Characterization of the pneumatic behavior of carbon/epoxy composites

The anisotropic nature of composite materials and environmental effects always make the behavior of composite materials more complicated than that of conventional materials. Applications of composite materials, including containers, boats, aircraft and aerospace structures, etc, must take into consideration several important environmental effects like hygric and thermal effects. A composite engineer should be familiar with the hygrothermal behavior of composite materials, particularly how temperature or moisture absorption induces hygrothermal strain. Except for temperature and moisture concentration, an unexpected environmental effect is found accidentally. Experimental results verify that varying the external air pressure may induce a dimensional change of carbon/epoxy composite material and the dimensional change 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 method termed curvature technique to characterize it. Carbon/epoxy laminate is characterized and the pneumatic expansion coefficients in both longitudinal and transverse directions are obtained.