The fatigue crack growth behavior of superelastic nickel titanium

Yaacoub, Jad

Permalink

https://hdl.handle.net/2142/106396 Copy

Description

Title

The fatigue crack growth behavior of superelastic nickel titanium

Author(s)

Yaacoub, Jad

Issue Date

2019-12-12

Director of Research (if dissertation) or Advisor (if thesis)

Sehitoglu, Huseyin

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Shape Memory Alloy
• NiTi
• Fatigue Crack Growth
• Superelasticity

Abstract

Understanding of fatigue crack growth phenomena in shape memory alloys under superelastic conditions continues to elude the scientific community: The stress induced martensite phase causes deviations of stress intensity and state at the tip from the classical handbook solutions widely relied on for crack growth characterization. In this work, novel methods of stress intensity factor extraction based on in situ and ex situ Digital Image Correlation are implemented to characterize the effective fatigue damage tolerance of NiTi single crystals under superelastic conditions. It is found that, due to crack tip stress induced martensite transformation, NiTi exhibits shielding (reduction from theoretical stress intensity factor calculations) of about 30\% on average. The stress intensity reduction levels from the superelastic austenite, stable martensite and stable austenite are also compared. It is found that the stable austenite-martensite crystal structures exhibit almost identical K reduction, attributed to plastic flow, while the superelastic austenite structure, exhibiting higher reduction levels, demonstrates the shielding effect of the stress induced transformation.

Graduation Semester

2019-12

Type of Resource

text

Permalink

http://hdl.handle.net/2142/106396

Copyright and License Information

Copyright 2019 Jad Yaacoub

Owning Collections