Nonwoven polyester interleaving for toughness enhancement in composites

Abstract

Various researchers have developed techniques to control delamination in laminated structures. One of these techniques is “interleaving,” adding high toughness material to key interfaces in a laminate. This paper studies using polyester veil as a low-cost interleaf alternative to other materials and focuses on a nonwoven, polyester spunbond material. Two different interleaf thicknesses, 0.18 mm and 0.74 mm, are primarily used. In addition, fine 4 g/m2 polyester was also compared. Carbon/epoxy composites are manufactured using 2 × 2 Twill 24″–12k carbon fibers embedded in an epoxy resin, with polyester interleaves at key interfaces. Specimens are fabricated using wet hand layup and cured at room temperature in a vacuum bag. Mode I fracture toughness is measured using the double cantilever beam test and Mode II fracture toughness is examined using the end-notched flexure test. Further evaluation is made using static indentation and full penetration impact testing. Toughness is compared, and the resulting fracture surfaces are investigated. Significant improvement is seen in Mode I testing. Up to a factor of 4 increase in propagation energy per unit area resulted from the inclusion of the interleaf material. Smaller improvements were observed in Mode II, with the best cases showing an increase in propagation energy to maximum load by about a factor of 2 compared with control cases. The polyester interleaf significantly influences the fracture morphology observed in static indentation and full penetration tests.