Two Dynamic Loading Conditions On The Shear Zone Of 7075 Aluminum Alloy, The Impact Of Self-organization And Injury

The present work was financially supported by the National Nature Science Foundation of China (Project No. 50671121). The major work was listed as follows.The evolution of multiple shear bands in aluminium alloy 7075 was investigated through the radial collapse of thick-walled cylinder at two different strain rates. The fracture of cylinder was basically dominated by the shear fracture induced by the adiabatic shear bands (ASBs) under external explosive loading. ASBs initiated at the inner surface of the aluminium alloy cylinder, and most of those were in spiral form along the cross-section of the cylinder towards counterclockwise direction. Tip of a shear band propagated along the direction of the maximum shear stress at an angle about 45 or 135 degrees with the radial. The special patterns of ASBs such as shielding, bifurcation, crossing and annihilation were observed. ASBs were the preferred sites for nucleation, growth and coalescence of microcracks. The coalescence of microcracks formed the crack within ASBs, and when the critical crack length was reached catastrophic fracture occured.The quantity and distribution of ASBs on the cross-sections at different radial strains were quantified investigated. The results indicated that the spacing, trace and length of ASBs were characterized as self-organized. The spacings of ASBs at two strain rates were close in early stage, while the evolutions were rather different. The experimental shear-band spacings were compared with existing theoretical predictions: the one-dimensional model under periodic perturbation couldn't predict the experimental results well, and could be only used for prediction when ASBs initiated uniformly; The GK model shows a relative good agreement with the behavior at the developed stage of shear bands; The Xue-Meyers model, a two-dimensional model, could predict the initiatory spacing well and explain the evolution of shear bands at two different strain rates. But it can't be used for prediction before experiment.For the first time the self-organization of multiple shear bands during the deformation process was numerically simulated. The nucleation and evolution of ASBs were analyzed in uniform model. The simulative model was validated for the periodic spacing under perturbation in good agreement with the one dimension model. In other case, an imperfect element was introduced in the model to demonstrate that the ASB with preferential initiation can limit the initiation and propagation of ASBs around it.