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Experimental and numerical investigation on plasticity and fracture behaviors of aluminum alloy 6061-T6 extrusions

Zhu Peihua, Zhang Qilin, Xu Hongjun, Ouyang Yuanwen

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 3

13--30

Aluminum alloy 6061-T6 (AA 6061-T6) extrusions have been widely applied in large-span reticulated shells. However, researches on behaviors of the aluminum alloy under large deformation and fracture by means of meso-mechanics are still insufficient. This paper focuses on the plastic and fracture behaviors of AA 6061-T6 extrusions over a wide range of stress states. Experiments on smooth and notched round bars, grooved plates and shear plates are conducted. It is observed that the yield stress decreases as the notch or groove radius decreases. The yield stress under plane strain or pure shear is lower than that under axisymmetric tension. In addition, true stress–true strain data obtained from tensile coupon tests overestimate the hardening behavior at large deformation. To fully describe these experimental observations, a new plastic model considering the pressure dependence, Lode angle effect, and hardening with post-necking correction is proposed. Regarding the ductile fracture, modified Mohr–Coulomb fracture model with damage-induced softening is adopted to predict crack initiation and propagation under different stress states. The material models of plasticity and fracture are numerically implemented into FE code ABAQUS/explicit by the material subroutine VUMAT. It is found that both the overall nominal stress–strain curves and fracture patterns for all specimens are well predicted by the material models. For practical engineering design, recommended reduced values of shear strength and high-triaxiality tensile strength of AA 6061-T6 extrusions are given.

Effect of Distilled Water and Kerosene as Dielectrics on Machining Rate and Surface Morphology of Al-6061 During Electricdischarge Machining

Arshad Rubab, Mehmood Shahid, Shah Masood, Imran Muhammad, Qayyum Faisal

Advances in Science and Technology. Research Journal

2019

Vol. 13, no 3

162--169

Electric Discharge Machining (EDM) is widely used for manufacturing complex metal parts. The machining parameters like dielectric fluid, electrode material, current, voltage and pulse rate during EDM are controlled to obtain desired Material Removal Rate (MRR) and it also affects the surface morphology of manufactured components. In this research, effect of changing machining parameters, dielectric fluid (distilled water and kerosene) and electrode materials (copper and graphite) on surface morphology of Al 6061 T6 alloy during EDM is investigated. It is observed that the distilled water reacts with the molten aluminum and produces deep pits / voids on the surface due to liberation of hydrogen gas. A micro crack network is seen radiating from the edge of these pits. It is believed that the very high thermal conductivity of distilled water is responsible for the micro crack network and reduced material removal rate when compared with non-reactive kerosene oil.