Elastic Core Research Articles

Experimental investigation of a multistage buckling-restrained brace

While buckling-restrained braces offer excellent energy dissipation characteristics, their low post-yield stiffness may result in large residual drifts and interstory drift concentration when used in simply supported frames. This paper introduces a new multistage buckling-restrained brace to help mitigate these design challenges. The proposed device features two low yield point (LYP) cores with LY225 and short yield lengths, and one high yield point (HYP) core with SA440B and a longer yield length. In a design level event, the LYP cores dissipate energy, while the parallel HYP core provides an elastic restoring force. At large drifts, the HYP core yields and the device acts similar to a high-capacity, ductile, conventional BRB.A 384 kN specimen was tested at up to 1.5% strain and the individual core contributions recorded using strain gauges attached to the elastic core segments inside the restrainer. The multistage response matched the predicted trilinear backbone, achieving 10 to 20% equivalent damping prior to yielding the HYP core, and a fatigue capacity exceeding three times the AISC 341-16 acceptance criteria. Interaction between the decoupled cores was studied using a 3D finite element model, indicating that minor detailing changes could further improve performance.

Finite element electrodynamics modeling of a layered piezoelectric composite shell with different materials by using numerical software

In this study, a three-layer axial symmetrical composite plate has simulated in numerical ANSYS and ABAQUS software. The structure has consisted of an elastic core (isotropic) and two piezoelectric layers (trans-trophic) that are symmetrical on both sides of an elastic layer. The elastic core is made of aluminum, and piezoelectric layers are in the form of piezoelectric materials (PZT5H). The polarization vector assumed on the Y-axis in simulation, and loading involves applying an electric charge (voltage) on the surface of the piezoelectric and imposing mechanical load (distributed load) on the upper plan level as well as the electromechanically load that is a combination. Boundary conditions include a hinged and fixed supports which are around the elastic layer. Analysis of the structure takes place in two static- and modal-state situations. Static analysis is conducted to determine the maximum deformation of the structure, and modal analysis is for calculating the natural frequencies and mode shapes of the plate in both short and open circuits. Finally, two software results are compared.

Manufacture and Evaluation of Auxetic Yarns and Woven Fabrics

Auxetic materials are a type of novel materials exhibiting negative Poisson's ratio (NPR) with potentials for special applications. Herein, the aim is to optimize the auxetic yarn and fabric manufacturing processes, establish the understanding of the influence of yarn and fabric parameters on the auxeticity of the engineered materials and explore the potential applications of auxetic textile materials. The auxetic yarns are manufactured based on a conversional helical structure composing initially a super elastic polyurethane core and a high modulus Nylon 6,6 binder. A hollow spindle machine is used to produce the auxetic yarn with optimized twisting and delivery speeds. Stable helical yarns with auxetic properties are manufactured using the optimized parameters, and woven fabrics are produced from the selected auxetic yarns in both warp and weft directions. Experiments show that the maximum NPR of helical auxetic yarns reaches a remarkable level of −5.6, and the auxetic fabrics display notable geometric changes compared with the nonauxetic fabrics with the same structural parameters. The auxeticity demonstrated in the fabrics implies applications in areas such as filtration and impact protection.

An innovative approach to theoretical analysis of partitioned width & stability of strip pillar in strip mining

