Superelastic nitinol Spring 0.040" (1.0mm) Wire on 3/4" Mandrel by Kellogg's Research Labs

Description

Superelasticity is a phenomenon observed in nitinol when heated above its transition temperature. The shape memory effect is well known and is the result of thermally induced martensite. However, if the temperature is above the transition temperature and the nitinol is stressed (a force exerted on it), then we get the reverse transition, creating stress induced martensite (SIM). What does this look like in real life? First, the spring behaves like a regular steel spring, up to about 2% deformation. At about 2% deformation, the spring hits what’s called the plateau stress. Above this deformation, the force really doesn’t change at all as the spring is lengthened. The % deformation is taken at the crystal level, not the length of the spring. Putting this in perspective, a stainless steel spring can only sustain a 0.5% deformation, whereas a superelastic spring can sustain up to a 50% deformation! The fatigue life of superelastic springs also is typically 100-1,000 times longer than steel springs.