Elastic Space Research Articles

All-Textile Electronic Skin Enabled by Highly Elastic Spacer Fabric and Conductive Fibers.

Electronic fabrics that combine traditional fabric with intelligent functionalities have attracted increasing attention. Here an all-fabric pressure sensor with a wireless battery-free monitoring system was successfully fabricated, where a 3D penetrated fabric sandwiched between two highly conductive fabric electrodes acts as a dielectric layer. Thanks to the good elastic recovery of the spacer fabric, the capacitance pressure sensor exhibits a high sensitivity of 0.283 KPa-1 with a fast response time and good cycling stability (≥20 000). Water-soluble poly(vinyl alcohol) template-assisted silver nanofibers were constructed on the high-roughness fabric surface to achieve high conductivity (0.33 Ω/sq), remarkable mechanical robustness, and good biocompatibility with human skin. In addition, the coplanar fabric sensor arrays were successfully designed and fabricated to spatially map resolved pressure information. More importantly, the gas-permeable fabrics can be stuck on the skin for wireless real-time pressure detection through a fiber inductor coil with a resonant frequency shift sensitivity of 6.8 MHz/kPa. Our all-fabric sensor is more suitable for textile technology compared with traditional pressure sensors and exhibited wide potential applications in the field of intelligent fabric for electronic skin.

In Situ Visualization of Structural Evolution and Fissure Breathing in (De)lithiated H2V3O8 Nanorods

Layered H2V3O8 material consisting of V3O8 layers features the elastic space for buffering volume change upon repeated ion (de)intercalations. However, its ion transport and phase transformations s...

Complex-Eigenfrequency Band Structure of Viscoelastic Phononic Crystals

The consideration of material losses in phononic crystals leads naturally to the introductionof complex valued eigenwavevectors or eigenfrequencies representing the attenuation of elastic wavesin space or in time, respectively. Here, we propose a new technique to obtain phononic band structureswith complex eigenfrequencies but real wavevectors, in the case of viscoelastic materials, wheneverelastic losses are proportional to frequency. Complex-eigenfrequency band structures are obtainedfor a sonic crystal in air, and steel/epoxy and silicon/void phononic crystals, with realistic viscouslosses taken into account. It is further found that the imaginary part of eigenfrequencies are wellpredicted by perturbation theory and are mostly independent of periodicity, i.e., they do not accountfor propagation losses but for temporal damping of Bloch waves.

A 3D analytical model for residual stress in flank milling process

Residual stress in metal cutting is critical due to its significant influence on the work performance of the workpiece. A 3D analytical model of residual stress appropriate for flank milling is established in this paper which takes both mechanical effect and thermal effect into consideration. Firstly, the 3D mechanical stress component is calculated considering its instantaneous and intermitted properties in the milling process. Elastic semi-infinite space contact mechanics and coordinate transformation are employed in the calculation process. Subsequently, the temperature distribution in the workpiece and corresponding thermal stress component are acquired based on the time-varying transient moving heat source model in the milling process. The plastic stress component is calculated based on the radial return method, in which all the stress components are updated during the plastic loading process. Finally, the measurement experiments for milling temperature and residual stress are performed to validate the theoretical models proposed in this work. The fine consistency between the prediction and the experiment demonstrates the accuracy of the prediction model. According to the calculation results of the proposed theoretical model, the plowing effect induced by the squeeze of the cutting edge on the work material is the major source of the residual stress.

The Mutual Influence of Disk-Shaped Cracks in Three-Dimensional Elastic Space

The mutual influence of three-dimensional disk-shaped cracks located in parallel planes of an elastic medium is studied. The medium is under tensile stress directed perpendicular to the crack planes. The cracks are modeled by mathematical cuts of the continuous medium with the possibility of a strong discontinuity of the displacement field on the faces of the cut. The discontinuous displacement method is used to solve the problem numerically.

