Cryogenic Microcracking of Carbon Fiber/Epoxy Composites: Influences of Fiber-Matrix Adhesion

The impact of fiber-matrix adhesion on the transverse microcracking of fiber reinforced polymeric materials thermally cycled at cryogenic temperatures was investigated using symmetric cross-ply carbon fiber/epoxy laminates containing fibers with different surface treatments. Past research explored the role of fiber-matrix adhesion in determining the room temperature properties of composite materials, but this work is original in that it examined how fiber-matrix adhesion affected the behavior of composite materials at cryogenic temperatures. Three fiber surfaces were used: Unsized but exposed to an oxidative surface treatment, epoxy sized, and surfactant sized. Modifications of the fiber surfaces changed the adhesion of the matrix to the fibers as determined by interlaminar shear strength and dynamic mechanical analysis. The extent of microcracking in the laminates exhibited a dependence on fiber-matrix adhesion, with high levels of adhesion corresponding to decreased microcracking.