A small-load micro-displacement tensile performance detection method and device based on the direct piezoelectric effect

Abstract

The present invention discloses a method and device for detecting the tensile performance of small loads based on the positive piezoelectric effect, including a V-shaped spring structure that converts the change in tensile force during the stretching process into a change in the charge quantity of a piezoelectric film, a clamping device for clamping a specimen, and a motion device for realizing the micro-displacement stretching of the specimen. By utilizing the conversion of tensile force-strain-charge, real-time and accurate monitoring of the transient force-displacement signal during the stretching process can be achieved, and the tensile performance detection of foil / film specimens can be realized. At the same time, the present invention adopts a small-pitch lead screw, which is connected to the motor through a coupling, and can realize the tensile test under the conditions of micro-displacement and small loads. The device of the present invention has the characteristics of simple structure, high precision, low cost, small volume, etc., and is particularly suitable for occasions where tensile performance detection needs to be carried out in a special space.

Description

Technical Field

[0001] The present invention relates to the technical field of tensile testing, and specifically relates to a method and device for detecting tensile properties based on the piezoelectric effect. Background Art

[0002] At present, one of the most important research contents in the disciplines of materials science and engineering mechanics is the preparation of new materials and the research of mechanical properties, especially various metal materials and alloy materials. The research on the preparation and mechanical properties of metal and alloy materials has always been a hot topic. When studying the mechanical properties of materials, the most commonly used equipment is a universal testing machine.

[0003] Researchers usually use a universal testing machine to conduct compression and tensile tests on metal specimens to understand the yield strength, tensile strength, tensile plasticity, etc. possessed by the materials.

[0004] However, many universal testing machines, especially large-tonnage testing machines, have poor detection accuracy and cannot complete the micro-tensile and micro-load mechanical property tests of specimens; at the same time, some experimental devices are inconvenient to carry due to their large volume; in addition, for tensile testing machines in special environments, which require delicate structural dimensions and sensitive responsiveness, the universal testing machine loses its applicability. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for detecting tensile properties based on the piezoelectric effect to solve the problems existing in the above-mentioned prior art. In this device, the change in force during the specimen stretching process is transmitted to the reed, thereby generating a corresponding strain / displacement response. The strain is converted into an electric charge amount through the direct piezoelectric effect of the piezoelectric film on the reed. Then, by monitoring the change in the electric charge amount in real time, the force during the stretching process is detected.

[0006] The technical solution of the present invention is: a tensile property detection device based on the piezoelectric effect, including a V-shaped reed (1), a frame (2), a lead screw (4), a first clamp (3), a motor (5), a second clamp (6), a bearing seat (8), a third clamp (9), and a coupling (10);

[0007] The two sides of the V-shaped reed (1) are provided with connecting plates with a trapezoidal cross-section, and threaded holes are opened on the connecting plates;

[0008] The upper ends of the two side columns of the frame (2) are provided with trapezoidal connection grooves and threaded holes. The trapezoidal grooves cooperate with the trapezoidal connecting plates of the V-shaped reed (1). Through the guiding action of the trapezoidal connecting plates and the 3° hypotenuse of the trapezoidal grooves, the two side V-shaped reeds are located on the same horizontal reference. Then, their movement is restricted by connecting with the threaded holes through screws. At the same time, bearing seats (8) for supporting the lead screw (4) are provided inside the two side columns;

[0009] On both sides of the first clamping plate (3), there are threaded holes that match the lead screw (4). In the middle, there is a rectangular groove for mating with the third clamping plate (9). At the same time, on both sides of the rectangular groove of the first clamping plate (3) and the third clamping plate (9), there are threaded holes, and the specimen is clamped through bolt connection;

[0010] The lead screw (4) cooperates with the third clamping plate (3), and both ends are connected to the bearing seats (8). At the same time, it is connected to the motor (5) through the coupling (10) at the lower end;

[0011] The lead screw (4), the motor (5), the bearing seats (8), and the coupling (10) are all used in pairs and placed on both sides of the frame (2) to ensure the stability of the stretching process;

[0012] On the second clamping plate (6), there is a trapezoidal groove that matches the trapezoidal connecting plate of the V-shaped spring piece (1). Through the guiding action of the trapezoidal connecting plate and the 3° hypotenuse on both sides of the trapezoidal groove, it is ensured that both sides of the second clamping plate (6) are on the same horizontal reference. On its upper surface, there are threaded holes for limiting, and on both sides, there are threaded holes for clamping the specimen.

