CHARACTERIZATION OF INHOMOGENEOUS ELASTIC-DEFORMATION WITH X-RAY-DIFFRACTION

In standard engineering practice, the stress/strain responses of polyc rystalline specimens are analyzed using models based on the equations of continuum mechanics: In general, these equations implicitly assume that the material is quasi-isotropic. This assumption requires a speci men whose volume exceeds a critical ''representative volume.'' Domains that are smaller than the representative volume do not exhibit quasi- isotropic behavior. In such volumes, the compatibility conditions dict ated by the local material distribution can cause significant perturba tions in the applied stress/strain field. Consequently, the constants linking stress to strain in small volumes may contain additional confi gurational terms. Due to the complex local material distribution in mo st real samples, these configurational terms are extremely hard to cal culate analytically. Experimental measurement of the local deformation is also nontrivial, and thus far there have been no measurements of t he configurational constants in the elastic regime. An X-ray method th at links the local strain perturbations in diffracting volumes to the overall applied strain is described. This method is then applied to al pha-brass and Ni specimens. It is seen that the average reaction strai ns within various diffracting subsets can be significantly different f rom each other and that such strains can be substantial fractions of t he applied strain.