After a review of the literature on the prognosis of ductile fracture, a damage indicator is developed which is based on micromechanical results and adapted to experiments. A calibration of this damage indicator is possible by inspecting in detail a load displacement curve for a long and smooth specimen. Relation to currently published damage indicators is discussed. The damage indicators can be used to indicate the onset of a local crack in a ductile structure.

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The influence of the specimen thickness B and the ligament length b on the Jn-curves is numerically investigated for CT specimens. The thickness effect is taken into account with 2-D analyses by dividing a plain sided specimen into a plane stress part and a plane strain part. The fracture process is controlled by experimentally determined critical values of the crack tip opening displacement for crack growth initiation (CTOD,) and the crack tip opening angle for stable crack growth (CTOAc). It is shown that for the global behaviour of a plain sided specimen, the B/b ratio is essential. The difference between the geometry dependence of the initiation value of the J-integral and the geometry dependence of the slope of the Ja-curves is also shown.

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