Mechanism of toughening due to local twinning transformation

Deformation twins near the crack tip of metals and alloys significantly affect the crack fracture toughness. To study this particular deformation of metals or alloys, in this article, a new analytical model of a semi-infinite crack interacting with a local twinning domain near the crack tip is developed based on Kolosov-Muskhelishvili complex potentials and Green's function method. In the model, the twinning domain as a stress source is equivalent to an assembly of edge dislocations, and thus the dislocation-crack interaction problem is analytically solved. Consequently, the stress intensity factor at the crack tip merely due to the twinning domain is derived for type-I and type-II modes and the influence of deformation twinning parameters on the fracture toughness as well as the shielding/anti-shielding effect is comprehensively analyzed. It is found that the presence of the twinning domain may lead significant stress concentration at the crack tip when its orientation angle of the domain is taken with some specific value. This study provides a new insight into the toughening mechanism of twinning transformation.