[0013] Furthermore, the V-shaped spring piece (1) is made of a material with high yield strength (≥800 MPa) and fatigue strength (≥550 MPa), and good plasticity and toughness. In this invention, alloy spring steel 60Si2Mn is used.

[0014] Furthermore, the surface of the V-shaped spring piece (1) is ground, and the surface roughness Ra is not greater than 6.4 μm to achieve reliable adhesion with the piezoelectric film (7).

[0015] Furthermore, the piezoelectric film (7) uses a PVDF piezoelectric film.

[0016] Furthermore, the contact surfaces of the first clamping plate (3), the second clamping plate (6), and the third clamping plate (9) with the specimen are rough surfaces, and the surface roughness Ra is not less than 25 μm.

[0017] Furthermore, the lead screw (4) uses a precision lead screw with a small pitch not greater than 2 mm and adopts a triangular fine pitch thread, so as to realize the tensile test detection of the specimen under small displacement conditions.

[0018] Furthermore, during the stretching process of the specimen, under the action of the tensile force, the surface of the V-shaped spring piece (1) is bent, which causes the piezoelectric film (7) to deform, and polarization phenomenon occurs inside it, becoming a charged state; due to different tensile forces on the specimen at different stretching stages, the strain amounts of the V-shaped spring piece (1) and the piezoelectric film (7) are different, resulting in different amounts of electric charge generated by the piezoelectric film (7). Through the change of the electric charge amount, the force and the force change trend during the stretching process can be detected in real time.

[0019] During the tensile process, materials generally go through different stages. For example, there are four stages in the tensile process of metal materials (elastic stage, yield stage, strengthening stage, necking and fracture stage). In these four stages, the changing trend of the force borne by the metal specimen is different. The change in force is converted into the change in the electric charge amount of the piezoelectric film through the reed, further realizing the real-time detection of the mechanical properties during the specimen tensile process.

[0020] Preferably, the V-shaped reed is made of alloy spring steel 60Si2Mn with high yield strength, fatigue strength, elastic limit, good plasticity and toughness.

[0021] Preferably, the piezoelectric film has the characteristics of good flexibility, high sensitivity, impact resistance, etc., and PVDF piezoelectric film is used.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The present invention is a device for tensile property detection, mainly including a V-shaped reed, a frame, a lead screw, a clamping plate, a motor, a piezoelectric film, etc.; the device designed by the present invention has a simple structure, high precision and low cost;

[0024] 2. The present invention can realize the detection of the tensile process under the conditions of small load and micro-displacement, filling the blank in the field of small tensile testing machines;

[0025] 3. The V-shaped reed of the present invention can be replaced according to the tested material, avoiding the situation that only a certain type of material can be detected.

[0026] The present invention provides a tensile property detection method and a small detection device, which can realize the tensile property detection of foil / film specimens, especially suitable for the static / transient mechanical property detection under the test conditions of small displacement and small load of specimens. The device has the characteristics of low cost, simple structure and small volume. Brief Description of the Drawings

[0027] Figure 1 is the overall structure diagram of the tensile detection device described in the present invention;

[0028] Figure 2 is the enlarged structure diagram of part A in the tensile detection device described in the present invention;

[0029] Figure 3 is the enlarged structure diagram of part B in the tensile detection device described in the present invention;

[0030] Figure 4 is the structure diagram of the V-shaped reed described in the present invention;

[0031] Figure 5 is the front structure diagram of the first clamping plate described in the present invention;

[0032] Figure 6 It is a schematic diagram of the upper surface structure of the first splint described in the present invention;