Foundation slabs bending model with variable stiffness ratio rested on elastic foundation

The study addresses the problem of designing slabs with variable stiffness to meet such requirements as reducing material consumption, ensuring reliability, durability and cost-effectiveness. The paper offers a solution of the spatial task of contact interaction of orthotropic slabs with elastic foundations. The system of integral−differential equations, which the task is reduced to, is solved numerically by a combination of the finite-difference method and the boundary elements method. The finite-differential scheme is considered to be a shock-capturing type, characterised by the fact that the boundaries of the areas with different mechanical properties are not explicitly highlighted, and in grid nodes the smoothing principle was applied. As the soil foundation models, the elastic linear-strain space and elastically compressional wedge were used. The contact pressure distributions, bending moments and deflections of rectangular slabs of variable stiffness fully adjacent to the base were found. The impact on slabs’ stress−strain behaviour, the degree of soil thickness uneven compressibility and its material orthotropic properties change were analysed. The developed method effectively simulates behaviour of slab-based foundation structures in complex geological conditions where it is necessary to take into account the heterogeneity of soil thickness compressed by a building or a facility.

Metal‐Organic‐Framework‐Derived FeSe2@Carbon Embedded into Nitrogen‐Doped Graphene Sheets with Binary Conductive Networks for Rechargeable Batteries

AbstractMetal selenides have been widely studied as anodes for lithium‐ion batteries, owing to the excellent electrochemical performance. However, the large volume change and poor conductivity may lead to unsatisfactory cycling stability and rate capability. Herein, the FeSe2/carbon matrix nanoparticles embedded into N‐doped graphene sheets (NGS) are designed and synthesized through a two‐step method. When employed as anodes for lithium‐ion batteries, the FeSe2/C@NGS composites exhibit high reversible specific capacities and excellent cycling stabilities of 757.0 mAh g−1 after 100 cycles at 100 mA g−1 and 593.8 mAh g−1 after 1000 cycles at 2000 mA g−1. The carbon matrix and NGS construct binary conductive networks, which not only improve the inner conductivity of FeSe2 and conductivity between FeSe2/C nanoparticles, but also provide elastic buffer space to sustain the structural strain and accommodate the volume expansion and contraction of electrodes during the discharge and charge process. Furthermore, the reversible redox reaction of FeSe2 involves the formation of Fe and Li2Se during the cycling process. This work may open a new avenue for electrode material synthesis methodologies using metal‐organic frameworks as a template and to explore the lithium storage mechanisms of metal selenides for next‐generation batteries.

Acoustic Field Excited by Single Force with Arbitrary Direction in Semi-Infinite Elastic Space

Acoustic Field Excited by Single Force with Arbitrary Direction in Semi-Infinite Elastic Space

Graphene/Co3O4 composites in application of electrochemical energy conversion and storage

This work summarizes the use of graphene/Co3O4 composites in electrochemical energy conversion and storage applications. Graphene is considered the most promising carbon material for accommodating multifarious nanoparticles and achieving excellent electrochemical performance, such as a high electrolyte contact area, electron transport rate and structural stability. This work presents different nanostructures of Co3O4 that consist of nanowires, nanotubes and ordered mesoporous structures, many of which have been poorly synthesized by facile strategies. Graphene can effectively house Co3O4 nanoparticles inside its 3D structure and greatly enhance the electrochemical performance of these nanoparticles. The synergistic effects of graphene and Co3O4 lead to a variety of attractive properties, such as excellent reversible capacity and good cycling stability. In addition, these unique properties are due to the many short diffusion pathways and active sites of nanosized Co3O4 and the elastic buffer space and conductive pathways provided by graphene. This comprehensive review outlines the excellent electrochemical performance of graphene/Co3O4 composites in electrocatalysis, supercapacitors, lithium-ion batteries and other batteries.

