Pure shear stable crack growth through compact-tension-shear specimen in plane state of stress

In this work the effect of assumption of plane state of stress (plane stress or plane strain) on the predictability of the experimental results observed during the in-plane shearing mode (mode II) stable crack growth (SCG) through 8 mm thick compact tension shear (CTS) specimen of a workhardening aluminium alloy (D16AT) has been studied. Experimental results include load-sliding displacement diagrams, extent of SCG, fracture surface fractographs, scanning electron micrographs, crack front geometry and variation of plastic zone in the thickness direction. The experimental observations show that the crack extends in its own plane, the fracture surface is flat, smooth, and free of any shear lip, the crack front geometry, which is mostly straight initially, remains so throughout the SCG. Furthermore, the plastic zone size is the same along the specimen thickness and the constraint on the plastic zone does not develop near the mid thickness. Numerical simulations based on the assumptions of plane stress and plane strain have been performed using a 2D elastic-plastic finite element scheme and the COA/COD criterion as the criterion governing the crack growth. Finite element results on the load sliding displacement diagrams, J-resistance curves, plastic zone sizes and variation of equivalent stress and strain along the crack-line ahead of the crack tip are presented. The resistance curve is a straight-line and the magnitudes of equivalent stress and strain show a tendency to increase as the crack extension proceeds. In general, experimental observations indicate that a plane stress state prevails throughout the thickness and the predictions based on the assumption of state of plane stress are closer to the experimental observations for the examined thickness.