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 constituents at 12 1 "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. M . J. Pindera:The modulus itself should not change appreciably but the yield point may change. We did not generate the stress-strain curve for AR-ALL-4 at room temperature. I would expect that in fiber direction the stress-strain curve of Al/aramid fiber-epoxy system will show not more than 10% change up to 250°F. In transverse, matrix dominated direction, the changes will be more dramatic.A. D. Osborne: Are you saying that the modulus of ARALL-4 will change 10% due to changes in epoxy modulus while the modulus of aramid fibers is constant up to 250"F? M . J. Pindera: The contribution of the matrix to a POLYMER COMPOSITES, OCTOBER, 1989, Yo/. 70, No. 5

Creep behaviour of FM906 glass-fibre epoxy as used in heated fibre metal laminates

“…Creep research has been performed by Pindera on ARALL (aramid fibre reinforced aluminium) at 121 C and mechanical stress levels between 207 and 345 MPa. 10 Daghigh et al 11 investigated the effect of creep in basalt FMLs at 200 C. The mechanical and thermal levels used by Pindera and Daghigh are not expected to be present in the case of a deicing leading edge application.…”

“…Creep research has been performed by Pindera on ARALL (aramid fibre reinforced aluminium) at 121℃ and mechanical stress levels between 207 and 345 MPa. 10 Daghigh et al. 11 investigated the effect of creep in basalt FMLs at 200℃.…”