The strip mining method is preferred to the extraction of coal resources under surface buildings, water bodies and railways in China. Strip pillars with appropriate widths play a significant role in controlling stress distribution and surface subsidence. The strip mining activity at Tangkou coal mine in Eastern China is taken as the engineering background in the paper. In order to evaluate the general strip pillar design of mining area no. 430, an innovative analytical model is developed to determine the yield width and the elastic core width of the strip pillar under the stress superimposition effect in this paper. In the proposed model, the strip pillar is divided into the yield zone and the elastic core zone on the basis of the existing reasonable structural division of the strip pillar. Based on the Drucker-Prager criterion which considers the influence of the intermediate principal stress, the formulae of the partitioned width of the strip pillar are inferred. The yield width of the strip pillar with one-sided goaf is derived based on the limit equilibrium theory and the Drucker-Prager criterion. The yield width of the strip pillar with two-sided goafs is obtained based on the stress superimposition method. The elastic core width of the strip pillar is obtained by the semi-inverse method with the consideration of mine pressure and the application of the Drucker-Prager criterion. As a case study, the proposed model is used to determine the yield width and the elastic core width of the strip pillar at Tangkou coal mine in China. Comparing the obtained results with the in-situ measurement data, it can be concluded that the proposed analytical model is effective in calculating the yield width and the elastic core width of the strip pillar. In order to evaluate the effects of the parameters in the proposed model on the yield width of the strip pillar with one-sided goaf and the elastic core width of the strip pillar with two-sided goafs, a detailed sensitivity analysis is conducted based on the actual data at from Tangkou coal mine.

Formulation of a Triaxial Three‐Layered Earth Rotation: Theory and Rotational Normal Mode Solutions

AbstractIn this study, we formulated a triaxial three‐layered anelastic Earth rotation theory considering various core‐mantle couplings, including the pressure and gravitational couplings acting on the elastic inner core by the outer core and mantle, and the viscoelectromagnetic couplings between the outer core and mantle and between the outer and inner cores. With this formulation, using the eigenvalue method, we solved four rotational normal modes, including the Chandler Wobble (CW), Free Core Nutation (FCN), Free Inner Core Nutation (FICN), and the Inner Core Wobble (ICW). The triaxiality of the actual Earth has notable effects on rotational normal modes, that is, 0.005, 0.0, 0.071, and 1.174 d (mean solar days), respectively, for the CW, FCN, FICN, and ICW. In the case that the triaxiality is bigger, for instance, if the Earth's equatorial dynamical ellipticity were , which is 1 order of magnitude larger than the presently determined ellipticity ( ), the CW and ICW periods will be lengthened by 3.579 and 94.912 d, and the FICN period will be decreased by 0.591 d. Based on our present knowledge, the numerical solutions of the four normal modes under the new rotation frame suggest that the periods of CW, FCN, FICN, and ICW are, respectively, 432.2, 429.9, 934.0, and 2,718.7 d. Our theory for Earth can be extended to other planets in our solar system.

Design and implementation of an elastic processor with hyperthreading technology and virtualization for elastic server models

The server models functioning in the industry are required to be more elastic in nature. They are constantly scaling-up and scaling-down on required computation power depending on different conditions. These elastic cloud platforms use accelerators like DSP’s, TPU’s, GPU’s, FPGA’s, and multi-core processors to provide exponential computing power and outsource their services. This process is not only costly and non-efficient but is also responsible for damaging the server’s hardware architecture. Furthermore, these additions degrade the level of threading and symmetric parallel processing capability of the architecture. Intel uses hyperthreading technology (HTT) to split the workload between hardware and operating system to avoid additions, but that too is only possible up until a certain limit. This paper presents design methodology and implementation of an elastic-natured 32-bit RISC-pipelined processor inspired from Intel Xeon and MIPS to function as a standard integrated platform for server models. It implements concepts of hyperthreading technology (HTT) and virtualization on hardware basis. It will allow to derive multiple outputs from units on hardware basis to enhance security and performance without compromising compatibility. The designed elastic core uses a probabilistic node-based closed-queuing network model for server analysis and implementation. Hence, elastic behavior from individual core microarchitecture to server model architecture enables a generic automated scaling self-aware optimization architecture.

