THEORY FOR DETERMINING KK FROM SMALL, NON-LEFM SPECIMENS, SUPPORTED BY EXPERIMENTS ON ALUMINUM

A new method is presented for measuring the plane-strain fracture toughness of ductile materials. The method is much simpler than JIc measurements, yet retains the advantage that the specimen can be much smaller than is required for a valid KIc test. The small specimen advantage results from selecting the short rod specimen configuration for which the material along the crack tip is well constrained to the plane-strain state, and from the measurement and elastic-plastic analysis of the load-displacement curve (including at least two unloading slopes) to determine the energy per unit crack area which is required to slowly advance a steady-state crack. The method is tested by the measurement of KIc of 6061-T651 aluminum using short rod specimens of four different diameters. The KIc data are found to be independent of the specimen size for diameters as small as {Mathematical expression}, the smallest tested. The KIc of this study compares satisfactorily with published data on 6061-T651 aluminimum. © 1979 Sijthoff & Noordhoff International Publishers.