Stiffness Of Layer Research Articles

Elastic Analysis of Three-Layer Concrete Slab Based on Numerical Homogenization with an Analytical Shear Correction Factor

Sandwich structures are widely used in construction, as well as in the aviation, spaceship, and electronics industries. The interesting result, among others, is the fact that individual layers can be freely selected to meet the planned requirements. In the case of sandwich structures in construction, they must meet the requirements of load-bearing capacity, thermal, and acoustic insulation, and additionally, they must be resistant to biological and chemical corrosion. The paper presents calculation algorithms for Hoff’s three-layer panels. In the first case, the well-known and proven method of finite differences in variation terms was used, assuming actual geometrical and material parameters. In the second case, the numerical homogenization method of the layered panel was used, replacing the stiffnesses of individual layers with a homogeneous equivalent plate with substitute stiffness corrected in shearing by an analytically derived shear correction factor. A comparative analysis of the results of the calculations with the use of both approaches was carried out. A good agreement between the displacement values and the calculated cross-sectional forces was obtained. On this basis, it can be assumed that the static analysis of a slab by simplified methods using numerical homogenization with an analytical shear correction factor is appropriate and can be applied to layer structures.

Recent Advances in Laterally-Loaded Piles within Mechanically-Stabilized Earth Walls

Pile foundations have been increasingly installed within mechanically-stabilized earth walls (MSE) on rocks or compressible soils to support structural loads. Integral abutment bridges, sound walls, and traffic signs are common examples of the structures supported by pile foundations installed within or behind MSE walls. These structures are often subjected to lateral loads resulting from earthquakes, traffic loads, wind loads, and/or thermal expansion and contraction of bridge girders. Typical approaches available to design MSE walls are limited to MSE walls without pile foundations present within reinforced fill. To minimize the interaction between piles and the MSE wall, designers often suggest to place the piles at a distance of six to eight times the pile diameter and/or isolate the piles from the MSE wall by using corrugated pipes. These suggested designs lead to increasing the cost of projects by increasing the length of bridge spans or the diameter of piles and requiring pile embedment. Recently, several studies have been conducted to understand the interaction between piles and MSE walls when the piles are constructed within and close to wall facing. This paper provides a literature review on full-scale tests, reduced-scale tests, and numerical studies of piles constructed within or behind MSE walls. The review will focus on the effects of three key influence factors on lateral capacities of laterally-loaded piles and facing deflections of MSE walls including the plie location behind the wall facing, the ratio of the reinforcement length to the wall height, and the stiffness of the reinforcement layer. This paper will also discuss the available approaches to estimate the forces in the reinforcement layers and the lateral earth pressures behind the MSE wall facing due to the laterally-loaded piles.

Effects of transversely isotropic layers on failure mechanism of non-homogeny concrete-soil specimens

The mechanism of the failure process and its modes were studied experimentally for transversely isotropic concretes and soils. The two materials, A (concrete) and B (dense soil), were specially prepared for making the layered specimens with a different arrangement of these two materials. The ratio of cement and water in the material A was taken as 4:1 (by weight), respectively. The stiffness and strength of the concrete layers were high compared to that of the dense soil layer (material B). On the other hand a dense layer of soil with low strength and low stiffness was used to represent the material B. Special boxes were built for the preparation of soil-concrete samples. The dimensions of the box were 10 * 10 * 24 cm. Two rectangular spaces were situated on one face. The metallic plates go through these spaces, and a different interface angel was initiated. Concrete and soil layers were formed by pouring the grout and soil into this box. Three different soil volumes have been built, i.e., 25, 50, and 75%. In this research, the laminated concrete specimens with one, two and three soil layers were compared at a constant soil volume. The concrete specimens with transversely isotropic layers of different orientations were examined experimentally and two types of failure were dominant, i.e., the tensile failure at right angles to the layers and the sliding failure parallel to the interfaces of the layers. With a fixed interface angle and fixed concrete volume, the compressive failure stress was increased by increasing the concrete layer. With a fixed layer number and fixed interface angle, the failure stress was increased by increasing the concrete volume. With a fixed layer number and fixed concrete volume, the failure stress has a minimum value when the interface angle is equal to 30°.

