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研究SiC纤维增强钛基复合材料(SiCf/Ti-6Al-4V)室温疲劳行为和损伤演化机制。疲劳试验条件:载荷控制、应力比0.1和加载频率10 Hz。采用疲劳断裂试验建立最大加载应力为600~1200 MPa内SiCf/Ti-6Al-4V的S-N曲线。采用疲劳中止试验以及SEM显微分析研究应力水平对SiCf/Ti-6Al-4V疲劳损伤演化的影响。结果表明,SiCf/Ti-6Al-4V疲劳损伤萌生模式与演化过程与应力水平密切相关。在高应力水平(Smax=1000 MPa),纤维开裂是主要损伤萌生模式。一旦2或3根纤维断裂后,纤维裂纹和基体裂纹开始联接并形成宏观扩展裂纹。在中等应力水平(Smax=800 MPa),基体裂纹萌生与扩展是主要损伤模式。多条基体裂纹萌生于试样外表面棱边和离外表面附近试样内部开裂的纤维基体界面处。基体裂纹均沿垂直于加载方向扩展,且大部分纤维未断裂并纤维桥接基体裂纹。在低应力水平(Smax=600 MPa),仅在C涂层和界面反应层之间和C涂层内部观察到局部界面脱粘现象。
Study on the fatigue behavior and damage evolution mechanism of SiC fiber reinforced titanium matrix composites (SiCf / Ti-6Al-4V) at room temperature. Fatigue test conditions: load control, stress ratio 0.1 and loading frequency 10 Hz. The S-N curve of SiCf / Ti-6Al-4V with the maximum loading stress of 600 ~ 1200 MPa was established by fatigue fracture test. The effect of stress level on the fatigue failure evolution of SiCf / Ti-6Al-4V was studied by fatigue test and SEM micrograph. The results show that the mode of fatigue damage initiation is closely related to the evolution and stress level of SiCf / Ti-6Al-4V. At high stress levels (Smax = 1000 MPa), fiber cracking is the major lesion initiation mode. Once two or three fibers rupture, the fiber crack and matrix crack begin to join and form macroscopic spreading cracks. At medium stress level (Smax = 800 MPa), matrix crack initiation and propagation are the main modes of damage. Multiple substrate cracks originate at the interface between the outer edge of the sample and the fiber substrate where the inner portion of the sample near the outer surface is cracked. The cracks in the matrix all extend perpendicular to the loading direction, and most of the fibers are not broken and fiber bridges the matrix cracks. At low stress levels (Smax = 600 MPa), localized interfacial debonding was observed only between the C-coating and interfacial reaction layers and inside the C-coating.