Pseudoelastic behaviour of perforated NiTi shape memory plates under tension

This paper reports the tensile deformation behaviour of near-equiatomic NiTi plates with circular, elliptical and square holes. The investigation is done both experimentally and by mathematical modelling. It is found that the nominal stress-strain curve of such structures deviates from typical stress-strain variation of NiTi with flat stress plateaus, by exhibiting stress gradients over the forward and reverse transformations of the hole-affected areas. The hole-affected length is nearly triple the lateral dimension of the hole, and when 33% of the gauge length is covered by (circular) holes, the entire sample behaves like a functionally graded material. Such mechanical behaviour is advantageous for achieving better load-displacement controllability and wider stress window for shape memory actuation and sensing. (C) 2014 Elsevier Ltd. All rights reserved.