Abstract
We revisit the classic problem of buckling of thin spherical shells under uniform external pressure and explore the effect thatgeometric imperfections can have on their buckling behavior. Since the 1960s, numerous theoretical and computational studieshave addressed the imperfection sensitivity of buckling of thin elastic shells. However, there is a lack of precise experiments to corroborate these predictions, especially for spherical shells, which is the central topic of this talk. First, we develop a novel fabricationtechnique to produce thin hemispherical elastic shells by the coating of spherical molds with a polymer solution. Upon curing the thin liquid film yields the elastic structure of nearly constant thickness. Secondly, we study the buckling of spherical shells that contain a precisely engineered geometric imperfection. Wesystematically vary the amplitude and width of the defect, and then we present a quantitative relationship between the critical buckling pressure and the defect geometry. Our results can be predicted by both the finite element method and numerical simulations of a reduced shell theory model. Finally, we fabricate hemispherical bilayer shells containing a defect by coating two different polymer solutions, layer by layer, onto the hemispherical molds. We find that the bilayer shell can self-repair or self-aggravatethe geometric imperfections due to residual swelling. Hence, thecritical buckling pressure can be increased or decreased depending on the order of coating of each polymer layer. Ourfabrication technique and experimental results open exciting new avenues in the study of the buckling of spherical shells, and we hope that it will instigate a resurgence of interest in this classic but
important field of mechanics.
Bio
Dr. Lee is an assistant professor of Mechanical Engineering at Pohang University of Science and Technology (POSTECH). Her research focuses on understanding the mechanics of thin structures accompanying large deformations and exploiting the functional mechanism that mechanical instabilities possess. She received her BS and MS both in Mechanical and Aerospace Engineering from Seoul National University in 2011 and 2013, respectively, and her Ph.D. in Mechanical Engineering from MIT in 2018. She then moved as a Post-Doc to École Polytechnique Fédérale de Lausanne (EPFL, 2018).She has been newly appointed at POSTECH since January of this year.
Host: Professor Sam Tawfick
