Off-axis fatigue strengths for high-temperature composites and effects of resin ductility

研究了不同强度和延性的基体树脂体系——高温热塑性聚酰亚胺和PEEK以及常规热固性环氧树脂对单向碳纤维复合材料离轴静态强度和疲劳强度的影响。所得结果可总结如下：1。离轴静态变形与断裂：T800H/环氧树脂和AS4/ peek复合材料在100ºC时的应力-应变曲线存在明显的非线性，尤其是离轴角rhea =10ºC -60ºC时。Forrheta=0和90，它们在最终骨折之前几乎是线性的。制备的T800H/聚酰亚胺复合材料具有良好的延展性，除rheta=10 30外，在离轴角测试中，T800H/聚酰亚胺复合材料的应力应变曲线基本为线性，且在较低的应力应变下断裂。在每一个离轴角下，AS4/PEEK具有最高的韧性和强度。在制造的T800H/聚酰亚胺复合材料中，纤维分布明显不均匀，影响了聚酰亚胺树脂的高性能。分别用正交各向异性线弹性理论和Tsai-Hill准则描述了碳纤维复合材料的弹性性能和离轴静态断裂强度。离轴疲劳强度：3种UD复合材料的离轴疲劳强度随离轴角的增大而降低。与离轴角无关，T800H/环氧树脂和AS4/PEEK复合材料的S-N在100℃时均呈线性关系。然而，对于T800H/聚酰亚胺，S-N关系不能用一个单一的线性函数来描述所有疲劳强度比，因为在高周疲劳范围内出现了显著的弯曲。在所有复合材料中，AS4/PEEK在包括高周疲劳在内的整个范围内表现出最高的离轴疲劳强度。考虑疲劳应变范围与疲劳破坏循环次数的关系，发现S-N数据分为两组，分别与纤维断裂和纤维-基体界面断裂相关。使用Hashin断裂模型描述了T800H/环氧树脂、AS4/PEEK和T800H/聚酰亚胺复合材料的离轴疲劳强度。少

The influence of matrix resin systems with different strength and ductility-high-temperature thermoplastic polyimide and PEEK and a conventional thermosetting epoxy-on the off-axis static and fatigue strengths of unidirectional carbon fiber composites has been studied. The results obtained may be summarized as follows :1.Off-Axis Static Deformation and Fracture :The stress-strain curves at 100ﾟC for the T800H/Epoxy and AS4/PEEKcomposites were accompanied by a significant non-linearity, especially for the off-axis angles rheta=10ﾟ-60ﾟ.Forrheta=0ﾟ and 90ﾟ,they were almost linear up to final fracture. In spite of the great ductility of the polyimide resin, the manufactured T800H/Polyimide composite exhibited almost linear stress-strain curves for most off-axis angles tested except for rheta=10ﾟ and 30ﾟ,and it fractured at relatively low stress and strain. Among these composites, AS4/PEEK showd the highest toughness and strength at 100ﾟC for every off-axis angle. A significant non-uniform … More fiber distribution in the as-manufactured T800H/Polyimide composite canceled the high performance of the polyimide resin. The elastic properties and offaxis static fracture strengths for these carbon fiber composites were appropriately described using the orthotropic linear elastic theory and Tsai-Hill criterion, respectively.2.Off-Axis Fatigue Strength :For three kinds of UD composites, the off-axis fatigue strengths at 100ﾟC decreased as the off-axial angles increased. The S-N relations at 100ﾟC for the T800H/Epoxy and AS4/PEEK composites had linear relationships, irrespective of the off-axis angles. For T800H/Polyimide, however, the S-N relation could not be described using a single linear function for all fatigue strength ratios due to a significant bent appeared in the high cycle fatigue range for rheta=10ﾟ.Among all these composites, AS4/PEEK showed the highest off-axis fatigue strength for the whole range including high cycle fatigue. By taking the relationships between the fatigue strain range and the number of cycle to fatigue failure, it was found that the S-N data were separated into two groups associated with the fractures of fibers and fiber-matrix interfaces, respectively. The off-axis fatigue strengths for the T800H/Epoxy, AS4/PEEK,and T800H/polyimide composites were described using the Hashin's fracture model. Less