Fundamental solutions in 3D elastodynamics for the BEM: A review

In this work, we attempt to collect all available fundamental solutions in 3D elastodynamics that would be suitable for use in Boundary Element Method (BEM) formulations. Given that research on transient and steady state cases involving the elastic, homogeneous and isotropic continuum commenced in the 1950′s, it is practically impossible to reference all work done since then, so we apologize a priori for any omissions on our part. When we use the term fundamental solution, what comes to mind is the elastic full space under a point load in space and time and with the radiation condition arising because the medium has no boundaries, i.e. it extends to infinity. However, this is far from being the end: If the full space becomes a half-space, then boundary conditions enter the picture and now we are talking about Green's functions. These are more desirable for BEM formulations because it now becomes unnecessary to discretize the free surface. In general, the more particular features of the problem at hand are included in the Green's function, the less discretization is necessary in the BEM formulation. What we aim for in this review is to present and briefly discuss the basic fundamental solutions and more specialized Green's functions in a 3D elastic continuum, in either the frequency or the time domain, for the following type of materials: (1) Isotropic and homogeneous; (2) isotropic and inhomogeneous; (3) anisotropic and homogeneous; (4) anisotropic and inhomogeneous. We also look at poroelastic materials with all above possible combinations. We note at this point that the continuously inhomogeneous (e.g., functionally graded) material is understood as one having its material parameters as functions of position. There is, of course, the category of layered media, considered here as discretely inhomogeneous materials. One final note of caution has to do with the numerical implementation of these solutions: Some are very difficult to program, despite the fact that they come in closed form, because they may involve integrals, or there may be turning points in the solution where the form available depends on the frequency, or because of round-off errors in computing special functions. In closing, there is a trade-off between easy to implement fundamental solutions that require substantial spatial discretization effort and advanced ones based on Green's functions that are difficult to implement but require minimal discretization effort. This points out the relevance of speeding up BEM computations, a subject that is treated in the Appendix.

Fretting Wear Modeling of Cylindrical Line Contact in Plane-Strain Borne by the Finite Element Method

This is the first study to develop an empirical formulation to predict fretting wear (volume removal) under frictional conditions for plane-strain line contacts as borne out by the finite element analysis (FEA). The contact is between a deformable half-cylinder rubbing against a deformable flat block. The FEA is guided by detailed physical conceptions, with results that subsequently lead to the methodical modeling of fretting wear. The materials in contact are first set to steel/steel, then to Alloy617/Alloy617, and finally to copper/copper. Various coefficients of friction (COFs) and the Archard Wear Model are applied to the interface. Initially, pure elastic conditions are investigated. The theoretical predictions for the wear volume at the end of the partial slip condition in unidirectional sliding contact agree very well with the FEA results. The empirical formulation for the initial gross slip distance is constructed, again revealing results that are in good agreement with those obtained from the FEA for different materials and for various scales. The Timoshenko beam theory and the tangential loading analysis of a half elastic space are used to approximate the deflection of the half-cylinder and the flat block, respectively. That theory supports well the empirical formulation, matching closely the corresponding FEA results. The empirical formulation of the wear volume for a general cycle under fretting motion is then established. The results are shown to be valid for different materials and various COFs when compared with the FEA results. Finally, plasticity is introduced to the model, shown to cause two phenomena, namely junction growth and larger tangential deformations. Wear is shown to either increase or decrease depending on the combined influences of these two phenomena.

Scattering and reflection of SH waves around a slope on an elastic wedged space

The scattering and reflection of SH waves by a slope on an elastic wedged space is investigated. A series solution is obtained by using the wave function expansion method. The slope on a wedged space is divided into two subregions by an artificial, auxiliary circular arc. The wave fields with unknown complex coefficients within each sub-region are derived. Applying Graf addition theorem, the scattered waves in the sub-regions are expressed in a global coordinate system. Fourier transform is adopted to derive a consistent form of standing waves in the inner region using the orthogonality of the cosine functions. The boundary-valued problem is solved by stress and displacement continuity along the artificial, auxiliary arc to obtain the unknown complex coefficients. Parametric studies are next performed to investigate how the topography from the slope on the wedged space will affect the scattering and diffraction, and hence the amplification and de-amplification of the SH waves. Numerical results show that the surface motions on the slope of the wedged space is influenced greatly by the topography. Amplification of the surface motions near the slope vertex is significant. The corresponding phases along the wedged space surfaces are consistent with the direction that the SH waves are propagating.

