Cylindrical Shells with Tunable Postbuckling Features Through Non-Uniform Patterned Thickening Patches

The research reported herein follows the increased interest in buckling-induced functionality for novel materials and devices with a focus on cylindrical shells as a suitable structural prototype. The paper proposes the concept of using patterned thickening patches on the surface of cylindrical shells to modify and control their elastic postbuckling response. Cylindrical shells with non-uniform thickness distributions (NTD) were fabricated through 3D printing to understand rules for pattern designs and then tested under loading-unloading cycles. Strategic thickening patches act as governing imperfections that modify the response type, the number, the location and the sequence of the localized buckling events. The use of patterned thickening patches and their layout provides diverse design opportunities for a desired elastic postbuckling response and can be potentially used in design materials and structures with switchable functionalities.

Selective buckling via states of self-stress in topological metamaterials

States of self-stress—tensions and compressions of structural elements that result in zero net forces—play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices.