The thermomechanical constitutive experimentation of NiTi shape memory alloy strips and rods

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references.Issued also on microfiche from Lange Micrographics.The purpose of this thesis was to study the effect of temperature on the thermomechanical constitutive behavior of NiTi shape memory alloy strip and rod specimens. The stress-strain relationship is analyzed for isothermal monotonic tensile testing of 50.1 at.% Ni-Ti strip and 49.9 at.% Ni-Ti. The threshold stress value was found to decrease, for detwinning martensite, as the test temperatures approached the martensite start temperature. The critical stress for stress-induced-martensite was found to increase with test temperature. These threshold-temperature relationships and material parameters determined from the tests, were used in thermomechanical models. Three models were evaluated; Tanaka's exponential model, Boyd-Lagoudas unified thermodynamic model, and Liang-Rogers' cosine model. The models were then compared to results of the thermomechanical tests. An additional phenomenon was observed during isothermal tensile tests of the strip specimen. Transformation fronts would nucleate and grow during the loading and recovery heating of the strip specimens. These transformation bands were found to introduces errors in the modeling techniques as well as the determination of the strain