Nonlinear viscoelastic stress singularities near free edges of unsymmetrically laminated composites

Nonlinear viscoelastic stress singularities near free edges of laminated composites are evaluated based on Pipes and Pagano's displacement field for laminates under a generalized plane deformation state and Schapery's nonlinear viscoelastic constitutive relations. The interlaminar stresses in unsymmetrically laminated composites due to axial strain and bending have been studied as a function of time and loading magnitude. Numerical studies show that the stacking sequence significantly affects the distributions of interlaminar stresses and the stress symmetric conditions about the midplane for an unsymmetrically laminated composite are different than those for a symmetric laminate. The results indicate a strong sensitivity to the nonlinearities of the viscoelastic constitutive relations. Increasing the load significantly increases nonlinear behavior. The rate of stress relaxation also varies with the magnitude of loading.