Sk. Sharma et Bv. Sankar, EFFECT OF STITCHING ON IMPACT AND INTERLAMINAR PROPERTIES OF GRAPHITEEPOXY LAMINATES/, Journal of thermoplastic composite materials, 10(3), 1997, pp. 241-253
Effects of through-the-thickness stitching on the impact damage resist
ance, impact damage tolerance, and interlaminar fracture toughness (Mo
de I and Mode II) of plain woven and uniweave textile graphite/epoxy l
aminates were investigated. The uniweave textile was formed by weaving
dry carbon-fiber rows with fiberglass fill tows. The content of fiber
glass fill tows was 2.5% by weight. The plain woven laminates were man
ufactured using resin infusion molding and the uniweave laminates by r
esin transfer molding. Kevlar(R) and glass yarns of various yarn numbe
rs were used for stitching. Static Indentation-Flexure, Compression-Af
ter-Impact, Double Cantilever Beam and End-Notched Flexure tests were
conducted. Stitching did not have any effect on the onset of impact da
mage. However, stitching leads to significant improvement (25-40%) in
impact damage tolerance as measured by CAI strength and impact damage
area. Mode I fracture toughness as characterized by critical strain en
ergy release rate (G(Ic)) was found to increase by at least an order h
igher (15-30 times) than the unstitched laminates. Mode II fracture to
ughness (G(Ilc)) increased by 5-15 times over the unstitched laminates
. New methods to estimate the Mode II critical strain energy release r
ate in the stitched laminates are presented. The stitched textile adva
nced composites are considered potentially superior to prepregs for hi
gh volume, low-cost and high-performance structural materials.