CONTINUUM DAMAGE MECHANICS MODEL FOR LOW-VELOCITY IMPACT DAMAGE ANALYSIS OF COMPOSITE LAMINATES

A three-dimensional anisotropic continuum damage mechanics (CDM) model, including damage characterization, damage initiation criterion and damage evolution law, was presented to analyze low-velocity impact damage of composite laminates. With considering affects of the fracture plane angle, material constitutive relation of damage states in the fracture plane coordinates was established by introducing damage state variable matrix in the material principal coordinates. The onset of damage was evaluated by the Puck criterion and the evolution of damage was controlled by equivalent strain on the fracture plane. Based on the viewpoint of strain energy release, the material was assumed to exhibit linear strain-softening behavior. Fiber fracture (FF) and inter-fiber fracture (IFF) were simulated within the lamina. Due to the experimental evidence which indicated that multiple intralaminar cracks developed in a composite laminate and coalesced in to one interface crack (delamination) under impact load, a intralaminar matrix crack density parameter at saturation was introduced to scale interlaminar delamination. The relevant low velocity damage response parameters of the laminates 0₃/45/-45_S and 45/0/-45/90_4S were predicted with the proposed model at various impact energies. A good agreement was achieved with experimentally obtained data and showed the validity of CDM model in this paper. Furthermore, results for different mesh-densities indicated that the approach by introducing a characteristic length of the element could alleviate the mesh dependency at the stage of material damage evolution.