Effect of a Soft Interleaf on Transverse Cracks in Thick Glass Fiber

Abstract

An interleaf has an effect on delamination, fracture and fatigue crack growth, and impact damage. Here, it is shown that a soft interleaf placed between plies of similar orientation will delay transverse cracks and extend laminate fatigue life. Fatigue test results on symmetric cross-ply laminate coupon specimens with a thick 90 -layer show that the interleaf did stall the rapid crack growth for a significant period before proceeding to the interior of the specimen. It was observed that the crack path was not straight but tended to translate along the interleaf–90 ply interface for some distance. A numerical analysis was used to study the effects of interleaf stiffness, thickness, and position. For a soft interleaf the crack energy release rate increases rapidly as the crack approaches the interleaf but then drops to a minimum value well below that of the laminate without interleaf when the crack tip is in and just past the interleaf. An increase in the soft interleaf thickness only slightly decreased this minimum value. The minimum energy release rate is shown to decrease as the interleaf is placed closer to the original crack tip near the outside surface of the laminate.

Keywords

glass fiber-reinforced epoxy interleaf fatigue crack finite element analysis

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Effect of a Soft Interleaf on Transverse Cracks in Thick Glass Fiber–Epoxy Cross-ply Laminates

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