fe-safe User Group Meetings
North American fe-safe User Group Meeting
Professor Timothy H Topper from The University of Waterloo.
Keynote Presentation: "Derivation of Effective Strain-Life Data, Crack Closure Parameters and Effective Crack Growth Data from Smooth Specimen Fatigue Tests"
Timothy H. Topper, John J.F. Bonnen and Maria O Mara.
Professor Topper has been active in fatigue and fracture research since 1959 when, after graduating in civil Engineering from the University of Toronto he started work on low cycle fatigue at Cambridge University as part of a PhD program. On graduating from Cambridge in 1962 he joined and has remained at The University of Waterloo where he is now a distinguished Professor Emeritus and a Research Adjunct Professor.
During his career Professor Topper and his students have pursued research on the mechanisms and mechanics of the initiation and propagation of small cracks in uniaxial and biaxial fatigue. An area of especial interest has been fatigue crack growth under variable amplitude service load histories. In the last twenty years Professor Topper has also been involved in investigations of the mechanisms of fatigue failure of corroded concrete structures and methods of repairing these structures.
“Derivation of Effective Strain-Life Data, Crack Closure Parameters and Effective Crack Growth Data from Smooth Specimen Fatigue Tests”
Timothy H. Topper, John J.F. Bonnen and Maria O Mara
Small crack growth from notches under variable amplitude loading requires that crack opening stress be followed on a cycle by cycle basis and taken into account in making fatigue life predictions. The use of constant amplitude fatigue life data that ignores changes in crack opening stress due to high stress overloads in variable amplitude fatigue leads to non-conservative fatigue life predictions. Similarly fatigue life predictions based on small crack growth calculations for cracks growing from flaws in notches are non-conservative when constant amplitude crack growth data are used. These non-conservative predictions have, in both cases, been shown to be due to severe reductions in fatigue crack closure arising from large (overload or underload) cycles in a typical service load history. The work in this paper is concerned with the derivation of crack closure constants for use in two models; the effective strain-life fatigue model that can be applied to predict fatigue lives for smooth and blunt notched specimens under constant and variable amplitude loading and the effective fatigue crack growth model that can be used to predict fatigue lives of short cracks growing out of notches or flaws under constant and variable amplitude loading. Fatigue life calculations based on equations using crack opening stress are shown to give accurate fatigue life predictions for smooth and notched specimens subjected to variable amplitude service load histories. The influence of metal hardness on crack opening stress behaviour is deduced by comparing data for the three metal hardness levels used in this investigation.
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