Response of bimaterials with interfacial tension subjected to axisymmetric body force

This paper presents an analytical treatment of the boundary value problem of an isotropic elastic bimaterial full space with interfacial tension subjected to an axisymmetric body force. The interfacial tension is modeled as the residual stress in the pre-tensed interfacial atom membrane on the basis of Gurtin and Murdoch’s surface theory. The generality of the present model is justified with several degenerated cases (e.g. classical bimaterials with bonded and unsinkable interface, homogeneous full space with interfacial tension, and half space with surface tension). By virtue of classical Hankel or Fourier transforms, the unconventional boundary value problems are addressed in a concise and systematic manner. The final solutions are all given in the form of a semi-infinite line integral. Particularly, the solutions for the interfacial response induced by interfacial point load can be obtained in exact closed form in terms of Struve and Bessel functions. Numerical results are presented to show the influence of interfacial tension on the induced responses. It is shown that the existence of interfacial tension can significantly influence the induced elastic fields and reduce the point load singularity. The results presented in this paper are useful and meaningful to the studies of nanocomposites, soft solids, and biological tissue, where the effects of surface/interface tension could be dominant.

Application of equivalent load method in finite-length elastic space with the consideration of two free-end surfaces

Non-conforming contact pairs, such as gears, roller bearings and rail-wheel systems, have free-end surfaces, and the classical Hertz theory generally is based on the assumption of half space, which neglects the influences of free-end surfaces. In this paper, the equivalent load method is presented to investigate the effect of free-end surfaces of finite-length elastic space on internal stresses and von-Mises stress. This method can effectively solve the free-edge problems and multi-direction stresses problem. The results obtained by the presented method are evaluated and validated by the results from quarter space model and finite element method. The distinctions among the half space model, the quarter space model and the finite-length space model are discussed. It can be found that when the edge distance is larger than 2a, the half space model can be approximately applied. And when the distances between two free end surfaces is less than 4a, the effect of two free end surfaces should be considered simultaneously.

Fundamental solution for a line source of heat in the fractional order theory of thermoelasticity using the new Caputo definition

The new Caputo Fabrizio fractional differential operator is used to investigate a problem in the fractional order theory of thermoelasticity. The problem concerns an infinite elastic space under the effect of a continuous line source of heat. The problem is solved using asymptotic expansions valid for short times. Laplace and Hankel transforms are used to solve the problem. A brief study to the nature of propagation of waves is introduced. Graphical results are presented and discussed.

A casa físsil: o corpo migrante e os paradoxos da hospitalidade na poesia de Eduardo Jorge

Resumo Se a casa é o centro geográfico a partir do qual os caminhos se abrem e a cidade se oferece, frequentemente a vivência do migrante altera a percepção desse “chez soi” e enfraquece sua oposição aos espaços públicos, abertos, compartilhados. A hospitalidade pode tornar-se hostilidade. O presente artigo busca examinar os abalos na representação do espaço doméstico na obra recente do poeta brasileiro Eduardo Jorge. Vivendo em regime temporário, mudando de endereço, dominando de modo precário a cidade e seus códigos, o migrante retratado nesta poesia sente muitas vezes a casa se reduzir à dimensão da roupa (forma mais elementar de abrigo) e do corpo, transformando-se em casca, espaço físsil, fóssil, elástico.

Elastic Waves in Curved Space: Mimicking a Wormhole.

Transformation optics (TO) can be used to investigate nontrivial spacetime structures with inhomogeneous materials. However, the extreme curvature and large refractive indices make the implementation of a wormhole challenging. By considering flexural waves on a curved plate with geometric curvature, the stringent material requirement can be relaxed, and we demonstrate a two-dimensional analog of a wormhole using homogeneous materials within a curved laboratory frame. TO is used to understand wave propagation in such a curved space. This curved elastic space approach allows us to investigate not only geodesics but also wave redirection, tunneling, and virtual caustics of the wormhole, and will be useful to develop curvature-driven wave front shaping in general.

Microanatomical changes and biomolecular expression at the PDL-entheses during experimental tooth movement.

