Statistical fatigue failure life of unidirectional CFRP under bending load

Our developed accelerated testing methodology (ATM) based on the matrix resin viscoelasticity for the failure life prediction of carbon-fiber reinforced polymers (CFRP) was applied for statistical prediction of long-term fatigue failure life under bending load for the longitudinal direction of unidirectional CFRP laminates, which is an important basic aspect of design for the durability of CFRP structures used for aircraft and other applications. First, the formulations for fatigue life prediction of FRP under cyclic loading are introduced. Second, the time-dependent and temperature-dependent viscoelasticity of matrix resin and the statistical flexural static strengths of CFRP laminates at various temperatures are introduced as the basic data of failure life prediction of CFRP laminates. Third, fatigue bending tests for CFRP laminates are performed at various load levels with various frequencies and temperatures. A master curve of non-dimensional fatigue strength versus number of cycles to failure (S-N master curve) is constructed by substituting data of the second and third steps into the formulations. Finally, the long-term fatigue strength data obtained under cyclic bending load for unidirectional CFRP laminates are compared with the long-term creep strength obtained in the previous paper.