On the relationship between uniaxial yield strength and resolved shear stress in polycrystalline materials

Attempts to correlate radiation-induced microstructural changes with changes in mechanical properties rely on a well-established theory to compute the resolved shear stress required to move dislocations through a field of obstacles. However, this microstructure-based shear stress must be converted to an equivalent uniaxial tensile stress in order to make comparisons with mechanical property measurements. A review of the radiation effects literature indicates that there is some confusion regarding the choice of this conversion factor for polycrystalline specimens. Some authors have used values of 1.73 and 2.0, based on an inappropriate application of the von Mises and Tresca yield criteria, respectively. The basic models pertinent to this area of research are reviewed, and it is concluded that the Taylor factor with a value of 3.06 is the correct parameter to apply in such work.