Modeling and evaluation of dynamic degradation behaviours of carbon fibre-reinforced epoxy composite shells

In this study, a segmented degradation model was established for the first time to predict and evaluate the dynamic degradation characteristics of carbon fibre-reinforced epoxy composite (CFRC) shells accurately by considering temperature variations during heating, maintenance, and cooling. The model is based on the Reddy's high-order shear deformation theory, complex modulus method, and coefficient fitting approach. First, explicit expressions of material parameters and thermal expansion coefficients (TECs) in different thermal degradation stages were proposed, followed by the derivation of the differential equations to solve the structural dynamic degradation characteristics. Moreover, an identification method for the fitting coefficients of the CFRC material was described, which is based on experimental tests and iterative calculations of elastic moduli, loss factors, and TECs at different degradation time points in different thermal degradation stages. Finally, the natural frequencies, damping ratios, and time-domain responses were measured using a novel testing system for the dynamic degradation of specimens subjected to a pulse excitation load to validate the developed model. Theoretical and experimental results indicate that the natural frequencies decreased as the degradation time increases at the heating-up and temperature maintenance stages, whereas they increased at the cooling stage. However, an uptrend in the damping and response behaviours was observed in the first two stages, whereas a downtrend was recognized at the cooling stage.