| Summary: | Continuum Damage Mechanics (CDM) accounts for material degradation (softening and ultimately failure) by modifying the load-bearing properties of the material (stiffness and strength) through a special state variable referred to as damage. Damage is typically represented by a scalar or a higher dimension object (such as vector or tensor) with values between zero for virgin material and unity for the material that lost all its bearing capacity. Considered in this way, damage becomes an additional field quantity that needs to be considered along with strain and stress, and can be computed either incrementally, or as a certain function of a suitable physical parameter such as inelastic strain. The advantage of enriching the formulation of a continuum deformation problem with a damage parameter is that it allows considering the material post-critical behaviour, i.e. its response under deformations exceeding those when the maximum load-bearing capacity is reached. Typically, this post-critical behaviour is associated with strain localisation, initiation, growth and interaction of discontinuities, and final fracture. Within the CDM framework, cracks are represented by diffuse regions of material damaged so that it lost all its strength in at least one direction. Computationally, modelling the post-critical (softening) behaviour of material represents a challenge in terms of the numerical stability of algorithms. Nonlocal description of damage appears to offer a rational route towards stable modelling. Nonlocal averaging of the plastic strain for the evaluation of damage also renders CDM models independent of the mesh size and orientation, and helps overcome numerical instabilities. The formulation that emerges can be referred to as coupled nonlocal damage-plasticity modelling [1, 2]. An important challenge remains, however, in developing this general approach into a flexible and material-specific modelling tool. This concerns the need to calibrate a large number of material parameters that emerge in this formulation. In order to address this challenge, recently we developed an approach for the calibration of CDM models of ductile materials that we propose to refer to as adaptive calibration. The calibration of the damage function is accomplished by matching the model prediction to the experimental data obtained from a single tensile test with multiple gauge length extensometry [3] used to capture strain localisation and size effects. We describe the application and validation of this approach to the damage function parameter calibration for the aluminium alloy AA 6082 T0. Excellent agreement with experimental measurements is obtained.
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