Strength and failure behavior of stitched carbon/epoxy composites |
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Authors: | Ryuta Kamiya Tsu-Wei Chou |
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Affiliation: | (1) Toyoda Automatic Loom Works, Ltd., Aichi, Japan;(2) Center for Composite Materials and Department of Mechanical Engineering, University of Delaware, 19716 Newark, DE |
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Abstract: | This article presents a study of the effect of through-the-thickness stitching yarns upon the strength and failure behavior
of multidirectionally reinforced composites. The in-plane yarns were placed in four directions (0,±45, 90) to form a quasi-isotropic
preform, which had open spaces between adjacent yarns. These interyarn spaces allowed easy insertion of the through-the-thickness
stitching yarns without significant damage of the in-plane fibers. Fiber volume fractions of over 54 pct were obtained by
this method. The through-the-thickness yarn sizes used in this study were 2, 4, and 6 kilo-filament (kf). Non-stitched performs
were also manufactured with the same fiber content and by the same procedure as the stiched preforms for the control experiments.
All preforms were infiltrated with epoxy resin by the resin transfer molding (RTM) technique. In-plane tensile and compressive
strength, interlaminar shear strength, and mode I fracture toughness of the carbon/epoxy composites were measured at three
through-the-thickness yarn contents. Although the through-the-thickness yarns significantly enhanced the mode I fracture toughness,
they tended to degrade the in-plane tensile and compressive strength. The failure process under interlaminar shear loading
by double notch shear tests showed two distinct stages: the fiber-matrix interfacial failure followed by the breakage/debonding
of the through-the-thickness yarns. The through-the-thickness yarns caused a reduction of the initial failure load in the
first stage but could enhance the final failure load in the second stage. In composites with 6 kf through-the-thickness yarns,
the final failure load could exceed the initial failure load. Scanning electron microscope (SEM) and optical microscopic examinations
were also conducted for observing the failure mechanisms and fracture surfaces.
This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October
11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite-Materials
Committee. |
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