Study And Verification Of Failure Parameters For 6061 H32 Aluminum Alloy

The demand for safety protection of impact and explosion loads is increasing in national defense and civil fields,and metal materials are widely used in protective structures.Safety assessment of protective structures in extreme environments requires a comprehensive study of the mechanical properties of materials.Theory,experiment and numerical calculation are combined to become a comprehensive and effective research method.Reliable numerical calculation depends on the model that can accurately describe the mechanical behavior of materials,and the establishment of the constitutive model and failure model of materials requires comprehensive and accurate experimental data.In this paper,6061H32 aluminum alloy was taken as the research material,and the constitutive model and failure criterion of the material were obtained through relatively complete experiments,and the model of the material was verified by impact experiment and simulation.Firstly,a series of material experiments were carried out in this paper,including quasistatic stretching at different temperatures,quasi-static stretching at different stress states and Hopkinson high strain rate stretching.In the quasi-static experiment,DIC technology was used to measure the strain field and the real failure strain of the material,and the real deformation and failure process of the material was studied.Through the analysis of the experimental results,it is found that the deformation ability of the material is underestimated either by using the engineering strain or by using the theory to convert the real strain from the engineering strain.However,the accurate obtaining of the strain and real failure strain in the necking region of the specimen by DIC is beneficial to the accurate establishment of the constitutive model and failure criterion of the material.The J-C constitutive model and the J-C failure criteria parameters are fitted on the basis of relatively complete experiments,and the fitting curves of J-C model obtained are consistent with the experimental data,which indicates that the model can accurately describe the mechanical behavior of materials at different temperatures and strain rates.It lays a foundation for the numerical simulation of missile impact in the next step.Secondly through penetration experiment research,studied the response of single-layer aluminum alloy target plate impacted by bullet with a hemispheric warhead,the main working conditions are vertical impact of different thickness of single-layer target and oblique impact of equal thickness of single-layer target,using high-speed camera shot the target plate back bullets in the process of target,measured the initial velocity and residual velocity of the bullet,and after the experiment measuring the deformation of the central region of the target plate parameters,geometric parameters and quality of the plug body.The parameters of the residual velocity prediction formula and the ballistic limit of the target plate are obtained by fitting the experimental data.The experimental results show that the failure morphology of the target plate with different thickness is different.The experimental study provides reference data for numerical simulation.Finally,the numerical simulation of the vertical impact and oblique impact on a singlelayer aluminum alloy target by the bullet with hemispherical head is carried out by using the established aluminum alloy constitutive model and failure criterion.The numerical simulation results of residual velocity,ballistic limit and the perforating process of the projectile are in good agreement with the experimental results.The numerical simulation successfully predicted the failure morphology of the target plate with different thickness by the direct impact of bullets.The 1.5mm target showed obvious "petal-like cracking",while the 4mm target did not show petal-like perforation.In addition,the numerical simulation of oblique impact successfully predicted the failure morphology of the target and the trajectory of the bullet.The applicability and reliability of J-C constitutive and failure model parameters of 6061 H32 aluminum alloy obtained through a series of experimental studies in this paper are verified.The results show that the J-C failure model obtained by this method can accurately predict the failure of the target plate.