Plane Stress Crack Resistance Curves of an Inclined Crack Under Biaxial Loading

摘要

Elastic-plastic stable crack growth under Mixed-Mode I and II loading in thin cruciform specimens of aluminum, A12024-T3, and structural steel, StE 550, was investigated using a biaxial test rig. Two cruciform specien types were considered, one containing an inclined through thickness crack, the other with inclined short cracks emanating from a hole (precrack length to hole radius ratio, a'_0/R = 0.286). It is shown that predominant Mode II loading drove the stable crack in the direction almost parallel to the fatigue pre-crack (maximum shear strain criterion). High (steel) or moderate (aluminum) Mode I crack-tip-opening components caused a crack path deviation, that is, the stable crack grew normal to the maximum tensile stress. The mixed-mode crack resistance curves are presented in the form of the magnitude of a crack-tip-displacement vector, delta_u = ( delta~2_I + delta~2_(II))~(0.5), and compared with conventional R-curves of standard compact-tension (C(T)) and center-cracked-tension (M(T)) specimens. The effect of the load biaxiality is discussed with regard to previous experiments with Mode I loaded cruciform specimens.