Scale effects in orthotropic composite assemblies as micropolar continua: A comparison between weak-and strong-form finite element solutions

The aim of the present work was to investigate the mechanical behavior of orthotropic composites, such as masonry assemblies, subjected to localized loads described as micropolar materials. Micropolar models are known to be effective in modeling the actual behavior of microstructured solids in the presence of localized loads or geometrical discontinuities. This is due to the introduction of an additional degree of freedom (the micro-rotation) in the kinematic model, if compared to the classical continuum and the related strain and stress measures. In particular, it was shown in the literature that brick/block masonry can be satisfactorily modeled as a micropolar continuum, and here it is assumed as a reference orthotropic composite material. The in-plane elastic response of panels made of orthotropic arrangements of bricks of different sizes is analyzed herein. Numerical simulations are provided by comparing weak and strong finite element formulations. The scale effect is investigated, as well as the significant role played by the relative rotation, which is a peculiar strain measure of micropolar continua related to the non-symmetry of strain and work-conjugated stress. In particular, the anisotropic effects accounting for the micropolar moduli, related to the variation of microstructure internal sizes, are highlighted

Mechanical Behavior of Anisotropic Composite Materials as Micropolar Continua

The macroscopic behavior of materials with anisotropic microstructure described as micropolar continua is investigated in the present work. Micropolar continua are characterized by a higher number of kinematical and dynamical descriptors than classical continua and related stress and strain measures, namely the micro-rotation gradient (curvature) and the relative rotation with their work conjugated counterparts, the micro-couple, and the skew-symmetric part of the stress, respectively. The presence of such enriched strain and stress fields can be detected especially when concentrated forces and/or geometric discontinuities are present. The effectiveness of the micropolar model to represent the mechanical behavior of materials made of particles of prominent size has been widely proved in the literature, in this paper we focus on the capability of this model to grossly capture the behavior of anisotropic solids under concentrated loads for which the relative strain, that is a peculiar strain measure of the micropolar model, can have a salient role. The effect of material anisotropy in the load diffusion has been investigated and highlighted with the aid of numerical parametric analyses, performed for two dimensional bodies with increasing degrees of anisotropy using a finite element approach specifically conceived for micropolar media with quadratic elements implemented within Comsol Multiphysics© framework. The present studied cases show that a significant diffusion and redistribution of the load is due to an increasing in the level of material anisotropy

Material Symmetries in Homogenized Hexagonal-Shaped Composites as Cosserat Continua

In this work, material symmetries in homogenized composites are analyzed. Composite materials are described as materials made of rigid particles and elastic interfaces. Rigid particles of arbitrary hexagonal shape are considered and their geometry described by a limited set of parameters. The purpose of this study is to analyze different geometrical configurations of the assemblies corresponding to various material symmetries such as orthotetragonal, auxetic and chiral. The problem is investigated through a homogenization technique which is able to carry out constitutive parameters using a principle of energetic equivalence. The constitutive law of the homogenized continuum has been derived within the framework of Cosserat elasticity, wherein the continuum has additional degrees of freedom with respect to classical elasticity. A panel composed of material with various symmetries, corresponding to some particular hexagonal geometries defined, is analyzed under the effect of localized loads. The results obtained show the difference of the micropolar response for the considered material symmetries, which depends on the non-symmetries of the strain and stress tensor as well as on the additional kinematical and work-conjugated statical descriptors. This work underlines the importance of resorting to the Cosserat theory when analyzing anisotropic materials

A Study on the Effect of Doping Metallic Nanoparticles on Fracture Properties of Polylactic Acid Nanofibres via Molecular Dynamics Simulation

All-atom molecular dynamics simulations are conducted to elucidate the fracture mechanism of polylactic acid nanofibres doped with metallic nanoparticles. Extensional deformation is applied on polymer nanofibres decorated with spherical silver nanoparticles on the surface layer. In the ob-tained stress–strain curve, the elastic, yield, strain softening and fracture regions are recognized, where mechanical parameters are evaluated by tracking the stress, strain energy and geometrical evolutions. The energy release rate during crack propagation, which is a crucial factor in fracture mechanics, is calculated. The results show that the presence of doping nanoparticles improves the fracture properties of the polymer nanofibre consistently with experimental observation. The na-noparticles bind together polymer chains on the surface layer, which hinders crack initiation and propagation. The effect of the distribution of nanoparticles is studied through different doping decorations. Additionally, a discussion on the variation of internal energy components during uniaxial tensile loading is provided to unravel the deformation mechanism of nanoparticle-doped nanofibres

New insights on homogenization for hexagonal-shaped composites as Cosserat continua

In this work, particle composite materials with different kind of microstructures are analyzed. Such materials are described as made of rigid particles and elastic interfaces. Rigid particles of arbitrary hexagonal shape are considered and their geometry is described by a limited set of parameters. Three different textures are analyzed and static analyses are performed for a comparison among the solutions of discrete, micropolar (Cosserat) and classical models. In particular, the displacements of the discrete model are compared to the displacement fields of equivalent micropolar and classical continua realized through a homogenization technique, starting from the representative elementary volume detected with a numeric approach. The performed analyses show the effectiveness of adopting the micropolar continuum theory for describing such materials

