An investigation was conducted to characterize the mechanical properties of intraply hybrids made from graphite fiber/epoxy matrix (primary composites) hybridized with varying amounts of secondary composites made from S-glass or Kevlar 49 fibers. The tests were conducted using thin laminates having the same thickness. The specimens for these tests were instrumented with strain gages to determine stress-strain behavior. The results show that the mechanical properties of intraply hybrid composites can be measured using available test methods such as the 10-deg off-axis method for intralaminar shear, and conventional test methods for tensile, flexure, and Izod impact properties. Intraply hybrids have linear stress-strain curves to fracture for longitudinal tension and nonlinear stress-strain curves for intralaminar shear.

The results also showed that combinations of high-modulus graphite/S-glass/epoxy matrix composites exist which yield intraply hybrid laminates with the “best” balanced properties: for example, 100 percent increase in impact resistance and 35 percent increase in tensile and flexural strengths, with no reduction in modulus compared with graphite fiber/epoxy matrix composites. In addition, the results showed that the translation efficiency of mechanical properties from the constituent composites to intraply hybrids may be assessed using a simple equation.