Annual Technical Report, Materials Research Laboratory July 1, 1979 - June 30, 1980.
Abstract
Research is directed toward development of sufficient understanding of the mechanisms of plastic deformation to be able to formulate constitutive relations that model plastic deformation of single crystals and, ultimately, structural metals. Both analytical and experimental investigations are being conducted. The size scale on which mechanisms are examined varies from the atomistic level in quantum rate theory calculations, through the microstructural level in dislocation mobility studies in single crystals, to the macroscopic scale of plastic deformation of polycrystals. Re-examination of the analysis of the decay of the elastic precursor in plate impact experiments on single crystals has drawn attention to the possible importance, and even dominance, of the effects of surface damage. A critical experiment to examine this possibility is being developed. In other work on dislocation mobility in single crystals, a technique is being developed for determining the attenuation and the change in elastic wave speed of ultrasonic waves during and immediately following plastic deformation caused by a relatively large amplitude stress pulse. The relationship between strain rate, stress, and temperature has been examined for bcc metals. Interesting strain rate history effects have been obtained at low temperatures (approx -190 deg C) for a hot-rolled steel. Possible models for strain-rate history effects and temperature history effects have been considered. On the atomistic level, quantum rate theory has been extended to the case of an asymmetric double-well potential. In addition, the form of the elastic moduli of centro-symmetric crystals has been derived in terms of the electron density and its distortion due to the crystal deformation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 30, 1980
- Accession Number
- ADA105382
Entities
Organizations
- Brown University