2. Temperature Dependence of Statistical Static Strengths for Unidirectional CFRP with Various Carbon Fibers

The statistical static strengths under the tension loading along the longitudinal direction of unidirectional CFRP with various kinds of carbon fibers are measured at various temperatures and discussed in the role of the viscoelasticity of matrix resin. First, the formulation for time and temperature dependent statistical static strength for CFRP laminates is performed based on the viscoelasticity of matrix resin. Second, the statistical static strengths of four kinds of carbon fibers, those are high strength and high modulus PAN based carbon fibers and low and high modulus pitch based carbon fibers, are measured by using single fibers of these four kinds of carbon fibers. Third, the temperature dependent tensile static strengths of unidirectional CFRP with four kinds of carbon fibers are statistically measured at various temperatures by using resin impregnated carbon fiber strands (CFRP strands) as the specimens of unidirectional CFRP, and the fractographs of CFRP strands with four kinds of carbon fibers failed at various temperatures are observed. Finally, the temperature dependences of tensile static strengths are discussed from the role of the viscoelasticity of matrix resin based on Christensen’s model of viscoelastic crack kinetics.