NiTi Belleville washers: Design, manufacturing and testing

Abstract

The thermomechanical properties of nickel–titanium-based Belleville washers have been analyzed in this investigation, together with their unusual mechanical and functional features, which can be attributed to the reversible phase transformation mechanisms of nickel–titanium alloys. In particular, numerical simulations have been carried out for a preliminary design of the Belleville washer, using a commercial finite element software and a special constitutive model for shape memory alloys. Subsequently, Belleville washers have been manufactured from a commercial pseudoelastic nickel–titanium alloy, by disk cutting and a successive shape setting by a thermomechanical treatment. Finally, the thermomechanical response of the washers, in terms of isothermal force–deflection curve and thermal cycles between phase transition temperatures, has been experimentally analyzed. The results highlighted a marked effect of the temperature on the characteristic curve, as well as good recovery capabilities under both mechanical and thermal cycles. In addition, nickel–titanium Belleville washers exhibit a marked hysteretic behavior, as a consequence of the hysteresis in the stress–strain response of the alloy. Thanks to these features, nickel–titanium Belleville washers can be used as smart elastic elements, that is, with tunable stiffness and damping properties, as well as solid-state actuators, due to their recovery capabilities.