A Computational Design Methodology for Assembly and Actuation of Thin-Film Structures via Patterning of Eigenstrains

Abstract

We develop a computational approach to design 3-D structures that can be fabricated and then assembled and/or actuated by spatially tailoring the layout of multilayer films with eigenstrains. Eigenstrains are stress-free strains when they occur in an unconstrained solid. They are almost an inevitable companion, albeit often unwanted, of thin-film processes. When they vary through the thickness, the constraint of the layers leads to internal stresses and bending and buckling deformations can occur; when they additionally vary in the plane of the film, more complex deformations can result. To advantageously use this phenomenon, we build on relatively simple mechanics ideas in a continuum formulation and combine geometrically nonlinear finite-element analysis of arbitrary-shaped multilayer films with a topology optimization methodology to determine the material layout in each layer so the film deforms into a prescribed shape. We expand our previous experimentally validated approach to include initially curved films and anisotropic eigenstrains. Using an extended system formulation for directly computing instability points allows us to tailor postbuckling response while explicitly controlling the design at limit and bifurcation points. We demonstrate the potential and versatility of our approach by applying it to a series of problems of contemporary and emerging interest.[ 2008-0306]Index Terms-Design methodology, microelectromechanical devices, patterning, thin film.

Active origami by 4D printing

“…We developed a theoretical model to describe the behavior of the printed active composite hinges and used it to design several active origami structures, including a self-assembling box and pyramid and two origami airplanes. While our design parameters here were limited to composite hinges placed at locations where we desired folding, a more flexible approach based on topology optimization with active materials could be used in more general situations (Howard et al 2009, Pajot et al 2006. Finally, we also demonstrated the direct printing of a complex 3D structure that can then be programmed to assume a simpler temporary shape (a flat sheet in our case) and then recover its original 3D shape.…”

Buckling-induced smart applications: recent advances and trends

“…Numerical algorithms that can track the nonlinear structural response following a path that exhibits snap-through behavior have been developed [194][195][196][197][198]. Recent efforts have also showcased the use of topology optimization to find material layouts that lead to larger displacement and energy release from snap-through behavior for different purposes, such as actuators [61,73,83,145,199], energy harvesters [53,56,200], dampers [67], multistable compliant mechanisms [201,202], thermoelectric generators [203], and flutter control [36]. Thus, topology optimization is a promising technique for finding new structural and material layouts to meet a targeted elastic unstable response.…”

Recent Trends in Continuum Modeling of Liquid Crystal Networks: A Mini-Review

“…In this respect, several numerical methods have been presented to address these problems by providing a predictive window for these interesting behaviors. Diverse aspects of LCNs ranging from the effect of different molecular compositions to structural behavior [18] to the programming of bending curvatures induced by changing macroscopic shapes of structures [19,20] have been investigated. Furthermore, multiscale methods where one or two numerical methods are intertwined have also been proposed [21][22][23].…”