On the dynamics of localization and fragmentation-IV. Expansion of Al 6061-O tubes
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In this series of papers, we investigate the mechanics and physics of localization and fragmentation in ductile materials. The behavior of ductile metals at strain rates of about 4,000–15,000 per second is considered. The expanding ring experiment is used as the vehicle for examining the material behavior in this range of strain rates. In Parts I–III, we examined the response of rings with cross-sectional aspect ratios in the range of 1–10, exhibiting a transition from diffuse necking to sheet-mode localization. In the present paper we report on experimental observations of high strain-rate expansion of Al 6061-O tubes. Through an innovative use of high-speed imaging aided with a conical mirror we determine the sequence of deformation and failure in the expanding tube. In particular, the conical mirror provides information of surface deformation on the tube. Forming limit diagrams at high strain rates are obtained from post-mortem measurement of the deformed tubes or fragments and are compared with analysis from quasi-static analysis. Numerical simulations are used to explain the experimental observations.
KeywordsExpanding tube experiment Ductility Electromagnetic forming
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