高低周复合载荷对钛合金疲劳裂纹扩展性能的影响

摘要

The rotor blade and disk in the fan and compressor of aero-engine is subjected with combined high and low cycle loading.In order to ascertain the effects of the combined cycle situation on the fatigue crack propagation,the combined cycle fatigue（CCF）,and low cycle fatigue（LCF） of TC11 titanium alloy have been carried out respectively.When ΔK（HCF）ΔKth,the combined loading accelerates crack growth.Scanning electron microscope is used to observe fractography.Fatigue fringe of LCF fracture surface is clearer and secondary cracks is deep,the direction and distribution of secondary cracks is messy.CCF fracture surface has the characteristics that obvious secondary cracks and small fatigue fringe are approximately equably distributed.For a given HCF ΔK,ΔKtotal in CCF is greater and crack opening is bigger.During the crack propagation under CCF loading,dimples and cleavage are clearer.%为研究高低周复合载荷对航空发动风扇/压气机叶片和轮盘材料钛合金疲劳裂纹扩展性能的影响,进行了TC11钛合金材料在低周载荷和高低周复合载荷下的裂纹扩展试验及分析。结果表明：在高周应力强度因子幅值大于裂纹扩展的门槛值条件下,叠加在低循环载荷上的振动载荷会引起裂纹的快速扩展。采用扫描电子显微镜（SEM）比较分析了不同类型载荷下的断口宏观和微观形貌特征。分析表明：低周载荷裂纹扩展断口的疲劳条带较明显,二次裂纹深度较大且方向和分布较凌乱;高低周复合疲劳裂纹扩展断口有明显的二次裂纹和疲劳条带混合特征,且二次裂纹深度相对较小且分布较均匀。在高周应力强度因子幅值相同条件下,高低周复合疲劳的总应力强度因子较大（随Rminor的增大而增加）,引起裂纹尖端张开程度较大,裂纹扩展过程中的韧窝、解理特征较明显。