Research On Cumulative Damage And Life Prediction Of Aviation Aluminum Alloy Under Corrosion/Fatigue

Aviation aluminum alloy is widely used in aircraft structures due to its excellent metal mechanical properties.However,due to the influence of the working environment,corrosion fatigue damage and structural failure of aircraft metal structures inevitably occur during the period of service.In order to ensure the safety of man and machine and the normal operation of aircraft,it is of great significance to understand the damage evolution of aluminum alloy materials in corrosive environments,the degradation law of mechanical properties under the action of corrosion fatigue,and the prediction of remaining fatigue life.The research and analysis of pre-corrosion fatigue experiment of aluminum alloy were carried out to study the relationship between the remaining fatigue life of aluminum alloy and corrosion time.Taking into account the interaction of electrochemistry and fatigue in the corrosion fatigue process of aluminum alloy,the pre-corrosion fatigue damage model is revised.Based on the pre-corrosion fatigue life data of aluminum alloy specimens,the relationship between corrosion damage and remaining fatigue life was determined,and the nonlinear corrosion fatigue coupling damage index under different corrosion times was calculated,and the coupling relationship between corrosion damage and fatigue damage was clarified..In order to fit the alternate damage mode of "ground corrosion and air fatigue" experienced by the aircraft during actual service,this paper carried out an alternate corrosion/fatigue experiment.The controlled variable method was used to study the remaining fatigue life of materials under different "alternative action sequences"(corrosion first and then fatigue or first fatigue and then corrosion),different number of load cycles and different corrosion time.The experiment found that the corrosion time is the same,but the fatigue life of the pre-corrosion test specimen is lower than that of the alternate test.Co MPared with the corrosion time and fatigue life of the "corrosion before fatigue" experiment,the corrosion time of the "corrosion before fatigue" experiment is shorter and the fatigue life is longer.For the same corrosion time(load cycle number),with the increase of the load cycle number(corrosion time),the fatigue life of the "corrosion first and fatigue" experimental material shows a trend of first reduction and then stability.A model of damage accumulation and life prediction under alternate corrosion/fatigue effects is established.Based on the nonlinear corrosion-fatigue coupling damage index,it is proposed to use the corrosion-fatigue coupling damage index and hysteresis load to describe the alternate corrosion fatigue damage mode under the same level of loading conditions considering the influence of each level of load.The "corrosion+fatigue" alternate damage mode is divided into two parts: "pre-corrosion coupling damage" and "fatigue+corrosion+fatigue..." alternate modes of damage.Considering the corrosionloading fatigue coupling index and hysteresis load to the traditional Miner linear accumulation The damage theory is revised.Establish the life calculation model of structural materials and conduct case analysis.The corrosion coupling damage in the experiment is determined,and a uniformly distributed hysteretic load is obtained by using the theory of low-load exercise effect.Through the case verification model,the results of the life calculation model proposed in this paper are more consistent with the experimental results,which are of great significance to the prediction of the remaining life of aircraft structural materials.