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In this investigation the interlaminar shear fatigue characteristics of three composite materials are examined: graphite-epoxy (HTS), boron-epoxy (AVCO 5505), and glass-epoxy (3M 1002 S/ply). Thick-laminate, short-beam shear specimens instrumented with electrical resistance strain rosettes were subjected to constant-amplitude sinusoidal loadings (positive/positive, R = 0.1). Both residual strength and stiffness data are presented and trends in the fatigue life of these materials are established. The results of this preliminary investigation indicate that the fatigue characteristics of composite materials in the interlaminar modes differ significantly from fatigue characteristics in the fiber mode. While the residual strength of composite materials in the fiber mode has been shown to be only slightly reduced from the static strength after 106 cycles, the interlaminar shear strength is found to be diminished to approximately 50 percent of the static shear strength after 106 cycles. The shear stiffness, unlike the strength, is shown to be only slightly diminished over a 106 cycle lifetime. Finally, residual strengths are evaluated at 106 cycles for each material.
composite materials, boron, graphite, glass, fatigue (materials), shear stress, residual strength
Drexel University, Philadelphia, Pa.