The nonlinear thermoviscoelastic behavior of composite thin plate from polyester reinforced with random fiber glass was investigated. The hereditary elasticity (viscoelastic) behavior described in new mathematical model predicted from experimental data from creep and relaxation tests to predict the creep compliance and relaxation modulus equations then apply that mathematical model in numerical and analytical analysis to describe the nonlinear viscoelastic behavior of thin composite plates at different loading and temperatures. The creep specimens and composite thin plate have the same volume fraction.
A very good agreement has been found between experimental, theoretical and FEM method. It is found that the deflection increases with approximate rate (50 %) at time (15 min.) and the shear stress (xy) increases with approximate rate (58%) at time (30 min.), as a result of increasing the distributed load (q=1.934e-3 N/mm2 to q=3.4488e-3 N/mm2) at temperature (30 Co) of relative dimension (a/b=0.5) and rectangular simply support plate. The increasing temperature from (30 Co- 60 Co) increases the deflection with approximate rate (34.6%).