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Interlaminar prestressing reinforcement of epoxy/glass fiber composites

This paper describes an innovative through-thickness fiber reinforcement technology that employs in situ shrinking fibers to provide supplemental strength-enhancing interlaminar prestresses for fiber-reinforced polymeric laminate structures. Interlaminar stitched fibers shrink and provide prestress. The shrinkage is heat-activated and timed to coincide with epoxy-curing steps. This new technology includes the design and fabrication of in situ shrinking fibers to improve the peel strength of epoxy/glass fiber composite layers. The epoxy specimens were shrink-reinforced under four different conditions; the fibers were activated when the epoxy matrix was cured for 4, 12, and 20 h, or without having any curing time beforehand. Then, the peel strengths and flexural strengths were compared. Also, in-plane tensile tests were conducted under identical conditions to investigate whether the through-thickness shrinking fibers affect the in-plane properties. The results indicated that the maximum improvement from the fiber activation was shown when the epoxy was cured for 4 h, while there was no significant effect from the in-plane tensile test.