阅读说明：本技术 一种形状记忆合金回复力性能测试方法及测试系统 (Method and system for testing restoring force performance of shape memory alloy ) 是由 王领 刘建伟 杨建鲁 王鹏飞 王新强 袁清泉 梁生云 钱兴 刘长义 徐绮薇 于 2020-12-06 设计创作，主要内容包括：本发明提供了一种形状记忆合金回复力性能测试方法及测试系统,将标准规格的形状记忆合金拉伸试样安装在专用测试装置上,采用经过校核的保温箱做为形状记忆合金规定温升速率的加热装置,加热过程中,对形状记忆合金进行温度和回复力值的测定。本发明能够实现在不同升温速率下测试形状记忆合金回复力的目的。(The invention provides a method and a system for testing the restoring force performance of a shape memory alloy. The invention can realize the purpose of testing the restoring force of the shape memory alloy at different heating rates.)

1. A method for testing the restoring force performance of a shape memory alloy is characterized by comprising the following steps:

1) the structure of the sample to be tested is designed into a cylindrical structure with the outer diameters of two ends larger than the outer diameter of the middle section or a sheet structure with the width of two ends larger than the width of the middle section, the outer diameter of the middle section of the cylindrical structure is consistent with the outer diameter of a product, the width of the middle section of the sheet structure is consistent with the width of the product, and the thickness of the sheet structure is consistent with the thickness of the;

2) symmetrically arranging a plurality of temperature measuring points on two sides of the central axis of the sample to be measured;

3) fixing one end of a sample to be tested, and connecting the other end of the sample to be tested with a dynamometer;

4) placing a sample to be tested in a heat preservation device, and heating according to a set temperature rise curve;

5) recording the temperature change of each temperature measuring point and the force value change curve of the dynamometer in the temperature rise process;

6) establishing a temperature-restoring force curve by taking the mean value of the measured values of the temperature measuring points As the temperature value of the sample to be measured, and determining an initial phase-changing point As and a termination phase-changing point Af of the sample to be measured;

7) providing pretightening force at one end of a sample to be tested, testing an initial phase change point As1 and a termination phase change point Af2 after phase change drift, and setting the phase change drift temperature delta A As 1-As.

2. A method for testing the restoring force performance of a shape memory alloy according to claim 1, wherein the outer diameter of the middle section of the cylindrical structure is phi, and the outer diameters of the two ends are phi +5 mm; the length of the middle section is not less than 90mm, wherein the calibration distance is 60 mm.

3. The method of claim 1, wherein the sheet-like structure has a middle section width of L5 and two ends width of L5+6 mm; the length of the middle section is not less than 90mm, wherein the calibration distance is 60 mm.

4. The method for testing the restoring force performance of the shape memory alloy according to claim 1, wherein before the step 3), the sample to be tested is subjected to pre-deformation treatment by applying a tensile force, and the tensile rate is not more than 1 mm/min.

5. The method for testing the restoring force performance of the shape memory alloy according to claim 1, wherein the step 6) removes the maximum value and the minimum value of the measured values of the temperature measuring points, and the average value of the measured values of the temperature measuring points is taken as the temperature test result of the sample to be tested.

6. The method for testing the restoring force performance of the shape memory alloy according to claim 1, wherein the step 6) determines the initial phase transformation point As and the final phase transformation point Af of the sample to be tested by using an included angle bisector method.

7. A shape memory alloy restoring force performance testing device for realizing the method of claim 1 comprises a to-be-tested sample fixing device, a thermocouple and an incubator, and is characterized in that the fixing device comprises a dynamometer 2, an extension sleeve 4, a pull rod 5, a chuck, a fixed seat 10, a pull rod 11, an adjusting sleeve 12 and an adjusting nut 13; the dynamometer and the adjusting sleeve are arranged on the fixed seat; the clamping heads are used for fixing two ends of a sample to be tested, one clamping head is fixedly connected with a pull rod, the pull rod extends into the extension sleeve, and the relative positions of the pull rod and the extension sleeve are adjusted and fixed through fixing screws; the extension sleeve is connected with the dynamometer; the other chuck is fixedly connected with a pull rod, the pull rod penetrates through the adjusting sleeve to be matched with the adjusting nut, and the pre-tightening force applied to the sample to be tested is changed by rotating the adjusting nut; the thermocouple is arranged on a sample to be measured; the sample to be measured is placed in an incubator with a heating function.

