The effect of physical aging on the viscoelastic response of cross-ply laminates to in-plane compression

The viscoelastic behaviors of simply-supported, cross-ply laminates with a physical aging phenomenon are examined. The laminates considered are under uniaxial in-plane compression and have various amplitudes of initial imperfection. Laminae exhibit different aging shift rates for the creep responses to the axial and shear loadings. The effective time theory is employed to construct the stress-strain relations. The stress function is obtained by solving the compatibility equation by the use of the Laplace transform and a numerical integration scheme. Deflections are calculated from the moment equation by the Galerkin method in conjunction with the numerical integration. Numerical results of creep deflections, edge shortenings and stress resultants for graphite-reinforced thermoplastic and glass-reinforced thermosetting laminates are presented. The effects of physical aging, pre-loading aging time, and the amplitude of imperfection on the creep responses are illustrated in the numerical examples.