考虑应力松弛的单晶涡轮叶片蠕变疲劳寿命预测

建立了民用航空发动机单晶涡轮叶片考虑应力松弛的蠕变疲劳寿命预测方法,该方法在热弹性蠕变有限元计算基础上,综合单轴等应变松弛模型及多轴应力修正因子预测全寿命周期内的应力松弛历程,应力下限取为一次应力.利用综合时间硬化隐式蠕变方程描述蠕变变形,结合损伤雨流计数法及Morrow方程计算疲劳损伤,基于Robinson法则的分段损伤线性累积方法计算全寿命周期内的蠕变损伤,总损伤达到临界损伤时获得蠕变疲劳寿命.通过对公开的单晶材料蠕变疲劳数据的分析,临界损伤定为0.5.结果显示,考虑应力松弛的蠕变疲劳寿命是不考虑应力松弛的45.6倍.为保证可靠性而兼顾经济性,叶片寿命预测时,可先有限元循环加载n个循环,再利用所提出的方法预测2n个循环内的应力松弛历程. 

Creep-fatigue life prediction of single crystal turbine blade with the influence of stress relaxation

The creep-fatigue life prediction method for the single crystal turbine blade of commercial aircraft engine with the influence of stress relaxation was established. Based on the thermal-elastic-creep finite element method analysis, the uniaxial iso-strain relaxation model with the multiaxiality adjustment factor was used to simulate the stress relaxation history in whole life. The stress-low-limit was set to the primary stress. The creep strain was modeled with the combined time hardening implicit creep equation. The fatigue damage was calculated by using damage-based rainflow counting algorithms and Morrow equation. The time-divided linear damage cumulative hypothesis based on Robinson rule was used to calculate the creep damage in whole life. The creep-fatigue life was predicted when the total damage reached the critical damage, which was set to 0.5 based on the creep-fatigue data of the single crystal material. Finally the creep-fatigue life calculated considering the stress relaxation is 45.6 times of the life without the stress relaxation. To predict the blade life with both the reliability and economy, the finite element method analysis could be performed in n cycles and then the stress history in 2n cycles could be predicted by using the method established hereto.