ABSTRACT
Type II and III stresses collectively are also called micro-stresses. These definitions are, however, not necessarily useful in analysis of diffraction peaks. A diffraction peak results from the coherent scattering of the incident beam from the periodic structure of a crystal. This means that only periodic domains of the material can be analysed by the diffraction techniques (X-rays or neutrons). However, the crystal structure is altered by any discontinuity in the material (vacancy, interstitial, substitution, dislocation, grain or sub-grain boundary, phase boundary, hole, crack, etc.). An accurate model of a true heterogeneous material needs
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therefore to define a small reference volume for which both the theories of diffraction and the concepts of continuous medium mechanics can be applied.
