In situ diffraction investigations of mechanisms that lead to path dependent mechanical behaviours of nickel-titanium shape memory alloys
type: CreativeWork
description: Development and characterization of Shape Memory alloys (SMAs) has taken big steps over half a century in understanding the role of alloying components, processing of alloys and microstructural optimization to real life engineering application. This has aided in the growth of application of SMAs to multi-billion-dollar industry but the component design with SMAs still follows that traditional route of prototyping and laboratory testing. Implementation of numerical simulations would help in making component’s design-time more efficient and design-cycle cost effective, but few bottle necks are present to fully implement the numerical models. Out of them, lack of multiaxial experimental data to deconvolute and interpret the role of multiple deformation mechanism has been on the top priority. Historically, lack of experimental capabilities to study in situ deformation mechanism like phase transformation and reorientation of variants was the main hindrance. But with development of modern diffraction technique, it has been possible to study deformation and correlate them with microstructure evolution. In this current work, we aim to provide some insights quantify evolution of internal state variables (ISVs) like volume fraction under biaxial loading conditions.The first part of the thesis examines the role of loading history on reorientation mechanics of martensitic NiTi. Deformation under mechanical loads of two sets of specimens with different initial microstructure were compared. Neutron diffraction data were collected at different interval for the texture evolution information. First set of samples with “Preferred Variants” deformed by deformation twins along with transformation twins whereas “Self-Accommodated” samples showed reoriented by transformation twins only. Although, the samples have same processing route, alterations in microstructure caused variation in stress strain response highlighting the influence of loading history. In the second part, austenitic NiT…
abstract: Development and characterization of Shape Memory alloys (SMAs) has taken big steps over half a century in understanding the role of alloying components, processing of alloys and microstructural optimization to real life engineering application. This has aided in the growth of application of SMAs to multi-billion-dollar industry but the component design with SMAs still follows that traditional route of prototyping and laboratory testing. Implementation of numerical simulations would help in making component’s design-time more efficient and design-cycle cost effective, but few bottle necks are present to fully implement the numerical models. Out of them, lack of multiaxial experimental data to deconvolute and interpret the role of multiple deformation mechanism has been on the top priority. Historically, lack of experimental capabilities to study in situ deformation mechanism like phase transformation and reorientation of variants was the main hindrance. But with development of modern diffraction technique, it has been possible to study deformation and correlate them with microstructure evolution. In this current work, we aim to provide some insights quantify evolution of internal state variables (ISVs) like volume fraction under biaxial loading conditions.The first part of the thesis examines the role of loading history on reorientation mechanics of martensitic NiTi. Deformation under mechanical loads of two sets of specimens with different initial microstructure were compared. Neutron diffraction data were collected at different interval for the texture evolution information. First set of samples with “Preferred Variants” deformed by deformation twins along with transformation twins whereas “Self-Accommodated” samples showed reoriented by transformation twins only. Although, the samples have same processing route, alterations in microstructure caused variation in stress strain response highlighting the influence of loading history. In the second part, austenitic NiT…
author: Dahal, Jinesh
language: eng
language: English
keywords: multiaxial loading, NiTiNOL, shape memory alloys, neutron diffraction, high energy x-ray diffraction, path dependence
identifier: T 8894
date published: 2020
date modified: 2026-07-24T01:41:48Z
provider: Colorado School of Mines
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Colorado School of Mines. Arthur Lakes Library

PropertyValue
property ID: Handle
value: https://hdl.handle.net/11124/174075