X-Ray Elastic Constants and Their Meaning for Al and Fe
Abstract
In the measurement of residual stresses via diffraction (using x-rays or neutrons) it is strains that are actually determined, by employing the interplanar spacing (d subscript hkl) of the (hkl) planes as an internal strain gauge. The change in this spacing is measured from the shift of diffraction peaks (and Bragg's law) at several orientations of the sample to the incident beam, and the resultant strains are converted to stresses with the diffraction elastic constants , S subcript 1(hkl) and S subscript 2(hkl)/2. While these take on the values (-v/E) and (1 + v)/E respectively for an isotropic solid, in anisotropic materials their values depend on many factors; preferred orientation, shape and orientation of second phases, interaction between grains. In fact there are reports of variation these constants with plastic deformation 2 and theory predicts variations with morphology. It is demonstrated that the diffraction elastic constants for residual stress measurements can be determined even in the presence of oscillations in interplanar spacing vs sin squared psi. Furthermore, these values can be employed to ascertain whether the oscillations are due to local fluctuations in plastic deformation, or elastic anisotropy.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1985
- Accession Number
- ADA158251
Entities
People
- I. C. Noyan
- Jerome B. Cohen
- R. M. Zhong
Organizations
- Northwestern University