Technical Field

The invention relates to the technical field of shape memory alloy testing, in particular to a performance test of the restoring force of a shape memory alloy.

Background

The shape memory alloy has shape memory effect, so that the application range of the shape memory alloy relates to the fields of aerospace, aviation, construction, biomedicine, daily life and the like, and the shape memory alloy is widely applied to the field of biomedicine in particular.

At present, a uniaxial tension method is mainly adopted for testing the restoring force of the shape memory alloy, and the method can be used for testing the restoring force performance of nickel-titanium shape memory alloy wires, rods and plates under different loading strains to obtain the restoring force performance parameters of the nickel-titanium shape memory alloy in a one-way tensile stress state, so that reference is provided for the design of the nickel-titanium shape memory alloy in practical application. The test method has the advantages that:

(1) the shape memory alloy can be rapidly heated, and the maximum restoring force of the shape memory alloy is measured;

(2) and a standard material tensile testing machine is adopted for testing, and the testing device is stable and good in consistency.

However, this method also has disadvantages including:

(1) the heating rate is not controllable, heating can be carried out only according to the heating rate initially set by the tensile test equipment, and the variable heating rate cannot be adjusted according to the use environment;

(2) the temperature of the shape memory alloy sample to be tested cannot be tested, and the heating test equipment in the tensile testing machine can only test the temperature of the ring mirror in the heating box and cannot test the real-time temperature of the sample to be tested;

(3) the universal tensile testing machine has fixed force measuring range or less selectable gear positions, and cannot meet the test force value requirement of a multi-specification test sample;

(4) the tensile testing machine can obtain a restoring force value curve, and a temperature-restoring force curve cannot be formed because the temperature of a sample to be tested cannot be tested;

(5) the existing testing method cannot provide the phase change drift temperature of the shape memory alloy.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for testing the restoring force performance of a shape memory alloy, wherein a shape memory alloy tensile sample with a standard specification is installed on a special testing device, a checked heat preservation box is adopted as a heating device for regulating the temperature rise rate of the shape memory alloy, and the temperature and the restoring force value of the shape memory alloy are measured in the heating process. The invention can realize the purpose of testing the restoring force of the shape memory alloy at different heating rates.

The technical scheme adopted by the invention for solving the technical problems is as follows: a method for testing the restoring force performance of a shape memory alloy comprises the following steps:

1) the structure of the sample to be tested is designed into a cylindrical structure with the outer diameters of two ends larger than the outer diameter of the middle section or a sheet structure with the width of two ends larger than the width of the middle section, the outer diameter of the middle section of the cylindrical structure is consistent with the outer diameter of a product, the width of the middle section of the sheet structure is consistent with the width of the product, and the thickness of the sheet structure is consistent with the thickness of the;

2) symmetrically arranging a plurality of temperature measuring points on two sides of the central axis of the sample to be measured;

3) fixing one end of a sample to be tested, and connecting the other end of the sample to be tested with a dynamometer;

4) placing a sample to be tested in a heat preservation device, and heating according to a set temperature rise curve;

5) recording the temperature change of each temperature measuring point and the force value change curve of the dynamometer in the temperature rise process;

6) establishing a temperature-restoring force curve by taking the mean value of the measured values of the temperature measuring points As the temperature value of the sample to be measured, and determining an initial phase-changing point As and a termination phase-changing point Af of the sample to be measured;

7) providing pretightening force at one end of a sample to be tested, testing an initial phase change point As1 and a termination phase change point Af2 after phase change drift, and setting the phase change drift temperature delta A As 1-As.

The outer diameter of the middle section of the cylindrical structure is phi, and the outer diameters of two ends of the cylindrical structure are phi +5 mm; the length of the middle section is not less than 90mm, wherein the calibration distance is 60 mm.

The width of the middle section of the sheet structure is L5, and the widths of the two ends are L5+6 mm; the length of the middle section is not less than 90mm, wherein the calibration distance is 60 mm.

And (3) applying a tensile force to the sample to be tested for pre-deformation treatment before the step 3), wherein the tensile rate is not more than 1 mm/min.

