The fatigue crack growth behavior of superelastic nickel titanium

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.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Yaacoub, Jad

Contributors dc:contributor

• Sehitoglu, Huseyin

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

Statement dc:rights

• Copyright 2019 Jad Yaacoub

Language dc:language

en

Handle dc:identifier

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

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/106396