The phenomenon of load relaxation for a specimen in a tension test configuration is not in itself a material property. The resultant record of load P as a function of elapsed time t is dependent on the conditions of loading in the test as well as on the material elastic and inelastic properties. For this reason, the term "load" relaxation seems preferable to "stress" relaxation as a nomenclature for the test, and we shall employ this term in the paper.

Our understanding and mode of description of the effects of irradiation on metal creep and deformation are not satisfactory as yet. This is due in part to the limitations on experimentation in radiation environment. Because of such limitations, theoretical considerations must play a strong role in the interpretation and representation of the phenomena. Reliable representations are necessary if we are to extrapolate the measured behavior beyond the experimental ranges of stress, temperature, flux, and time duration. Virtually all of the theoretical considerations currently employed are based on micromechanical models for the deformation behavior. While the fundamental mechanisms proposed, in fact, may be identified correctly, it is not at all clear that the quantitative conclusions from them are accurate. After all, the detailed micro-mechanical description of deformation even in the absence of irradiation is still moot.