Void effects on the interlaminar shear strength of unidirectional graphite-fiber-reinforced composites

A study was conducted to evaluate the effect of voids on the interlaminar shear strength (ILSS) of a polyimide matrix composite system. The graphite/PMR-15 composite was chosen for study because of the extensive amount of experience that has been amassed in the processing of this material. Void contents were calculated and the void geometry and distribution were noted using microscope techniques such as those used in metallography. A good empirical correlation between ILSS and composite density was found. The most acceptable relationship between the ILSS and density was found to be a power equation that closely resembles theoretically derived expressions. It was found that void-free composites could be processed in matched metal die molds at pressures greater than 1.4 MPa and less than 6.9 MPa.