Time-dependent damage analysis for viscoelastic-viscoplastic structural laminates under biaxial loading

Many composite structures are required to sustain severe thermo-mechanical loads over extended periods of time, during which viscoelastic and viscoplastic behavior can cause the progression of micro-damage. In this paper, a new computational multi-scale model that couples micro-damage mechanics with Schapery's theory of viscoelasticity and viscoplasticity has been developed to predict time-dependent damage evolution in laminates under constant biaxial loading. After validation with experimental data, the new model capabilities are showcased by predicting damage evolution in two distinct laminates under different axial and transverse loads over time. It is found that damage evolution in both laminates is highly sensitive to the biaxial loading levels, and that crack multiplication in each ply is dependent on stacking sequence and ply orientation. The developed multi-scale model may be a suitable design tool for composite structures required to endure long-term loads in demanding environments.