(Received 18 February 2000; accepted 8 May 2001)
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In order to use the Iosipescu V-notch beam test for determining the in-plane shear strength of high strength 2D 2 × 2 biaxial braided composites, two modifications were made to the specimen geometry. First, they were tabbed to prevent buckling at the gage section and pinching of the specimen at grip sections. Tabbed specimens having gage sections of 0.50″, 0.35″, 0.188″ were studied. Also, to reduce the load required for failure, the shear area was decreased by deepening the V-notch. Failure modes of specimens having notch widths of 0.425″, 0.350″, 0.325″, and 0.300″ were examined. In this investigation, high toughness PR520 epoxy resin was selected to make panels by resin transfer molding (RTM). An initial study was conducted to find the best possible specimen geometry using ±45° braid. Then, both ±45° and ±60° braid angles were studied for the selected geometry. In order to investigate the cut direction effects on the ±60° braid in-plane shear modulus and the strength, the specimens were cut in both 0° and 90° directions of the panel. Tabbed specimens with a gage length of 0.188″ demonstrated the highest average shear strength. The notch width of 0.325″ produced acceptable failures. Thus, it was selected as the minimum notch width. Then, both ±45° and ±60° specimens having gage section of 0.188″ and notch width of 0.325″ were tested for shear properties. The tabs minimized the bending loads due to buckling and pinching of the specimens across the gage section. Modifications increased the in-plane shear strength by about 33–55% for ±45°. The 0° cut-direction specimens, which had ±30° fibers with respect to the loading path, had lower strength and modulus values than that of the 90° cut-direction specimens. Modulus results for ±60° specimens were close to analytical predictions regardless of the cut direction.
Assistant professor, Wichita State University, Wichita, KS
Research associate, National Institute for Aviation Research, Wichita, KS
Stock #: CTR10999J