The role of loading path in ductile fracture

Abstract eng:
The ductile fracture in monotonic loading applies after extensive straining and may arise after various complex loading paths. The role of loading path has been studied by experiments designed to evaluate, how the deviation from proportional loading influenced the point of fracture. Key role in this process plays the damage accumulation, which is in many applications often assumed as a linear function of cumulative plastic strain. Nevertheless, a number of non-linear damage evolution laws have already been proposed in recent literature. Adopting these, stepwise loading experiments were suggested and realized to provide a basis for calibration of models describing such behaviour. Those experiments are based on loading the specimen under one stress state, changing the conditions, and straining until fracture. Changing the stress state might be performed by elevating the hydrostatic pressure during the experiment, which is unfortunately rather expensive. Another possible way is to change the specimen geometry between subsequent loading steps. This strategy was adopted here and applied to calibration of the damage accumulation law of 2024-T351 aluminium alloy. Very high sensitivity of calibrated parameter to change of state variables entering the calculations was observed, which complicated obtaining relevant data applicable to computational simulations of real industrial cold forming processes.

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