Off-axis tensile creep rupture of unidirectional CFRP laminates at elevated temperature

Off-axis tensile creep fracture behavior of unidirectional carbon/epoxy T800H/Epoxy laminates is studied at 100 °C under constant load conditions. Off-axis creep rupture data on plain coupon specimens are obtained within the time range up to 10 h for four kinds of off-axis fiber orientations. The log–log plots of the creep stress against the rupture time can approximately be described by straight lines with negative slopes over the range of creep life for all the fiber orientations. The static tensile strengths extrapolated from those straight lines almost agree with the experimental results for respective fiber orientations. The creep rupture data normalized with respect to the static strength approximately falls on a single creep rupture curve. These observations suggest that the fiber orientation dependence of creep rupture strength is similar to that of static tensile strength. The creep fracture occurs along reinforcing fibers in a brittle manner without accompanying the appreciable secondary and tertiary creep stages, regardless of the fiber orientations, and thus the off-axis creep deformation prior to fracture is characterized by the primary creep stage for all the fiber orientations. Then, a phenomenological model for the creep deformation and rupture behaviors of the unidirectional composite is developed, with a view to making preliminary predictions of creep life from a limited amount of data. It is demonstrated that the proposed model can moderately describe the observed features of the creep deformation and creep rupture behaviors under off-axis loading conditions.