Differential quadrature method for magneto-hygrothermal bending of functionally graded graphene/Al sandwich-curved beams with honeycomb core via a new higher-order theory

Based on the differential quadrature method (DQM), the bending of sandwich-curved beams with graphene platelets/aluminum (GPLs/Al) nanocomposite face sheets and aluminum honeycomb core is investigated using a new shear and normal deformations curved beam theory. The present new model is resting on elastic foundation and subjected to a circumferential magnetic field, thermal load, and humid conditions. The face sheets are made of several bonded composite layers with randomly oriented and uniformly distributed graphene platelets in each layer. The mechanical and hygrothermal properties of the faces are assumed to be functionally graded (FG) using a piece-wise law by varying the weight fraction of the GPLs in the face thickness direction. Four governing differential equations are derived based on a novel four-variable curved beam theory taking into account the thickness stretching effect. The governing equations are solved for various boundary conditions on the basis of the DQM. The displacements presented by the DQM are compared with those obtained by Navier solution. Impacts of various parameters such as geometric shape parameters, magnetic parameter, temperature, moisture, elastic foundation parameters, core thickness, boundary conditions, and graphene weight fraction on the displacements and stresses of the functionally graded graphene/aluminum sandwich-curved beams are illustrated.

Liquid metal based smart fiber sensor for human-computer interaction

Flexible electronic devices based on liquid metal fibers have attracted the attention of many laboratories in the world due to their convenient use and characteristics of being able to be woven into flexible textiles or applied directly on the body surface. In this research, we utilized the liquid metal mixed with copper particles (Cu-EGaIn) as the outer conductive layer of stretchable fiber, developing a highperformance composite conductive fiber based on liquid metal. The composite conductive fiber has three layers: stretchable elastic fiber core; adhesion layer; liquid metal layer. Specifically, the stretchable elastic fiber core provides the high tensile property, the adhesion layer is used to hold the liquid metal on the fiber surface, and the liquid metal layer makes the fiber have a high electrical conductivity. This kind of fiber not only has the characteristic of high electrical conductivity of metal materials, but also can always maintain high electrical conductivity even in large-scale tensile state. Therefore, we developed a tension sensor based on liquid metal intelligent fiber for human-computer interaction.

Stability of a Sandwich Cylindrical Shell with Core Subject to External Pressure and Pressure in the Inner Cylinder*

A generalized design model is proposed to study the stability and initial post-buckling equilibrium trajectory of sandwich cylindrical shells with elastic core that resists only transverse tension–compression. The model includes nonlinear equilibrium mixed-form equations, asymptotic equations obtained by the Koiter–Budiansky method, and the analytical solution of a homogeneous eigenvalue problem and inhomogeneous problem to find the values of the unknown functions at the critical point. The numerical results obtained indicate that the internal pressure strongly influences the critical load and initial post-buckling behavior of the shells.

Design a Reasonable Width of Coal Pillar Using a Numerical Model. A case study of Khe Cham basin, Vietnam

Problems in surrounding rock displacement, roadway deformation and complex support are the hallmarks of the long wall mining system. Such problems seriously affect the safety and efficient production of coal mines. To control the deformation of the rocks around the roadway next to the goaf, to reduce the support pressure, in Vietnamese underground mines often leave supporting coal pillars. Identification of a reasonable design for roadway supporting pillars by a numerical simulation study was conducted under the geological and technical foundation of I-10- 2 working faces at the Khe Cham coal mine, Vietnam . The characteristics of stress and pressure distribution of roof layers on coal pillars are modeled under different pillar widths. The results show a great linear increase of the vertical stress on the narrow coal pillar and as the width of the coal pillar increases, the area of the elastic core area also increases and the level of stress increase tends to be stable without any apparent uptrend. Coal pillar deformation decreases with increasing coal pillar width, but it leads to large coal loss and waste of resources. Therefore, with the current supporting solutions to increase the stability of the coal pillar, the size range of a coal pillar is determined to be 6-8 m through numerical simulation. The conclusions obtained may provide a certain reference number to choose the logical location of the furnace lines under similar geological conditions.