[0033] Figure 7 It is a schematic diagram of the front surface structure of the second splint described in the present invention;

[0034] Figure 8 It is a schematic diagram of the upper surface structure of the second splint described in the present invention;

[0035] Figure 9 It is a force analysis diagram during the tensile process of the specimen;

[0036] Figure 10 It is a schematic diagram of the principle of the tensile detection method described in the present invention;

[0037] Figure 11 It is a signal processing circuit diagram of the tensile detection device described in the present invention;

[0038] Figure 12 It is a schematic diagram of the test principle in the elastic stage of the metal specimen;

[0039] Figure 13 It is a schematic diagram of the test principle in the yield stage of the metal specimen;

[0040] Figure 14 It is a schematic diagram of the test principle in the strengthening stage of the metal specimen;

[0041] Figure 15 It is a schematic diagram of the test principle in the necking stage of the metal specimen.

[0042] Among them, 1 - V-shaped spring piece, 2 - frame, 3 - first splint, 4 - lead screw, 5 - motor, 6 - second splint, 7 - piezoelectric film, 8 - bearing seat, 9 - third splint, 10 - coupling; Specific embodiments

[0043] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0044] The purpose of the present invention is to convert force - strain - electric charge, so as to convert the change of force during the tensile process of the specimen into the change of strain of the spring piece, and then convert the strain into electric charge through the piezoelectric film on the spring piece, so as to perform real-time detection on the tensile process.

[0045] As Figure 1 shown, the detection device includes: 1 - V-shaped spring piece, 2 - frame, 3 - first splint, 4 - lead screw, 5 - motor, 6 - second splint, 7 - piezoelectric film, 8 - bearing seat, 9 - third splint, 10 - coupling; As Figure 2 、 Figure 3On both sides of the shown V-shaped spring piece 1 are trapezoidal connecting plates, on which positioning threaded holes are provided. At the same time, trapezoidal grooves and threaded holes are provided on the frame 2 and the second clamping plate 6. Through the cooperation of the connecting plate with the trapezoidal groove and the screw with the thread, the connection between the frame and the V-shaped spring piece and between the V-shaped spring piece and the second clamping plate is realized, and it is ensured that they are on the same horizontal plane. Bearing seats 8 are provided on the two side columns of the frame 2 for supporting the lead screw 4. Threaded holes matching with the lead screw 4 are provided on both sides of the first clamping plate 3, and the lead screw 4 is connected to the motor 5 through a coupling 10. The rotation of the motor 5 drives the lead screw 3 to rotate, thereby realizing the up and down movement of the first clamping plate 3. To ensure smooth transmission during the stretching process, transmission mechanisms are equipped on both the left and right sides, and the two motors 5 are controlled by a unified controller to work in coordination.

[0046] As Figure 5 、 Figure 6 shown, a rectangular groove is provided in the middle of the first clamping plate 3 for cooperation with the third clamping plate 9. At the same time, threaded holes are provided on both sides of the rectangular groove of the first clamping plate and the third clamping plate 9. The two clamping plates are connected by bolts to clamp one side of the specimen. As Figure 7 、 Figure 8 shown, threaded holes are also provided on both sides of the second clamping plate 6, and the two second clamping plates are fixed by bolts to clamp the other side of the specimen. The contact surface between the clamping plate and the specimen is the surface, and the surface roughness of the clamping surfaces of the first clamping plate 3, the second clamping plate 6, and the third clamping plate 9 is a rough surface greater than 25μm, which can generate frictional force with the specimen to avoid problems such as loosening and sliding at the clamping position resulting in inaccurate test results. As Figure 4 shown, the piezoelectric film 7 is pasted on the surface of the V-shaped spring piece 1. When the force changes during the stretching process of the specimen, it causes strain in the piezoelectric film 7 and the V-shaped spring piece 1, thereby generating a change in the amount of charge.

