The flow stress contribution of the dislocation 'forest' in bcc lattices

The athermal flow stress contribution by junction reactions of a glide dislocation with a 'forest' of density rho is usually written as tau = alpha mu b rho ^1/2. The strength coefficient alpha has been computed for the bcc lattice by virtual displacement of triple nodes following the method of Puschl et al. (1982, Physica status solidi (a), 74, 211). In the isotropic approximation, the values for glide dislocations with 0, 30, 60 and 90^o character are as alpha = 0.18, 0.21, 0.19 and 0.22 respectively. A comparison with values calculated previously by Frydman is made, and good agreement is found when differences in the cut-off radii of the linear elastic solution are accounted for.