The present paper studies fatigue damage and life of single-lap bolted joints tightened with different torque magnitudes subjected to uniaxial load cycles. The adherends were constructed from E-glass/epoxy layers using a hand layup technique and assembled by 1.5, 3, and 8 N m of applied torques. Increasing the torque magnitude benefitted the final fatigue life of the joints so that the high-cycle fatigue life of the joint sample tightened with 8 N m was as high as 10 times that of the joint tightened with 1.5 N m. In the numerical section of this study, a three-dimensional finite element analysis was employed, and the impacts of applied torques were included in the progressive damage model to assess damage and failure in the bolted joints. For the joints tightened with higher torque levels, numerical results revealed higher fatigue lives but at the cost of more delamination at the vicinity of the hole. Laminate fracture surface was investigated through scanning electron microscopy and more cracking/damage progress was evidenced in matrix, fiber, and matrix–fiber interface as composite joints experienced fatigue cycles. Experimental life data of tested joints agreed with those anticipated through the use of finite element analyses indicating the developed model as an appropriate tool in evaluating the effects of applied torques on the fatigue fracture behavior of bolted laminates.

中文翻译：

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不同拧紧扭矩大小下单搭接螺栓层压板的渐进疲劳行为

本论文研究了在单轴载荷循环下以不同扭矩大小拧紧的单搭接螺栓接头的疲劳损伤和寿命。被粘物由 E 玻璃/环氧树脂层使用手糊技术构建，并通过 1.5、3 和 8 N m 的施加扭矩组装。增加扭矩幅度有利于接头的最终疲劳寿命，因此用 8 N·m 拧紧的接头样品的高周疲劳寿命高达用 1.5 N·m 拧紧的接头的 10 倍。在本研究的数值部分，采用了三维有限元分析，并将施加扭矩的影响包含在渐进式损坏模型中，以评估螺栓接头的损坏和失效。对于以更高扭矩级别拧紧的接头，数值结果显示疲劳寿命更长，但代价是孔附近更多的分层。通过扫描电子显微镜研究了层压板的断裂表面，随着复合材料接头经历疲劳循环，在基体、纤维和基体-纤维界面中证明了更多的开裂/损坏进展。测试接头的实验寿命数据与通过使用有限元分析所预期的数据一致，表明开发的模型是评估施加扭矩对螺栓层压板疲劳断裂行为影响的合适工具。和基体-纤维界面，因为复合材料接头经历了疲劳循环。测试接头的实验寿命数据与通过使用有限元分析所预期的数据一致，表明开发的模型是评估施加扭矩对螺栓层压板疲劳断裂行为影响的合适工具。和基体-纤维界面，因为复合材料接头经历了疲劳循环。测试接头的实验寿命数据与通过使用有限元分析所预期的数据一致，表明开发的模型是评估施加扭矩对螺栓层压板疲劳断裂行为影响的合适工具。