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Size effects in 2D Triaxially Braided Carbon Fiber Composites (2DTBC)
PI: Anthony M. Waas, coPI: Zdenek Bazant (Northwestern)
Particpant: Amit Salvi


2DTBCs are finding increased use in automotive and aerospace structural applications. These composites are lighter than metals and offer superior fracture toughness due to their complex fiber tow architecture. Currently we are investigating size effects in these composites. We are studying three different types of braids, namely (0° /±30°), (0°/±45°) and (0°/±60°) where the axial tows are 0° and the bias tows are at an angle to the axial tows. Specimens are cut in four different geometrically scaled sizes. The specimens are loaded using a three point bend fracture configuration on a hydraulic MTS machine as shown. Load and displacement response is measured and crack path in the specimens is recorded using a high resolution Nikon digital camera. In addition, surface speckle pattern imaging is used to extract full-field in-plane displacements and strains. The information obtained from these experiments serve towards developing and validating size effect laws for strength. In addition, the experimental results are used to understand fracture toughness and ductility in the specimens, and the mechanisms by which toughness is enhanced. This understanding leads to mechanism based models that can be used to optimize the textile architecture for various applications.

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