Dissertation/Thesis Abstract

Beneficial Tensile Mean Strain Effects on the Fatigue Behavior of Superelastic NiTi
by Rutherford, Benjamin Andrew, M.S., Mississippi State University, 2017, 89; 10266594
Abstract (Summary)

In this work, beneficial effects of tensile mean strain on fatigue behavior and microstructure of superelastic NiTi (i.e. Nitinol) are studied. Most applications, such as endovascular stents made with NiTi, are subjected to a combination of constant and cyclic loading; thus, understanding the fatigue behavior of NiTi undergoing mean strain loading is necessary. Cyclic strain-controlled fatigue tests are designed to investigate the effects of tensile mean strain on fatigue of superelastic NiTi. Experimental observations show that combinations of large tensile mean strains and small strain amplitudes improve the fatigue life of superelastic NiTi. This behavior arises from reversible, stress-induced phase transformations. The phase transformations cause “stress plateaus” or strain ranges with no change in stress value. Scanning electron microscopy (SEM) of the fracture surfaces of specimens revealed generally short crack growth. Electron backscatter diffraction (EBSD) found the amount of residual martensite to be about ~8%, regardless of loading conditions.

Indexing (document details)
Advisor: Stone, Tonya W.
Commitee: Priddy, Matthew W., Shamsaei, Nima
School: Mississippi State University
Department: Mechanical Engineering
School Location: United States -- Mississippi
Source: MAI 56/04M(E), Masters Abstracts International
Subjects: Mechanical engineering, Materials science
Keywords: Mean strain, NiTi, Scanning electron microscopy, Superelastic
Publication Number: 10266594
ISBN: 9781369706055
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