Fatigue Reliability Analysis Of Fir-tree Tenon Structure Based On Cumulative Damage Theory

As the power part of aircrafts,aero engines have shown a significant impact on the aircraft safety.Harsh working environment causes aero engine components to bear complex loadings.Structural integrity of hot section components are critical for ensuring the overall performance of aero engines.As the main connecting form of turbine disc/blade component,the fir-tree tenon structure is subjected to airflow vibration,high temperature,high pressure and complex cyclic loading,while failures frequently occur in the aero engine.In order to ensure the safety of turbine disc/blade component,the structural strength assessment and fatigue reliability analysis of fir-tree tenon structure are lacking and desired.Thus,researches on fatigue failure of the fir-tree tenon structure have been conducted in this thesis as below:1)Nonlinear cumulative damage model considering the influence of static toughness exhaustion.Failure has frequently occurred due to the accumulation of damage under cyclic loadings in fir-tree tenon structure.According to this,based on isodamage line theory,a cumulative damage model considering the effect of static toughness exhuastion is proposed by analyzing the damage evolution process of materials.Experimental data of five materials under two-stage loading are used for model validation and comparsion,results show that the proposed model provides better predictions than the other four models.2)Contact stress analysis of the fir-tree tenon structure under uncertainty.Hot section components like fir-tree tenon structure are influenced by multi-source uncertainties in service,which shows a significant impact on the structural strength of hot section components.Considering the fretting fatigue issue of fir-tree tenon structure,a fir-tree tenon structure model is established.Monte-Carlo simulation is introduced to quantify load variation by combining finite element(FE)analysis with numerical simulations.Then,FE analysis of fir-tree tenon structure under load variations is performed to obtain the relation between loading and contact stress,which provides the foundation for further fretting fatigue analysis.3)Fatigue reliability analysis of fir-tree tenon structure based on cumulative damage theory.By analyzing the variational characteristics of material property and loading,the stochastic FE analysis of fir-tree tenon structure is carried out.The stress-strain response at the dangerous point of the fir-tree tenon structure are extracted.Note from FEA results,probabilistic fatigue life of the fir-tree tenon structure is calculated using multiaxial fatigue model.The cumulative damage model considering influence of static toughness exhaustion is utilized for reliability analysis of fir-tree tenon structure,which combines reliability analysis method based on damage-life interference.