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Title: Fatigue damage accumulation in nickel base superalloys
Author: Lambert, David
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 1994
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Tangentially oriented Waspaloy specimens taken from the bore section of a turbine disc were subjected to low cycle fatigue in the form of cyclic four point bend tests. Substantial differences in grain size and structure occurred across the section of the disc. Fatigue damage occurred primarily as a result of persistent slip band formation, cell formation, Orowan looping and precipitate shearing. A small number of grains exhibited dislocation cells, normally associated with higher stacking fault energy materials. The number and width of persistent slip bands increased with the number of cycles, but varied both between grains and stress levels. It is proposed that initially looped precipitates were subsequently sheared. Crack initiation was observed as early as 1/12 of fatigue lifetime, predominantly from inclusions. A stage-I/stage-II crack propagation transition occurred at approximate 4Kl values of 30MPa.m1/ 2 , when the plastic zone size was comparable to the material grain size. Results imply that short crack growth requires prior slip band formation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available