Through-the-thickness stitching is a method that increases the translaminar strength and apparent fracture toughness of laminated composites. A novel test fixture was developed to measure mixed mode fracture toughness under combined Mode I and Mode II loadings. This fixture allowed the ratio between Mode I and Mode II to be varied in order to perform tests under a wide range of mixed mode conditions. Through testing it has been shown that stitching increases Mode I fracture toughness 20—50 times while playing a less significant role in increasing Mode II fracture toughness.
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