RESEARCH ON HIGH-LOW CYCLE COMPLEX FATIGUE AND ACCUMULATIVE DAMAGE FOR Ti-ALLOY TC11

The high low cycle complex fatigue behaviours of Ti alloy TC11 were researched systematically at room and elevated temperatures.At the same time,the effects of complex stress ratio m ,test temperature and prestress overload for SEN specimen on complex fatigue life N fL were taken into consideration.The work comes to the conclusion that:The complex fatigue life decreases obviously with m increased,especially when m =35%,the N_fl decreases more than 10 times,and there occurs a knee on the m —log N_fL curve near m =10%.The complex fatigue of the alloy TC11 is very sensitive to test temperature under the same m ratio and LCF stress,as test temperature rises from room temperature to 150℃,the complex fatigue life N_fL drops by 66% under m =10% and σ max =945MPa.If the temperature comes up continuously to 300℃,its fatigue life approaches to zero.In addition,a model of the accumulative damage for complex cyclic fatigue is formulated as follows: 1/N_fL =1/N L+n/N_f .