Energy Dissipation Rate and Crack Opening Angle Analyses of Fully Plastic Ductile Tearing

The effects of geometry on the JR-curve for ductile tearing toughness of a titanium alloy are investigated in a series of notch bend tests taken to large amounts of growth in the fully plastic regime. For this material there is a remarkably small effect of thickness over a nine-fold range from 4 to 35 mm, but for thicknesses of 17.5 mm and greater, the R-curves are lower for wider specimens. The results are then analyzed in terms of energy dissipation rate and crack opening angle. Both terms fall rapidly just after initiation and pass to a near steady-state regime after about 10% growth. In steady-state tearing the crack opening angle is substantially constant with growth, while the steady-state dissipation rate can be split into areal and volumetric components. It is concluded that stable ductile tearing of this material at limit load conditions is controlled by processes of plastic deformation that, if expressed as conventional R-curves, show a definite dependence on width. However, interpretation by either crack opening angle or dissipation rate model is sensitive to how the data are analyzed. The dependence of the models on the degree of plane stress or plane strain is not yet clear so that extrapolation to other sizes of specimens is still uncertain.

Energy Dissipation Rate and Crack Opening Angle Analyses of Fully Plastic Ductile Tearing Conferences