Design and Analysis of Woven Shape Memory Alloy Fabric

Abstract

Shape Memory Alloys (SMA) are smart materials that can memorize a shape and return to that shape after deformation upon the application of stress or heat. The most commonly used SMA is Nitinol (NiTi) which consists of equal parts nickel and titanium. Nitinol has two primary crystalline phases, Martensite and Austenite. The crystalline phase of Martensite occurs at lower temperatures and higher stresses whereas the crystallization of Austenite occurs at higher temperatures and lower stresses. These phases cause the material to experience two different properties: super elastic (Austenite at room temperature) and shape memory (Martensite at room temperature). Nitinol comes in many forms including wire, tubes, plates, and springs. A literature review indicates that the author has woven Nitinol wire into the first ever known Nitinol woven fabric. The main objective of this thesis is to establish a relationship between a single Nitinol wire and woven Nitinol fabric to predict the apparent elastic modulus of the fabric. First, the wire and fabric were heat treated and aged for various temperatures and times. The heat treatment showed that as the heat treatment temperature increased, the transformation temperature(s) increased during heating and decreased during cooling. Upon the heat treatment, both single wire and fabric were experimentally tested at various temperatures, and their elastic modulus derived. Modeling for woven Nitinol fabric is initially derived from both composite analysis and fabric weaving. From the model, an equation is derived that predicts the woven fabric’s characteristic, specifically the apparent elastic modulus. The analytical and experimental data were examined, and the results show that the model has a 6.45% error on average. This demonstrates that the proposed analytical model offers a useful tool for design and simulation of woven Shape Memory Alloy fabrics.