Mechanisms by Which Humidity Alters Ductility.
Abstract
The ductility of surface of Al 2219-T851 has been measured in two regimes of plastic strain. In the small strain regime, we determined the microplastic strain which develops within individual grains, at the surface, during fatigue at cyclic stress amplitudes substantially below the bulk yield strength. Initially the deformation is elastic; but, with increasing fatigue, local plastic strains under tensile load develop within individual grains and can approach 0.5%. It is these plastic strains which lead to crack initiation at the surface. The measurement technique is described, and data are presented for two different heats of 2219 taken in dry and in humid air. These materials are thought to differ substantially in as-received hydrogen content. It appears from our results that internal hydrogen increases the rate of development of microplasticity at the surface during fatigue, accelerating crack initiation. The role of surface oxide in determining surface ductility is complex, and is apparently a function of the internal hydrogen content of the alloy. In the large strain regime, the ductility of the surface is assessed by measuring the opening displacements of the tips (CTOD) of small surface cracks.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1981
- Accession Number
- ADA105530
Entities
People
- Michael R. James
- R. V. Inman
- W. L. Morris