Dynamic Fracture Toughness Measurement And Characterization Of 2024-T3 Aluminum Alloy Under Electromagnetic Environment

2024-T3 aluminum alloy has been used widely in the fuselage wings,shear ribs and webs et al.,due to its high strength and fatigue fracture toughness.The current researches about 2024-T3 aluminum mainly focus on the composition,heat treatment and creep aging process,the systematic research about its fracture toughness under impact loading is lacking.Research of dynamic fracture toughness of 2024-T3 aluminum alloy is crucial and meaningful for evaluating the safety of the material structure and the failure analysis under dynamic loading.The reported literature mainly measuring the dynamic fracture toughness by introducing the resistance strain gauge method.However,the position of the strain gauge is strict and the strain signal is easy to be disturbed by uncertain factors,which results in inaccuracy of the measurement.In order to solve this problem,the strain strain gauge method was improved to firstly.Different from the direct connected between lead wire of the strain gauge with terminal,the lead wire of the resistance strain gauge is insulated in this work,and the lead wire is connected with the terminal in a twisted pair way.And then the sample with strain gauge was put in the magnetic field,detecting the factors that affect the strength of electromagnetic interference signal.On the basis of above research,a electromagnetic shielding device was constructed,which can reduce or even eliminate the electromagnetic interference,in this case,we successfully measured the dynamic strain of 2024-T3aluminum al oy under the electromagnetic environment.Secondly,the dynamic strain signals under three-point bend loading,pendulum impact loading and Hopkinson pressure bar were successfully recorded by using this equipment.According to Dally and Berger,the stress intensity factor can also be measured by strain signal,and the dynamic fracture toughness of the 2024-T3 aluminum alloy under different loading conditions was calculated.The results showed that the dynamic fracture toughness of the 2024-T3 al uminum alloy remains unchanged(35MPam^1/2)at low loading rate(less than 10³MPam^1/2s^-1).While when the loading rate reaches to 10⁵MPam^1/2s^-1,the dynamic fracture toughness increases dramatically to 101MPam^1/2.The fracture analysis exhibited that the fracture morphology is microporous aggregation at low loading rate(less than 10³MPam^1/2s^-1).While the fracture feature changes from ductile dimple to quasi-cleavage morphological when the loading rate exceeds 10⁵MPam^1/2s^-1.Theoretical analysis revealed that the size of dislocation area around crack tip decreases with increasing loading rate,in this case the dislocation of the crack tip stress field shielding effect becomes large,resulting in the transition from dimple state to the quasi-cleavage state after crack initiation.Finally,the constitutive model of 2024-T3 aluminum alloy under dynamic loading by using Hopkinson pressure bar at room temperature was constructed according to Johnson-Cook model.At the same time,the finite element simulation was carried out by ANSYS to analyze the fracture process under various loading rates.The simulated results are consistent with the established Johnson-Cook model,demonstrating that the model is reasonable and feasible.The present results will provide strong experimental and theoretical support for the application and development of 2024-T3 aluminum alloy.