical problem of the blank research on the micro-tensile mechanical property of the conventional normal loading thin plate, wherein a first pressure head is arranged in a frame body and is connected with a first pressure head fixing block, the first pressure head fixing block is connected with a nitrogen spring, and a guide column is in sliding connection with the first pressure head fixing block; the second pressure head is connected with the pressure sensor and the second pressure head fixing block; the first pressure head and the second pressure head are opposite, and the edges of the end surfaces of the first pressure head and the second pressure head are provided with fillets; the frame body is provided with a threaded through hole, the threaded through hole is matched with the screw rod, and one end of the screw rod penetrates through the threaded through hole to be connected with the nitrogen spring; the screw is matched with the threaded through hole, so that the rotary motion of the screw is converted into linear motion, the screw applies pressure to the nitrogen spring, the nitrogen spring applies pressure to the first pressure head fixing block and the first pressure head, and normal stress is applied to the sample to be tested; the adjustment of the normal stress of the sample to be tested is realized by screwing in or out the screw rod, and the device can be widely applied to the technical field of mechanical property testing of thin plates.
Description
Technical Field
The application relates to the technical field of mechanical property testing of thin plates, in particular to a device and a method for testing micro-tension of a normally loaded thin plate.
Background
Micro-electro-mechanical systems (MEMS) have a wide application prospect in electronics, medicine, industry, automobiles and aerospace systems due to the characteristics of miniaturization, intellectualization, multifunction, high integration level, suitability for mass production and the like. With the increasing demand for thin metal plate parts due to the continuous development of MEMS technology, how to manufacture thin metal plate micro parts with high quality is one of the key points for promoting the development of MEMS technology. The plastic micro-forming technology is a micro-processing technology for manufacturing the metal sheet micro-parts, has the advantages of good part performance, high precision, low cost, simple device structure, suitability for batch production and the like, and is a key for solving the problem of controllable manufacturing of the metal sheet micro-parts. However, with the reduction of the thickness of the tensile sample, the specific surface area is obviously increased, the plasticity of the material is obviously deteriorated, and a remarkable scale effect phenomenon appears, so that the application of the sheet metal plastic micro-forming technology in the manufacturing of sheet metal parts is severely limited. Research shows that the plasticity of the material can be improved by applying hydrostatic pressure, the material is applied to a sheet forming process such as hydro-mechanical drawing, and the hydro-mechanical drawing technology is also applied to a plastic micro-forming technology in recent years.
However, in the metal sheet plastic micro-forming technology, the research on the sheet micro-stretching mechanical property under normal loading is still blank, especially on the aspect of the sheet material mechanical property influenced by the scale effect, and the main reason is that a corresponding testing device is lacked, especially a stretching testing device which can eliminate the friction influence and only considers the normal loading influence. This limits to some extent the application of normal loading techniques to plastic microforming.
Disclosure of Invention
The invention aims to solve the technical defects, and provides a device and a method for testing the micro-stretching of a normally loaded thin plate, so that the friction force of the thin plate and the mechanical property of a material during normal loading are measured, and the blank of research on the micro-stretching mechanical property of the thin plate under normal loading in the conventional metal thin plate plastic micro-forming technology is filled.
Therefore, the invention provides a normal loading thin plate micro-tensile test device which is provided with a frame, wherein the frame is provided with a frame body, and a first pressure head, a second pressure head, a first pressure head fixing block, a second pressure head fixing block, a nitrogen spring and a guide post are arranged in the frame body; the first pressure head is connected with a first pressure head fixing block, the first pressure head fixing block is connected with a nitrogen spring, the guide post penetrates through the first pressure head fixing block, and the first pressure head fixing block is connected with the guide post in a sliding mode; the second pressure head is respectively connected with the detection end of the pressure sensor and a second pressure head fixing block, and the second pressure head fixing block is connected with the frame body; the end faces of the first pressure head and the second pressure head are arranged oppositely, and the edges of the end faces of the first pressure head and the second pressure head, which are contacted with a sample to be tested, are provided with fillets; a threaded through hole penetrates through the frame of the frame body, a screw rod is arranged in the threaded through hole in a matched threaded connection mode, and one end of the screw rod penetrates through the threaded through hole and extends into the frame body to be connected with the nitrogen spring; the screw rod is matched with the threaded through hole, so that the rotary motion of the screw rod is converted into linear motion, the screw rod applies pressure to the nitrogen spring, the nitrogen spring is compressed due to the pressure, the first pressure head fixing block and the first pressure head are further applied with pressure, and finally normal stress is applied to a sample to be tested loaded between the first pressure head and the second pressure head; by loosening or screwing the screw rod, the adjustment of the normal stress of the sample to be measured can be realized.
The invention also provides a test method of the normal loading thin plate micro-tensile test device, which comprises the following steps:
1) preparing a processed metal sheet, and pretreating two surfaces of the metal sheet, wherein the thickness of the metal sheet is not more than 4 mm; cutting a metal sheet to prepare a sample to be tested, wherein the sample to be tested is a rectangular sample and a tensile sample (35) respectively, and the thicknesses of the rectangular sample and the tensile sample are the same; the method comprises the following steps that a tensile sample is a dumbbell-shaped sample, and the scale distance is calibrated on the dumbbell-shaped sample, wherein the scale distance is a tensile deformation area of the dumbbell-shaped sample;
2) placing the normal loading thin plate micro-tensile test device below a tensile test machine, and enabling the frame body (2) to be located between an upper chuck and a lower chuck of the tensile test machine;
3) respectively and uniformly coating liquid lubricating liquid on the end surfaces of the first pressure head and the second pressure head; placing the rectangular sample prepared in the step 1) between the end faces of a first pressure head and a second pressure head, clamping and fixing the upper end clamping part of the rectangular sample by an upper clamping head of a tensile testing machine, and unfixing the lower end clamping part of the rectangular sample; the end surfaces of the first pressure head and the second pressure head are completely the same in shape and structure and are arranged oppositely;
4) loading a normal force to the nitrogen spring by screwing the screw rod, and further transmitting the normal load to the surfaces of the rectangular samples in the clamping areas of the end faces of the first pressure head and the second pressure head; a first normal load value is obtained through the output of the pressure sensor, and the first normal load value is divided by the area of a contact area of the rectangular sample and the end face of the first pressure head, so that a first normal stress value born by the contact area is obtained through calculation; adjusting the magnitude of the first normal stress value by further unscrewing or screwing the screw, wherein the first normal stress value is required not to exceed the yield stress value of the rectangular sample;
during operation, the rectangular sample in the step 3) and the step 4) is required not to exceed the end face edges of the first pressure head and the second pressure head in the width direction, and the central axis of the rectangular sample is superposed with the action line of the tensile testing machine so as to ensure that the rectangular sample is always kept in a vertical centering state;
5) starting a tensile testing machine, wherein an upper chuck of the tensile testing machine moves upwards at a constant speed to drive the whole rectangular sample to slide upwards relative to a first pressure head and a second pressure head, and in the process, the tensile speed is controlled to be 0.001-100 mm/min to ensure that the rectangular sample is kept intact all the time; outputting a first displacement load curve through a testing system of a tensile testing machine, wherein the constant load in the first displacement load curve is the friction value of the rectangular sample in the first normal stress loading process, and the friction value is divided by the contact area of the rectangular sample and the end surface of the first pressure head to obtain the friction value f of the unit contact surface of the rectangular sample in the sliding process 1 ；
6) Loosening the screw rod, uniformly coating liquid lubricating liquid on the end surfaces of the first pressure head and the second pressure head respectively, operating the tensile testing machine to enable an upper chuck of the tensile testing machine and the rectangular sample to move downwards to the original position, taking down the rectangular sample, replacing the tensile sample prepared in the step 1), clamping and fixing the upper end clamping part of the tensile sample through the upper chuck, and clamping and fixing the lower end clamping part of the tensile sample through the lower chuck; at the moment, the gauge length of the tensile sample is arranged between the end faces of the first pressure head and the second pressure head;