And 6) removing the maximum value and the minimum value in the measured values of the temperature measuring points, and averaging the measured values of the remaining temperature measuring points to obtain a temperature test result of the sample to be tested.

And 6) determining an initial phase change point As and a termination phase change point Af of the sample to be tested by adopting an included angle bisector method.

The invention also provides a device for testing the restoring force performance of the shape memory alloy, which comprises a fixing device of a sample to be tested, a thermocouple and an incubator.

The fixing device comprises a dynamometer 2, an extension sleeve 4, a pull rod 5, a chuck, a fixed seat 10, a pull rod 11, an adjusting sleeve 12 and an adjusting nut 13; the dynamometer and the adjusting sleeve are arranged on the fixed seat; the clamping heads are used for fixing two ends of a sample to be tested, one clamping head is fixedly connected with a pull rod, the pull rod extends into the extension sleeve, and the relative positions of the pull rod and the extension sleeve are adjusted and fixed through fixing screws; the extension sleeve is connected with the dynamometer; the other chuck is fixedly connected with a pull rod, the pull rod penetrates through the adjusting sleeve to be matched with the adjusting nut, and the pre-tightening force applied to the sample to be tested is changed by rotating the adjusting nut; the thermocouple is arranged on a sample to be measured; the sample to be measured is placed in an incubator with a heating function.

The invention has the beneficial effects that:

1) the testing method and the testing system can realize the adjustability of the heating rate and test the restoring force of the shape memory alloy at different heating rates;

2) according to the test method and the test system, the heating device is a heat preservation test box, and the heating environment can simulate the actual use working condition;

3) according to the testing method and the testing system, the temperature thermocouple is directly bonded on the piece to be tested of the shape memory alloy, so that the temperature of the shape memory alloy can be acquired in real time;

4) according to the testing method and the testing system, the force value measurement adopts the universal dynamometer, and the force value testing range can be freely selected according to the testing force value during testing;

5) according to the testing method and the testing system, the acquisition system adopts a universal static test acquisition device, the temperature and the restoring force value change of the shape memory alloy sample to be tested in the testing process can be recorded, and a temperature-restoring force value curve under different heating rates is formed.

6) The test system disclosed by the invention is simple in structure, good in universality and suitable for testing the recovery performance of various shape memory alloys.

7) The test system can effectively test the relation between the stress state and the phase change drift of the shape memory alloy through the test method evaluation of the invention when the test shape memory alloy is in different prestress states in the test process, and provides effective data support for product design.

8) The size design of the middle section of the cylindrical dumbbell sample is consistent with the structure of a product, various performances of the product in the use process can be fully represented, the actual performance of the product can be predicted, sufficient data basis can be provided for subsequent improvement design, the size of the clamping part can effectively ensure that the piece to be tested is reliably clamped in the test process, and the test precision and accuracy are improved;

9) the size design of the square dumbbell sample is consistent with the structure of a product, various performances of the product in the using process can be fully represented, the actual performance of the product can be predicted, sufficient data basis can be provided for subsequent improvement design, the size of the clamping part can effectively ensure that a piece to be tested is reliably clamped in the testing process, and the testing precision and accuracy are improved;

10) the testing method can accurately test the phase change drift temperature of the shape memory alloy, and has the advantages of simple operation process, high testing precision, high response speed, simple structural equipment and low manufacturing cost. The test temperature range is-50 ℃ to 300 ℃, and the sensitivity is +/-5 ℃.

Drawings

FIG. 1 is a view showing the structure of a shape memory alloy fixing apparatus according to the present invention.

FIG. 2 is a view showing the structure of a sample to be measured in the present invention.

Fig. 3 is a temperature-restoring force curve of a sample to be measured in the present invention.

Fig. 4 is a temperature drift curve of the sample to be tested in different pre-stress states.

Detailed Description

The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.

The invention provides a shape memory alloy testing method, which is characterized in that a shape memory alloy tensile sample with standard specification is installed on a special testing device, a checked heat preservation box is adopted as a heating device for setting the temperature rise rate of the shape memory alloy, and the temperature and the recovery force value of the shape memory alloy are measured in the heating process.

The special testing device mainly comprises the following parts: a temperature and force value acquisition system, a dynamometer, a temperature thermocouple and a shape memory alloy fixing device.

