Study On Mechanical Properties And Failure Mechanism Of 2024-T3 Aluminum Alloy Sheet Under Complex Damage Conditions

During the service of aircraft,structural damage has a significant effect on its service performance and life.Common structural damages include multi-site damage,foreign object damage and environmental corrosion.Severe damage conditions can reduce the tensile,fatigue and corrosion resistance of the material,resulting in decreasing of service life.In this paper,the mechanical properties of 2024-T3 aluminum alloy used in aerospace and its failure mechanism are studied for different damage conditions.It is a great significance to evaluate the damage resistance of aluminum alloy objectively,prolong the service life of aircraft and develop high-performance aluminum alloy.For multi-site damage,it mainly focuses on the staggered rivet hole arrangement and the multi-site damage phenomenon in the aged aircraft,and investigates the changes of the mechanical properties of the aircraft after the occurrence of multi-site damage.The pre-cracking method is used to simulate the multi-site damage structure.Based on the combination of experimental test,numerical calculation and finite element analysis,the fatigue life is obtained from the three aspects of rivet hole row spacing,column spacing and hole edge crack direction,and analysed by digital image correlation.The result indicates that the residual strength and fatigue life of the specimens in the range specified by the aircraft design manual increase with the increase of the row spacing and the column spacing,in addition,the numerical results agree well with the experimental data.For foreign object damage,the effects of different impact energys,insert sizes and insert shapes on the fatigue life of aluminum alloy sheets were studied.The strain field distribution of structure containing dent damage under fatigue loading and the initiation of fatigue cracks are analyzed by digital image correlation.A simplified model is proposed based on the nonlinear fatigue damage model to evaluate the fatigue life of impacted specimen.ABAQUS/Explicit and Fe-safe is combined to predict fatigue life.From the result,the fatigue life of the specimen after impact is significantly reduced with the increase of dent depth.Both the simplified model and the finite element simulation have good prediction results.For environmental corrosion damage,the in-situ corrosion-fatigue properties of aluminum alloys in different corrosive media environments and different concentrations were studied.Corrosion fatigue tests of in-situ salt spray and salt solution were carried out by self-designing in-situ corrosion device and in-situ corrosion fatigue test platforms.The results show that for in-situ salt spray fatigue test,with a low concentration range of 2% to 3.5%,the hydrogen embrittlement caused by salt spray dominates,and the in-situ corrosion-fatigue life decreases;furthermore,in the relative high concentration range of 3.5% to 5%,the crack tip closure caused by salt particles and corrosion product dominates,which delays crack propagation behavior and increases fatigue life;the low-cycle fatigue life of the specimens in the salt solution is not sensitive to variations of concentration.