Fatigue Damage Mechanism of Heat-Resistant Composites for Primary Structures of Future High-Speed Civil Transport

未来高速民用运输（HSCT）最重要的技术被认为是具有高韧性的耐热聚合物复合材料，以显著减轻车辆结构的重量。一种有前途的候选复合材料系统是碳纤维/耐热热塑性复合材料，例如IM 600/PIXA-M。PIXA-M树脂属于日本开发的热塑性聚酰亚胺家族。在本研究中，在室温、100℃和200℃下测量了IM 600/PIXA-M的力学性能。在室温和200℃下对该复合材料层合板进行了低周疲劳试验，结果表明，在室温和200℃以下的高温下，纤维方向的杨氏模量几乎不变。纤维方向的拉伸强度在200℃时下降到室温时的60%左右。在200℃下，杨氏模量和横向拉伸强度分别下降到室温的80%和20%，在准各向同性层合板[+30_2/-30_2/90_2]s的拉伸试验中，200℃下的拉伸强度下降到室温的70%左右。自由边缘脱层仅延伸到远离边缘的层压厚度长度，甚至就在试样断裂之前。采用经典层合板理论和失效准则分析了层合板的首次失效后行为。分析结果与室温和200℃下的实验结果吻合较好，在室温和200℃下的低周疲劳试验中，自由边缘分层直到试样断裂前才发生。因此，疲劳寿命取决于自由边缘分层的开始。

The most important technology for future High-Speed Civil Transport (HSCT) is considered to be heat-resistant polymer composites with high toughness for dramatic weight reduction in a vehicle structure. A promising candidate composite system is a carbon fiber/heat-resistant thermoplastic composite, e.g. IM600/PIXA-M.The PIXA-M resin belongs to a thermoplastic polyimide family developed in Japan. In this research, mechanical properties of the IM600/PIXA-M were measured at room temperature, 100℃, and 200℃. Low cycle fatigue tests of laminates made of this composite system were also conducted at room temperature and 200℃.Young's modulus in fiber direction was almost constant at room and elevated temperatures up to 200℃. However, tensile strength in fiber direction at 200℃ decreased to about 60% of one at room temperature. Young's modulus and tensile strength transverse to fiber direction at 200℃ dropped to about 80% and 20% of ones at room temperature, respectively.In tensile tests of a quasi-isotropic laminate [+30_2/-30_2/90_2]s, tensile strength at 200℃ decreased to about 70% of one at room temperature. Free-edge delamination extended only to the laminate-thickness length away from the edge even just before fracture of the specimen. Post-first-failture behavior of the laminates was analyzed using classical lamination theory with failure criterion. The analytical results were in good agreement with the experimental results at room temperature and 200℃.In low cycle fatigue tests of the laminate, the free-edge delamination did not occur until just before fracture of the specimen at room temperature and 200℃ as well. Hence, fatigue life is decided by the onset of the free-edge delamination.