This investigation addresses the interaction mechanisms of time dependent material behavior and cyclic damage during fatigue loading of fiber reinforced composite laminates. A new term 'damorheology' has been coined to describe such physical behavior. The lamina has been chosen as the building block and a cross ply laminate configuration was the selected test case. The chosen material system is the Radel X/T65-42 thermoplastic composite by Amoco. The fatigue performance at the lamina level is represented by the dynamic stiffness, residual strength and fatigue life of unidirectional laminates. The time dependent behavior is represented at the lamina level by a Pseudo-Analog Mechanical model. The thermo-rheological characterization procedure combines mechanical (creep) and thermal (dynamic mechanical analysis) techniques. / Ph. D.