Abstract
Studies have been actively conducted on systems that prevent the breakage of water pipes from freezing in winter. Shape memory alloy (SMA) coil springs have been used as the key components of actuators that can operate automatically by detecting the real-time outside temperature changes, but research on its use as an actuator that can operate at sub-zero temperatures is insufficient. This study proposes the anti-freezing system using Ni-44.08Ti-1.46Co (wt.%) SMA coil springs that operate near sub-zero temperatures to prevent the freezing accident of water pipes. After fabricating the SMA coil springs, the test for performance evaluation of the springs applied static load conditions was conducted on the specific outside temperature. To examine the operation of anti-freezing systems applied the SMA coil spring as an actuator, the water discharge test (WDT) was also conducted along with the computational fluid simulation. The results of water discharge measurement obtained by WDT, simulations, and theoretical equations applied to the fluid resupply system constructed were compared with each other to verify the reliability. Consequently, it was confirmed that water discharge can be automatically controlled in real time according to temperature changes of SMA coil springs in the anti-freezing system.
Highlights
Shape memory alloy (SMA) called “smart materials” is attracting attention as a key component material of actuators owing to its excellent mechanical properties such as high resilience and suitable weight-to-power ratio until a recent date
When the temperature of the SMA coil spring is slowly reduced by the outside temperature, and constant water pressure is consistently applied in the pipe, it seems to decrease numerically due to the recovery properties of SMA coil springs, spring constant values do not change in reality
K is the spring constant, G is the stiffness coefficient, E is the modulus of elasticity, Na is the number of active coils, D is the mean diameter of the coil, d is the diameter of the wire, ν is Poisson’s ratio, F is the static load applied on the spring, and δ is the spring deflection in the y-axis direction
Summary
SMA called “smart materials” is attracting attention as a key component material of actuators owing to its excellent mechanical properties such as high resilience and suitable weight-to-power ratio until a recent date. The mechanical properties and operational conditions containing the temperature and load at which phase transformation first occurs in the system are different according to the X element content It has been applied in various fields depending on the forming method such as welding and casting [2,3]. The shape memory effect (SME) related to the recovery property of SMA is a phenomenon in which the alloy returns to the geometry before plastic deformation owing to the occurrence of bidirectional transformation of the austenite and martensitic phases in the alloy when the SMA subjected to plastic deformation is heated to a temperature above the critical point Pseudoelasticity, which is another property of SMA, refers to a characteristic in which recovery deformation occurs as a load is applied or removed while a constant temperature is maintained for SMA, and it occurs above the austenite finish temperature (Af). If the shape memory effect is utilized to SMA coil springs, it means that the occurrence of spring deflection can be iteratively generated depending on changes in the outside temperature
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