| Summary: | Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. === Cataloged from PDF version of thesis. === Includes bibliographical references (pages 37-39). === Aluminum 1235-H18 foils with sub-micron grain dimensions are often used as current collectors in Li-ion batteries. Due to their contribution to the structural integrity of batteries under impact loading, their plastic and fracture response is investigated in detail. Using a novel micro-tensile testing device with a piezoelectric actuator, dogbone specimens with a 1.25 mm wide and 5.7 mm long gage section are tested for three different in-plane material orientations and for strain rates ranging from 10-5/s to 10-2/s. It was found that the stress at a proof strain of 2% increased by about 25% from 160MPa to 200MPa within this range of strain rates. Furthermore, pronounced inplane anisotropy is observed as reflected by Lankford ratios variations from 0.2 to 1.5 .A material model is proposed which borrows elements of the anisotropic Yld2000-2d plasticity model and integrates these into a basic viscoplasticity framework that assumes the multiplicative decomposition of the equivalent stress into a strain and strain rate dependent contributions. The an isotropic fracture response is characterized for a strain rate of 10-3 /s using notched tension and Hasek punch experiments. It is found that a simple stress state independent version of the anisotropic MMC fracture initiation model provides a reasonable approximation of the observed experimental results. === by Colin Bonatti. === S.M.
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