An Objectivity Algorithm for Strain Softening Material Models

Predictive techniques for the analysis and design of metallic or composite components and structures subject to severe loading can lead to significant mesh sensitivity if cracking or tearing or penetration occurs. This is especially important for composite materials in which the material has an elastic brittle response with little or no plastic behaviour, in which energy could be dissipated. Hence, the full potential use of composite in the design of advanced composites and structures has not yet been exploited fully. This work constitutes an effort directed towards the development of an objectivity algorithm for strain softening material models based on the ‘smeared cracking formulation’. The algorithm has been implemented into LS-DYNA for hexahedron solid elements and correctly accounts for crack directionality effects. Thus enabling the control of energy dissipation associated with each failure mode regardless of mesh refinement and element topology. The advantage of the present technique is that mesh size sensitivity on failure is removed leading to results, which converge to a unique solution, as the mesh is refined. If such a scheme were not introduced results could change significantly from mesh to mesh leading to an incorrect structural response. The proposed algorithm has been validated by a series of benchmark tests using different degrees of mesh refinement and element topologies.