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The interlaminar fracture toughness of a plain-weave carbon-epoxy composite was studied under Mode I, Mode II and Mixed-Mode I and II loading. The objective was to compare results for a composite material with two different fiber forms: unidirectional tape and plain-weave fabric (PW). Tests were performed using the double-cantilever beam (DCB), four-point end-notch flexure (4ENF) and mixed-mode bending (MMB) configurations. Delamination initiation values were obtained as well as propagation values. The specimens were made of 24 layers of IM7/8552 plain-weave fabric. The results were compared with tests performed by Hansen and Martin  on IM7/8552 unidirectional tape. For all Mode I, Mode II and Mixed-Mode tests, the woven initiation Gc are quite similar to the corresponding initiation values for the tape material. The woven Gc propagation values, however, are much higher (2.6 times in Mode I and 3.1 times in Mode II) than the corresponding propagation values for the tape material. Furthermore, these propagation values may have more significance to structural components than propagation values for tape laminates.
delamination, woven composites, fracture toughness
National Research Council, NASA Langley Research Center, Hampton, VA
The Boeing Company, Philadelphia, PA
U.S. Army Research Laboratory, Vehicle Technology Directorate, NASA Langley Research Center, Hampton, VA