Determination of Prefracture Fatigue Damage.
Abstract
X-ray double crystal diffractometry and reflection topography were employed to examine the deformation response of single crystals and Al 2024 alloy specimens. A propensity for preferential work hardening of the surface layers compared to the bulk material was demonstrated for both tensile-deformed and fatigue-cycled metals. The cyclically induced defect distribution with depth from the specimen surface was also investigated as a function of the fraction of fatigue life. This led to a capability for predicting the fatigue life by a nondestructive x-ray diffraction method. Single crystals of silicon and aluminum pulled in tension exhibited a highly fragmented 'debris' layer, extending to about 100 microns in depth, and a core region featuring a much lower excess dislocation density and considerably less lattice breakup and misorientation. A similar decreasing gradient in the excess dislocation density from the surface to the bulk material was obtained for plastically deformed gold monocrystals for which no oxide layer is formed. Aluminum monocrystals cycled in the push-pull fatigue mode revealed a work-hardened surface layer and a transitional subsurface region between the surface layer and the core material. At sufficiently low stress amplitudes, no cyclic damage was introduced in the bulk despite the rapid generation and interaction of dislocations in the surface layer.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1980
- Accession Number
- ADA079538
Entities
People
- Irvin R. Kramer
- Robert Pangborn
- Sigmund Weissmann
Organizations
- Rutgers School of Engineering