Comparative fracture prediction study for two materials under a wide range of stress states using seven uncoupled models

The prediction of ductile failure is crucial for the progress of metal forming industries. Therefore, uncoupled fracture models have been proposed and continuously extended, trying to improve their forecasting abilities. However, without an assessment analysis of their predictive ability, it is difficult to establish the most suitable model, for describing the onset of failure under a wide range of loading conditions. Actually, a fair comparison of models' predictive ability requires the use of an extensive experimental database and a similar calibration procedure. In this context, seven uncoupled fracture models are chosen and revisited to study the effect of the type and number of tests used for calibration on their predictive ability. Experimental datasets available in literature were considered for 2024-T351 aluminium alloy and for DP600 steel. For each material, the experimental dataset was split in two subsets. The first one includes tests that were carried out under plane stress conditions that were used in the calibration procedure. For the aluminium alloy, different groups of 6 tests, covering distinct stress states, were elicited from the experi-mental subset and applied in the calibration of the seven models. The remaining tests were used to assess the predictive ability and their sensibility regarding the group used in models' cali-bration. Different trends of the fracture loci are observed, depending on the selected models and the tests used in their calibration. However, the analysis of the results indicates that a set of at least 6 experimental tests is appropriate to calibrate fracture models, providing that they enable covering a wide range for the stress triaxiality and Lode parameter. Finally, the conclusions provide some recommendations for the improvement of the calibration procedure.

Automated summary

The prediction of ductile failure is vital for metal forming industries, and uncoupled fracture models have been developed and expanded to improve their predictive abilities. However, without assessing their ability to accurately predict failure, it is challenging to determine the most suitable model for different loading conditions. This study revisits seven uncoupled fracture models and examines the impact of test types and quantities used for calibration on their predictive abilities.