THE EFFECT OF STRESS TRIAXIALITY AND STRAIN-RATE ON THE FRACTURE CHARACTERISTICS OF DUCTILE METALS

Notched tensile tests have been carried out on three common metals (pu re iron, mild steel and aluminium alloy BS1474) over a wide range of s train-rates (10(-3) to 10(4) s(-1)) and the strain-to-failure measured . The ductility of all three materials was found to be strongly depend ent on the level of stress triaxiality in the specimen, this dependenc y being greatest for the ferrous materials and least for the aluminium alloy. No significant effect of strain-rate could be ascertained from the experimental results provided fracture remained fully ductile. Ho wever, for mild steel, a transition to a brittle fracture mode was obs erved for a given level of stress triaxiality as the strain-rate was i ncreased. Numerical simulations of the experiments have been used to d erive constants of a semi-empirical fracture model from the measured r esults. This model was found to give reasonable predictions of fractur e over the range of conditions investigated.