Rate-Dependence of Off-Axis Tensile Behavior of Cross-Ply: CFRP Laminates at Elevated Temperature and Its Simulation

The present paper focuses on experimental verification of the ply-by-ply basis inelastic analysis of multidirectional laminates. First of all, rate dependence of the tensile behavior of balanced symmetric cross-ply T800H/epoxy laminates with a [0/90]3S lay-up under off-axis loading conditions at 100°C is examined. Uniaxial tension tests are performed on plain coupon specimens with various fiber orientations [/(90 - )]3S ( = 0, 5, 15, 45 and 90°) at two different strain rates (1.0 and 0.01%/min). The off-axis stress-strain curves exhibit marked nonlinearity for all the off-axis fiber orientations except for the on-axis fiber orientations = 0 and 90°, regardless of the strain rates. Strain rate has significant influences not only on the off-axis flow stress in the regime of nonlinear response but also on the apparent off-axis elastic modulus in the regime of initial linear response. A macromechanical constitutive model based on a ply viscoplasticity model and the classical laminated plate theory is applied to predictions of the rate-dependent off-axis nonlinear behavior of the cross-ply CFRP laminate. The material constants involved by the ply viscoplasticity model are identified on the basis of the experimental results on the unidirectional laminate of the same carbon/epoxy system. It is demonstrated that good agreements between the predicted and observed results are obtained by taking account of the fiber rotation induced by deformation as well as the rate dependence of the initial Young's moduli.