Research On Fatigue Properties Of SiC_f/Ti Composite Under Two-stage Loading

Aero-engine is a pillar of the nation.To achieve breakthroughs in this field is of great significance for promoting the development of national economy and enhancing the core competitiveness of our country.According to the complicated working conditions of metal matrix composites in the actual load-bearing process.In order to lay a foundation for the wide application of metal matrix composites in aero-engines,so this paper focuses on the fatigue properties of metal matrix composites under two-stage cyclic loading.In this paper,a typical SiC_f/Ti composite material was used as the research carrier.Experiments of metal matrix composites under two-stage cyclic loading have been conducted,which aiming at high cyclic stress-low cyclic stress and low cyclic stress-high cyclic stress.The evolution law of fatigue hysteresis loop and the damage forms of the composites during loading were analyzed.Then,the fracture surface and internal damage of the composites were observed by optical microscope and XCT tomography combined coordinate measuring system.On this basis,the fatigue failure mechanism of SiC_f/Ti composite under two-stage loading was analyzed and predicted.Based on the analysis of fatigue properties,a mesoscopic mechanic model of metal matrix composites under two-stage cyclic load was developed.It is found that the main damage form of metal matrix composites under two-stage cyclic load are interfacial debonding,fiber fracture and matrix cracking.fatigue hysteresis behavior is that the fibers slip forward and backward relative to the matrix during loading and unloading.The interfacial shear stress degradation criterion and fiber failure criterion have been considered,and the fatigue hysteresis loop of SiC_f/Ti fiber reinforced composites under two-stage variable amplitude load based on the law of interface friction and slip has been investigated.The effects of fiber volume fraction,loading sequence and fiber shape parameters on the fatigue hysteresis loop of SiC_f/Ti based composites under variable amplitude load were analyzed.The simulation results is consistent with the experiment results.At last,the effect of the different loading sequence on fatigue life of metal matrix composites under two-stage cyclic load was analyzed.Several common fatigue damage accumulation rules are introduced.Based on the non-linear damage accumulation rule,the damage variation of composites is defined.The results show that the life under high cyclic stress-low cyclic stress is longer than that under low cyclic stress-high cyclic stress.