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Title: High temperature creep of copper
Author: Palmer, C. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2003
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The key observations that have underpinned traditional power law approaches to creep mechanism identification have been re-evaluated using information obtained for pure copper and aluminium, and also for various other metals and alloys. Specifically, data is presented which show stress/creep rate plots for copper and aluminium over extended stress ranges to be well represented by continuous curves, contradicting the common assumption that a transition in mechanisms occurs as the stress is reduced. Data is also presented from a series of stress interruption tests on pure copper, with strain/strain rate responses which also suggest that essentially the same mechanism dominates creep behaviour at high and low stresses. Furthermore, results for copper single crystals and polycrystals are shown which contradict the assumption that dislocation creep processes are grain size independent so the creep rate increases rapidly with decreasing grain diameter only when diffusional mechanisms are dominant at low stresses. Evidence is also introduced to demonstrate that the theoretical and practical limitations of power-law descriptions of steady-state creep rates can be overcome by quantifying the shapes of normal creep curves and the variations in curve shape with changing stress conditions. The superior predictive capabilities of curve shape analysis are then illustrated by results showing accurate predictions of creep behaviour in the low stress region may be obtained from data generated experimentally at far high stresses. Finally, results are presented showing the effects of a range of room temperature prestrains which illustrate the importance of distinguishing between the contributions made by the grain interiors and the grain boundary zones to the overall rates of strain accumulation during creep.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available