Hydromechanical impact of basement rock on injection-induced seismicity in Illinois Basin

The common explanation of observed injection-induced microseismicity is based on the measured stress state at the injection interval and the assumption that it remains the same in the vicinity. We argue here that representing the stress state in different geologic formations over the injection site with the single Mohr’s circle is insufficient due to local stratigraphic features and contrast in compressibilities of the involved formations. The role of hydromechanical coupling in the microseismic response is also crucial for the proper assessment of the problem. Thoroughly monitored Illinois Basin Decatur Project revealed the majority of CO2 injection-associated microseismic events being originated in the crystalline basement. Even though basement faults can serve as the conduits for fluid flow—the predicted pressure increase seems to be insufficient to trigger seismicity. To address this issue, accurate laboratory measurements of rock properties from the involved formations are conducted. The pre-injection stress state and its evolution are evaluated with the hydromechanically coupled numerical model. It appears that the presence of an offset in a stiff competent layer affects the stress state in its vicinity. Therefore, both the pre-injection stress state and its evolution during the fluid injection should be addressed during the induced seismicity assessment.

A novel helix contact model for predicting hysteretic behavior of unbonded flexible pipes

This paper presents novel equivalent layered contact numerical and analytical models to predict the bending hysteretic behavior of unbonded flexible pipes. A double helix contact beam model, instead of surface-to-surface contact algorithm, is proposed to simulate normal contact and tangential friction behavior between tensile armor tendons and supporting layers. The spatial beam distance is evaluated based on Hertz contact theory. The proposed model is validated through comparison with bending moment-curvature relations obtained from experimental data, a full layered finite element model, and existing analytical models considering or not shear interactions. The shear stiffness is determined by accounting steel armor layers as boundary conditions. The initial contact pressure is introduced into analytical models by accounting residual stress in cylindrical layers and residual strain in helical layers. The bending stresses and relative slip displacements of tensile armor tendons are cross validated between the proposed model and available data. The results show that the proposed model could give consistent bending hysteretic consequences, while shorten simulation time due to significantly reduction of total elements. Sensitivity studies including definition of helix contact beams, equivalent material properties of inner core layer and tangential stick stiffness between layers are performed to validate feasibility of the proposed model.

Viscoelastic free vibration analysis of in-plane functionally graded orthotropic plates integrated with piezoelectric sensors: Time-dependent 3D analytical solutions

This paper proposes an accurate three-dimensional framework for elastic and viscoelastic free vibration investigation of in-plane functionally graded (IPFG) orthotropic rectangular plates integrated with piezoelectric sensory layers. The developed analytical framework is capable of considering layer-wise unidirectional linear functional gradation in both stiffness and density of the orthotropic composite layers. 3D piezoelasticity-based governing equations of motion are formulated in mixed form by employing Hamilton’s principle, and further solved analytically for Levy-type support conditions using the power-series-based extended Kantorovich method (EKM) jointly with Fourier series. The displacements, stresses, and electrical variables (electric field and electric potential) are solved as the primary variables that ensure the point-wise interlayer continuity and electro-mechanical support conditions. The viscoelastic property of the orthotropic interlayer is defined by employing Biot model, which is similar to the standard linear viscoelastic model. The correctness and efficacy of the present mathematical model are established by comparing the present numerical results with published literature and 3D finite element results, obtained by utilizing user material subroutine in the commercial FE software ABAQUS. An extensive numerical study is performed for various configurations and thickness ratios to investigate the influences of in-plane gradation, viscoelasticity and their coupled effects on the free-vibration response of hybrid laminated plates. It is found that in-plane gradation of stiffness and density remarkably alters the flexural frequencies and corresponding mode shapes of the hybrid intelligent rectangular plates. The flexural frequencies and stresses in the plate can be modified by selecting suitable grading indexes. Another interesting observation is that the in-plane gradation shows a considerably less effect on the electrical response of piezoelectric layers, which can play a vital role in the design of sensors and actuators for dynamic applications. Further, the numerical study demonstrates a potential time-dependent structural behaviour based on the present viscoelastic modelling. The consideration of viscoelasticity could be crucial for analysing the mechanical behaviour of a wide range of polymer composites more realistically and for prospective temporal programming in smart structural systems by exploiting the viscoelastic effect. Although the present analytical solution has been proposed for the free-vibration investigation of smart in-plane functionally graded (IPFG) viscoelastic plates, it can also be utilized directly to analyze the symmetric and asymmetric laminated piezoelectric smart plates with constant properties.

