T-stress effects on crack deflection: Straight vs. curved crack advance

T-stress effects on crack deflection in notched brittle materials are investigated by means of an average stress approach. It is shown that the crack advance always reveals to be straight if the T contribution is negligible. On the contrary, if T is different from zero, the trajectory tends to curve: the higher is |T|, the larger is the curvature parameter, its value being either positive or negative depending on the sign of T. Analogies and differences with respect to straight crack propagation are quantified in terms of the fracture loci and of the critical kinking angle. The investigation on the stability of crack deflection under mode I loading conditions concludes the paper, together with a discussion on experimental observations.