A damage function formulation for nonlocal coupled damage-plasticity model of ductile metal alloys

Continuum Damage Mechanics (CDM) extends the principles of continuum mechanics to include material degradation (softening and failure) and can be used within the finite element framework with greater ease than “discontinuous” models. CDM considers cracks as bands of damaged material, damage within an element being represented by a number between zero (for virgin, undamaged material) and unity (for material that lost all its bearing capacity). Nonlocal averaging of the plastic strain renders CDM models virtually independent of the mesh size and orientation, and overcomes numerical instabilities. However, one of the long-standing and persistent challenges is the task of calibrating the large number of material parameters involved. Recently, we developed a CDM model for ductile materials that has been shown to fulfil the requirements of stability and mesh-independence. In the present study a novel approach to damage function and parameter calibration based on a single tensile test on a dog-bone specimen in aluminium alloy AA6082 T0, nickel-based super-alloy IN718 and titanium alloy Ti–6Al–4V is assessed. The newly developed adaptive damage calibration shows excellent agreement with the experimental measurements and captures the attendant size effects.