7) loading a normal force to a nitrogen spring by screwing a screw, further transferring the normal load to the surface of a tensile sample in a clamping area of the end faces of a first pressure head and a second pressure head, outputting through a pressure sensor to obtain a second normal load value, dividing the second normal load value by the area of a contact area of the tensile sample and the end face of the first pressure head, and calculating to obtain a second normal stress value born by the tensile sample; adjusting the magnitude of the second normal stress value by further loosening or screwing the screw rod, wherein the second normal stress is required not to exceed the yield stress of the tensile sample, and the second normal stress is equal to the first normal stress value in the step 4);
during operation, the tensile sample in the step 6) and the step 7) is required not to exceed the end face edges of the first pressure head and the second pressure head in the width direction, and the central axis of the tensile sample is superposed with the force action line of the tensile testing machine so as to ensure that the tensile sample is always in a vertical tensile state and in a vertical centering state;
8) starting the tensile testing machine, wherein an upper chuck of the tensile testing machine moves upwards at the same constant speed in the step 5), and in the process, the tensile sample is in a tensile deformation state, and the gauge length of the tensile sample is required to be not beyond the upper edges of the end surfaces of the first pressure head and the second pressure head during tensile deformation; outputting a second position load curve of the tensile sample when the second normal stress is loaded through a testing system of the tensile testing machine; the load value of any point on the second position load-carrying curve is equal to the sum of the instantaneous actual contact friction force f and the plastic deformation load value at the point;
9) calculating the axial strain epsilon of the gauge length when the tensile sample is subjected to tensile deformation according to a real strain calculation formula I l The first formula is: epsilon l ＝lnl/l 0 Wherein, epsilon l Is the axial strain of the gauge length during the tensile deformation of the tensile sample, l is the instantaneous length of the gauge length during the tensile deformation of the tensile sample, l 0 The original gauge length of the tensile sample;
calculating the width direction strain epsilon of the gauge length during the tensile deformation of the tensile sample according to a formula II b The second formula is: r ═ epsilon b /ε t ＝ε b /[-(ε b +ε l )]Then e b ＝-[r/(1+r)]ε l (ii) a In the formula two, ∈ b The wide strain of the gauge length during the tensile deformation of the tensile sample, r is the thickness anisotropy coefficient of the tensile sample, epsilon l Is the axial strain of the gauge length, epsilon, during the tensile deformation of a tensile specimen t The thickness strain of the gauge length is the thickness strain of the tensile sample during tensile deformation; calculating the axial strain epsilon of the gauge length during the tensile deformation of the tensile sample according to the formula I l And the thickness anisotropy coefficient r of the tensile sample, and calculating to obtain the width strain epsilon of the gauge length when the tensile sample is subjected to tensile deformation b ；
Calculating the instantaneous width w of the gauge length when the tensile sample is subjected to tensile deformation according to a third formula, wherein the third formula is as follows: epsilon b ＝lnw/w 0 Wherein, epsilon b Is the wide strain of the gauge length during the tensile deformation of the tensile sample, w is the instantaneous width of the gauge length during the tensile deformation of the tensile sample, w 0 The original gauge length width of the tensile sample; calculating the width-direction strain epsilon of the gauge length during the tensile deformation of the tensile sample according to a formula II b And the original gauge width w of the tensile specimen 0 Calculating to obtain the instantaneous width w of the gauge length when the tensile sample is subjected to tensile deformation;
calculating the instantaneous contact area S of the gauge length and the end surface of the first pressure head during the tensile deformation of the tensile sample according to the formula IV 11 The formula four is: s 11 L is the instantaneous length of the gauge length when the tensile sample is subjected to tensile deformation, and w is the instantaneous width of the gauge length when the tensile sample is subjected to tensile deformation; multiplying the instantaneous length l of the gauge length during the tensile deformation of the tensile sample in the formula I and the instantaneous width w of the gauge length during the tensile deformation of the tensile sample in the formula III to calculate the instantaneous contact area S between the gauge length during the tensile deformation of the tensile sample and the end surface of the first pressure head 11 ；
Calculating the instantaneous contact area S of the tensile sample and the first pressure head according to the formula V 1 The fifth formula is: s 1 ＝S 11 +S 12 Wherein S is 11 Is the instantaneous contact area between the gauge length and the end face of the first pressure head during the tensile deformation of the tensile sample, S 12 To be stretchedThe instantaneous contact area between the area outside the gauge length and the end face of the first pressure head when the sample is subjected to tensile deformation; calculating to obtain the instantaneous contact area S of the gauge length and the end surface of the first pressure head during the tensile deformation of the tensile sample according to the formula IV 11 The instantaneous contact area S of the area outside the gauge length and the end face of the first pressure head when the tensile sample is subjected to tensile deformation is calculated through conventional measurement 12 Adding the two to obtain the instantaneous contact area S of the tensile sample and the first pressure head 1 ；
And (3) calculating the instantaneous actual contact friction force f during the tensile deformation of the tensile sample according to a formula six, wherein the formula six is as follows: f ═ S 1 f 1 +S 2 f 2 ＝2S 1 f 1 Wherein S is 2 The instantaneous contact area S of the tensile sample and the first pressure head is obtained from the instantaneous contact area S of the tensile sample and the second pressure head and the formula V 1 Equal; f. of 2 The friction value of the unit contact surface when the tensile sample is in tensile deformation and the friction value f of the unit contact surface when the rectangular sample obtained in the step 5) slides 1 Equal;
in the stretching process of the tensile sample, the displacement of the tensile sample corresponds to the instantaneous actual contact friction force f of the tensile sample in the stretching deformation, which is obtained by calculation according to the formula six, namely, an actual contact friction force and displacement curve of the tensile sample in the stretching deformation is obtained when the second normal stress is loaded;
10) and (3) correspondingly subtracting the actual contact friction force obtained in the step (9) from the load value at any point on the second position load transfer curve obtained in the step (8) and the instantaneous actual contact friction force f which is positioned on the displacement curve and is at the same displacement value as the second position load transfer curve, so as to obtain the plastic deformation load value at the displacement value, and finally obtaining the displacement load curve of the plastic deformation of the tensile sample during the second normal stress loading.
The invention has the beneficial effects that: the invention provides a device and a method for testing normal loading thin plate micro-stretching, which can flexibly change the normal pressure on one hand through a screw mechanical pressing mode (electric or hydraulic pressing can also be used). By utilizing the characteristic that the pressure of a piston rod of the nitrogen spring is slightly influenced by small expansion, the problems of normal pressure reduction and the like caused by thickness reduction due to deformation of a tensile sample can be effectively avoided, and the accuracy and the stability of the normal loading test are ensured; on the other hand, the invention not only can test the tensile mechanical property of the thin plate under normal loading, but also can test the friction behavior in the plastic deformation process of the thin plate, and can realize the friction behavior measurement in the plastic deformation process of the small thin plate under different interface conditions through a pressure head; thirdly, the device provided by the invention has the advantages of ingenious structural design, convenient component replacement and better flexibility.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
FIG. 1 is a schematic structural diagram of a perspective view of one aspect of the present invention;
FIG. 2 is a schematic perspective view of the alternate view of FIG. 1;
FIG. 3 is a schematic top view of the present invention;
FIG. 4 is a schematic structural view of a partial sectional view A-A shown in FIG. 3;
FIG. 5 is a schematic view of the structure shown in FIG. 3 in partial cross-section;
FIG. 6 is a schematic structural diagram of FIG. 4 illustrating loading of a sample to be tested;
FIG. 7 is a schematic structural diagram of FIG. 5 illustrating loading of a sample to be tested;
FIG. 8 is a schematic view of an enlarged view of the portion A shown in FIG. 6;
FIG. 9 is a schematic view of an enlarged view of the portion B shown in FIG. 7;
FIG. 10 is a schematic view of an alternative configuration of the first ram or the second ram;
FIG. 11 is an enlarged view of the portion C shown in FIG. 10;
FIG. 12 is a schematic diagram of a structure for preparing a rectangular sample and a tensile sample by cutting a metal sheet;
fig. 13 is a schematic structural view of loading a rectangular sample, wherein (a) is a schematic structural view of loading the rectangular sample between a first pressure head and a second pressure head in an original gauge length state, and (b) is a schematic structural view of the entire rectangular sample in an upward sliding state relative to the first pressure head and the second pressure head;
fig. 14 is a schematic structural diagram of a loaded tensile specimen, wherein (a) is a schematic structural diagram of the tensile specimen loaded between a first pressure head and a second pressure head in an original gauge length state, and (b) is a schematic structural diagram of the tensile specimen loaded between the first pressure head and the second pressure head in an upward tensile deformation state;
fig. 15 is a schematic diagram showing a structure in which two different regions are marked on the enlarged view of the portion D shown in fig. 14 (b) (the regions are distinguished by oblique lines, and the regions are the same in the same direction and different in the direction).
