The J integral, which is widely used in elastic-plastic fracture mechanics, is not the true driving force any more if the crack is propagating. This leads to some inconsistencies when ductile tearing resistance is characterized in terms of J , especially for large crack extensions. Instead, Turner has proposed the energy dissipation rate as a physically more meaningful quantity. His concept is discussed and more evidence is given that will provide a better understanding of ductile tearing. It is shown how this quantity can be determined by measuring the heat production ahead of a fast running crack, or calculated in a finite element analysis, or re-evaluated from J-R test records of bend and tensile specimens. The energy dissipation rate is decreasing with crack extension in gross plasticity and approaches a stationary state. From these relations, the shapes of the cumulative J-R curves can be derived for different specimen geometries.
Stable crack growth in fracture mechanics specimens, i.e. side-grooved compact tension C(T), side-grooved middle tension M(T) and side-grooved part-through surface tension PS(T) specimens, is experimentally performed and numerically analysed by finite element calculations using the node shift node release technique. The crack propagation is either controlled by J-resistance curves for the C(T) and M(T) specimens, which are modelled two-dimensionally assuming plane strain conditions, or by local CMOD-resistance curves for the PS(T) specimen, which is modelled three-dimensionally. The triaxiality, i. e. the ratio of the hydrostatic part of the stress tensor to its deviatoric part, is introduced as the quantity characterizing the stress state at the crack tip.
For all specimens, the relation between the triaxiality and the slope of the J-resistance curves is shown and analysed, indicating that a decreasing triaxiality results in an increasing slope for the global J-resistance curves concerning the C(T) and M(T) specimens as well as for the local J-resistance curves regarding the PS(T) specimen.
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