A "String Art" approach to the design and manufacturing of optimal composite materials and structures

In this paper we report a new promising idea on the design and manufacturing of ply composite structures, tailored to exhibit maximum stiffness under given weight constraints and loading conditions. It is based on the idea behind an artistic technique known as "string art" - the representation of an image with a single thread, tensioned between pins on the flat frame. A discrete optimization algorithm has been employed recently to formalize the process of finding a configuration of thread windings that fuses into a given greyscale image. We demonstrate how this algorithm can be employed to approximate the two-dimensional distribution of isotropic material, computed by a conventional topology optimization algorithm. An optimal composite design is thus found as a result of the following two-stage process. At the first stage, topology optimization procedure produces regular grid of greyscale values of stiffness. At the second stage, this distribution is approximated with a polyline, representing the stiff reinforcement fiber in a soft matrix, according to ``string art'' optimization algorithm. The efficiency of the proposed approach is illustrated with few simple numerical examples. Our development opens a wide avenue for the industrial design of the new generation of fibrous composite structures

Collapse modes in SC and BCC arrangements of elastic beads

Collapse modes in compressed simple cubic (SC) and body-centered cubic (BCC) periodic arrangements of elastic frictionless beads were studied numerically using the discrete element method. Under pure hydrostatic compression, the SC arrangement tends to transform into a defective hexagonal close-packed or amorphous structure. The BCC assembly exhibits several modes of collapse, one of which, identified as cI16 structure, is consistent with the behavior of BCC metals Li and Na under high pressure. The presence of a deviatoric stress leads to the transformation of the BCC structure into face-centered cubic (FCC) one via the Bain path. The observed effects provide important insights on the origins of mechanical behavior of atomic systems, while the elastic spheres model used in our work can become a useful paradigm, expanding the capabilities of a hard sphere model widely used in many branches of science

Rigid Clumps in the MercuryDPM Particle Dynamics Code

Discrete particle simulations have become the standard in science and industrial applications exploring the properties of particulate systems. Most of such simulations rely on the concept of interacting spherical particles to describe the properties of particulates, although, the correct representation of the nonspherical particle shape is crucial for a number of applications. In this work we describe the implementation of clumps, i.e. assemblies of rigidly connected spherical particles, which can approximate given nonspherical shapes, within the \textit{MercuryDPM} particle dynamics code. \textit{MercuryDPM} contact detection algorithm is particularly efficient for polydisperse particle systems, which is essential for multilevel clumps approximating complex surfaces. We employ the existing open-source \texttt{CLUMP} library to generate clump particles. We detail the pre-processing tools providing necessary initial data, as well as the necessary adjustments of the algorithms of contact detection, collision/migration and numerical time integration. The capabilities of our implementation are illustrated for a variety of examples

How Fast are Domino Waves?

The paper is concerned with the problem of toppling propagation velocity in domino-like mechanical systems. We build on the work of Efthimiou and Johnson, who developed the theory of perfectly elastic collisions of thin rigid dominoes on a frictional foundation. This theory nicely predicts important aspects of domino wave propagation, however, it leads to infinite propagation velocity for the limit of zero spacing between dominoes. In our work we account for finite stiffness of the dominoes and obtain a refined theory of fast domino waves, taking into account a limit velocity of the perturbation propagation in the system of dominoes. Moreover, finite collision time allows to extract dynamic quantities of collisions and establish upper and lower borders for domino separations where the theory is still applicable. Within the established bounds, our theory agrees with the results of real experiments and DEM numerical modeling of domino waves

Anharmonic acoustic effects during DNA hybridization on an electrochemical quartz crystal resonator

The paper describes a sensor for single-stranded DNA (ssDNA) biomarker based on anharmonic acoustic signals arising during hybridization with complementary thiolated ssDNA functionalised on the gold electrode of an electrochemical quartz crystal resonator. The steps of sensor preparation and hybridization are carried out in an electrochemical microfluidic flowcell. While the electrochemical impedance spectroscopy does not allow a definitive interpretation, the changes in resonance frequency and third Fourier harmonic current of the resonator on actuation at the fundamental mode indicate formation of a flexibly bound layer. The functionalization and hybridization steps monitored by the anharmonic detection technique (ADT) are described with a simple model based on Duffing nonlinear equation