An experimental study is presented of the effect of loading rate and temperature on the fracture initiation toughness of a rate-sensitive steel. Dynamic and static fracture tests were performed on specimens of a 1018 cold-rolled steel at selected temperatures over the range −157°C to 107°C; the dynamic tests being conducted with a Kolsky (split-Hopkinson) bar adapted to tensile fracture. The results are used to assess the influence of local plastic deformation on the fracture process. In addition, microstructural models of both cleavage and ductile fracture initiation mechanisms are presented and the local fracture criteria which result from these models are discussed. It is shown finally, that the macroscopic fracture behavior of 1018 cold-rolled steel as predicted from these local criteria is consistent with experimental results.

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