Abstract Carbon fiber-reinforced polymers (CFRPs) are commonly used in structures in which weight and strength determine energy efficiency, such as automobiles and aircraft. CFRPs are light in weight, and they provide design flexibility, low thermal expansion, and high specific strength. Bonding CFRPs to make larger structures, however, is problematic. Recently, laser pretreatment has been used to improve bonding of CFRPs. This study investigates the effects of uniform surface pretreatment with a laser on the resistance of secondary bonded carbon fiber reinforced structures to mode-I fatigue crack growth. The joint fatigue limit was characterized by carrying out displacement-controlled cyclic testing on treated double cantilever beam specimens. A mid-infrared-range CO 2 pulse laser with a 10.6 μ m wavelength was used to treat the CFRP substrates with the aim to increase the substrates’ fatigue limit and thereby expand the design envelope for secondary bonding. The cured substrates were treated uniformly with either high (laser-ablated) or low (laser-cleaned) CO 2 laser irradiation and compared with specimens that were treated with a baseline Teflon film treatment such that their bonding surfaces were smooth. Our results show that uniform laser treatment increased the fatigue limit evaluated at a threshold crack growth rate of 10−5 mm/cycle. Furthermore, the laser-ablated specimens, in which the carbon fibers were totally exposed, achieved triple the strain energy release rate threshold value of the laser-cleaned samples.

中文翻译：

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激光处理的胶粘复合材料接头中的疲劳裂纹扩展：实验检验

摘要 碳纤维增强聚合物 (CFRP) 常用于汽车和飞机等重量和强度决定能源效率的结构中。CFRP 重量轻，设计灵活，热膨胀低，比强度高。然而，粘合 CFRP 以制造更大的结构是有问题的。最近，激光预处理已被用于改善 CFRP 的粘合。本研究调查了使用激光进行均匀表面预处理对二次粘合碳纤维增强结构抗 I 型疲劳裂纹扩展能力的影响。通过对处理过的双悬臂梁试样进行位移控制循环测试来表征接头疲劳极限。中红外范围的 CO 2 脉冲激光器，具有 10. 6μm波长用于处理CFRP基材，目的是增加基材的疲劳极限，从而扩大二次键合的设计范围。固化的基材用高（激光烧蚀）或低（激光清洁）CO 2 激光照射均匀处理，并与用基线特氟隆薄膜处理的样品进行比较，从而使它们的粘合表面光滑。我们的结果表明，均匀的激光处理提高了疲劳极限，阈值裂纹扩展速率为 10-5 毫米/周期。此外，碳纤维完全暴露的激光烧蚀样品达到了激光清洁样品应变能释放率阈值的三倍。固化的基材用高（激光烧蚀）或低（激光清洁）CO 2 激光照射均匀处理，并与用基线特氟隆薄膜处理的样品进行比较，从而使它们的粘合表面光滑。我们的结果表明，均匀的激光处理提高了疲劳极限，阈值裂纹扩展速率为 10-5 毫米/周期。此外，碳纤维完全暴露的激光烧蚀样品达到了激光清洁样品应变能释放率阈值的三倍。固化的基材用高（激光烧蚀）或低（激光清洁）CO 2 激光照射均匀处理，并与用基线特氟隆薄膜处理的样品进行比较，从而使它们的粘合表面光滑。我们的结果表明，均匀的激光处理提高了疲劳极限，阈值裂纹扩展速率为 10-5 毫米/周期。此外，碳纤维完全暴露的激光烧蚀样品达到了激光清洁样品应变能释放率阈值的三倍。我们的结果表明，均匀的激光处理提高了疲劳极限，阈值裂纹扩展速率为 10-5 毫米/周期。此外，碳纤维完全暴露的激光烧蚀样品达到了激光清洁样品应变能释放率阈值的三倍。我们的结果表明，均匀的激光处理提高了疲劳极限，阈值裂纹扩展速率为 10-5 毫米/周期。此外，碳纤维完全暴露的激光烧蚀样品达到了激光清洁样品应变能释放率阈值的三倍。