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

研究了不同强度和韧性的基体树脂体系--高温热塑性聚酰亚胺、聚醚醚酮和传统的热固性环氧树脂对单向碳纤维复合材料离轴静强度和疲劳强度的影响。1.离轴静态变形与断裂：T800 H/Epoxy和AS 4/PEEK复合材料在100 ℃下的应力-应变曲线具有明显的非线性，特别是在离轴角reta =10 °-60 °范围内，当reta =0 °和90 °时，应力-应变曲线几乎呈线性直至断裂。尽管聚酰亚胺树脂具有很大的延展性，但所制造的T800 H/聚酰亚胺复合材料在所测试的大多数离轴角（除了rheta=10 °和30 °）下表现出几乎线性的应力-应变曲线，并且在相对低的应力和应变下断裂。在这些复合材料中，AS 4/PEEK在100 ℃下对每个离轴角都表现出最高的韧性和强度。一个显著的不均匀 ...更多信息 T800 H/聚酰亚胺复合材料中的纤维分布抵消了聚酰亚胺树脂的高性能。采用正交各向异性线弹性理论和Tsai-Hill准则分别对碳纤维复合材料的弹性性能和偏轴静态断裂强度进行了描述。2.偏轴疲劳强度：三种UD复合材料在100 ℃下的偏轴疲劳强度均随偏轴角的增大而降低。T800 H/Epoxy和AS 4/PEEK复合材料在100 ℃下的S-N关系具有线性关系，与离轴角无关。对于T800 H/聚酰亚胺，由于在reta =10 μ m的高周疲劳范围内出现了明显的弯曲，因此不能用单一的线性函数来描述所有疲劳强度比的S-N关系。在所有这些复合材料中，AS 4/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。根据疲劳应变范围与疲劳失效循环次数的关系，发现疲劳S-N数据可分为两组，分别与纤维断裂和纤维-基体界面断裂有关。使用Hashin断裂模型描述了T800 H/Epoxy、AS 4/PEEK和T800 H/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