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

In standard engineering practice, the stress/strain responses of polycrystalline 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 specimen 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 dictated by the local material distribution can cause significant perturbations in the applied stress/strain field. Consequently, the constants linking stress to strain in small volumes may contain additional configurational terms. Due to the complex local material distribution in most real samples, these configurational terms are extremely hard to calculate analytically. Experimental measurement of the local deformation is also nontrivial, and thus far there have been no measurements of the configurational constants in the elastic regime. An X-ray method that links the local strain perturbations in diffracting volumes to the overall applied strain is described. This method is then applied to alpha-brass and Ni specimens. It is seen that the average reaction strains within various diffracting subsets can be significantly different from each other and that such strains can be substantial fractions of the applied strain.