The labels in the figure are: 1. a frame; 2. a frame body; 3. a first ram; 4. a second ram; 5. a first pressure head fixing block; 6. a second pressure head fixing block; 7. a nitrogen spring; 8. a guide post; 9. a pressure sensor; 10. a sample to be tested; 11. round corners; 12. a threaded through hole; 13. a screw; 14. a first ram mounting hole; 15. a nitrogen spring mounting hole; 16. a pressure sensor mounting hole; 17. a second ram mounting hole; 18. a first cushion block; 19. a second cushion block; 20. a first bolt; 21. a second bolt; 22. a wiring hole; 23. a first nut; 24. a first backing plate; 25. a second nut; 26. a second backing plate; 27. a base; 28. a pillar; 29. a support; 30. a gap; 31. steel molding; 32. soft molding; 33. the convex-concave matching structure; 34. a rectangular sample; 35. stretching a sample; 36. a gauge length line; 37. a metal thin plate; 38. the instantaneous contact area of the gauge length and the end face of the first pressure head 3 when the tensile sample 35 is subjected to tensile deformation; 39. the instantaneous contact area between the area outside the gauge length when the tensile sample 35 is subjected to tensile deformation and the end face of the first indenter 3; l 0 Original gauge length for tensile specimen 35; l is the instantaneous length of the gauge length when the tensile sample 35 is subjected to tensile deformation; w is a 0 Original gauge length width for tensile specimen 35; w is the instantaneous width of the gauge length at which the tensile specimen 35 is deformed.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application. The method used in the invention is a conventional method if not specially specified; the raw materials and the apparatus used are, unless otherwise specified, conventional commercially available products.
As shown in fig. 1, 2, 4 and 5, the invention provides a normal loading thin plate micro-tensile test device, which is provided with a frame 1, wherein the frame 1 is provided with a frame body 2, and a first pressure head 3, a second pressure head 4, a first pressure head fixing block 5, a second pressure head fixing block 6, a nitrogen spring 7 and a guide column 8 are arranged in the frame body 2. The first pressure head 3 is connected with a first pressure head fixing block 5, the first pressure head fixing block 5 is connected with a nitrogen spring 7, the guide post 8 penetrates through the first pressure head fixing block 5, and the first pressure head fixing block 5 is in sliding connection with the guide post 8; the second pressure head 4 is connected with the detection end of the pressure sensor 9 and the second pressure head fixing block 6 respectively, and the second pressure head fixing block 6 is connected with the frame body 2. The end faces of the first pressure head 3 and the second pressure head 4 are arranged oppositely, and the edges of the end faces of the first pressure head and the second pressure head, which are contacted with a sample 10 to be tested, are provided with round corners 11, which is shown in fig. 8; when the first pressure head 3 and the second pressure head 4 load the sample 10 to be tested together, when the sample 10 to be tested is stretched, the sample 10 to be tested is respectively in relative sliding connection with the first pressure head 3 and the second pressure head 4, and the design of the fillet 11 mainly has three functions, on one hand, the influence of the edge on the friction force of the sample 10 to be tested is reduced to the maximum extent; secondly, protecting the sample to be tested 10 and avoiding the edge from pulling the surface of the sample to be tested 10; thirdly, the clearance 30 between the sample 10 that awaits measuring and the fillet 11 of edge has the lubricated liquid, and when first pressure head 3, second pressure head 4 and the sample 10 that awaits measuring relative sliding friction, this clearance 30's lubricated liquid can constantly follow this clearance 30 to the contact surface infiltration, makes the contact surface continuously keep lubricated, makes frictional force keep invariable. The frame of framework 2 runs through and is equipped with screw thread through-hole 12, and the adaptation threaded connection is equipped with screw rod 13 in the screw thread through-hole 12, and wherein one end of screw rod 13 passes screw thread through-hole 12 and stretches into in the framework 2 and is connected with nitrogen gas spring 7. The screw 13 is matched with the threaded through hole 12, so that the rotary motion of the screw 13 is converted into linear motion, the screw 13 applies pressure to the nitrogen spring 7, the nitrogen spring 7 is compressed due to the bearing of the pressure, the pressure is applied to the first pressure head fixing block 5 and the first pressure head 3, and finally normal stress is applied to the sample 10 to be tested loaded between the first pressure head 3 and the second pressure head 4; by loosening or tightening the screw 13, the magnitude of the normal stress of the sample 10 to be measured can be adjusted, as shown in fig. 5 and 7.
As a preferred embodiment, as shown in fig. 4 and 5, in order to fix the relevant components more firmly, the left and right sides of the first ram fixing block 5 are respectively provided with a first ram mounting hole 14 and a nitrogen spring mounting hole 15, the first ram 3 is mounted in the first ram mounting hole 14 and extends out of the first ram mounting hole 14, and the nitrogen spring 7 is mounted in the nitrogen spring mounting hole 15; the left side and the right side of the second pressure head fixing block 6 are respectively provided with a pressure sensor mounting hole 16 and a second pressure head mounting hole 17 which are communicated with each other, wherein a pressure sensor 9 is arranged in the pressure sensor mounting hole 16, a second pressure head 4 which can slide along the hole is arranged in the second pressure head mounting hole 17, the second pressure head 4 extends out of the second pressure head mounting hole 17, when the second pressure head 4 is subjected to external pressure from the first pressure head 3, the second pressure head 4 can slide inwards along the second pressure head mounting hole 17 to press the detection end of the pressure sensor 9, and a display instrument of the pressure sensor 9 outputs a normal load value; the second ram 4 is preferably a clearance fit with the inner wall of the second ram mounting hole 17. As a further preferred embodiment, the cylinder of the nitrogen spring 7 is installed in the nitrogen spring installation hole 15, and the piston rod of the nitrogen spring 7 is extended out of the nitrogen spring installation hole 15, so that one end of the screw 13 directly acts on the piston rod of the nitrogen spring 7. As a further preferable embodiment, a first cushion block 18 is further arranged in the frame body 2, the first cushion block 18 is a cylindrical structure with two open ends, an opening at one end of the first cushion block 18 is sleeved on the screw 13 and then connected with the frame body 2, a piston rod of the nitrogen spring 7 is inserted into an opening at the other end of the first cushion block 18, the first cushion block 18 and the first pressure head fixing block 5 cooperate to further position the nitrogen spring 7, so that one end of the screw 13 directly acts on the piston rod of the nitrogen spring 7, the rotary motion of the screw 13 is converted into linear motion, and the screw 13 applies pressure to the nitrogen spring 7 more stably and reliably.
As a preferred embodiment, as shown in fig. 4 and 5, a second spacer 19 is further disposed in the frame 2, the second ram fixing block 6 is connected to the frame 2 through the second spacer 19, and the distance between the second ram 4 and the first ram 3 is further adjusted according to actual requirements by disposing the second spacer 19.
