When a crack is subjected to cyclic shear-mode loading, crack faces interference wedge the crack open and reduce the effective D K II . The methods proposed in the literature to prevent it or to derive the effective D K I and D K II are discussed. It is shown that when crack tip plas- ticity becomes important it tends to make displacements larger than those predicted by LEFM and to ''hide" friction effects. Finite element simulations combining friction and plas- ticity can separate these two effects, but the analysis of force-sliding displacement loops derived from displacement field measurements based on image correlation is a more straightforward and efficient method