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Title: Creep and creep fracture of alpha + beta titanium alloy
Author: Ward, A. R.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2002
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High precision uniaxial constant stress creep tests were carried out at 773K for the α+β titanium alloy Ti Repeat data at 580 MPa provided a unique opportunity to identify stochastic creep properties and to use this information to build a probabilistic creep damage assessment for this alloy. The stochastic nature of creep properties both at a single test condition (using a generalised gamma distribution) and at various test conditions (by combining this distribution with the Monkman - Grant relation) was identified. In addition, the theta prediction methodology was extended so that life predictions for materials operating under long service conditions can be made that also have a degree of confidence associated with them. Ways in which the theta model can be applied to the fatigue as well as the creep of all materials are also discussed. For comparison purposes two failure criteria are built into the stochastic model and the determinants of failure derived. This stochastic theta model is then used to investigate the nature of the creep failure time distribution for the Ti alloy under constant uniaxial conditions. The corrosion resistance between 723K and 1123K of Ti has also been investigated. There was evidence in favour of parabolic rather than linear increases in weight gain with time and the activation energy associated with parabolic oxidation was estimated at 216KJ/mol. The life of Ti-6246 in argon at 773K was found at certain stresses to be almost twice that obtained in air. This difference could not be explained by the loss of load bearing cross-section area following oxidation. Biaxial creep tests were also carried out at an effective stress of 800 MPa to determine the part taken by the stress state on damage and fracture in the alloy.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available