Computational approach for form-finding optimal design

In this paper, an optimization strategy for a canopy, based on computational modelling approaches is presented. The design approach is applied to a realistic roof structure of an ecological island (waste collection centre) and has been completely redesigned with the aid of a Genetic Algorithm and a Dynamic Relaxation Algorithm. The preliminary design of the roof structure can be formulated as a shape optimization problem, involving functional needs and constraints at different scales of the structure. The proposed hypothesis solution was studied by using an optimization procedure through algorithms in the software Rhinoceros3D®/Grasshopper®. The main aim of this work is to explore different modelling approaches for form-finding that can be built from the use of numerical simulations based on algorithms. To this aim, the need to meet various requirements (structural, functional, formal) involving a team of architects and engineers can be interpreted as a matter of structural optimizatio

Application of column buckling theory to steel aluminium foam sandwich panels

In steel structures, a lot of attention is paid to lightweight structures, i.e. reduction of dead load without compromising structural safety, integrity and performance. Thanks to modern steel aluminium foam sandwich panel manufacturing technology a new possibility became available for lightweight structural design. Assessment and understanding of the behaviour of this sandwich panel under in-plane compression or flexure is crucial before its application in steel structures. Column buckling theory is considered and applied to the steel aluminium foam sandwich panel to evaluate its behaviour under in-plane compressive load. In this work, various assumptions are made to generalise Euler’s buckling formula. The generalisation requires modification of the buckling stiffness expression to account for sandwich panel composite properties. The modified analytical expression is verified with finite element simulation employing various material models specific to steel faceplates and aluminium foam as well as various geometric imperfections. Based on this study, it can be concluded that Euler’s buckling formula can be successfully modified and used in the prediction of the load-carrying capacity of a sandwich panel

Experimental and Numerical Analysis of Thermoplastic Laminates Reinforced with Jute Fabric

Over the last decades, a growing interest has been directed, on one hand, towards the development of new materials with competitive performance while ensuring environmental sustainability and, on the other hand, towards the implementation of effective end-of-life strategies such as to ensure the compliance with circularity criteria. In this context, outstanding attention is devoted to thermoplastic matrix composite materials, intrinsically recyclable compared to thermosetting ones, containing natural reinforcing phases such as vegetable fibres. In this work, jute fabric-reinforced laminates based on bio-based thermoplastic matrices were fabricated using hand lay-up and hot compaction procedures and systematically explored by mechanical tests and numerical tools. The multiscale modelling of the present composite was consider

Bovine lactoferrin-induced CCL1 expression involves distinct receptors in monocyte-derived dendritic cells and their monocyte precursors

Lactoferrin (LF) exhibits a wide range of immunomodulatory activities including modulation of cytokine and chemokine secretion. In this study, we demonstrate that bovine LF (bLF) up-modulates, in a concentration- and time-dependent manner, CCL1 secretion in monocytes (Mo) at the early stage of differentiation toward dendritic cells (DCs), and in fully differentiated immature Mo-derived DCs (MoDCs). In both cell types, up-modulation of CCL1 secretion is an early event following bLF-mediated enhanced accumulation of CCL1 transcripts. Notably, bLF-mediated up-regulation of CCL1 involves the engagement of distinct surface receptors in MoDCs and their Mo precursors. We show that bLF-mediated engagement of CD36 contributes to CCL1 induction in differentiating Mo. Conversely, toll-like receptor (TLR)2 blocking markedly reduces bLF-induced CCL1 production in MoDCs. These findings add further evidence for cell-specific differential responses elicited by bLF through the engagement of distinct TLRs and surface receptors. Furthermore, the different responses observed at early and late stages of Mo differentiation towards DCs may be relevant in mediating bLF effects in specific body districts, where these cell types may be differently represented in physiopathological conditions

Early Literacy Skills and Later Reading and Writing Performance Across Countries: The Effects of Orthographic Consistency and Preschool Curriculum

Background Studies have reported a strong association between children's early literacy skills at preschool and their reading and writing skills at primary school. However, it is unclear whether this association is affected by language and curriculum practices. Objective The study investigates (i) whether early literacy skills are influenced by orthographic consistency and by preschool curriculum, and (ii) how early skills are related to later literacy skills across countries. Method Three countries, Italy (n = 73), Romania (n = 65), and Belgium (n = 109) were involved in the study, for a total of 247 children. Language and early literacy in preschool were assessed using a novel assessment tool (the ‘Talk’). Early visual-phonological and manual aspects integration were investigated using rapid automatized naming and grapho-motor tasks. The children’s reading and writing skills nine months later were assessed using standardized tests. Results Results showed higher early literacy scores for the groups of children speaking languages with more transparent orthographic systems and for the group taking part in preschool activities designed to enhance literacy acquisition. Later reading and writing skills were predicted by early competences, albeit with differences across countries. Conclusions Findings suggest that literacy acquisition trajectories are not only associated with early skills but are also influenced by language characteristics and curriculum practices. The study also presents preliminary findings relative to the ‘Talk’, an assessment tool that may have important implications for early identification and intervention of language and literacy difficulties, as well as for improving cross-country curriculum practices