As a preferred embodiment, as shown in fig. 3 and 4, in order to make the first indenter 3 and the pressure sensor 9 more firmly mounted and fixed, the first indenter fixing block 5 is provided with a first threaded hole, the first threaded hole is communicated with the first indenter mounting hole 14, and a stud of the first bolt 20 is screwed into the first threaded hole and presses and fixes the first indenter 3 in the first indenter mounting hole 14; the second pressure head fixing block 6 is provided with a second threaded hole, the second threaded hole is communicated with the pressure sensor mounting hole 16, and a stud of a second bolt 21 is screwed into the second threaded hole and presses and fixes the pressure sensor 9 in the pressure sensor mounting hole 16. As a further preferred embodiment, as shown in fig. 3 and 4, the second pressure head fixing block 6 is further provided with a wire hole 22, the wire hole 22 is communicated with the pressure sensor mounting hole 16, and a transmission cable or other lines of the pressure sensor 9 pass through the wire hole 22 for electrical connection between the pressure sensor 9 and an external power supply and an acquisition interface circuit.
As a preferred embodiment, as shown in fig. 3 and 5, one end of the guiding column 8 passes through one frame of the frame body 2 and extends out to be connected with the first nut 23, and a first backing plate 24 is connected between one frame and the first nut 23; the other end of the guide post 8 passes through the other frame of the frame body 2 and extends out to be connected with a second nut 25, and a second cushion plate 26 is connected between the other frame and the second nut 25. In addition, the first base plate 24 and the second base plate 26 can be inserted into the frame body 2, and one end of the screw 13 can sequentially penetrate through the first base plate 24 and the frame body 2 and extend into the frame body 2 to be connected with the nitrogen spring 7. The guide posts 8 are preferably provided in a pair and spaced apart.
As a preferred embodiment, as shown in fig. 1 and fig. 2, the present invention further comprises a base 27, a pillar 28 and a bracket 29, the pillar 28 is connected to the base 27, the pillar 28 is provided with an external thread, the bracket 29 is provided with a threaded hole adapted to the external thread, the pillar 28 is connected to the bracket 29 in a threaded manner, the bracket 29 is connected to the frame 1, and the position of the bracket 29 on the pillar 28 is adjusted by rotating the base 27 and the pillar 28. The base 27, the support 28 and the brackets 29 are preferably provided in two sets, and the two sets of brackets 29 are respectively connected to opposite sides of the frame 1.
As a preferred embodiment, as shown in fig. 10 and 11, the first ram 3 and the second ram 4 both adopt a rigid-soft mold composite structure, and are provided with a steel mold 31 and a soft mold 32, the steel mold 31 is connected with the soft mold 32, and the joint of the two is a convex-concave matching structure 33, so as to improve the bonding strength of the steel mold 31 and the soft mold 32; the shore hardness of the soft mold 32 is preferably 45-120 HA, the soft mold 32 in the first indenter 3 and the soft mold 32 in the second indenter 4 are respectively arranged as the end faces of the soft mold and the soft mold, the edge of the soft mold is preferably provided with the fillet 11, and the size of the fillet 11 is R0.1-0.5. The range requirement of the Shore hardness of the soft mold 32 material is 45-120 HA, so that the soft mold 32 cannot deform in the longitudinal direction in the upward stretching process of the sample 10 to be tested, and can be always tightly attached and loaded on the sample 10 to be tested under the acting force of the nitrogen spring 7. Preferably, the thickness of the soft mold 32 is 0.5 to 2 times of the thickness of the sample 10 to be measured. The steel die 31 is made of tungsten-cobalt hard alloy, and the soft die 32 is made of soft material such as silicon rubber or epoxy resin.
As a preferred embodiment, the first indenter 3 and the second indenter 4 may also be of an integrated structure, the two indenters may be made of tungsten-cobalt hard alloy or may be made of an existing elastic material, and in the process of upward stretching of the sample 10 to be measured, the end surfaces of the sample do not deform in the longitudinal direction, and can be always tightly attached to and loaded on the sample 10 to be measured under the action of the nitrogen spring 7; the size of a fillet 11 at the edge of the end faces of the two is R0.1-0.5; the surface roughness of the end surfaces of the two, which are in contact with the sample 10 to be measured, is Ra 0.01-0.08.
As a preferred embodiment, the pressure sensor 9 may be a non-calibrated button-type high-precision pressure sensor with a maximum range of 10000N and a precision of 0.05% f.s. The nitrogen spring 7 can be a non-calibration nitrogen making spring, the maximum measuring range is 10000N, and the elastic pressure increment of unit temperature is +/-0.1%/DEG C.
The invention also provides a test method of the normal loading thin plate micro-tensile test device, which comprises the following steps:
1) as shown in fig. 12, a processed metal thin plate 37 is prepared, and both surfaces of the metal thin plate 37 are pretreated, and the thickness of the metal thin plate 37 is not more than 4 mm; a test sample 10 to be tested is prepared by cutting a metal sheet 37, the test sample 10 to be tested is a rectangular test sample 34 and a tensile test sample 35, the thickness of the rectangular test sample 34 and the thickness of the tensile test sample are the same, the rectangular test sample 34 is a rectangular sheet structure with a fixed length, a wide width and a thick, and the tensile test sample 35 is a dumbbell-shaped test sample. The rectangular sample 34 and the tensile sample 35 are preferably cut in parallel at intervals on the metal sheet 37, and the rectangular sample and the tensile sample can be cut transversely or longitudinally or obliquely relative to the metal sheet 37, and preferably, the length of the rectangular sample and the width of the clamping part are also the same; to achieve that the rectangular specimen 34 and the tensile specimen 35 are consistent except for the shape of the specimens. As shown in fig. 14 (a), the dumbbell specimen is calibrated with a gauge length, which is the tensile deformation region of the dumbbell specimen; usually, one parallel gauge length line 36 is drawn on each side of the surface of the middle part of the dumbbell-shaped test sample, the gauge length line 36 is perpendicular to the long side of the middle part, the middle part between the two gauge length lines 36 is used as a gauge length, and the gauge length is used as a tensile deformation area when the dumbbell-shaped test sample is stretched.
2) The normal loading thin plate micro-tensile test device is arranged below a tensile testing machine, and the frame body 2 is positioned between an upper chuck and a lower chuck of the tensile testing machine.
3) The end faces of the first pressure head 3 and the second pressure head 4 are respectively and uniformly coated with liquid lubricating liquid, and the liquid lubricating liquid can be vegetable oil such as castor oil and peanut oil. Placing the rectangular sample 34 prepared in the step 1) between the end faces of the first pressing head 3 and the second pressing head 4, clamping and fixing the upper end clamping part of the rectangular sample 34 through an upper clamping head of a tensile testing machine, and fixing the lower end clamping part of the rectangular sample 34; the end surface shapes and structures of the first pressing head 3 and the second pressing head 4 are completely the same and are arranged oppositely.
4) A normal force is loaded on the nitrogen spring 7 by screwing the screw rod 13, and then the normal load is transmitted to the surface of the rectangular sample 34 in the clamping area of the end faces of the first pressure head 3 and the second pressure head 4; a first normal load value is obtained through the output of the pressure sensor 9, and the first normal load value is divided by the area of a contact area of the rectangular sample 34 and the end face of the first pressure head 3, so that a first normal stress value born by the contact area is calculated; the screw 13 is further unscrewed or screwed to adjust the magnitude of the first normal stress value, so that the first normal stress value is required not to exceed the yield stress value of the rectangular test piece 34, and the rectangular test piece 34 is prevented from being extruded and deformed. The first normal stress is preferably controlled to be 0 to 200 MPa.
