Crescimento de trincas em ligas de memória de forma sob vida em fadiga

Abstract

Shape memory alloys are a class of metallic alloys that arouse interest in both the academic and industrial spheres due to their properties of shape memory effect and superelasticity that arise from the reversible transformation of martensite. This type of alloy was discovered in the early 1930s when reversible martensitic transformations and pseudoelastic behavior were first observed. As studies in LMF advanced and more practical applications were developed a commercial opportunity was created for this class of metal alloys and in 1960, in a laboratory in the United States a NiTi alloy was developed under the trade name NiTiNOL, in reference to the laboratory where it was developed, Naval Ordnance Laboratory. Over time, LMFs have gained ground in different commercial applications in the automotive, aerospace and robotics industries. They have also been introduced in the field of medicine and dentistry for their good biocompatibility and biofunctional properties. Like conventional metal alloy components, LMFs are also subject to fatigue fractures. This work aims to relate some concepts of fracture mechanics with the study of how the crack propagation rate is affected by some factors such as the temperature at which the alloy is subjected as well as its characteristic temperatures for phase transition, grain size, anisotropy and texture. The understanding of how the propagation rate is influenced by these factors is of paramount importance so that it is possible to improve designs and components by increasing fatigue life, efficiency and the possibility of designing new applications