Atomic insights into synergistic effect of pillared graphene by carbon nanotube on the mechanical properties of polymer nanocomposites

Molecular dynamics simulations have been performed to explore the underlying synergistic mechanism of pillared graphene or non-covalent connected graphene and carbon nanotubes (CNTs) on the mechanical properties of polyethylene (PE) nanocomposites. By constructing the pillared graphene model and CNTs/graphene model, the effect of the structure, arrangement and dispersion of hybrid fillers on the tensile mechanical properties of PE nanocomposites was studied. The results show that the pillared graphene/PE nanocomposites exhibit higher Young’s modulus, tensile strength and elongation at break than non-covalent connected CNTs/graphene/PE nanocomposites. The pull-out simulations show that pillared graphene by CNTs has both large interfacial load and long displacement due to the mixed modes of shear separation and normal separation. Additionally, pillared graphene can not only inhibit agglomeration but also form a compact effective thickness (stiff layer), consistent with the adsorption behavior and improved interfacial energy between pillared graphene and PE matrix.

Evaluating the performance of inverted pavement structure using the accelerated pavement test (APT)

• Full-scale inverted pavement was investigated. • Accelerated pavement test was applied to the inverted pavement. • Rutting performance between inverted and conventional pavements was compared. • Inverted pavement structure outperformed the conventional flexible pavement. Inverted pavement is considered an unconventional type of flexible pavement structure. In this pavement structure, an unbound aggregate base (UAB) with a low initial modulus is sandwiched (layered) between two stiffer layers, a thinner asphalt concrete layer (AC) and a cement-treated base layer (CTB). This paper presents a comparison study of the rutting performance (permanent deformation) between conventional and inverted pavement structures. In addition, the inverted pavements with different thicknesses of UAB and CTB were studied. The accelerated pavement test (APT) method was conducted on a full-scale pavement consisting of two inverted pavement lanes and one typical three-layer conventional flexible pavement lane as the control section for performance comparison. Significant permanent deformation was observed in all three pavement lanes after the completion of 100,000 passes of APT. Comparisons of the measured total deformations showed that the inverted pavement structure outperformed the conventional pavement. Furthermore, the inverted pavement with a thicker CTB layer exhibited less deformation compared with the inverted pavement with a thicker UAB layer. The stiffness of the UAB layer of the inverted pavement increased with the loading passes. A stiffer UAB could provide a cushion for the thin AC layer, resulting in less deformation in the AC surface compared with that of the conventional pavement. Furthermore, the loading on the pavement surface had a larger affected area in the inverted pavement structure. Based on the overall pavement conditions, the inverted pavement can be regarded as a promising alternative to the conventional flexible pavement, and the asphalt mixture layer thickness can be reduced during the construction.

Modelling and Stress Analysis of Shaft Work Subsidence of Underground Power Transmission Line Tunnel

This research presents an analysis of soil subsidence around shaft work under its construction process and drilling tunnel by finite element method (FEM). The study is focused on the underground power transmission tunnel in the Chao Phraya River construction project (Southern Bangkok Station to Suksawat Road, Thailand) of the Metropolitan Electricity Authority. This research aims to provide information for designing shaft work and preventing drilling tunnel problems. The research analyzed the soil subsidence around shaft work with 12 m of inside diameter and 1 m of thickness that located 33 m underground during constructing a tunnel chimney by sinking method. It is assumed that the analyzed horizontal reaction is the net resistance of the lateral earth pressure around the shaft work. This study found that the subsidence of soil around shaft work during the construction and drilling process had the value between 0.80 - 53.30 mm. In the part of the base slab, the soil subsidence value is between 3.40 - 16.00 mm. It can be concluded that the top of shaft work during the construction and drilling process had a soil subsidence value of 53.30 mm with dmax/H ratio of 0.00162.
 HIGHLIGHTS
 