Analytical Solution for the Ultimate Strength of Sandwich Panels under In-plane Compression and Lateral Pressure

The paper presents a closed-form analytical solution for the ultimate strength of sandwich panels with metal faces and an elastic isotropic core during combined in-plane compression and lateral pressure under clamped boundary condition. By using the principle of minimum potential energy, the stress distribution in the faces during uni-axial edge compression and constant lateral pressure was obtained. Then, the ultimate edge compression was derived on the basis that collapse occurs when yield has spread from the mid-length of the sides of the face plates to the center of the convex face plates. The results were validated by nonlinear finite element analysis. Because the solution is analytical and closed-form, it is rapid and efficient and is well-suited for use in practical structural design methods, including repetitive use in structural optimization. The solution applies for any elastic isotropic core material, but the application that stimulated this study was an elastomer-cored steel sandwich panel that had excellent energy absorbing and protective properties against fire, collisions, ballistic projectiles, and explosions.

Third-order electro-elastic analysis of sandwich doubly curved piezoelectric micro shells

The present paper studies size dependent electro-elastic analysis of sandwich doubly curved piezoelectric micro shells. The structure is composed of a micro elastic core and two piezoelectric micro layers as sensor and actuator. The kinematic relations are developed based on third-order shear deformation theory proposed by Reddy. The principle of virtual work is used to derive governing equations in terms of primary displacements, rotation components, and electric potential. The sandwich doubly curved micro shell is resting on Pasternak’s foundation. After verification of numerical results, the analytical results are presented in terms of important parameters such as micro length scale parameter, applied electric potential, and some geometric parameters of the problem. The numerical results indicate that the in-plane deformation and out of plane displacement are decreased with increase of micro length scale parameter and decrease of applied electric potential.

Vibrations of the plate with elastic core resting on the Winkler foundation caused by a moving oscillator

In the paper a structure consisting of two Kirchhoff plates connected by an elastic Winkler layer is considered. The structure rests on the Winkler foundation and is subjected to a one-mass visco-elastic oscillator, moving at a constant speed on the upper plate, parallel to one of the plate sides. Forced and free vibrations of the plates and the oscillator are analysed. In the case of such a complex system vibration of the plates is described by two coupled differential equations, or one differential equation with elevated order. In addition, due to the nature of the moving load (inertial load), these equations have variable, time-dependent coefficients. The solutions are illustrated by numerical examples.

Wrinkling in sandwich panels with bi‐modular core

AbstractThe paper is concerned with wrinkling of thin facings in sandwich structures with a bi‐modular elastic core. Bi‐modularity of core implies a different stiffness in tension and compression. The solution to the wrinkling problem is obtained by an extension of the Hoff method. One of two bounding cases are the classical Hoff solution where the stiffness of the core in tension is equal to that in compression. In the second case demonstrated in the paper the mismatch in the stiffness of the core in tension and compression is so large that the higher stiffness can be assumed infinite. The solution for intermediate cases where the ratio of the core stiffness in tension to that in compression is finite is also presented in the paper. In addition, the approach to the analysis of wrinkling utilizing the stresses in the core derived by the theory of elasticity is discussed and the closed‐form solution obtained in the particular case of equal tensile and compressive moduli. It is shown that a mismatch in the elastic moduli of the core in tension and compression results in the change in the mode shape of wrinkling as compared to the core with equal tensile and compressive stiffness. An increase in the stiffness of the facing or using a stiffer bi‐modular core results in a higher wrinkling stress. It is also demonstrated that a higher stiffness of a bi‐modular core in either tension or compression causes only a limited reduction in the energy absorbed prior to wrinkling.

Field and numerical investigations of gateroad system failure under an irregular residual coal pillar in close‐distance coal seams

AbstractThe Gaojialiang Coal Mine in Inner Mongolia in China was used as an example to investigate the process of chain pillar and gateroad failure in the lower coal seam under the effect of an irregular residual coal pillar in the upper close‐distance coal seam. The results indicated that after the longwall face in the lower coal seam retreated through the area under the large irregular residual coal pillar in the upper coal seam, the bearing area of the residual coal pillar decreased and the roof pressure continuously concentrated in the elastic core area of the residual coal pillar. Isolated triangular slab rock was formed above the triangular residual coal pillar, and the weight of the overlying strata was transferred downward through the triangular slab rock. When the chain pillar under the residual coal pillar was destroyed due to loading that exceeded its carrying capacity, the upper triangular slab rock rotated and sank, which resulted in the intensification of the concentrated stress in the solid rib of the gateroad in the lower coal seam. Based on the analysis, it is suggested that in the design of a longwall system, a gateroad under an isolated residual coal pillar in the upper coal seam should be avoided when mining in close‐distance coal seams.

