Abstract
This paper proposes a new force-displacement model for superelastic shape memory alloy (SMA) springs under complex loading and unloading. For the SMA wires used to make superelastic springs, a new multilinear constitutive model based on a modification of the 1D Motahari model is developed. In the modified model, the stress-strain relation curves are changed to fit the experimental results. Furthermore, the established force-displacement relationship of the springs considers the impact of not only the torque but also the moment on the cross sections of the SMA wires. Afterwards, a series of tension tests are performed on four NiTi helical spring specimens under various loading conditions. From the numerical simulations and experimental results, it is shown that, compared with the force-displacement curves for the SMA springs simulated by the Motahari model, those simulated by the proposed model can better approximate the experimental results. The new model inherits the advantage of simple computation of the multilinear constitutive model and can predict the force-displacement relation for superelastic SMA springs very well. Furthermore, due to the self-sensing properties of the SMA springs, the new model is very significant for establishing a new strategy for measuring the displacements or forces of SMA springs under complex loading and unloading.
Highlights
A shape memory alloy (SMA) is a smart material that has unique shape memory and superelastic effects and good damping characteristics, fatigue resistance and corrosion resistance
It is worth mentioning that the force-displacement curve or major loop of each specimen in Case I is basically the same as that of the specimen in Case II when the displacement amplitudes of loading are identical. These results demonstrate that if the displacement amplitudes of loading are identical, the loading and unloading paths of the major loops of the SMA helical springs are stable for different cases of loading
The new model inherits the advantage of simple relationship of helical superelastic SMA springs
Summary
A shape memory alloy (SMA) is a smart material that has unique shape memory and superelastic effects and good damping characteristics, fatigue resistance and corrosion resistance. Researchers mainly study the mechanical properties of SMA springs based on the complex thermodynamic stress-strain constitutive model of SMA materials in a superelastic state. To establish the force-displacement relationship for an SMA helical spring, it is required to solve a large number of nonlinear thermodynamic equations in the stress-strain-temperature model. To improve the simulation efficiency of the force-displacement relationship, a multilinear constitutive model of an SMA material was proposed by Motahari and Ghassemieh [49] to replace the nonlinear function models driven by solving the nonlinear thermodynamic equations Inspired by this idea, this paper proposes a new mechanical model of SMA springs based on a modification to the 1D model proposed by Motahari and Ghassemieh. Using self-sensing characterizations, such as the displacement-resistance relationship and the displacement-coil inductance relationship for the SMA springs, this new model will be very useful for providing a new strategy to measure the displacements or forces of SMA springs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