In operation, the rectangular test sample 34 in the width direction in the steps 3) and 4) is required not to exceed the end face edges of the first indenter 3 and the second indenter 4; the central axis of the rectangular sample 34 is overlapped with the action line of the tensile testing machine so as to ensure that the rectangular sample 34 is always kept in a vertical centering state; as shown in fig. 13 (a), the rectangular sample 34 is loaded between the first indenter 3 and the second indenter 4 in the original gauge length state.
5) Starting the tensile testing machine, the upper chuck of the tensile testing machine moves upwards at a constant speed to drive the whole rectangular sample 34 to slide upwards relative to the first pressure head 3 and the second pressure head 4, and in the process, the tensile speed is controlled to be 0.001-100 mm/min, so that the rectangular sample 34 is ensured to be in quasi-static deformation in the upwards sliding process, and the rectangular sample 34 is kept intact all the time. As shown in fig. 13 (b), the rectangular sample 34 is in an upward sliding state with respect to the first indenter 3 and the second indenter 4. Outputting a first displacement load curve through a testing system of the tensile testing machine, wherein the constant load in the first displacement load curve is the friction value of the rectangular sample 34 in the first normal stress loading process, and the friction value is divided by the contact area of the rectangular sample 34 and the end face of the first pressure head 3 to obtain the friction value f of the unit contact face when the rectangular sample 34 slides 1 。
6) Loosening the screw 13, uniformly coating liquid lubricating liquid on the end faces of the first pressing head 3 and the second pressing head 4 respectively, operating the tensile testing machine, enabling an upper chuck of the tensile testing machine and the rectangular sample 34 to move downwards to the original position, taking down the rectangular sample 34, replacing the tensile sample 35 prepared in the step 1), clamping and fixing the upper end clamping part of the tensile sample 35 through the upper chuck, and clamping and fixing the lower end clamping part of the tensile sample 35 through the lower chuck; the gauge length of the tensile specimen 35 is now located between the end faces of the first indenter 3 and the second indenter 4.
7) Loading a normal force to the nitrogen spring 7 by screwing the screw 13, further transmitting the normal load to the surface of the tensile sample 35 in the clamping area of the end faces of the first pressure head 3 and the second pressure head 4, outputting through the pressure sensor 9 to obtain a second normal load value, dividing the second normal load value by the area of the contact area of the tensile sample 35 and the end face of the first pressure head 3, and calculating to obtain a second normal stress value borne by the tensile sample 35; adjusting the value of the second normal stress by further loosening or screwing the screw 13, wherein the second normal stress is required not to exceed the yield stress of the tensile sample 35, so as to prevent the tensile sample 35 from being extruded and deformed; and the second normal stress is equal to the first normal stress value in the step 4); the friction influencing conditions of the tensile tests of the rectangular sample 34 in the step 5) and the tensile sample 35 in the step 8) are consistent, and the friction coefficients are the same.
In operation, it is required that the step 6) and the step 7) do not extend the test piece 35 beyond the end face edges of the first indenter 3 and the second indenter 4 in the width direction, and it is clear that "in the above step 4), it is required that the step 3) and the step 4) do not extend the rectangular test piece 34 beyond the end face edges of the first indenter 3 and the second indenter 4 in the width direction" in operation, thereby ensuring that the friction influence conditions of the step 5) for the rectangular test piece 34 and the step 8) for the test piece 35 are the same, and the friction coefficients are the same. The central axis of the tensile sample 35 coincides with the force action line of the tensile testing machine to ensure that the tensile sample 35 is always in a vertical tensile state and in a vertical centering state; as shown in fig. 14 (a), the tensile specimen 35 is loaded between the first indenter 3 and the second indenter 4 in the original gauge length state.
8) Starting the tensile testing machine, the upper chuck of the tensile testing machine moves upwards at the same constant speed in the step 5), and the friction influence conditions of the tensile tests in the step 5) for the rectangular sample 34 and the step 8) for the tensile sample 35 are consistent, and the friction coefficients are the same. In the process, the tensile sample 35 is in a tensile deformation state, the gauge length of the tensile sample 35 is required to be not beyond the upper edges of the end faces of the first indenter 3 and the second indenter 4 during the tensile deformation, and the gauge length line 36 positioned on the upper side of the gauge length of the tensile sample 35 does not exceed the upper edges of the end faces of the first indenter 3 and the second indenter 4 during the operation. As shown in fig. 14 (b), the tensile specimen 35 is loaded between the first indenter 3 and the second indenter 4 in an upward tensile deformation state. Outputting a second displacement load curve of the tensile sample 35 when the second normal stress is loaded through a testing system of the tensile testing machine; the load value at any point on the second displacement load curve is equal to the sum of the instantaneous actual contact friction force f and the plastic deformation load value at the point.
9) Calculating the axial strain epsilon of the gauge length when the tensile sample 35 is subjected to tensile deformation according to a real strain calculation formula I l The first formula is: epsilon l ＝lnl/l 0 Wherein, epsilon l Is the axial strain of the gauge length during the tensile deformation of the tensile specimen 35, l is the instantaneous length of the gauge length during the tensile deformation of the tensile specimen 35, l 0 The original gauge length of the tensile specimen 35.
Calculating the width strain epsilon of the gauge length when the tensile sample 35 is subjected to tensile deformation according to the formula II b The second formula is: r ═ epsilon b /ε t ＝ε b /[-(ε b +ε l )]Then e b ＝-[r/(1+r)]ε l (ii) a In the formula two, ∈ b Is the wide strain, epsilon, of the gauge length during the tensile deformation of the tensile specimen 35 l Is the axial strain, epsilon, of the gauge length during the tensile deformation of the tensile specimen 35 t The thickness strain of the gauge length when the tensile sample 35 is subjected to tensile deformation; r is the anisotropy coefficient of the tensile specimen 35, and according to the material and the thickness of the tensile specimen 35, the r value can be found in the prior literature, for example, the r value of 0.5mm thickness of TC1 titanium alloy is 1.025; the thickness r value of 0.8mm of the TC1 titanium alloy is 1.93 (see Wujiajun, Zhouweixian. basic theory of sheet formability. northwest university of industry Press 2010.P17), or another titanium alloy can be prepared by cuttingAll the same tensile specimens 35 were subjected to a tensile test to calculate r values. Calculating the axial strain epsilon of the gauge length during the tensile deformation of the tensile sample 35 according to the formula I l And the thickness anisotropy coefficient r of the tensile sample 35, and calculating the width strain epsilon of the gauge length when the tensile sample 35 is subjected to tensile deformation b 。
Calculating the instantaneous width w of the gauge length when the tensile sample 35 is subjected to tensile deformation according to a third formula: epsilon b ＝lnw/w 0 Wherein, epsilon b Is the width-wise strain of the gauge length during the tensile deformation of the tensile specimen 35, w is the instantaneous width of the gauge length during the tensile deformation of the tensile specimen 35, w 0 Original gauge length width for tensile specimen 35; calculating the width-direction strain epsilon of the gauge length during the tensile deformation of the tensile sample 35 according to the formula II b And the original gauge width w of the tensile specimen 35 0 And calculating to obtain the instantaneous width w of the gauge length when the tensile sample 35 is subjected to tensile deformation.
Calculating the instantaneous contact area S between the gauge length and the end surface of the first pressure head 3 during the tensile deformation of the tensile sample 35 according to the formula IV 11 The formula four is: s 11 L is the instantaneous length of the gauge length when the tensile sample 35 is subjected to tensile deformation, and w is the instantaneous width of the gauge length when the tensile sample 35 is subjected to tensile deformation; shown in fig. 14 (b). Multiplying the instantaneous length l of the gauge length when the tensile sample 35 is subjected to tensile deformation in the formula I and the instantaneous width w of the gauge length when the tensile sample 35 is subjected to tensile deformation in the formula III to calculate the instantaneous contact area S between the gauge length when the tensile sample 35 is subjected to tensile deformation and the end surface of the first indenter 3 11 I.e. the area of the instantaneous contact area 38 of the gauge length with the end face of the first indenter 3 during the tensile deformation of the tensile specimen 35, which is always in the state of tensile deformation, as shown in fig. 15.