The specific test method is as follows:

1) the test sample structure that awaits measuring generally designs for dumbbell type structure cylinder structure or square slice structure, and to cylinder type dumbbell sample, sample middle section external diameter size phi is unanimous with product external diameter size, and the external diameter size of chuck part is phi +5mm, and sample middle section length L2 is not less than 90mm, and calibration distance L is 60 mm.

For the square sheet type dumbbell sample, the middle section width L5 is consistent with the product width, the width L6 of the chuck part is equal to L5+6mm, the length L2 of the middle section of the sample is not less than 90mm, the calibration distance L is 60mm, and the thickness h of the sample is consistent with the product.

2) When the sample to be tested is subjected to pre-deformation treatment, the elongation is determined according to the use condition of the product on the basis of the standard distance of the sample to be tested, and the stretching speed is not more than 1 mm/min.

3) The number of the temperature measuring points of the sample to be measured is 8, the temperature measuring points are respectively A1-A8, 4 points are equally distributed along the scale distance on one side, and 4 points are distributed on the opposite side.

4) Fixing a sample to be detected on a shape memory alloy fixing device;

5) connecting the shape memory alloy fixing device with a dynamometer;

6) the thermocouple and the dynamometer are connected with the acquisition system;

7) after the system is connected, the locking nut at the tail end of the shape memory alloy fixing device is adjusted to close the gap of each connecting part, and the force value display is controlled to reach 20N-50N.

8) Placing the shape memory alloy fixing device into a special heat preservation box, setting a heating program, and heating the heat preservation box according to the actual requirement by adopting a program control mode;

9) and recording the temperature change and force value change curves of the shape memory alloy in the temperature rise process.

10) The locking nut in the shape memory alloy fixing device is adjusted, the stress state of the shape memory alloy sample is adjusted, and the change of the restoring force value of the shape memory alloy can be tested under different stress states.

11) And during data processing, the maximum value and the minimum value are removed from the temperature test points, and the average value of the remaining six temperature test points is taken as the temperature change test result of the sample to be tested.

12) And establishing a temperature-restoring force curve, and determining an initial phase change point As and a termination phase change point Af of the sample to be tested by adopting an included angle bisector method.

13) Through a pretightening nut, pretightening force F is provided, and an initial phase change point As1 and a final phase change point Af2 after phase change drift are obtained through testing, wherein the phase change drift temperature delta A is As 1-As.

As shown in FIG. 1, the shape memory alloy test fixture of the present invention comprises: go up fixing base 1, dynamometer 2, set screw 3, extension sleeve pipe 4, pull rod 5, fixed block 6, chuck 7, stationary blade 8, the sample 9 that awaits measuring, lower fixing base 10, pull rod 11, adjusting sleeve pipe 12 and adjusting nut 13. The upper fixing seat 1 and the fixing block 6 are fixed on the lower fixing seat 10 through fixing screws 3. The fixing block 6 and the clamping head 7 clamp and fix the sample 9 to be tested through the fixing screw 3, and the clamping head 7 and the pull rod 5 pass through the fixing screw 3. The pull rod 5 is connected through a hole in the fixed block 6, and the pull rod 5 can move freely in the fixed block 6. The dynamometer 2 is in threaded connection and fixed with the upper fixed seat 1 and the extension sleeve 4, and the extension sleeve 4 penetrates through a hole of the upper fixed seat 1 and can move freely. The adjusting sleeve 12 is sleeved on the pull rod 11 and is in threaded connection with the pull rod 11 through an adjusting nut 13. The clamping head 7 is connected with the pull rod 5 and the pull rod 11 through the fixing screw 3.

After the upper fixing seat 1, the dynamometer 2, the fixing screw 3, the extension sleeve 4, the pull rod 5, the fixing block 6, the chuck 7, the fixing plate 8, the sample to be tested 9, the lower fixing seat 10, the pull rod 11, the adjustment sleeve 12 and the adjustment nut 13 are installed according to the diagram, the dynamometer and the thermocouple are connected to the collector. And (4) placing the force measuring device into the heat insulation box, setting the heating rate, and performing a heat insulation test. After the test was completed, a temperature-force value curve was formed.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.