Sergio Pellegrino

Bio: Sergio Pellegrino is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Finite element method & Deployable structure. The author has an hindex of 47, co-authored 348 publications receiving 8870 citations. Previous affiliations of Sergio Pellegrino include University of Cambridge.

Review of Form-Finding Methods for Tensegrity Structures

Abstract: Seven form-finding methods for tensegrity structures are reviewed and classified. The three kinematical methods include an analytical approach, a non-linear optimisation, and a pseudo-dynamic iteration. The four statical methods include an analytical method, the formulation of linear equations of equilibrium in terms of force densities, an energy minimisation, and a search for the equilibrium configurations of the struts of the structure connected by cables whose lengths are to be determined, using a reduced set of equilibrium equations. It is concluded that the kinematical methods are best suited to obtaining only configuration details of structures that are already essentially known. The force density method is best suited to searching for new configurations, but affords no control over the lengths of the elements of the structure. The reduced coordinates method offers a greater control on elements lengths, but requires more extensive symbolic manipulations.

Deployment dynamics of tape springs

Abstract: Tape springs are straight, thin–walled strips with a curved cross–section. Following recent proposals for large deployable structures exploiting the structural simplicity and robustness of such springs as deployment actuators, the paper investigates the dynamic deployment of a tape spring that is either coiled around a circular hub, or folded into a zig–zag pattern. It is shown that in both cases the spring deforms by forming an elastically deformed region with zero transverse curvature and uniform longitudinal curvature. The process of formation and growth of a fold belongs to a wide class of propagating instabilities. It is characterized by a high peak moment and a lower propagation moment. A compact characterization of the moment–rotation relationship for an elastic fold is presented. A key feature is that the bending moment on either side of a fold moving along a uniform tape spring, away from any end supports, is constant, whereas this moment increases near a support. Compact and accurate two–dimensional theories are developed to simulate the self–actuated deployment of tape springs. It is shown that conservative energy formulations are appropriate for coiled springs, where the velocity field is smooth, but not for springs with localized folds. To simulate the motion of such localized folds a non–conservative impulse–momentum formulation is proposed, and it is found that this model can accurately predict both the steady motion of the folds along the tape spring and their rebound against the end supports.

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Controlled ripple texturing of suspended graphene and ultrathin graphite membranes

Abstract: Graphene is nature's thinnest elastic material and displays exceptional mechanical and electronic properties Ripples are an intrinsic feature of graphene sheets and are expected to strongly influence electronic properties by inducing effective magnetic fields and changing local potentials The ability to control ripple structure in graphene could allow device design based on local strain and selective bandgap engineering Here, we report the first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains We are able to control ripple orientation, wavelength and amplitude by controlling boundary conditions and making use of graphene's negative thermal expansion coefficient (TEC), which we measure to be much larger than that of graphite These results elucidate the ripple formation process, which can be understood in terms of classical thin-film elasticity theory This should lead to an improved understanding of suspended graphene devices, a controlled engineering of thermal stress in large-scale graphene electronics, and a systematic investigation of the effect of ripples on the electronic properties of graphene

The properties of foams and lattices.

Abstract: Man and nature both exploit the remarkable properties of cellular solids, by which we mean foams, meshes and microlattices. To the non-scientist, their image is that of soft, compliant, things: cushions, packaging and padding. To the food scientist they are familiar as bread, cake and desserts of the best kind: meringue, mousse and sponge. To those who study nature they are the structural materials of their subject: wood, coral, cancellous bone. And to the engineer they are of vast importance in building lightweight structures, for energy management, for thermal insulation, filtration and much more. When a solid is converted into a material with a foam-like structure, the single-valued properties of the solid are extended. By properties we mean stiffness, strength, thermal conductivity and diffusivity, electrical resistivity and so forth. And the extension is vast-the properties can be changed by a factor of 1000 or more. Perhaps the most important concept in analysing the mechanical behaviour is that of the distinction between a stretch- and a bending-dominated structure. The first is exceptionally stiff and strong for a given mass; the second is compliant and, although not strong, it absorbs energy well when compressed. This paper summarizes a little of the way in which the mechanical properties of cellular solids are analysed and illustrates the range of properties offered by alternative configurations.

Strong, lightweight, and recoverable three-dimensional ceramic nanolattices

Abstract: Ceramics have some of the highest strength- and stiffness-to-weight ratios of any material but are suboptimal for use as structural materials because of their brittleness and sensitivity to flaws. We demonstrate the creation of structural metamaterials composed of nanoscale ceramics that are simultaneously ultralight, strong, and energy-absorbing and can recover their original shape after compressions in excess of 50% strain. Hollow-tube alumina nanolattices were fabricated using two-photon lithography, atomic layer deposition, and oxygen plasma etching. Structures were made with wall thicknesses of 5 to 60 nanometers and densities of 6.3 to 258 kilograms per cubic meter. Compression experiments revealed that optimizing the wall thickness-to-radius ratio of the tubes can suppress brittle fracture in the constituent solid in favor of elastic shell buckling, resulting in ductile-like deformation and recoverability.