Calculating the instantaneous contact area S of the tensile sample 35 and the first indenter 3 according to the formula V 1 The fifth formula is: s 1 ＝S 11 +S 12 Wherein S is 11 Is the instantaneous contact area, S, of the gauge length and the end face of the first indenter 3 during the tensile deformation of the tensile specimen 35 12 The instantaneous contact area between the area outside the gauge length and the end face of the first indenter 3 when the tensile sample 35 is subjected to tensile deformation isThe area of the instantaneous contact area 36 between the area outside the gauge length when the tensile specimen 35 is subjected to tensile deformation and the end face of the first indenter 3 is always in a tensile undeformed state, and the area is very regular in shape and can be calculated by conventional measurement, as shown in fig. 15. Calculating the instantaneous contact area S between the gauge length and the end surface of the first pressure head 3 during the tensile deformation of the tensile sample 35 according to the formula IV 11 The instantaneous contact area S of the area outside the gauge length of the tensile specimen 35 at the time of tensile deformation with the end face of the first indenter 3, which is calculated by conventional measurement 12 Adding the two to obtain the instantaneous contact area S of the tensile sample 35 and the first indenter 3 1 。
Calculating the instantaneous actual contact friction force f during the tensile deformation of the tensile sample 35 according to a formula six, wherein the formula six is as follows: f is S 1 f 1 +S 2 f 2 ＝2S 1 f 1 Wherein S is 2 The instantaneous contact area S of the tensile sample 35 and the first indenter 3 is obtained from the instantaneous contact area S of the tensile sample 35 and the second indenter 4 and the formula V 1 Equal; the reason is that the first indenter 3 and the second indenter 4 have the same end surface area and are disposed facing each other, and the tensile sample 35 is sandwiched in common, and the tensile sample 35 does not exceed the end surface edges of the first indenter 3 and the second indenter 4 in the width direction. f. of 2 The friction value per unit contact surface of the tensile specimen 35 during tensile deformation and the friction value f per unit contact surface of the rectangular specimen 34 obtained in step 5) during slippage 1 Equal; the reason is mainly two, on one hand, the second normal stress in the step 7) is equal to the first normal stress value in the step 4), that is, the normal stress values received by the tensile sample 35 and the rectangular sample 34 are equal; on the other hand, the upper chuck of the step 8) tensile testing machine is moved upward at the same constant speed as in the step 5), that is, the tensile speeds of the tensile specimen 35 and the rectangular specimen 34 are the same.
In the stretching process of the tensile sample 35, the displacement of the tensile sample corresponds to the instantaneous actual contact friction force f of the tensile sample 35 in the stretching deformation, which is obtained through calculation according to the formula six, that is, the actual contact friction force and displacement curve of the tensile sample 35 in the stretching deformation when the second normal stress is loaded is obtained.
10) And (3) correspondingly subtracting the actual contact friction force obtained in the step (9) from the load value at any point on the second position load transfer curve obtained in the step (8) and the instantaneous actual contact friction force f which is positioned on the displacement curve and is at the same displacement value as the second position load transfer curve to obtain the plastic deformation load value at the displacement value, and finally obtaining the displacement load curve of the plastic deformation of the tensile sample 35 during the second normal stress loading.
As a preferred embodiment, in step 10), after obtaining the displacement load curve of the plastic deformation of the tensile specimen 35 at the time of the second normal stress loading, the real strain ∈ is calculated by the formula one l Calculating the true stress sigma by the formula seven pl Finally, a stress-strain curve of the tensile specimen 35 at the second normal stress loading is obtained, wherein:
the first formula is as follows: epsilon l ＝lnl/l 0 Wherein, epsilon l The axial strain of the gauge length when the tensile sample 35 is subjected to tensile deformation, namely the true strain; l is the instantaneous length of the gauge length during the tensile deformation of the tensile specimen 35, l 0 Original gauge length for tensile specimen 35; shown in fig. 14 (a) and (b).
The seventh formula is: sigma pl P/F, and
after finishing, the method comprises the following steps:
wherein σ pl The true stress of the tensile specimen 35 during the tensile deformation, P is the tensile load of the second displacement load curve obtained in the step 8), F is the instantaneous cross-sectional area of the gauge length of the tensile specimen 35 during the tensile deformation, e is the natural logarithm, and the value is 2.71828,. epsilon. l True strain in the case of tensile deformation of the tensile specimen 35, F 0 Original gauge cross-sectional area, F, for tensile specimen 35 0 ＝w 0 d 0 Wherein w is 0 Original gauge width, d, of the tensile specimen 35 0 The original gauge length thickness of the tensile sample 35 can be obtained by measurement, and the original gauge length thickness are multiplied to finally obtain the productF 0 。
And (4) repeating the steps 1) to 10), changing the first normal stress value in the step 4) or changing the stretching speed in the step 5), and obtaining stress-strain curves of the material under different normal stress loads and different strain speeds.
The invention provides a device and a method for testing normal loading thin plate micro-stretching, which have the following main beneficial effects:
on one hand, the mechanical pressing mode through the screw 13 can also be replaced by electric or hydraulic pressing, and the normal pressure can be flexibly changed. By utilizing the characteristic that the pressure of the piston rod of the nitrogen spring 7 is slightly influenced by small amount of expansion and contraction, the problems of normal pressure reduction and the like caused by thickness reduction due to deformation of the tensile sample 35 can be effectively avoided, so that the accuracy and the stability of the normal loading test are ensured;
on the other hand, the invention not only can test the tensile mechanical property of the thin plate under normal loading, but also can test the friction behavior in the plastic deformation process of the thin plate, and can realize the friction behavior measurement in the plastic deformation process of the small thin plate under different interface conditions through a pressure head.
Thirdly, the device provided by the invention has the advantages of ingenious structural design, convenient component replacement and better flexibility.
In the description of the present invention, it is to be understood that the terms "left", "right", "upper", "lower", "top", "bottom", "front", "rear", "inner", "outer", "back", "middle", and the like, indicate orientations and positional relationships based on those shown in the drawings, are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. It should be noted that, in the above-mentioned embodiments, the terms "first", "second" and "third" do not represent absolute differences in structure and/or function, nor represent a sequential order of execution, but merely serve to facilitate description.
