Time-dependent stress variations in symmetrically viscoelastic composite laminates under uniaxial tensile load

In this paper, we report an analytical approach for time-dependent stress variations in symmetrically viscoelastic composite laminates under plane deformation state based on a stress function based equivalent single layer theory. The theory initially adopts the stress function separated by the in-plane stress function and out-of-plane stress function as field assumption, instead of using the displacement field. The viscoelastic properties are simply expressed by the Maxwell model for the analysis of relaxation effect on the free edge stresses in viscoelastic laminates. The constitutive equation in the integral form for linear viscoelastic materials under constant uniaxial strain load can be simplified. By taking the principle of complementary virtual work, the governing equation can be obtained and further solved by solving a general eigenproblem. Convergent stress distributions are obtained and validated by the 3-D finite element method using commercial package. The free edge stresses are function of time and loading conditions in viscoelastic composite laminates and the relaxation effect on the free edge stresses is clearly shown in the numerical results of viscoelastic composite laminates with various layup stacking sequences.