Effect of Specimen Size and Geometry on Ductile Crack Growth Resistance in C-Mn Steel

摘要

The effect of specimen size and geometry on the ductile crack growth resistance of a C-Mn steel has been investigated. The resistance, expressed in the form of J-R curves, was measured using the conventionally calculated J(J sub r) and the Ernst modified J(J sub m) in a range of specimen geometries loaded in bending and tension. The overall resistance of the non-sidegrooved specimens was apportioned into contributions arising from the flat fracture and shear tip regions found on the fracture surfaces. Using this approach, the effects of specimen size and geometry have been rationalized, and the limits of (J sub r) and (J sub m) controlled crack growth determined in terms of the maximum allowable crack extension and minimum w(b/J x dJ/da) values. The results show that for specimens of given thickness the effect of specimen geometry was due to a change in the shear tip and not the flat fracture contribution. This conclusion is consistent with the geometry invariance found in measurements of the crack opening displacement at the growing crack tip in the flat fracture region. In addition, it has been shown that J sub m can characterize crack growth resistance over a wider range of conditions than J sub r.