A Method of Detecting the Onset of Localized Necking Based on Surface Geometry Measurements
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To more accurately capture the onset of localized necking and obtain necking limit strains, this paper proposes a method of detecting the onset of localized necking in the Marciniak test (i.e. under in-plane deformation). The method is merely based on the measured surface geometry of the test specimen using digital image correlation (DIC) techniques. It was inspired by the observation of a sudden increase of the surface curvature obtained from 2D curvature fits along the direction across the surface of the sheet. This increase of the surface curvature is detected just before the dimples, which form the final localized neck, become obvious in the DIC measurements. The appearance of this signal is explained by a neck expansion theory defined by propagation of the instability along the direction of the neck, which is a physical behavior of materials.
KeywordsLocalized necking Neck expansion Forming limit curve Digital image correlation Marciniak test
Junying Min would like to thank the generous support from Alexander von Humboldt Foundation who awarded him a research fellowship at the Ruhr-University Bochum and the support from General Motors Global Research & Development. Jianping Lin would like to acknowledge the financial support for this research provided through the GM collaborative research.
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