Time‐dependent response of aramid‐epoxy‐aluminum sheet, ARALL, laminates

Abstract Selected results of an ongoing investigation aimed at characterizing the timedependent response of an aramid‐epoxy‐aluminum sheet laminate and its constitutents at 121°C are outlined in this paper. This laminate is a recently developed hybrid composite developed by the Aluminum Company of America, marketed under the ARALL‐4 tradename. The paper addresses the time‐dependent response of the above hybrid composite under creep loading. It is illustrated that ARALL‐4 laminates may exhibit substantial creep effects at stress levels below the proportional limit. The creep response is a nonlinear function of time and the applied stress level and is primarily due to the creep characteristics of the aluminum layers. An analytical model based on the assumptions of the classical lamination theory developed to model the time‐dependent response of these laminates under creep and thermal loading is shown to yield good correlation with the experimental data. It is also illustrated that the residual state of stress can influence the extent of creep. This offers the possibility of minimizing the creep effects by altering the state of residual stress with mechanical prestraining.