A general formulation of Bead Models applied to flexible fibers and active filaments at low Reynolds number

This contribution provides a general framework to use Lagrange multipliers for the simulation of low Reynolds number fiber dynamics based on Bead Models (BM). This formalism provides an efficient method to account for kinematic constraints. We illustrate, with several examples, to which extent the proposed formulation offers a flexible and versatile framework for the quantitative modeling of flexible fibers deformation and rotation in shear flow, the dynamics of actuated filaments and the propulsion of active swimmers. Furthermore, a new contact model called Gears Model is proposed and successfully tested. It avoids the use of numerical artifices such as repulsive forces between adjacent beads, a source of numerical difficulties in the temporal integration of previous Bead Models.Comment: 41 pages, 15 figure

Integrated movable micromechanical structures for sensors and actuators

Movable pin-joints, gears, springs, cranks, and slider structures with dimensions measured in micrometers have been fabricated using silicon microfabrication technology. These micromechanical structures, which have important transducer applications, are batch-fabricated with an IC-compatible process. The movable mechanical elements are built on layers that are later removed so that they are freed for translation and rotation. An undercut-and-refill technique, which makes use of the high surface mobility of silicon atoms undergoing chemical vapor deposition, is used to refill undercut regions in order to form restraining flanges. Typical element sizes and masses are measured in micrometers and nanograms. The process provides the tiny structures in an assembled form avoiding the nearly impossible challenge of handling such small elements individually

Reconfigurable Surfaces Employing Linear-Rotational and Bistable-Translational (LRBT) Joints

Reconfigurable surfaces are useful in many applications. This paper proposes a type of reconfigurable surfaces that consist of rigid elements (tiles) connected by novel compliant joints. Depending on the actuation, these novel connecting joints can either operate as torsional hinges, which create isometric transformation (like origami folding) between connected tiles, or bistable translational springs, which accommodate metric-changing transformation between connected tiles. A specific example of a reconfigurable surface with square tile shape that can morph into flat, cylindrical (in two different directions), and spherical configurations with simple actuation is given

Reconfigurable Surfaces Employing Linear-Rotational and Bistable-Translational (LRBT) Joints

Reconfigurable surfaces are useful in many applications. This paper proposes a type of reconfigurable surfaces that consist of rigid elements (tiles) connected by novel compliant joints. Depending on the actuation, these novel connecting joints can either operate as torsional hinges, which create isometric transformation (like origami folding) between connected tiles, or bistable translational springs, which accommodate metric-changing transformation between connected tiles. A specific example of a reconfigurable surface with square tile shape that can morph into flat, cylindrical (in two different directions), and spherical configurations with simple actuation is given

A general formulation of Bead Models applied to flexible fibers and active filaments at low Reynolds number

This contribution provides a general framework to use Lagrange multipliers for the simulation of low Reynolds number fiber dynamics based on Bead Models (BM). This formalism provides an efficient method to account for kinematic constraints. We illustrate, with several examples, to which extent the proposed formulation offers a flexible and versatile framework for the quantitative modeling of flexible fibers deformation and rotation in shear flow, the dynamics of actuated filaments and the propulsion of active swimmers. Furthermore, a new contact model called Gears Model is proposed and successfully tested. It avoids the use of numerical artifices such as repulsive forces between adjacent beads, a source of numerical difficulties in the temporal integration of previous Bead Models

Biaxial test on composite and polymeric materials

The development of the aircraft with the use of composite materials involves the mechanical characterization of these materials that have the suitable properties to be used in the design phases. The characterization of these materials is made in the mono axial field. However, research activities in recent years are focusing the attention on the study of biaxial tests to get more information to use during the design for the best use of materials. My thesis has been mainly focused on the development of a new biaxial equipment about composite and polymeric materials. It will try to show that the equipment is able to correctly load the specimens in two perpendicular directions. Then the selected test setup was applied experimentally for biaxial tests on a general aviation carbon resin. The thesis is divided into four sections. In the first one, the machines and equipment for biaxial tests present in the literature are only presented. Then the forms of biaxial test specimens most used by researchers in the last years for both metallic, composite and polymeric materials have been described. In the second section, the agreement that led to the creation of a new test rig, with which the tests have been described, are in the fourth section. The third part deals with the choice and optimization of a specimen shape through the use of finite element analysis. In the fourth section, the new equipment and the shape of the specimen chosen in the previous section have been used to carry out tests on a composite material in carbon resin. Here, the materials and the methods used to perform the experimental exercise are described. The used material is provided within the Tabasco project promoted by the Campania DAC. This project concerns the technologies and the production processes of low-cost components for general aviation. Conclusive remarks, where the main results are summarized, close this work

