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Effects of Crimped Fiber Paths on Mixed Mode Delamination Behaviors in Woven Fabric Composites

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Technical Report

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Naval Undersea Warfare Center Division Newport United States

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This research investigated the fracture toughness and crack propagation behaviors of woven fabric polymer composite laminates subjected to single- and mixed-mode loadings using numerical models. The objectives were to characterize the fracture behaviors and toughness properties at the fibermatrix interfaces and to identify mechanisms that can be exploited for increasing delamination resistance. The mode I and mode II strain energy release rates Gsub I and Gsub II, the effective critical strain energy release rate Gceff, and crack growth stabilities were determined as functions of crimped fiber paths using mesoscale, two-dimensional multi-continuum finite-element models. Three variations of a plain-woven fabric architecture-each of which had different crimped fiber paths-were considered. The presence of mixed strain energy release rates at the mesoscale due to the curvilinear fiber paths was shown to influence the interlaminar fracture toughness and was explored for pure single-mode and mixed-mode global loadings. It was concluded that woven fabric composites provided a fracture toughness conversion mechanism FTCM and their toughness properties were dependent on and variedwith position along the crimped fiber paths. The FTCM was identified as an advanced tailoring mechanism that can be further utilized to improve toughness and damage-tolerance thresholds especially when the mode II fracture toughness Gsub IIc is greater than the mode I fracture toughness Gsub Ic.

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