A MODEL FOR TIME-INDEPENDENT AND TIME-DEPENDENT DAMAGE EVOLUTION AND ITS INFLUENCE ON CREEP OF MULTIDIRECTIONAL POLYMER COMPOSITE LAMINATES

摘要

Time-independent and time-dependent damage (TID and TDD) in multidirectional polymer composite laminates develop during manufacturing due to process-induced residual stress as well as during quasi-static loading and creep loading, degrading its modulus and strength. A model to predict both time-independent and time-dependent transverse cracking in multiple plies of a multidirectional polymer composite laminate is presented. The stress state in the intact regions of the plies are determined using the lamination theory and incremental loading to the desired load. The stored elastic energy, determined using this stress state, is compared with a critical value for failure to determine if a ply would fail after the increment. If failure is predicted, variational analysis is used to determine the perturbation in ply stresses due to cracking and the crack density. The new stress state is used to determine the laminate modulus after cracking and the ply stress after next increment. This procedure is repeated to determine the crack evolution and the degradation in modulus. Model predictions compare very well with experimental results for a [±θ_m/90_n]_s laminate.