The elastic serrated gasket of the flange bolted joints

The paper presents the experimental as well as numerical research of a bolted flange joint with an elastic serrated gasket. Two constructions of a metal core were proposed. Their cross-section shapes were different in relation to the standard solution. Results of the experimental research showed that the elastic core provides a considerable increase of the joint tightness compared to the tightness of the joint sealed with a standard gasket. Next, numerical analysis was conducted whose aim was to determine contact pressure on the interfacing surface between the gasket and flange. It appeared that proper forming of the core cross-section provides quite regular distribution of contact pressure along the gasket width. The final part verified the numerical computation and explains the effect of the increased tightness of the joint with an elastic core.

A new solution of the semi-metallic gasket increasing tightness level

Abstract The paper presents new type of the semi-metallic gasket characterized with elastic core. Thanks to this solution more elastic recovery as well as more uniform contact stress distribution on the gasket’s surface were obtained which consequently caused that tightness level of the flange joint increased by 1000% in contrast to joint gasketed with traditional solution. The tightness characteristic of the traditional as well as new solution of the gaskets were determined experimentally and discussed.

Buckling and Thermomechanical Vibration Analysis of a Cylindrical Sandwich Panel with an Elastic Core Using Generalized Differential Quadrature Method

In this paper, the vibrational and buckling analysis of a cylindrical sandwich panel with an elastic core under thermo-mechanical loadings is investigated. The modeled cylindrical sandwich panel as well as its equations of motions and boundary conditions is derived by Hamilton’s principle and the first-order shear deformation theory (FSDT). For the first time in the present study, various boundary conditions is considered in the cylindrical sandwich panel with an elastic core. In order to obtain the temperature distribution in the cylindrical sandwich panel in the absence of a heat-generation source, temperature distribution is obtained by solving the steady-state heat-transfer equation. The accuracy of the presented model is verified using previous studies and the results obtained by the Navier analytical method. The novelty of the present study is considering thermo-mechanical loadings as well as satisfying various boundary conditions. The generalized differential quadrature method (GDQM) is applied to discretize the equations of motion. Then, some factors such as the influence of length-to-radius ratio, circumferential wave numbers, thermal loadings, and boundary conditions are examined on the dynamic and static behavior of the cylindrical sandwich panel.

Deformation of three-layer cylindrical shells with transversally elastic core in a vicinity of the critical compression

Deformation of three-layer cylindrical shells with transversally elastic core in a vicinity of the critical compression

Mode I crack tip fields: Strain gradient plasticity theory versus J2 flow theory

The mode I crack tip asymptotic response of a solid characterised by strain gradient plasticity is investigated. It is found that elastic strains dominate plastic strains near the crack tip, and thus the Cauchy stress and the strain state are given asymptotically by the elastic K-field. This crack tip elastic zone is embedded within an annular elasto-plastic zone. This feature is predicted by both a crack tip asymptotic analysis and a finite element computation. When small scale yielding applies, three distinct regimes exist: an outer elastic K field, an intermediate elasto-plastic field, and an inner elastic K field. The inner elastic core significantly influences the crack opening profile. Crack tip plasticity is suppressed when the material length scale ℓ of the gradient theory is on the order of the plastic zone size estimation, as dictated by the remote stress intensity factor. A generalized J-integral for strain gradient plasticity is stated and used to characterise the asymptotic response ahead of a short crack. Finite element analysis of a cracked three point bend specimen reveals that the crack tip elastic zone persists in the presence of bulk plasticity and an outer J-field.