Fracture mechanics in design and service: ‘living with defects’ - Elastic—plastic aspects of fracture stress analysis: methods for other than standardized test conditions

The J contour integral analysis, despite certain limitations, appears to be the most embracing engineering theory of fracture currently available. It is seen as most relevant for cases where high constraint is maintained as the extent of plasticity increases because it is that case that can be related to the linear elastic fracture mechanics (l.e.f.m.) datum case. Stable crack growth is described in terms of plastic work absorption rate rather than as an increase in toughness of a metallurgical nature so that the R-curve expressed in terms of J is seen as work dissipation rate normalized in terms of shape and size factors b and rj. Unstable ductile crack growth can be described in terms of an imbalance of deformation, energy rate or characterizing terms, all giving the same results for small amounts of crack growth, with the material tearing resistance described by TmU = ( E / o r . A J-based design curve is described, analogous to the well known crack opening displacement (c.o.d.) design curve. The use of an effective toughness beyond that found at the onset of initiation without the complexity of a full instability analysis is outlined. Methods for avoiding unstable ductile tearing before a stated degree of plastic collapse are now available, although the circumstances when a change to a different micro-mode of separation might occur are still not describable in continuum mechanics terms.