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首页> 外文期刊>Journal of Materials Engineering and Performance >Hygrothermal Effect on Composites Under In-Plane Fatigue at Stress Ratios of R=-1 and R=0.1: An Analysis of Quasi-Isotropic Stitched Carbon Fibers
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Hygrothermal Effect on Composites Under In-Plane Fatigue at Stress Ratios of R=-1 and R=0.1: An Analysis of Quasi-Isotropic Stitched Carbon Fibers

机译：在r = -1和r = 0.1的应力比下在面内疲劳下对复合材料的湿热效应：准各向同性缝合碳纤维的分析

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The aeronautic structures normally operate under high levels of hygroscopic moisture from the surrounding environment at different temperature ranges while in service. Under such conditions, the behavior of laminate composite submitted to cyclic or static loadings can change drastically. In order to understand those effects in stitched fabrics, fatigue tests with open-hole specimens were carried out with a stress ratio of R=-1 and R=0.1. The specimens were fatigue-tested as provided (environmental conditions) and after exposed to hygrothermal weathering conditions. Based on evidences from recent studies available in the open literature, e.g., effect of water diffusion on epoxy matrix, the overall results indicated a significant reduction in stiffness after the specimens are exposed to hygrothermal effects. The reduction in matrix stiffness, in this case, enhanced the fatigue strength in tension-tension load (R=0.1) when compared to the specimens in normal conditions. The opposite occurs for the specimens loaded with stress ratio of R=-1, in which the delamination mechanisms changed during the loading reversion from tension to compression that promoted early delamination. Therefore, this process reduced the fatigue life of the specimens under hygrothermal condition. Then, by fractographic investigation, it was verified fracture patterns that regard to mode II damage in R=-1, in which mode II fracture toughness is known to decrease in the presence of water molecules.
机译：航空结构通常在围绕服务时从周围环境的高水平吸湿水分下操作。在这种条件下，提交给循环或静载荷的层压复合材料的行为可以大幅变化。为了理解缝合织物中的那些效果，用r = -1和r = 0.1的应力比进行疲劳试验。样品疲劳测试，如提供（环境条件）和暴露于湿热的风化条件后。基于开放文献中最近的研究的证据，例如，水分扩散对环氧基质的影响，总结果表明样品暴露于湿热效应后刚度显着降低。在这种情况下，基质刚度的降低增强了与正常条件下试样相比的张力张力载荷（r = 0.1）中的疲劳强度。对于r = -1的应力比，该样品的发生相反，其中分层机构在加载升压到促进早期分层的压缩期间发生变化。因此，该过程降低了湿热条件下试样的疲劳寿命。然后，通过法式调查，验证了在r = -1中的模式II损伤的验证骨折模式，其中已知模式II断裂韧性在水分子存在下降低。

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