 The Metropolitan Electricity Authority has an underground power transmission tunnel in the Chao Phraya River Construction (Southern Bangkok Station to Suksawat Road, Thailand) project which used to distribute electricity from the source station to the other side of the Chao Phraya River
 This research studied the behavior of the shaft work in sinking reinforced concrete shaft work and drilling tunnel process by finite element method (FEM) with the Midas Gen 2021 program
 The analysis results of the maximum soil subsidence around the shaft work wall occurred in the top area (very soft to medium stiff clay layer)
 
 GRAPHICAL ABSTRACT

Semi-analytic shooting methods for Burgers’ equation

We implement new semi-analytic shooting methods for the stationary viscous Burgers’ equation by modifying the classical time differencing methods. When the viscosity is small, a very stiff boundary layer appears and this boundary layer causes significant difficulties to approximate the solution for Burgers’ equation. To overcome this issue and improve the numerical quality of the shooting methods with the classical Integrating Factor (IF) methods and Exponential Time Differencing (ETD) methods, we first employ the singular perturbation analysis for Burgers’ equation, and derived the so-called correctors that approximate the stiff part of the solution. Then, we build our new semi-analytic shooting methods for the stationary viscous Burgers’ equation by embedding these correctors into the IF and ETD methods. By performing numerical simulations, we verify that our new schemes, enriched with the correctors, give much better approximations, compared with the classical schemes.

Thermal modeling and uncertainty quantification of tool for automated garment assembly

In this work, a thermal Finite Element model is developed to simulate the performance of a blade-like tool for robotic work cells performing automated garment production using a novel thermoplastic stiffening layer. Uncertainty quantification and sensitivity analysis are applied to determine the most important design properties and optimize key performance metrics for swift and reliable garment assembly. Attention is focused on the geometric and thermal design properties that minimize sensitivity to environmental conditions while maximizing expected productivity. An example design is shown for illustrative purposes. This work may inform future design innovation for similar heating tools and reduce the need for physical experiments and long calibration times on the factory floor.

Ferroelectric/paraelectric superlattices for energy storage.

The polarization response of antiferroelectrics to electric fields is such that the materials can store large energy densities, which makes them promising candidates for energy storage applications in pulsed-power technologies. However, relatively few materials of this kind are known. Here, we consider ferroelectric/paraelectric superlattices as artificial electrostatically engineered antiferroelectrics. Specifically, using high-throughput second-principles calculations, we engineer PbTiO3/SrTiO3 superlattices to optimize their energy storage performance at room temperature (to maximize density and release efficiency) with respect to different design variables (layer thicknesses, epitaxial conditions, and stiffness of the dielectric layer). We obtain results competitive with the state-of-the-art antiferroelectric capacitors and reveal the mechanisms responsible for the optimal properties.

Origin of noncollinear magnetization coupling across RuX layers

We present a simple atomistic model for the description of noncollinear coupling in magnetic multilayers with hybrid spacer layers made of Ru alloyed to ferromagnetic atoms such as Fe. In contrast to previous analytical and micromagnetic models that explain the noncollinear coupling by means of lateral fluctuations in the coupling constant, the presented model accounts for atom-atom coupling in all three spatial dimensions within the spacer layer. The model is able to accurately predict the dependence of the macroscopic bilinear and biquadratic coupling constants on the spacer-layer composition and thickness, showing much better quantitative agreement than lateral-fluctuation models. Moreover, it predicts that the noncollinear coupling is virtually independent of the exchange stiffness in the ferromagnetic layers, which goes beyond the predictions of previous models. This prediction is validated by experimental measurements.