The novel aspect of this study was to contextualize the co-localization of biomolecular expression in widened and narrowed periodontal ligament (PDL)-space within a mechanically activated periodontal complex. The PDL is unique as it is the only ligament with both innervation and vascularization. Maxillary molars in 6-week-old male C57BL/6 mice (N=5) were experimentally translated for 2weeks using an elastic spacer. Contralateral teeth were used as controls. Mechanical testing of the periodontal complex of a mouse in situ and imaging using X-ray micro-computed tomography (micro-XCT) illustrated deformations within blood vessels (BV) of the PDL. PDL-bone and PDL-cementum entheses at the widened and narrowed PDL-spaces following experimental tooth movement (ETM) illustrated osterix (OSX), bone sialoprotein (BSP), cluster of differentiation 146 (CD146), and protein gene product 9.5 (PGP9.5), indicating active remodeling at these sites. PGP9.5 positive nerve bundles (NBs) were co-localized with multinucleated cells (MCs), Howship's resorption lacunae, and CD146 positive BVs. Association between nerves and MC was complemented by visualizing the proximity of osmium tetroxide stained NBs with the ultrastructure of MCs by performing scanning transmission electron microscopy. Spatial association of NB with BV, and NB with MC, provided insights into the plausible co-activation of NBs to initiate osteoclastic activity. Resorption of mineral occurred as an attempt to restore PDL-space of the load-bearing complex, specifically at the PDL-entheses. Mapping of anatomy-specific structural elements and their association with regenerative molecules by correlating light and electron micrographs provided insights into the use of these extracellular matrix molecules as plausible targets for pharmacological interventions related to tooth movement. Within the realm of tissue regeneration, modulation of load can reverse naturally occurring mineral formation to experimentally induced resorption, and naturally occurring mineral resorption to experimentally induced formation at the enthesial sites to permit tooth translation.

Choreographed Soft Morphologies: exploring new ways of ideating soft architecture through material elasticity

This research aims to contribute to the current field of architectural design by offering evidence of how a collaborative and embodied approach to soft architecture can inform a new physical-digital design process. Current design technologies (e.g. sensors, 3D scanners, procedural modelling software), together with the use of the body as a source for designing a space, offer new methods and tools for designing architecture (Hirschberg, Sayegh, Frühwirth and Zedlacher 2006). However, the potential for experiencing and digitally capturing a soft and elastic material interaction through the body as a dynamic system capable of informing soft architectural design has not yet been widely explored. By using the felt experience as a tool for design, we allow the material to express its qualities when activated by the body, revealing its form instead of it being imposed from outside (DeLanda 2015). Taking an embodied approach used in interaction design and fashion design (Loke and Robertson 2011; Wilde, Vallgårda, and Tomico 2017), this research proposes a hybrid method to explore a textile-body ontology as an entity that has the potential to design a space, along with the use of motion capture technology in an effort to re-connect the experiential (the body) with the architecture (the space).
 Through a custom-made interface, made of soft and hard materials, we explored the dynamic and spatial qualities of material elasticity through choreographed body movements. The interface acts as a deformable space that can be shaped by the body, producing a collection of form expressions, ranging from subtle surface modifications to more prominent deformations. Such form-giving processes were captured in real time by three Kinect sensors, offering a distinct digital raw material that can be conveniently manipulated and translated into architectural simulations, validating the method as a new way to inform soft architectural design processes.
 The findings showed that: 1) the direct experience of collaboratively interacting with a soft and elastic interface allows the identification of the dynamic qualities of the material in relation to oneself and others, facilitating an immediate spatial meaning-making process; 2) exploring the design of a soft and elastic space through choreography and motion capture technology contributes to the creation of augmented relational scales across physical and digital realms, proposing a new hybrid design method; 3) the soft and elastic interface becomes a new entity when shaped by the body (textile-body ontology) giving the opportunity for a variety of formal expressions and offering a source of digital raw material for architectural design.

ГРАНИЧНЫЕ УСЛОВИЯ КОНТАКТНОГО ТИПА В ЗАДАЧЕ О КРУГОВОЙ ЦИЛИНДРИЧЕСКОЙ ПОЛОСТИ В УПРУГОМ ПРОСТРАНСТВЕ

A three-dimensional problem of the theory of elasticity is considered, when contact-type conditions (normal displacements and tangential stresses) are given on a cylindrical cavity in elastic space. The solution is obtained on the basis of the Fourier method with respect to the Lame equations in cylindrical coordinates. The solvability and uniqueness of the problem for these boundary conditions is proved. Normal and tangential stresses are found in the elastic body. A numerical comparison is made of the influence of the boundary conditions in the form of displacements and boundary conditions of the contact type on the stressed state of the elastic space.