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Investigation of fracture toughness of laminated stitched composites.

机译：层压缝合复合材料的断裂韧性研究。

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The major objective of this research was to develop new test procedures to investigate the fracture toughness of laminated stitched composites. Graphite-epoxy laminated composites have very high stiffness-to-weight and strength-to-weight ratios that make them very attractive in structural applications. The properties of these materials depend strongly on fiber orientation and ratio of fiber to resin. The strength along the translaminar direction of this material is dominated by the matrix and is typically about 5% of the strength along the fiber direction. Hence, these materials are very easy to delaminate. Through-the-thickness stitching is one of the ideal ways to improve the translaminar properties and prevent crack propagation. In order to understand the stitch's effect, a series of test procedures was developed and was successfully used to test Mode I, Mode II and Mixed Mode fracture toughness of stitched laminated composites.; A secondary objective was to model stitched laminated composites to predict their properties. Finite element models were proposed to understand the effect of stitching on improving the fracture toughness for Mode I and Mode II of stitched laminated composites. From these models, “effective G” (effective strain energy release rate) and “parent G” (strain energy release rate of the parent laminate) can be isolated where stitches can be treated as “an extra structure.” The “parent G” is an intrinsic parent material property and almost never changes regardless of whether the laminated composites are stitched or not. However, the “effective G” is dramatically increased by the stitching. The author also found that changing the thickness of stitches has a more profound impact on the “effective G” than changing the density of stitches.
机译：这项研究的主要目的是开发新的测试程序，以研究层压缝合复合材料的断裂韧性。石墨-环氧树脂层压复合材料具有很高的刚度重量比和强度重量比，这使其在结构应用中非常有吸引力。这些材料的性能在很大程度上取决于纤维的取向和纤维与树脂的比例。该材料沿层间方向的强度主要由基质决定，通常约为沿纤维方向的强度的5％。因此，这些材料非常容易分层。贯穿厚度的缝合是改善层间性能并防止裂纹扩展的理想方法之一。为了了解缝线的效果，开发了一系列测试程序，并成功地用于测试缝制层压复合材料的I，II和混合模式断裂韧性。第二个目标是对缝合的层压复合材料进行建模以预测其性能。提出了有限元模型，以了解缝合对提高缝制层压复合材料的模式I和模式II的断裂韧性的影响。从这些模型中，可以将“有效G”（有效应变能释放率）和“母体G”（母层压体的应变能释放率）隔离开来，在这些情况下，针迹可以视为“额外的结构”。 “母体G”是固有的母体材料特性，并且无论层压复合材料是否被缝合，几乎都不会改变。但是，“有效G”会通过缝合显着增加。作者还发现，改变针迹的厚度比改变针迹的密度对“有效G”的影响更大。

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