[0047] During operation, in the first step, both ends of the specimen are respectively placed between the first clamping plate 3 and the third clamping plate 9 and the two second clamping plates 6, and the specimen is clamped by connecting the threaded holes on the clamping plate with bolts. Then, the motor 5 is started to drive the lead screw 4 to rotate through the coupling 10. Through the cooperation of the lead screw 4 with the threaded holes on both sides of the first clamping plate 3 to form a screw drive, the up and down movement of the clamping plate is realized.

[0048] As Figure 9 、 Figure 10 shown, during the stretching process of the specimen, the lead screw 4 drives the first clamping plate 3 and the third clamping plate 9 to move downward, and the tensile force on the material is F. At this time, the force received by the second clamping plate is also F. At this time, the connecting plate of the two V-shaped spring clamping plates 1 on both sides will respectively receive a force of F / 2. According to the cantilever beam deflection formula f = Pl 3 / 3EI, where f is the deflection deformation amount, P is the load, l is the length of the rod, E is the elastic modulus of the V-shaped spring piece, and I is the moment of inertia of the cross-section. At this time, substituting P = F / 2 can obtain the relationship between the deformation amount and the force, that is, 2f = Fl3 / 3EI.

[0049] Before the test, the charge quantity Q of the piezoelectric film 7 should be calibrated to obtain the relationship between the deflection deformation and the charge quantity: Q = Q(f). Then, by directly detecting the charge quantity, the magnitude of the force F during the stretching process can be determined.

[0050] When the piezoelectric film 7 deforms with the V-shaped spring piece 1, charges will accumulate on the surfaces of its two electrodes. The charge quantities on the surfaces of the two electrodes are equal, but the polarities are opposite. At this time, it is equivalent to a capacitor. As Figure 11 shown, where C1 and R1 are the equivalent capacitance and equivalent insulation leakage resistance of the piezoelectric film 7, C2 is the equivalent capacitance of the cable, R2 and C3 are the input impedance and input capacitance of the amplifier, and R3 and C4 are the feedback impedance and feedback capacitance. At this time, the deformed piezoelectric film 7 is equivalent to a charge source in parallel with a capacitor. Then, the weak signal of the piezoelectric film is amplified by the charge amplification circuit, and the interference and noise in the power grid are eliminated by the filter and then transmitted to the oscilloscope for detection.

[0051] During the tensile process of the metal specimen, it generally experiences four stages, namely the elastic stage, the yield stage, the strengthening stage, and the necking stage. In these four stages, the change trend of the tensile force borne by the metal specimen is different. The change in force is converted into the change in the charge quantity of the piezoelectric film through the spring piece, and further realizes the real-time detection of the mechanical properties during the specimen stretching process.

[0052] As Figure 12 shown, in the elastic stage OA, the stress and strain increase proportionally, that is, the tensile force of the specimen. At this time, through the detection device described in the present invention, under the action of the tensile force, the V-shaped spring piece 1 and the piezoelectric film 7 deform together. As the tensile force continues to increase, the charge quantity generated by the piezoelectric film gradually increases from zero.

[0053] As Figure 13 shown, in the yield stage AB, the elongation of the specimen continues to increase, but the tensile force of the specimen hardly changes, and its magnitude fluctuates within a small range. At this time, the charge quantity generated by the piezoelectric film 7 is basically unchanged, and its value fluctuates up and down. By detecting the charge quantity at this time, the yield strength of the test can be obtained.

[0054] As Figure 14 shown, in the strengthening stage BC, the resistance in the specimen will continue to increase, and the tensile force required for the specimen also continues to increase. At this time, the charge quantity generated by the piezoelectric film 7 will continue to increase. When the charge quantity is the largest, that is, at point C in the figure, it is the moment of the maximum tensile strength of the material.

[0055] As Figure 15 shown, in the necking stage, the test tensile force continuously decreases, and the charge quantity generated by the piezoelectric film 7 will also continuously decrease until it breaks, and the charge quantity is zero at this time.