The above description is only a preferred embodiment of the present application and should not be taken as limiting the present application, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (7)
1. A normal loading thin plate micro-tensile test device is provided with a frame (1), wherein the frame (1) is provided with a frame body (2), and a first pressure head (3), a second pressure head (4), a first pressure head fixing block (5) and a second pressure head fixing block (6) are arranged in the frame body (2); the first pressure head (3) is connected with the first pressure head fixing block (5), the second pressure head (4) is connected with the second pressure head fixing block (6), and the second pressure head fixing block (6) is connected with the frame body (2); the end faces of the first pressure head (3) and the second pressure head (4) are arranged oppositely, and the edges of the end faces of the first pressure head and the second pressure head, which are contacted with a sample (10) to be tested, are provided with round corners (11); a threaded through hole (12) penetrates through the frame of the frame body (2), and a screw rod (13) is arranged in the threaded through hole (12) in a matched threaded connection manner; the screw (13) is matched with the threaded through hole (12), so that the rotary motion of the screw (13) is converted into linear motion; the device is characterized in that a nitrogen spring (7) and a guide post (8) are also arranged in the frame body (2); the first pressure head fixing block (5) is connected with the nitrogen spring (7), the guide column (8) penetrates through the first pressure head fixing block (5), and the first pressure head fixing block (5) is in sliding connection with the guide column (8); the second pressure head (4) is also connected with the detection end of the pressure sensor (9), and one end of the screw rod (13) penetrates through the threaded through hole (12) and extends into the frame body (2) to be connected with the nitrogen spring (7); the screw (13) applies pressure to the nitrogen spring (7), the nitrogen spring (7) is compressed due to bearing pressure, then the pressure is applied to the first pressure head fixing block (5) and the first pressure head (3), and finally normal stress is applied to the sample (10) to be tested loaded between the first pressure head (3) and the second pressure head (4); the adjustment of the normal stress of the sample (10) to be tested can be realized by loosening or screwing the screw (13);
the left side and the right side of the first pressure head fixing block (5) are respectively provided with a first pressure head mounting hole (14) and a nitrogen spring mounting hole (15), the first pressure head (3) is mounted in the first pressure head mounting hole (14) and extends out of the first pressure head mounting hole (14), and the nitrogen spring (7) is mounted in the nitrogen spring mounting hole (15); the left side and the right side of the second pressure head fixing block (6) are respectively provided with a pressure sensor mounting hole (16) and a second pressure head mounting hole (17) which are communicated with each other, the pressure sensor (9) is arranged in the pressure sensor mounting hole (16), the second pressure head (4) which can slide along the second pressure head mounting hole is arranged in the second pressure head mounting hole (17), and the second pressure head (4) extends out of the second pressure head mounting hole (17);
the cylinder body of the nitrogen spring (7) is arranged in the nitrogen spring mounting hole (15), and the piston rod of the nitrogen spring (7) extends out of the nitrogen spring mounting hole (15);
a first cushion block (18) and a second cushion block (19) are further arranged in the frame body (2), the first cushion block (18) is of a cylindrical structure with two open ends, an opening at one end of the first cushion block (18) is sleeved on the screw rod (13) and then connected with the frame body (2), and a piston rod of the nitrogen spring (7) is inserted into an opening at the other end of the first cushion block (18); and the second pressure head fixing block (6) is connected with the frame body (2) through the second cushion block (19).
2. The device for testing the micro-stretching of the normally loaded thin plate according to claim 1, wherein the first pressure head fixing block (5) is provided with a first threaded hole, the first threaded hole is communicated with the first pressure head mounting hole (14), and a stud of a first bolt (20) is screwed into the first threaded hole and presses and fixes the first pressure head (3) in the first pressure head mounting hole (14); a second threaded hole is formed in the second pressure head fixing block (6), the second threaded hole is communicated with the pressure sensor mounting hole (16), and a stud of a second bolt (21) is screwed into the second threaded hole and presses and fixes the pressure sensor (9) in the pressure sensor mounting hole (16); and the second pressure head fixing block (6) is also provided with a wire-passing hole (22), and the wire-passing hole (22) is communicated with the pressure sensor mounting hole (16).
3. The device for testing the micro-tension of the normally loaded thin plate according to claim 1, wherein one end of the guide column (8) penetrates through one frame of the frame body (2) and extends out to be in threaded connection with the first nut (23), and a first cushion plate (24) is connected between one frame and the first nut (23); the other end of the guide column (8) penetrates through the other frame of the frame body (2) and extends out to be in threaded connection with a second nut (25), and a second base plate (26) is connected between the other frame and the second nut (25).
4. The device for testing the micro-stretching of the normally loaded thin plate according to claim 1, further comprising a base (27), a pillar (28) and a bracket (29), wherein the pillar (28) is connected to the base (27), the pillar (28) is provided with an external thread, the bracket (29) is provided with a threaded hole matched with the external thread, the pillar (28) is in threaded connection with the bracket (29), the bracket (29) is connected with the frame (1), and the position of the bracket (29) on the pillar (28) is adjusted by rotating the base (27) and the pillar (28).
5. The device for testing the micro-stretching of the normally loaded thin plate according to claim 1, wherein the first indenter (3) and the second indenter (4) both adopt a rigid-soft mold composite structure, and are provided with a steel mold (31) and a soft mold (32), the steel mold (31) is connected with the soft mold (32), the connection between the steel mold and the soft mold is a convex-concave matching structure (33), the shore hardness of the soft mold (32) is 45-120, and the soft mold (32) in the first indenter (3) and the soft mold (32) in the second indenter (4) are respectively arranged as the end faces of the two in a facing manner.
6. A method of testing a normally loaded sheet micro-tensile testing apparatus according to any of claims 1-5, comprising the steps of:
1) preparing a processed metal sheet (37) and pretreating both surfaces of the metal sheet (37), the metal sheet (37) having a thickness of not more than 4 mm; cutting the metal sheet (37) to prepare the sample (10) to be tested, wherein the sample (10) to be tested is a rectangular sample (34) and a tensile sample (35) which are the same in thickness; the tensile test sample (35) is a dumbbell-shaped test sample, and the scale distance is calibrated on the dumbbell-shaped test sample, wherein the scale distance is a tensile deformation area of the dumbbell-shaped test sample;
2) placing the normal loading thin plate micro-tensile test device below a tensile test machine, and enabling the frame body (2) to be located between an upper chuck and a lower chuck of the tensile test machine;
3) respectively and uniformly coating liquid lubricating liquid on the end surfaces of the first pressure head (3) and the second pressure head (4); placing the rectangular sample (34) prepared in the step 1) between the end faces of the first pressing head (3) and the second pressing head (4), and clamping and fixing the upper end clamping part of the rectangular sample (34) through the upper clamping head of the tensile testing machine, wherein the lower end clamping part of the rectangular sample (34) is not fixed; the end surfaces of the first pressure head (3) and the second pressure head (4) are completely the same in shape and structure and are arranged oppositely;
4) loading a normal force on the nitrogen spring (7) by screwing the screw (13), and further transmitting the normal load to the surface of the rectangular test sample (34) in the end face clamping area of the first pressure head (3) and the second pressure head (4); obtaining a first normal load value through the output of the pressure sensor (9), dividing the first normal load value by the area of a contact area of the rectangular test sample (34) and the end face of the first pressure head (3), and calculating to obtain a first normal stress value born by the contact area; adjusting the magnitude of the first normal stress value by further unscrewing or screwing the screw (13) so as to require the first normal stress value not to exceed the yield stress value of the rectangular test piece (34);
during operation, the rectangular sample (34) in the step 3) and the step 4) is required not to exceed the end face edges of the first pressure head (3) and the second pressure head (4) in the width direction, and the central axis of the rectangular sample (34) is overlapped with the action line of the tensile testing machine force so as to ensure that the rectangular sample (34) is always kept in a vertical centering state;
5) starting the tensile testing machine, wherein an upper chuck of the tensile testing machine moves upwards at a constant speed to drive the whole rectangular sample (34) to slide upwards relative to the first pressure head (3) and the second pressure head (4), and in the process, the tensile speed is controlled to be 0.001-100 mm/min to ensure that the rectangular sample (34) is kept intact all the time; outputting a first displacement load curve through a testing system of the tensile testing machine, wherein the constant load in the first displacement load curve is the friction value of the rectangular sample (34) in the first normal stress loading process, and the friction value is divided by the contact area of the rectangular sample (34) and the end surface of the first pressure head (3) to obtain the friction value f of a unit contact surface when the rectangular sample (34) slides 1 ；
