264 research outputs found

    Finite element analysis of shear resistant mechanisms for biolaminate interfaces

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    The Alligator gar possesses a flexible dermal armor consisting of overlapping ganoid scales. Each scale is a bilayer hydroxyapatite and collagen-based bio-laminate for protection against predation. The exoskeleton fish scale is comprised of a stiff outer ganoine layer, a characteristic sawtooth pattern at the interface and a compliant bone inner layer with all materials exhibiting a decreasing elastic modulus, yield strength and density through the thickness. Experiments on ganoid scales revealed properties such as damage mitigation and energy dissipation that are unique to biological dermal armor. The objective of this investigation is to develop a fundamental understanding of the stress response of a fish scale under tensile and shear loading conditions and to compute effective elastic properties. The effects of material grading and the influence of the geometrically and materially nonlinear interface between the ganoine and bone layers on the elastic properties were also considered. A three dimensional finite element method (FEM) was used by employing ABAQUSÂź code. The current work also investigated possible mechanisms associated with delamination resistance and energy dissipation of the bio-laminate structures. The model structure for the fish scale in the FEM was Alligator gar. The finite element analysis (FEA) is based on a microscopic representative volume element (RVE) of the fish scale with an overall thickness of 800 micron. The FEA RVE had one million uniform 8-micron cubical 8-node elements. The geometrically nonlinear sawtooth features are explicitly modeled. An elastic-plastic model described the nonlinear material response. The analysis focused on evaluating the nonlinear material response in terms of energy dissipation and stress redistribution at the ganoine-bone interface. The results indicate that a complex redistribution of stresses across the 800 micron thickness occurred due to functional gradation of properties, from the stiff mineralized ganoine to the soft bone layer. While the stress concentration was limited to the interface between the saw tooth and the surrounding bone layer, the average stresses in the ganoine layer were much lower as compared to the distributions in the bone layer. The internal energy at the ganoine-bone interface is reduced and energy is dissipated across the sawtooth junction points

    Linking between Multi-scale Behaviours of Brittle Rocks at Deep Underground Excavation

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    Rock fracturing is a hot issue in rock engineering. The macroscopic fracture development is associated with the microscopic damage evolution. Therefore, this research investigated the failure mechanism based on multi-scale analysis methods, including micro-scale (grain scale), meso-scale (laboratory scale), and macro-scale (field scale). This research combined the microscopic data and laboratory-scale mechanical properties to create a valid field-scale model based on the comparison with the in-situ data

    Taking aim at moving targets in computational cell migration

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    Cell migration is central to the development and maintenance of multicellular organisms. Fundamental understanding of cell migration can, for example, direct novel therapeutic strategies to control invasive tumor cells. However, the study of cell migration yields an overabundance of experimental data that require demanding processing and analysis for results extraction. Computational methods and tools have therefore become essential in the quantification and modeling of cell migration data. We review computational approaches for the key tasks in the quantification of in vitro cell migration: image pre-processing, motion estimation and feature extraction. Moreover, we summarize the current state-of-the-art for in silico modeling of cell migration. Finally, we provide a list of available software tools for cell migration to assist researchers in choosing the most appropriate solution for their needs

    Computational Homogenization of Architectured Materials

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    Architectured materials involve geometrically engineered distributions of microstructural phases at a scale comparable to the scale of the component, thus calling for new models in order to determine the effective properties of materials. The present chapter aims at providing such models, in the case of mechanical properties. As a matter of fact, one engineering challenge is to predict the effective properties of such materials; computational homogenization using finite element analysis is a powerful tool to do so. Homogenized behavior of architectured materials can thus be used in large structural computations, hence enabling the dissemination of architectured materials in the industry. Furthermore, computational homogenization is the basis for computational topology optimization which will give rise to the next generation of architectured materials. This chapter covers the computational homogenization of periodic architectured materials in elasticity and plasticity, as well as the homogenization and representativity of random architectured materials

    Smart polymers for advanced applications: a mechanical perspective review

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    Responsive materials, as well as active structural systems, are nowadays widely used to develop unprecedented smart devices, sensors or actuators; their functionalities come from the ability of responding to environmental stimuli with a detectable reaction. Depending on the responsive material under study, the triggering stimuli can have a different nature, ranging from physical (temperature, light, electric or magnetic field, mechanical stress, ...), chemical (pH, ligands, 
), or biological (enzymes, 
) type. Such a responsiveness can be obtained by properly designing the meso- or macroscopic arrangement of the constitutive elements, as occurs in metamaterials, or can be obtained by using responsive materials per se, whose responsiveness comes from the chemistry underneath their microstructure. In fact, when the responsiveness at the molecular level is properly organized, the nanoscale response can be collectively detected at the macroscale, leading to a responsive material. In the present paper, we review the huge world of responsive polymers, by outlining the main features, characteristics and responsive mechanisms of smart polymers and by providing a mechanical modeling perspective, both at the molecular as well as at the continuum scale level. We aim at providing a comprehensive overview of the main features and modeling aspects of the most diffused smart polymers. The quantitative mechanical description of active materials plays a key role in their development and use, enabling the design of advanced devices as well as to engineer the materials’ microstructure according to the desired functionality

    Challenges in multi-scale hard rock behaviour evaluation at deep underground excavations

