A Nonlinear Viscoelastic Modeling of Fiber Metal Laminates

A new class of advanced composite materials namely the fibermetal laminates (FMLs) such as ARALL (Aramid Reinforced Aluminum laminate) and GLARE (Glass Reinforced Aluminum laminate) has been developed for primary load bearing components of aircraft fuselage and wings. The FML is composed of alternating layers of fiber reinforced polymer (FRP) and aluminum sheets and shows good fatigue resistance. The metal layers are placed on the top and bottom of the laminate to provide good impact resistance and resistance to extreme environments (moisture, ultraviolet radiation and solvent). Krishnakumar (1994) has provided a survey of extensive works on manufacturing, testing, and modeling of the FMLs. The FMLs exhibit nonlinear viscoelastic and/or plastic behaviors due to the existence of FRP and metal alloy layers. The nonlinearity and time-dependent responses in the FMLs are intensified under high load levels, elevated temperatures, and humid environments. A predictive capability on the overall nonlinear viscoelastic response of the FMLs that recognizes different responses in the FRP and metallic layers becomes necessary. Literature indicates a few advances in this direction by the consideration of the elastic-plastic behavior and the use of classical lamination theory (Chen & Sun, 1989; Hashagen et al., 1995). Pindera et al. (1989) have carried out an experimental investigation of the creep response of ARALL laminates at 121°C. A pronounced viscoelastic behavior is observed in ARALL at stress levels below its proportional limit. Aluminum exhibits a nonlinear viscoelastic behavior while aramid-FRP shows a linear viscoelastic behavior. The classical lamination theory (CLT) was used to model the overall creep response of the laminates.