SYMPOSIA PAPER Published: 01 January 1984
STP30201S

Mixed-Mode Strain-Energy-Release Rate Effects on Edge Delamination of Composites

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Unnotched [±θ/0/90]s graphite/epoxy laminates, designed to delaminate at the edges under static and cyclic tensile loads, were tested and analyzed. The specimen stacking sequences were chosen so that the total strain-energy-release rate, G, for edge delamination was identical for all three layups. However, each layup had different percentages of crack-opening and shear-mode strain-energy-release rates, GI and GII, respectively. Results with composites made from T300 graphite fibers and 5208 epoxy, a brittle resin, indicated that only GI contributed to delamination onset under static loading. However, results with composites made from C6000 fibers and H205 epoxy, a tougher resin, indicated that the total G governed the onset of edge delaminations under cyclic loads. In addition, for both materials, the threshold level of G for delamination onset in fatigue was significantly less than the critical Gc measured in static tests. Furthermore, although the C6000/H205 material had a much higher static Gc than T300/5208, its fatigue resistance was only slightly better. A series of mixed-mode tests, like the ones in this study, may be needed to evaluate toughened-resin composites developed for highly strained composite structures subjected to cyclic loads.

Author Information

O'Brien, TK
Structures Laboratory, U.S. Army Research and Technology Laboratories (AVRADCOM), NASA Langley Research Center, Hampton, Va.
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Details
Developed by Committee: E08
Pages: 125–142
DOI: 10.1520/STP30201S
ISBN-EB: 978-0-8031-4902-1
ISBN-13: 978-0-8031-0218-7