[0056] The above embodiments are only used to illustrate the design concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made according to the principles and design concepts disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A tensile property detection device based on the piezoelectric effect, characterized in that It includes a V-shaped spring leaf (1), a frame (2), a lead screw (4), a first clamping plate (3), a motor (5), a second clamping plate (6), a bearing block (8), a third clamping plate (9), and a coupling (10); On both sides of the V-shaped spring leaf (1), there are connecting plates with a trapezoidal cross-section, and threaded holes are provided on the connecting plates; At the upper ends of the two side columns of the frame (2), there are trapezoidal connection grooves and threaded holes. The trapezoidal grooves are matched with the trapezoidal connecting plates of the V-shaped spring leaf (1). Through the guiding action of the trapezoidal connecting plates and the 3° hypotenuse of the trapezoidal grooves, the two side V-shaped spring leaves are located on the same horizontal reference plane. Then, they are connected by screws to the threaded holes to limit their movement. At the same time, inside the two side columns, there are bearing blocks (8) for supporting the lead screw (4); On both sides of the first clamping plate (3), there are threaded holes that match the lead screw (4). In the middle, there is a rectangular groove for mating with the third clamping plate (9). At the same time, on both sides of the rectangular groove of the first clamping plate (3) and the third clamping plate (9), there are threaded holes, and the specimen is clamped by bolt connection; The lead screw (4) cooperates with the third clamping plate (9), and both ends are connected to the bearing blocks (8). At the same time, it is connected to the motor (5) through the coupling (10) at the lower end; The lead screw (4), the motor (5), the bearing blocks (8), and the coupling (10) are all used in pairs and placed on both sides of the frame (2) to ensure the stability of the stretching process; On the second clamping plate (6), there are trapezoidal grooves that match the trapezoidal connecting plates of the V-shaped spring leaf (1). Through the guiding action of the trapezoidal connecting plates and the 3° hypotenuse of the trapezoidal grooves, it is ensured that both sides of the second clamping plate (6) are on the same horizontal reference plane. On its upper surface, there are threaded holes for position limiting, and on both sides, there are threaded holes for clamping the specimen.

2. The tensile property detection device based on the piezoelectric effect according to claim 1, characterized in that The V-shaped spring leaf (1) is made of a material with high yield strength (≥800 MPa) and fatigue strength (≥550 MPa), and good plasticity and toughness.

3. The tensile property detection device based on the piezoelectric effect according to claim 2, wherein, The V-shaped spring leaf (1) is made of alloy spring steel 60Si2Mn.

4. A tensile property detection device based on the piezoelectric effect according to claim 1, characterized in that, The surface of the V-shaped spring leaf (1) is ground, and the surface roughness Ra is not greater than 6.4 μm to achieve reliable bonding with the piezoelectric film (7).

5. The tensile property detection device based on the piezoelectric effect according to claim 1, wherein The piezoelectric film (7) uses a PVDF piezoelectric film.

6. The tensile property detection device based on the piezoelectric effect according to claim 1, wherein The contact surfaces of the first clamping plate (3), the second clamping plate (6), and the third clamping plate (9) with the specimen are rough surfaces.

7. The tensile property detection device based on the piezoelectric effect according to claim 6, characterized in that, The surface roughness Ra is not less than 25 μm.

8. A tensile property detection device based on the piezoelectric effect according to claim 1, characterized in that, The lead screw (4) uses a precision lead screw with a small pitch not greater than 2 mm.

9. The tensile property detection device based on the piezoelectric effect according to claim 8, characterized in that, The lead screw (4) uses a triangular fine-thread screw to realize the tensile test detection of the specimen under small displacement conditions.

10. The detection method of a tensile property detection device based on the piezoelectric effect according to claim 1, characterized in that, During the stretching process of the specimen, under the action of the tensile force, the surface of the V-shaped spring leaf (1) is bent, which causes the piezoelectric film (7) to deform, and polarization occurs inside it, becoming a charged state; since at different stretching stages, the tensile force applied to the specimen is different, the strain of the V-shaped spring leaf (1) and the piezoelectric film (7) is different, resulting in different amounts of electric charge generated by the piezoelectric film (7). Through the change in the amount of electric charge, the force and the trend of force change during the stretching process can be detected in real time.

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