Possible Experimental X-Ray Diffractometry Evidence of Couple-Stresses

Abstract

The technique of measuring residual strain using X-ray diffractometry is examined with respect to prior attempts to experimentally validate couple-stress or micropolar theories. When subjected to grinding, polycrystalline materials (such as steel or others of technical interest) exhibit residual strains with very peculiar features whose explanation is still controversial. This paper suggests how a formally correct explanation can be formulated in terms of the theories based on couple-stresses. This new hypothesis is critically compared with competing theories found in the recent literature. It is proposed that, for the case of thin layers subjected to extremely high stress gradients, X-ray diffractometry is the most appropriate technique for investigating couple-stress or micropolar phenomena.