6) Loosening the screw (13), uniformly coating the liquid lubricating liquid on the end surfaces of the first pressing head (3) and the second pressing head (4) respectively, operating the tensile testing machine, enabling an upper chuck of the tensile testing machine and the rectangular sample (34) to move downwards to the original position, taking down the rectangular sample (34), replacing the tensile sample (35) prepared in the step 1), clamping and fixing an upper end clamping part of the tensile sample (35) through the upper chuck, and clamping and fixing a lower end clamping part of the tensile sample (35) through the lower chuck; the gauge length of the tensile sample (35) is arranged between the end faces of the first pressing head (3) and the second pressing head (4);
7) loading a normal force on the nitrogen spring (7) by screwing the screw (13), further transmitting the normal load to the surface of the tensile sample (35) in the end face clamping area of the first pressure head (3) and the second pressure head (4), obtaining a second normal load value through the output of the pressure sensor (9), dividing the second normal load value by the area of the contact area of the tensile sample (35) and the end face of the first pressure head (3), and calculating to obtain a second normal stress value borne by the tensile sample (35); adjusting the magnitude of the second normal stress value by further unscrewing or screwing the screw (13) so that the second normal stress does not exceed the yield stress of the tensile specimen (35) and is equal to the first normal stress value of step 4);
in operation, the tensile sample (35) in the step 6) and the step 7) is required not to exceed the end face edges of the first pressure head (3) and the second pressure head (4) in the width direction, and the central axis of the tensile sample (35) is overlapped with the action line of the tensile testing machine force, so that the tensile sample (35) is always kept in a vertical tensile state and is in a vertical centering state;
8) starting the tensile testing machine, wherein an upper clamping head of the tensile testing machine moves upwards at the same constant speed in the step 5), in the process, the tensile sample (35) is in a tensile deformation state, and the gauge length of the tensile sample (35) is required to be not more than the upper edges of the end faces of the first pressure head (3) and the second pressure head (4) during tensile deformation; outputting a second displacement load curve of the tensile test sample (35) when a second normal stress is loaded through a test system of the tensile tester; the load value of any point on the second position load transfer curve is equal to the sum of the instantaneous actual contact friction force f and the plastic deformation load value at the point;
9) calculating the axial strain epsilon of the gauge length when the tensile sample (35) is subjected to tensile deformation according to a real strain calculation formula I l The first formula is as follows: epsilon l ＝lnl/l 0 Wherein, epsilon l Is the axial strain of the gauge length when the tensile sample (35) is subjected to tensile deformation, l is the instantaneous length of the gauge length when the tensile sample (35) is subjected to tensile deformation, l 0 Is the original gauge length of the tensile sample (35);
according to the formula II, the width direction strain epsilon of the gauge length during the stretching deformation of the stretching sample (35) is calculated b The second formula is: r ═ epsilon b /ε t ＝ε b /[-(ε b +ε l )]Then e b ＝-[r/(1+r)]ε l (ii) a In the second formula, ∈ b The wide strain of the gauge length when the tensile sample (35) is subjected to tensile deformation, r is the thickness anisotropy coefficient of the tensile sample (35), epsilon l Is the axial strain of the gauge length, epsilon, during the tensile deformation of the tensile specimen (35) t The thickness direction strain of the gauge length is the tensile strain of the tensile sample (35) during tensile deformation; according toThe formula I calculates the axial strain epsilon of the gauge length during the stretching deformation of the tensile sample (35) l And the thickness anisotropy coefficient r of the tensile sample (35) consulted by the tool book, and the width direction strain epsilon of the gauge length when the tensile sample (35) is subjected to tensile deformation is calculated b ；
And calculating the instantaneous width w of the gauge length when the tensile sample (35) is subjected to tensile deformation according to a third formula: epsilon b ＝lnw/w 0 Wherein epsilon b Is the width-direction strain of the gauge length when the tensile sample (35) is subjected to tensile deformation, w is the instantaneous width of the gauge length when the tensile sample (35) is subjected to tensile deformation 0 Is the original gauge length width of the tensile sample (35); according to the formula II, the width direction strain epsilon of the gauge length during the stretching deformation of the stretching sample (35) is obtained by calculation b And the original gauge width w of the tensile specimen (35) 0 Calculating to obtain the instantaneous width w of the gauge length when the tensile sample (35) is subjected to tensile deformation;
calculating the instantaneous contact area S of the gauge length and the end surface of the first pressure head (3) when the tensile sample (35) is subjected to tensile deformation according to the fourth formula 11 The fourth formula is: s 11 L is the instantaneous length of the gauge length when the tensile sample (35) is subjected to tensile deformation, and w is the instantaneous width of the gauge length when the tensile sample (35) is subjected to tensile deformation; multiplying the instantaneous length l of the gauge length when the tensile sample (35) in the formula I is subjected to tensile deformation and the instantaneous width w of the gauge length when the tensile sample (35) in the formula III is subjected to tensile deformation by the instantaneous length l, and calculating to obtain the instantaneous contact area S between the gauge length when the tensile sample (35) is subjected to tensile deformation and the end surface of the first indenter (3) 11 ；
Calculating the instantaneous contact area S of the tensile sample (35) and the first pressure head (3) according to the formula V 1 The fifth formula is: s. the 1 ＝S 11 +S 12 Wherein S is 11 Is the instantaneous contact area of the gauge length and the end face of the first pressure head (3) when the tensile sample (35) is in tensile deformation, S 12 The instantaneous contact area of the area outside the gauge length of the tensile sample (35) during tensile deformation and the end face of the first pressure head (3) is obtained; calculating the instantaneous contact area S between the gauge length and the end surface of the first pressure head (3) when the tensile sample (35) is subjected to tensile deformation according to the formula IV 11 The instantaneous contact area S of the area outside the gauge length and the end face of the first pressure head (3) when the tensile sample (35) is subjected to tensile deformation is calculated through conventional measurement 12 Adding the two to obtain the instantaneous contact area S of the tensile sample (35) and the first pressure head (3) 1 ；
And calculating the instantaneous actual contact friction force f during the tensile deformation of the tensile sample (35) according to a sixth formula: f is S 1 f 1 +S 2 f 2 ＝2S 1 f 1 Wherein S is 2 The instantaneous contact area S of the tensile sample (35) and the first pressure head (3) is obtained by the formula five and is the instantaneous contact area of the tensile sample (35) and the second pressure head (4) 1 Equal; f. of 2 The friction value of the unit contact surface when the tensile sample (35) is in tensile deformation is the same as the friction value f of the unit contact surface when the rectangular sample (34) obtained in the step 5) slides 1 Equal;
in the stretching process of the tensile sample (35), the displacement of the tensile sample corresponds to the instantaneous actual contact friction force f of the tensile sample (35) obtained by calculation according to the formula VI during stretching deformation, and the actual contact friction force and displacement curve of the tensile sample (35) during stretching deformation is obtained when the second normal stress is loaded;
10) correspondingly subtracting the actual contact friction force obtained in the step 9) from the load value at any point on the second displacement load curve obtained in the step 8) and the instantaneous actual contact friction force f on the displacement curve, which is at the same displacement value as the second displacement load curve, to obtain the plastic deformation load value at the displacement value, and finally obtaining the displacement load curve of the plastic deformation of the tensile test sample (35) during the second normal stress loading.
7. The testing method of the device for testing micro-tension of thin plate with normal loading according to claim 6, wherein in the step 10), after obtaining the displacement load curve of the plastic deformation of the tensile sample (35) at the time of the second normal stress loading, respectively calculating true through the formula IActual strain epsilon l Calculating the true stress sigma by the formula seven pl Finally, obtaining a stress-strain curve of the tensile test piece (35) when the second normal stress is loaded;
the first formula is as follows: epsilon l ＝lnl/l 0 Wherein, epsilon l The axial strain of the gauge length when the tensile sample (35) is subjected to tensile deformation is the real strain; l is the instantaneous length of the gauge length during the tensile deformation of the tensile specimen (35), l 0 Is the original gauge length of the tensile sample (35);
the seventh formula is: sigma pl P/F, and
after finishing, the method comprises the following steps:
wherein σ pl The real stress of the tensile sample (35) during tensile deformation is obtained, P is the tensile load of the second displacement load curve obtained in the step 8), F is the instantaneous cross-sectional area of the gauge length of the tensile sample (35) during tensile deformation, e is the natural logarithm, and the value is 2.71828 epsilon l Is the true strain of the tensile specimen (35) during tensile deformation, F 0 Is the original gauge length cross-sectional area of the tensile sample (35);
and repeating the steps 1) to 10), and changing the first normal stress value in the step 4) or the tensile speed in the step 5), so as to obtain stress-strain curves of the material under different normal stress loads and different strain speeds.
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