The complexity of luminescence dating of tidal sand body revealed by the discrepancy of paired quartz OSL ages

Optically stimulated luminescence (OSL) dating is becoming a useful technique to yield absolute age of organic-poor sandy deposits. The buried tidal sand body (BTSB) in the coastal zone of northern Jiangsu Province, China, has been suggested to have the same origin as the offshore radial sand ridge in the Yellow Sea. However, chronological constrain of the BSTB is still quite limited. In this study, OSL measurements were conducted using silt-sized multi-grain and coarse-grained single-grain quartz to constrain the depositional history of a 25.6 m core from the BTSB. A low luminescence sensitivity of quartz was observed, and only ∼1.04% of the grains passed the standard rejection criterion for single-grain measurement. Analysis of paired OSL ages from two grain-size fractions using different protocols showed that silt-sized quartz ages were underestimated of 0.14–1.35 ka in comparison to coarse-grained quartz in the depth interval of 5.8–22.4 m. We interpret such an age discrepancy as the effects of lateral infiltration of fine-grained sediment into the sand body due to dynamic feature of channel-ridge system on the shelf. As far as we know, it is the first time that such infiltration is demonstrated through OSL dating. Our OSL data indicated that there is a significant hiatus between the Late Pleistocene stiff clay layer (50–18 ka) and the Holocene sequence. Holocene deposits only occurred in the last 2 ka, with rapid accumulation of ∼17 m-thick sediments at ∼2–1 ka, a slower accumulation between ∼1 and 0.1 ka and rapid land emergence through an accretion of ∼4 m-thick sediment over the past ∼0.1 ka. This study highlights the complexity of OSL dating in highly dynamic sedimentary environments. Therefore, examining different grain size fractions and comparing different measurement protocols are highly deserved in carrying out OSL dating in such environments. • We compared multi-grain silt-sized quartz and single-grain coarse-grained quartz ages for a tidal sand body. • Silt-sized quartz underestimated ages due to ‘younger’ sediment infiltration into tidal sand body. • The buried tidal sand body in the northern Jiangsu Province of China was formed in the last 2 ka.

Toward the application of the layer-wise displacement theory in passenger ships—a quasi-static response

This paper introduces an application of the layer-wise displacement theory for response analysis of multilayer ship girders. Quadrilateral, 6-node finite membrane elements are used for which 8 displacement degrees of freedom at corners, and 4 shear strain degrees of freedom at mid-side nodes, are defined. This approach enables accurate estimates of the shear strain between adjacent layers with different stiffness. A simple cantilever beam, non-uniform stepped girder with constant layer stiffness, and uniform girder with varying stiffness is used in the validation analysis. An excellent agreement between the fine mesh finite element model and the proposed model is observed.

Variable stiffness composite laminated beams - nonlinear free flexural vibration behavior using a sinusoidal based shear flexible structural theory accounting for Poisson’s effect

In the present work, formulation for the nonlinear free vibrational behavior of laminated variable stiffness composite beams with curvilinear fibers is made incorporating sinusoidal function for representing the transverse shear flexibility, geometrical nonlinearity, and accounting for Poisson’s effect through the constitutive equation for analyzing beams with general composite lay-up. Applying Hamilton’s principle combining with a finite element approach based on three-noded C1 beam element, the governing equations are formed through matrices. The solutions for the developed governing equations are evaluated iteratively by introducing eigenvalue analysis and the results are viewed through the frequency–amplitude relationship. A large number of design parameters like curvilinear fiber angles in a layer, number of layers, lay-up sequence, thickness ratio, etc. is assumed to visualize the nonlinear free vibration characteristics of VSCL beams. Also, for the practical situation, the influence of thermal environment and restraint elastically against beam ends rotation, to accommodate other than classical boundary conditions, hybrid beam (consisting of constant and variable stiffness layers) on the non-linear free vibrational behavior is presented.

Incorporating the effect of approach slab to the dynamic response of simply supported bridges under moving vehicle

Reinforced concrete approach slabs serve as a transitional component between the roadway pavement and the bridge deck. Due to the settlement of the embankment soil, the slab is bent, and its slope grade will be suddenly changed resulting in bumps at both ends of the deck; this may increase the dynamic response of bridges induced by the interaction with moving vehicles. In addition, the presence of such bumps not only causes an uncomfortable ride but also exhibits a potentially hazardous condition to the traffic. Since most of the studies have considered either the interaction model between the slab and soil or between the bridge and moving load; in this study, a novel finite element model is established for the bridge under traffic loads, considering the presence of the approach slab that is simulated as a beam rested on a dynamic soil model. The separated models of the approach slab and bridge deck are validated by previous studies and demonstrate their accuracy in predicting the dynamic response of the bridge-vehicle system. A comprehensive parametric study is then performed considering the effect of the soil stiffness, the stiffness of the shear layer of the foundation, and the approach slab length. The results of the study are useful criteria for the practice design of the approach slab in different embankment conditions.

