Gad Marom 教授 特別講演会

During their service exposure, composite structures may be subjected to local heating under which three dimensional temperature gradients may develop with temperature differences that can exceed 150°C. The differential thermal expansion that is associated with such temperature gradients can generate a range of thermal stresses. An example that was studied recently is one of spot heating of the outer surface of a composite plate, generating compressive thermal stresses around the periphery of the heated zone, leading potentially to delamination by buckling. It was also found that a threshold level of moisture is a prerequisite for the occurrence of such delamination.

Following those observations we studied the combined effects of non-uniform heating and moisture in glass and carbon fiber reinforced epoxy composite laminates. The main conclusion is that delamination damage in a form of bulge occurs only in the presence of absorbed moisture. In fact only in the presence of a threshold level of moisture of about 1 wt% does non-uniform heating cause bulging. This threshold level corresponds to the critical moisture content found to produce major mechanical property reduction and inter-lamina separation.

Non-uniform heating per se is not responsible for the mechanism of bulging as the in plane and normal stresses that it generates are too small to cause either buckling or delamination, respectively. Instead, the proposed mechanism comprises a chain of consequences induced by moisture, wherein chemical degradation of the inter-lamina hot region is followed by mechanical inter-lamina separation and bulging caused by steam pressure.

The paper will present in detail the results of the effect of moisture on the mechanical properties, the simulation experiments of non-uniform heating including in-situ measurements of temperatures and strains, the finite element model used to calculate the resulting mechanical stresses and a schematic model of the observed delamination by bulging.