Theoretical and Experimental Investigation on SMA Superelastic Springs

Abstract

The mechanical behavior of superelastic springs is investigated in this study. The goal is to evaluate the device response and to exploit the material superelastic behavior, main concerns being material and geometrical response nonlinearity. The investigation is made of two parts, i.e., an experimental campaign and a numerical model proposal. Experimental tests have been performed on superelastic SMA coil springs considering load history in tension and compression for three different spring geometrical configurations. Tested specimens experience a maximum elongation larger than the original spring axis length. The response is not symmetric and under compression it is affected by buckling instability. Nevertheless, experimental results show a very good superelastic behavior with no damage and with negligible residual displacements. Numerical analyses have been performed to reproduce the experimental campaign results. A simple finite element model is proposed. Experimental and numerical result agreement is very good. The numerical model turns out to be a powerful design tool even for the very complex geometrical and material nonlinear conditions under investigation. Hence, it is proposed as a useful tool for spring design validation and response prediction.

Macroscopic modeling of functional fatigue in shape memory alloys

“…The first assumption to be relaxed is the generalization of the studies here presented to non-homogeneous deformations (Auricchio and Petrini, 2004b;Attanasi et al, 2011). The onset of plastic deformations is indeed a local phenomenon that is to be expected to occur close to points where local stresses increase, such as clamps or inclusions (Urbano, 2012).…”

Innovative Superelastic Isolation Device

“…2 (see also Attanasi et al, 2011b, for more details). Few test snapshots from the experimental campaign on SMA springs described in detail in Attanasi et al [2011a] are reported in Fig. 3.…”

“…The superelastic isolator device response has been numerically predicted using the finite element model experimentally validated as reported in Attanasi et al [2011a]. The numerical prediction has been computed using the finite element analysis program ABAQUS [2003].…”

Design Method for Constant Force Components Based on Superelastic SMA

“…The superelasticity of SMA is the ability to undergo large deformations in loading–unloading cycles without showing permanent deformations [16,17]. It is evaluated that the superelastic behavior of springs are made with the wire of shape memory alloys [18,19]. To obtain good constant force properties, the structure optimization of SMA is needed.…”