On the post-buckling behavior of laterally constrained multilayers

Material layering occurs in natural, biological, geological and synthetic load-bearing structures. The bucking and post-buckling behavior of such structures is a subject of great interest. While many studies were devoted to the case of a thin film attached to a thick substrate, little is available on the behavior of multilayers. We explore this subject using a model system consisting of 2-D, linearly elastic hard/soft multilayer under uniform edge displacement. The lateral edges of the multilayer are constrained by rigid, frictionless walls. The number of stiff layers n and layer-to-interlayer thickness and elastic moduli ratios, h and E, are systematically varied. The deformation and stresses in the multilayer are obtained with the aid a FEA. Buckling initiates in the interior layers and spreads to the outer ones. The layers adjacent to the constraining walls tend to flatten as the load is increased. For relatively large h or small E, this causes large membrane stresses that may lead to a buckling mode transition. As many as ≈ 50 stiff layers are needed in order for the multilayer to approach a laminate configuration (n ≫ 1). The multilayer as a whole displays nonlinear elastic stress–strain response. By a proper choice of the system variables n, h and E, a variety of strain hardening effects as well as large energy absorption can be achieved. The results of this study provide useful insights into the effects of b.c., material choice and load level on the response of multilayers in general.

Atomic perspective of contact protection in graphene-coated high-entropy films

Covering graphene (Gr) coatings on high-entropy alloy (HEA) films is a promising approach to avoid its contact damage. However, current understanding regarding the underlying strengthening mechanisms of these systems at atomic level remains limited. Here, the contact mechanical behavior and strengthening mechanism of Gr-coated HEA films during nanoindentation were unravelled by means of molecular dynamics (MD) simulations. The results demonstrated that an increase of about 80.3% in indentation hardness of the composites can be endowed by covering a Gr layer, meaning a dramatically enhanced carrying capacity. More importantly, it would be further improved as Gr layers varied from monolayer to trilayer (increases of about 129.3% and 160.2% for the bilayer and trilayer cases, respectively). Moreover, we confirmed that due to the high in-plane stiffness, Gr coatings can effectively decrease the contact stress and inhibit the dislocation nucleation, which facilitated the decreased subsurface damage. Meanwhile, high-density Shockley and Stair-rod dislocations induced by an increase of the actual loading area synergistically promoted a strong strain hardening effect in the composites. It was deemed that the capability of contact protection of HEA films can be further improved after covering Gr coatings which can be ascribed to the high in-plane stiffness of Gr layers coupled with its induced strong strain hardening effect. These findings may contribute to the development and design of Gr-coated HEA composites with better mechanical properties.

Effect of Four Groups of GO-CF/EP Composites with Ideal Infiltration Structure and Different Layering Ways on Damping Properties.

In this paper, four groups of graphene oxide and carbon fiber hybrid-reinforced resin matrix (GO-CF/EP) composites with different layering ways were prepared by a vacuum infiltration hot pressing system (VIHPS). The damping properties of the specimens with different layering ways were tested by the force hammer method, and the micromorphology of the specimens was photographed by scanning electron microscope. The experimental results showed that the damping properties of GO-CF/EP composites gradually increased with the increase in the number of Y-direction layers. The [XYXYXY]6 has the best damping property, with a damping ratio of 1.187%. The damping ratio is 5.3 times higher than that of [XXXXXX]6 layer mode, and the first-order natural frequency is 77.7 Hz. This is mainly because the stiffness of the X-direction layer is larger than that of the Y-direction layer, and its resistance to deformation is considerable. Therefore, its decay rate is slower. The Y-direction layer has weak resistance to deformation and fast energy attenuation. The increase in the number of Y-direction layers will lead to the overall increase in, and the improvement of, the damping properties of GO-CF/EP composites.