Mechanisms by Which Humidity Alters Ductility
Abstract
The effects of atmospheric humidity and of internal hydrogen on localized surface ductility of a A1 2219-T851 alloy have been characterized. A reference gauge technique was used to measure the peak tensile plastic strains which develop during fatigue within individual grains at the surface of the alloy. These are sensitive to environment and can exceed 0.5%, even when the bulk deformation is linearly elastic. The average strain at the surface is controlled by the subsurface, resulting in a mixed pattern of tensile and compressive strains from grain to grain. The hysteresis loops open more rapidly with fatigue within grains having large distances of slip between boundaries at the surface. Constituent particles are fractured when the width of the local stress-strain hysteresis loop increases to a critical value. A simple strain energy criterion for particle fracture is used to model the probability of particle fracture from the distance of slip from the particle to the grain boundary. Agreement is achieved with experimental data by assuming that environmental factors alter only the local ductility of the matrix material within individual grains, and not the particle fracture surface energy. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1982
- Accession Number
- ADA116030
Entities
People
- Michael R. James
- R. V. Inman
- W. L. Morris