Progressive damage of a unidirectional composite with a viscoelastic matrix, observations and modelling

International audienceIn this paper phenomenological observations of the creep rupture under maintained combined traction and torsion loading are first presented. They show the importance of the matrix's behavior in the long-term durability of the material. Understanding and foreseeing creep rupture of unidirectional fiber reinforced polymers (UD FRP) involves comprehension at the fibers' scale of various time-dependent interactions among the fibers and between the matrix and the fibers. Shear-lag models have been successfully applied in the modeling at the micro-scale of these interactions, some of them even introducing time dependence. Long-term durability of macro-scale structure demand further developments of such models to be able to predict the macro-damage cluster and their evolution. The aim of the present contribution that is an extension from existing models is to investigate the progressive damage of a 0o UD composite material subjected to combined shear-traction loading including a high number of interacting fibers, with a viscoelastic matrix, debondings and random distribution of fiber flaws. Results of simulations including different loadings and matrix viscoelastic properties will be shown and discussed for a better comprehension of the role of composite's components in the creep rupture phenomenon. In particular, the long-term influence of matrix's shear stiffness on the material's lifespan is shown, and the impact of an additional uniform shear stress is studied. This combined shear-traction loading is of interest in real-scale structures where shear stress can result from torsion or shear forces (such as those due to anchor points, misalignment and coupling). Moreover, this model is a first step to approach the long term failure of 0o composites subjected to torsion-bending loading, what is shown decisive in the second section of this work. Further experimental works in combined traction-torsion loadings are needed to validate this simulations with a specific attention on the identification of required parameters