Abstract
Fracture toughness in terms of J and COD at or beyond initiation to ductile tearing were investigated using mainly three point bend pieces of HY130 steel in a variety of proportions. J values are adjusted for crack growth to obtain the resistance curve ( R-curve). The R-curve was observed to become shallower with increasing width and thickness of test piece, and for longitudinal (TL) rather than short transverse (TS) crack propagation, but steeper with scaling to smaller absolute sizes, and decreasing thickness and width. For full thickness plates, the R-curve for tension was much steeper than bending. Discussion is given on the size requirements for a geometry independent R-curve, according to the present test data.

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