Pseudoelastic behaviour of perforated NiTi shape memory plates under tension

• Perforated pseudoelastic NiTi plates deform with a distinctive stress gradient.
• The stress gradient can be adjusted by hole design.
• A simple and robust mathematical model is developed to aid design of perforated NiTi plates.

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.

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