Influence of Configuration on R-Curve Shape and G_c When Plane Stress Conditions Prevail

Following a brief introduction, an examination is presented of the factors which define the fracture toughness, R-curve relationships, and the extent of stable crack extension. Use is made of the compliance calibrations for a center cracked sheet and a compact tension specimen to show how configuration influences the shape of the R-curve in specimens of equivalent width and identical thickness. The change in the shape of the R-curve is shown to affect stable crack extension and the G-curve tangency requirement to result in differing toughness levels in the different configurations.

In support of the analytical results, tests have been conducted on two high strength aluminium alloys to establish the variations in the shape of R-curves, using both compliance-indicated and measured absolute values of crack length. Various toughness values which highlight the influence of plastic deformation on toughness have been calculated.