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    As a consequence of rapid growing trend of resource extraction in world, depth of excavations for resource exploitation increases. Eventually excavations faces with transition from low stress to high stress condition. In this paper, comprehensive aspects on rock behaviour at deep underground excavation were investigated. The state of art of rock behaviour at micro- meso- and macro-scale were discussed and relevant challenges along with achieved knowledge, experiences, and research results were presented. At micro-scale, research results revealed that, apart from chemical bonding, rock behaviour significantly influenced by deficiencies such as; particle-crystal boundaries, heterogeneity, pores and micro-cracks, which reduces the rock strength 2-3 order of magnitude. Granite SEM images proves the deficiencies between crystals, micro-cracks and pores at each crystal, and weakness and foliation of mica components. When stresses applied on specimen, new tensile cracks nucleated and initiated from the edge of existing micro-cracks, and rate of crack propagation depends on the differential stress level. At meso-scale, true triaxial testing makes it possible to apply different stress paths in the ranges of ground in situ stresses, concentrated stresses and even dynamic loads. Careful assessment of the full stress–strain curves of the true triaxial test results of granite and conventional triaxial test results of Marble shows that rock mechanical properties such as magnitude of linear elasticity, ductility domain, peak strength value, ranges of brittleness, and residual strength level significantly differs with changing confining stresses. The rock stress – strain behaviour variation were categorised to four distinct stages consisting; 1) Elastic-stable micro-cracking, 2) Stable - unstable micro-cracking, 3) Unstable micro-cracking-brittle failure, and 4) Brittle failure-residual strength. The ranges of rock behaviour at each stage with different confining stresses were illustrated, which could be used as input for mechanical parameters in design analysis. At macro-scale, counteraction between ‘Rock Mass Composition (RMC)’, ‘Active Stress Condition (ASC)’, and ‘Excavation Method, Size and Orientation (EMSO)’ to estimate the ‘Rock Mass Behaviour (RMB)’ were discussed and presented as a verbal equation. To reduce the sudden failure risk, a micro-seismic monitoring system were designed and implemented for perdition and warning of failure and evacuation in timely manner. To verify the presented approaches, rock mass behaviour and failure mechanisms were illustrated in a deep gold mine in Western Australia. To manage the ground behaviour; considering the static and dynamic loading and interlocked nature of rock masses at deep underground excavations, the ratio of “Ground energy demand” to “support energy absorption capacity” is mostly used for stability evaluation. Finally, it should be noted that, the geomechanics at general and deep underground geomechanics specifically is a developing field due to incapability to achieve proper ground characteristics, huge number of variables and their coupled interactions, and incompetence in analysis them properly. Therefore, the results from current analysis should not be taken as granted and always solid engineering judgement must involve in interpretation and design. It is also hoped that future development in sophisticated ground exploration technologies along with advances in computation science will assist geomechanics engineers to mature their knowledge of rock mass behaviour and safe and economic design in engineering activities

    Simulation of feedback instability in the coupled magnetosphere-ionosphere system

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    [1] Quiet auroral arcs formation has been investigated theoretically and numerically in a self-consistent dynamic way. By using a three-dimensional magneto-hydro-dynamics simulation of a dipole magnetosphere-ionosphere coupling system, it is shown that multiple longitudinally striated structures of the ionospheric plasma density and the field-aligned current are formed, resulting from nonlinear feedback instability. The areas where these structures appear are consistent with the prediction by the integrated feedback theory that includes the effects of the spatially non-uniform electric field and non-uniform plasma density. Effects of the difference of the field line lengths between the ionosphere and the magnetospheric equator over the auroral latitudes are also discussed on the feedback instability

    De-aluminated metakaolin-cement composite modified with commercial titania as a new green building material for gamma-ray shielding applications

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    Sustainable disposal of dealuminated metakaolin (DAK) is a crucial environmental issue for the alum production industry. In previous studies, DAK was utilized as eco-friendly cementitious materials, but only 10 wt% was used instead of cement as DAK's high percentage has a detri-mental effect on the mechanical properties, so the environmental problem of DAK has not yet been solved. In this study, commercial titanium oxide (TiO2) was incorporated in a cement matrix containing DAK that reached 50 wt% to benefit from TiO2's properties in enhancing the me-chanical performance of binding materials and producing cementitious blends used as blocking materials against harmful gamma radiation. Five pastes were prepared to reach the main target; ordinary Portland cement (OPC), OPC-10%DAK (D10), OPC-30%DAK (D30), OPC-50%DAK (D50) and OPC-45%DAK-5%TiO2 (D45-T5). By means of a mini-slump test, all fresh blends have very close flowability using the appreciated additions of polycarboxylate superplasticizer. The hardened composites were cured in tap water for up to 28-days. Compressive strength results at 28 days for OPC, D10, D30 and D50 were 80, 94.6, 60.8 and 57.6 MPa, respectively. An obvious turning point in strength value from 57.6 to 88 MPa after replacement of DAK by 5 wt% TiO2 (D45-T5). A gamma-ray shielding test was performed using two radioactive isotopes (Co-60 and Cs-137). The inclusion of 5% TiO2 has a great impact on the development of shielding power of D45-T5 compared with OPC; the linear attenuation coefficient (mu) values were enhanced from 0.127 +/- 0.003 cm(-1) to 0.199 +/- 0.007 cm(-1) at 661.6 Kev and from 0.118 +/- 0.003 cm(-1) to 0.144 +/- 0.005 cm(-1) at 1332.5 Kev. The unique properties of specimens containing the anatase phase may be attributed to the fact that the TiO2 may act as a nano-filler and active seeds for the formation of further hydration products such as CSHs, CAHs and CASHs as detected by X-ray diffraction (XRD), thermal analyses techniques (TGA/DSC) and scanning electron microscope (SEM/EDX). TiO2 caused rearrangement of the textural structure of D45-T5 composite to meso pores, as proved by N-2-adsorption/desorption technique. Moreover, the TiO2's tetragonal struc-ture makes it has dosimetric characteristics of high adsorbent for gamma rays
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