The stress in a zirconium alloy due to the hydride precipitation misfit strains .1. Hydrided region in an infinite solid or at a free surface

In the context of modelling delayed hydride cracking (DHC), this paper shows that with a lenticular shaped hydrided region, i.e. one whose length is large compared with its thickness, the compressive stress sigma(H) induced within the region by hydriding is markedly influenced by the unconstrained transverse precipitation strains as well as the unconstrained norma I strain. For the case of DHC initiation at a pla nar surface or the surface of a very blunt flaw, the values of sigma(H) obtained by assuming (a) the overall unconstrained expansion strain associated with hydride precipitation is confined entirely to the normal direction or (b) the strain is partitioned approximately equally between the three orthogonal directions, are approximately equal. This means that assuming the strain is entirely in the normal direction allows for both precipitation strain scenarios.