INTERLAMINAR STRENGTH AND TOUGHNESS OF FIBERGLASS LAMINATES.

The interlaminar tensile and shear strength and fracture toughness have been studied as a function of fiber surface treatment, style of reinforcement, and matrix material. Suitable tests were developed to achieve pure states of tension and shear stress and opening mode (cleavage) crack propagation. The interlaminar fracture surface work was significantly greater than that of the unreinforced matrix for all except rubber-toughened epoxy. Interlaminar shear and tensile strength were less than those observed with the unreinforced matrix; failure occurred primarily in the interface. Both the strength and toughness were insensitive to the fiber surface treatment, but the toughness could be increased significantly by the inclusion of a small amount of glass or nylon fiber in the thickness direction and to a lesser extent by the inclusion of chopped nylon fibers between the plies.