Thesis-2009-Patman.pdf (24.84 MB)
High strain rate properties of a near equi-atomic NiTi shape memory alloy
thesis
posted on 2014-05-09, 08:23 authored by Andrew J. PatmanThe effects of strain rate and testing temperature on the mechanical response of a near
equi-atomic NiTi alloy have been investigated. All experiments have been conducted in
compression, at testing temperatures of room .temperature (-20°C), 30°C, 40°C and
50°C.
Quasi-static experiments were performed using a Hounsfield HK50 universal testing
machine, and high strain rate measurements were obtained using the split Hopkinson
pressure bar technique. The primary differences in the behaviour of the material within
these deformation rate regimes appeared to be the presence of a possible transformation
inhibition mechanism that occurs for high rates of strain, which manifests itself as an
accommodation of applied load after the onset of transformation, increased strain rate
sensitivity at high rates, and temperature dependence not evident at low rates.
Initial material characterisation was achieved' through microhardness testing, DSC,
DMTA, X-ray and electron diffraction, resulting in clarification of the transformation
temperatures, martensitic volume fraction and microstructure of the alloy. A post
experiment X -ray investigation was also performed in order to establish the
microstructural response of the material to deformation.
From the stress-strain data collected, the strain rate sensitivity and entropy of·
transformation of the alloy have been calculated. The application of a standard
Arrhenius type equation has also been attempted, in order to estimate the material
parameters of activation volume, and the free energy of transformation in the absence of
stress. This model was found to be reasonably representative of the response of the
alloy, although the results calculated demonstrated a high degree of intrinsic error.
History
School
- Science
Department
- Physics
Publisher
© Andrew John PatmanPublication date
2009Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.507347Language
- en