Properties and behavior of shape memory alloys in the scope of biomedical and engineering applications

Abstract

Shape memory alloys (SMA) are widely and frequently applied in cases when it is useful to employ their advantages through specific behavior (pseudoelasticity or shape memory effect) in various conditions. Effects of shape memory and pseudoelasticity can be employed in innovative ways as actuating or sensing elements in many nowadays applications. There are various alloying elements which can form a SMA such as Ni, Ti, Cr, Cu, etc., but the most frequently used and known alloy is NiTi. By addition of other alloying elements the properties of the SMA can be changed to fit demands of the consumers. The investigation of such materials is very important for successful application, so the researchers investigate procedures and algorithms for comparison of experimental and numerical results to provide the best performance of SMA devices. Strong thermomechanical coupling is observed during the SMA loading, so SMA are known as highly thermosensitive materials what can be used as advantage, but also it can be a problem during the alloy production process. The strong thermomechanical coupling and the related high thermosensitivity increase the need for simulation of complex thermomechanical response in realistic problems. The complex stress states and deformation range impose the requirements for accurate analysis of large strain problems. Application of SMA started several decades ago with an engineering application in pipe couplings, while today one of the most commonly known are biomedical applications (i.e. cardiovascular stents and orthodontic braces). The main reasons for wide range of biomedical applications of NiTi alloys are the specific behavior, good biocompatibility and good fatigue performance what is important factor under the high cyclic external loading.