Calculations of the Room-Temperature Shapes of Unsymmetric Laminatestwo

Abstract

The cured shape of unsymmetric laminates do not always conform to the predictions of classical lamination theory. Classical lamination theory predicts the room-temperature shapes of all unsymmetric laminates to be a saddle. Experimental observations, however, indicate some unsymmetric laminates have cylindrical room-temperature shapes. In addition, some unsymmetric laminates exhibit two stable room-temperature configurations, both cylindircal. This paper presents a theory which explains these characteristics. The theory is based on an extension of classical lamination theory which accounts for geometric nonlinearities. A Rayleigh-Ritz approach to minimizing the total potential energy is used to obtain quantitative information regarding the room-temperature shapes of square T300/5208 [02/902] T and [04/904] T graphite-epoxy laminates. It is shown that, depending on the thickness of the laminate and the length of the side of the square, the saddle shape configuration is actually unstable. For values of length and thickness that render the saddle shape unstable, it is shown that two stable cylindrical shapes exist. The predictions of the theory are compared with existing experimental data.