Research On Fatigue Characteristics Of Aircraft Heat Exchanger Under Alternating Load

The working environment of the aviation heat exchangers is much tougher than heat exchangers work on the ground.In the service of aviation heat exchangers,the thermal fatigue and mechanical fatigue of them have an important impact on the degradation of heat exchanger equipment.After the formation of the relevant fatigue mechanism,during the operation of the heat exchanger,the equipment will grow cracks,structural cracking and lead to leakage.The characteristics of fatigue fracture damage such as stealthiness,burstiness and cumulativity determine that equipment fatigue is not easy to be detected early during operation.In this case,it is of great significance and engineering value to establish an applicable evaluation method and carry out predictive analysis for the fatigue and lifetime of the aviation heat exchanger.The research work is done by combining with theoretical analysis,numerical simulation and experimental research.The main research content of the paper is as follows:(1)Summarize the main degradation modes of heat exchangers and their degradation mechanisms,focusing on the fatigue degradation and mechanism in aviation heat exchangers.It is concluded that fatigue mechanism faced by the aircraft heat exchanger in complex working environment is mainly the thermal fatigue under high temperature and the mechanical fatigue under the pressure alternating;(2)A pressure alternating experiment of various working conditions is designed for the fuelhydraulic oil heat exchanger,and the structural stress response of the product under the designed working condition is obtained.The structural simulation analysis results are in good agreement with the experimental monitoring results.The numerical simulation calculation can obtain the dynamic response characteristics of the heat exchanger structure to the alternating load.(3)Performing a thermodynamic experiment to obtain the principal stress of the air-air secondary radiator focusing structure area.The numerical coupling simulation analysis shows the temperature distribution of the heat exchanger structure,then obtain the thermal stress distribution of the region of interest.The comparison results show that the numerical simulation results of the heat exchanger are in good agreement with the experimental results.The stress load spectrum data obtained on this basis can meet the life prediction accuracy requirements;(4)Based on the nominal stress method,the full-life fatigue analysis of the aviation heat exchanger structure is carried out.The stress results obtained by the finite element analysis are input into nCode Designlife,and the residual life prediction simulation of the aerospace heat exchanger under the complex working environment is obtained.The conclusions provide a basis for predicting the fatigue life of heat exchangers in service in airborne systems.