Temperature memory effect/triple-shape memory effect in niti shape memory alloys and shape memory effect in keratin

Abstract

Besides the shape memory effect (SME), in which the permanent shape can be recovered at the presence of the right stimulus, the temperature memory effect (TME) is another feature of shape memory materials. The TME refers to a phenomenon that a particular temperature can be memorized in a certain manner. A systematical investigation of the mechanism from energy point of view for the TME in NiTi shape memory alloys (SMAs) is presented based on the results of a series of differential scanning calorimeter (DSC) tests. The traditional approach for the TME is expanded, and a modified one is identified, which can be utilized to monitor over-heating temperature with high accuracy. The triple-shape memory effect (triple-SME), which is easily achievable in shape memory polymers (SMPs) but not in SMAs, is achieved in a few types of NiTi SMAs. Two approaches, namely small strain program and larger strain program are proposed. The conditions on both material and programming parameters, as well as the mechanisms for the triple-SME, are identified and the influence of programming parameters is investigated. Both heating-induced and water-induced SMEs in human nail and silkworm silk, in which keratin is their main component, are systematically investigated. The influence of water content is studied. The triple-SME utilizing multiple-stimuli is realized in nail. The fundamentals behind the difference in heating and water based SMEs are studied.