Testing and Analysis of Shape Memory Alloys

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Reza Mirzaeifar

Considerable increase in the use of shape memory alloys (SMAs) for introducing novel devices in a vast range of applications in recent years reveals the potential of SMAs to revolutionize many products in various applications including biomechanics, aerospace, mechanical and civil engineering. Extensive interest in using SMAs for manufacturing devices is mostly due to their unique ability in generating relatively large inelastic deformations and high stresses. The distinctive properties of SMAs are due to their ability of changing crystallographic structure by solid state transformation between a high symmetry parent phase (austenite) and a low symmetry phase (martensite) in response to mechanical and/or thermal loading. As a result of the solid-solid phase transformation (martensitic phase transformation), and according to the specific way the transformation occurs, SMAs exhibit two significant macroscopic phenomena: the shape memory effect and pseudoelasticity.  Due to shape memory effect, SMAs are capable to recover the residual strain after a loading-unloading cycle by being heated to a specific temperature. According to pseudoelasticity, SMAs can recover relatively large strains in specific temperatures. During this pseudoelast loading-unloading cycle, the SMAs show a hysteretic response that makes these materials an efficient candidate for being used as energy dissipating devices in seismic applications.

Our research is focused on the testing and analysis of SMAs in various shapes and loading conditions including large scale cables, bars and helical springs subjected to quasi-static and dynamic loadings (Figure 1). We introduce analytical and semi-analytical solutions for these SMA devices. Our analytical solutions are exact, fast and capable of simulating complicated coupled thermo-mechanical response of SMAs considering the ambient conditions and the rate dependency (Figure 2).

Figure 1 Figure 2
Figure 1: Large scale shape memory alloy cables, bars and helical springs. Figure 2: Analytical solution for studying the temperature effect on the response of an SMA helical spring.

Selected publications:

  1. Mirzaeifar R, DesRoches R, Yavari A. A combined analytical, numerical, and experimental study of shape-memory-alloy helical springs. 2011. International Journal of Solids and Structures.  2011. 48(3-4): 611-624
  2. Mirzaeifar R, DesRoches R, Yavari A. Exact solutions for pure torsion of shape memory alloy circular bars. Mechanics of Materials. 2010; 42(8): 797-806.
  3. Mirzaeifar R, Shakeri M, DesRoches R, Yavari A. A semi-analytic analysis of shape memory alloy thick-walled cylinders under internal pressure. Archive of Applied Mechanics. 2010. DOI 10.1007/s00419-010-0468-x.
  4. Mirzaeifar R, DesRoches R, Yavari A. Analysis of the Rate-Dependent Coupled Thermo-Mechanical Response of Shape Memory Alloy Bars and Wires in Tension. Submitted.