Micromechanical modelling of the elastoplasticity and damage in ductile metals

Even though the computational constitutive modelling of the mechanical behavior of ductile metals at macroscopic scale has been studied extensively, the complexities in the mechanical behavior of ductile metals continue to challenge the existing models. Ideally the model must predict accurately the elastoplastic behavior of the material under both proportional and non-proportional loadings, its fracturing behavior under both uniaxial and multiaxial stress states as well as its behavior under cyclic loadings. Furthermore, the model must be tested against various test data obtained from specimens made of the same metal alloy. In this study, we present a constitutive model using the microplane approach in which the stress–strain relations are defined on various planes in terms of stress and strain vectors, which are independently activated depending on the strain tensor, effectively creating a multisurface plasticity model. The constitutive relations consist of two separate stress–strain boundaries applied on any given microplane: One for the shear behavior and another for the deviatoric behavior. Data fitting experience revealed that stress triaxiality must be considered only in the deviatoric boundary. Damage evolution is incorporated into both boundaries. The model is calibrated against experimental data obtained from specimens made of Aluminum alloys (6061-T6, 2024-T4 and 7075-T651) and the model predictions are compared against experimental data obtained from specimens made of the same alloy. Furthermore, the model predictions are compared to a different microplane model called the model MPJ2. In addition to test data at various stress triaxialities, test data on Vertex effect and Bauschinger effect are also taken into account.