Inject water into the bathtub. The memory spring is stretched from the contracted state to the extended state, and the initial coordinate value and temperature value indicated by the pointer at this time are recorded. When the power is turned on, the electric water bath is heated by the electric furnace. At this time, it can be observed that as the temperature rises, the spring contracts and deforms, and the weight is pulled up. For every 1 °C increase in temperature, record the coordinate value of the contraction deformation of the memory spring until the memory alloy spring reaches the full contraction state. From this, the temperature deformation curve of the memory spring can be drawn.
The deformation curve of the memory alloy spring under the weight of 200g, the temperature is from 15 to 60 °C, and the memory spring is contracted from the extended state to the memory state. If the weight is changed (270g), the temperature 2 deformation curve under different external stresses can also be observed. As can be seen from the figure, the phase transition temperature of the memory alloy is 30 ° C, and the temperature at the end of the transformation is 50 ° C.
The current 2 deformation memory effect of the memory alloy spring is a device design for measuring the current 2 deformation effect of the memory alloy spring. During the experiment, the ends of the memory alloy spring were connected by wires and the spring was stretched. One end of the spring is attached to the top of the bracket and the other end is suspended by a counterweight. Record the starting coordinate value at this time.
When the power is turned on and the current intensity is adjusted by the slider varistor, the memory spring shrinkage deformation can be observed. By recording the coordinate values ​​of the memory spring contraction at different current intensities, the current 2 deformation curve can be plotted. The current intensity 2 shrinkage curve of the memory alloy spring is given when the current intensity is from 0.1A to 0.8A under 240g weight and room temperature 18°C.
During the phase change process during electrothermal driving, the contraction deformation speed of the spring first increases with the increase of the contraction displacement. When the contraction displacement approaches the intermediate position, the speed reaches a maximum value, and the maximum speed remains constant for a period of displacement. Thereafter, it decreases as the contraction displacement increases, and the velocity is zero when the memory length is reached. By controlling the current, the contraction deformation speed of the spring can be controlled, but the current of too high or too low cannot be selected, otherwise the memory function will be destroyed. When using a spring with a 4 current intensity 2 deformation curve, the appropriate load and tensile deformation length should be selected. The excessive load not only makes the shrinkage deformation speed become slow, but also causes the spring to undergo incomplete shrinkage deformation, thereby reducing The cyclic working life of the spring. Excessive stretch deformation length will also reduce its cycle working life.
Conclusion Through this experiment, students can qualitatively understand the following phenomena and rules: 1) The memory metal has an initial memory temperature point, and the initial memory point of the memory spring is 30 °C. 2) Before the memory point, when the temperature changes, the spring deformation is not obvious. When the temperature exceeds the memory point, the spring shrinkage becomes significant, and the shrinkage is close to 3.5cm. 3) When the temperature reaches 50°C, the memory metal spring reaches the full-shrink memory state. 4) The external force of the memory spring is different. The starting point coordinate and the ending coordinate of the contraction are different. The larger the external force, the more difficult it is for the memory spring to restore the full-contracted memory state. 5) The memory metal spring also has a memory effect on the current intensity. Its initial memory current intensity is about 0.4A, and the termination deformation current intensity is about 0.7A (measured at room temperature of 18 ° C and load of 240 g). Memory spring The current memory effect is still the temperature memory. When the current thermal effect and the heat dissipation of the memory spring are balanced, the memory alloy maintains a relatively stable temperature. If the current increases, the temperature of the spring also increases, causing shrinkage deformation.
The experimental design is feasible at the level of physical experiment teaching and can be used as a physical design experiment.
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