Abstract : In 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.