A study on the fundamental behaviour of soil-structure interaction and mitigating effects of EPS geofoam inclusions in integral abutment bridges

The traditional construction procedure of bridges involves the use of expansion joints to allow for unrestricted superstructure movements against the temperature induced deformations. However, expansion joints have been demonstrated to be vulnerable to deterioration thus requiring frequent and costly maintenance. In that regard, the Integral Abutment Bridge (IAB) system presents an attractive alternative to overcome such problems. In addition to the advantages achieved by eliminating the expansion joints, the IABs have desirable structural performance and offer simple and rapid construction procedures. In the last few decades, IABs have been increasingly utilised in many countries around the world. Nowadays, the integral and semi-integral abutment bridges are becoming the first choice in the construction of bridges. Nevertheless, the IABs yet have their unique problems that ensue from the regular expansions and contractions (including shrinkage) in the superstructure. These problems have negated some of the advantages of IABs and restricted their use. The complex soil-structure interaction mechanism in IABs has made it difficult for engineers to find the appropriate solution to address the approach issues in this type of bridges. Adopted remedy measures include the use of run-on concrete approach slabs, heavily compacted approach fill, compressible inclusion between the soil and the abutment, and self-stable MSE approach fill with gap separation between the abutment and the MSE fill. However, no single solution can adequately address the broad array of IAB cases, each under a different setting, across the world. The present thesis extends current insights on the soil-structure interaction of IABs, with particular emphasis on the effects on the soil settlement and the lateral pressure at the integral abutment approach. The aim is to provide a sound basis to develop potential or improve current mitigating solutions. The thesis then investigates using EPS geofoam as a mitigating solution through a study of soil-EPS and EPS–abutment interactions. A combination of physical modelling and numerical analyses has been utilized to perform these investigations. In the thesis, a comprehensive review of the existing practices in dealing with the soilstructure interaction effects in IABs has been undertaken. A novel analytical solution is developed to estimate the passive earth pressure based on an earlier hypothesis of Terzaghi. This solution provides an efficient tool to calculate the passive earth pressure which represents a fundamental input in the estimation of earth pressure in IABs

Sliceforms: Deployable structures from interlocking slices

A sliceform is a volumetric, honeycomb-like structure assembled from an array of cross-sectional planar slices that are interlocked via pairs of complementary slots placed along each intersection. If the slices are thin, these slotted intersections function as revolute joints, and the sliceform is foldable if the geometry of the embedded spatial linkage permits it, for example a lattice sliceform (LS) is bi-directionally flat-foldable. This thesis concerns a study of such sliceforms toward the design of novel deployable structures. A sliceform torus, composed of two sets of inclined slices arranged at regular intervals about a central axis of symmetry, has been discovered to exhibit a surprising and intriguing folding action whereby its incomplete form can be collapsed to a flat-folded stack of coplanar slices. On deployment, the assembly expands smoothly about an arc until the slices have rotated to their design inclination, then, without reaching any apparent physical limit, abruptly ‘locks out’. With a full complement of slices, the outermost intersections can be interlocked to complete and rigidify the ring. The torus is an example of a rotational sliceform (RS), and analysis of these structures proceeds by noting that their structural geometry comprises an array of pyramidal cells that is commensurate to a spherical scissor grid. The conditions for flat-foldability are determined by examination of the intrinsic geometry of each cell; the incompatibility of the slices with apparent rigid-folding revealed by assessment of the extrinsic motion of the slices. Investigation of their compliant kinematics reveals the articulation to be a bistable transition admitted by small transverse deflections of the slices. This structural form is generalised by development of a technique for generating sliceforms along a smooth spatial curve – curve sliceforms (CS). Their synthesis is more involved than for an RS, but a range of sliceform ‘tubes’ are generated and manufactured. Each example retains the flat-foldable, deployable characteristic of an RS, despite the apparent intrinsic rigidity of each constituent skew cell. Examination of the small-scale models indicates that deployable motion is achieved via imperfect action of the slots, and a simple model of the articulation of a single cell is constructed to investigate how this proceeds, verifying that motion is kinematically admissible via local deformations