Characterization of the pneumatic behavior of carbon/epoxy composites

The anisotropic nature of composite materials and environmental effects alw ays make the behavior of composite materials more complicated than that of conventional materials. Applications of composite materials, including cont ainers, boats, aircraft and aerospace structures, etc, must take into consi deration several important environmental effects like hygric and thermal ef fects. A composite engineer should be familiar with the hygrothermal behavi or of composite materials, particularly how temperature or moisture absorpt ion induces hygrothermal strain. Except for temperature and moisture concen tration, an unexpected environmental effect is found accidentally. Experime ntal results verify that varying the external air pressure may induce a dim ensional change of carbon/ epoxy composite material and the dimensional cha nge is proportional to the change of air pressure. The behavior induced by the change in air pressure is referred to here as pneumatic behavior. This research presents the discovery of the pneumatic behavior and a novel metho d termed curvature technique to characterize it. Carbon/epoxy laminate is c haracterized and the pneumatic expansion coefficients in both longitudinal and transverse directions are obtained. (C) 2001 Elsevier Science Ltd. All rights reserved.