Stiffness Of Layer Research Articles

Mitigation of railway-induced vibrations by using periodic wave impeding barriers

Railway-induced vibrations can cause significant environmental issues. This paper proposes an efficient analytical method to investigate the mitigation of railway-induced vibrations by using periodic barriers in a layered half-space. The general solutions for layered ground and multiple inclusions are derived by using the potential decomposition and multiple scattering theory. The conversion equation between cylindrical and exponential functions and the addition theorem are introduced to achieve the transformation between plane and cylindrical wave functions and the translation between cylindrical wave functions. Combined with the transfer matrix method, the fundamental solution for the soil-inclusion dynamic interaction in a layered half-space is derived. The railway train and track are subsequently coupled to the ground-inclusion system. Numerical results demonstrate that the phononic crystal effect induced by the periodic distribution of barriers improves the mitigation efficiency at high frequencies. The increase in the number, size, and stiffness of barriers can give a higher mitigation efficiency in a wider frequency range. The mitigation efficiency of periodic barriers can be guaranteed when their depth is shorter than half the Rayleigh wavelength in the considered frequency range. Owing to the scattering of waves at layer interfaces, the periodic barriers beneath the track have a higher efficiency than those located next to the track, which does not appear in the homogeneous half-space. The performance of periodic barriers is significantly affected by the soil stiffness of the upper shallow layer, while it is less affected by the soil stiffness of the bottom stiffer layer.

Biomechanical fracture mechanics of composite layered skin-like materials.

Most protective biological tissues are structurally comprised of a stiff and thin outer layer on top of a soft underlying substrate. Examples include mammalian skin, fish scales, crustacean shells, and nut and seed shells. While these composite skin-like tissues are ubiquitous in nature, their mechanics of failure and what potential mechanical advantages their composite structures offer remains unclear. In this work, changes in the puncture mechanics of composite hyperelastic elastomers with differing non-dimensional layer thicknesses are explored. Puncture behavior of these membranes is measured for dull and sharp conical indenters. Membranes with a stiff outer layer of only 1% of the overall composite thickness exhibit a puncture energy comparable to membranes with a stiff outer layer approximately 20 times thicker. This puncture energy, scaled by its flexural capacity, achieves a local maximum when the top layer is approximately 1% of the total membrane, similar to the structure of numerous mammalian species. The mode of failure for these regimes is also investigated. In contrast with puncture directly beneath sharp tips caused by high stress concentrations, a new type of 'coring' type fracture emerges at large indentation depths, resulting from accumulated tensile strain energy along the sides of the divot as the membrane is deformed with a blunt indenter. These results could enhance the durability and robustness of stretchable materials used for products such as surgical gloves, packaging, and flexible electronics.

Silver Sintering of Packaged GaN-Devices on Printed Circuit Board

Abstract Despite the higher thermal conductivity and the higher lifetime offered by silver sintering technologies, most packaged GaN devices are attached using solders due to technological difficulties in the sintering process. In this work, a silver sintering process for a packaged GaN power transistor on a printed circuit board (PCB) was successfully developed. Different sintering paste types were examined regarding their suitability for this application. Electrical measurements, shear tests, and metallographic cross sections were used for the evaluation. Numerical analyses were used to study the internal stress distribution in the GaN package after sintering depending on the paste structure. In the final sintering process, a shear strength of 20 MPa for sintering at 15 MPa and 240°C, for 300 s with electrical functional devices could be obtained by using nanoscale sintering paste. The authors contribute this to the high initial stiffness of the silver layer, which is obtained much earlier in the sintering process compared with the stiffness of a microscale silver paste. This high initial stiffness counteracts the semiconductor device deflection from the applied sintering pressure and reduces the stresses inside the semiconductor.

Improved Performance of Raft Foundation Using Detached Pile Columns in Loose Subsoil Conditions

Piles act as settlement reducers in case of connected piled‐raft foundation and hence decrease the settlements of the raft. The design concept of the connected piled‐raft foundations is to lessen the number of piles and utilize the bearing capacity of the system piled raft. Due to significant straining actions at the pile head‐raft connection, an alternative technique is proposed to disconnect the piles from the raft. A granular layer (cushion) beneath the raft is incorporated. The disconnection has a beneficial effect on reducing axial load compared to connected piles. For small piled rafts, nonconnected piled rafts show less stiffness than connected piled rafts, and the soil is highly stressed and shows greater raft settlement. In the case of the large piled raft, nonconnected piled rafts show greater settlement efficiency. Cushion stiffness was realized to be more substantial for a nonconnected piled raft with shorter piles than one with longer piles. The results show that the load transfer mechanism in a nonconnected piled raft is mainly governed by the thickness and stiffness of the cushion layer and by the stiffness of the subsoil.

Uporedna analiza betonskog integralnog nadputnjaka pri različitim karakteristikama tla

In this paper concrete integral overpass with span of 30 meters on magistral road which based on piles is considered. It is analysed influence of soil stiffness on value of design forces and pile stress. Three types of soil is considered in this analysis, where stiffness of soil was determined with characteristic of soil layers. For this analysis was made numerical model of this overpass in software CSiBridge v20 where is soil modeled with "springs" (flexible supports) placed along the piles whose stiffness match with stiffness of soil layer.

Laboratory evaluation of an indigenous developed light weight deflectometer as a quality control tool for pavement construction

The mechanistic empirical pavement design concepts are largely based on the theory of elastic layers, and the design is assessed with the characterization of materials used in pavement construction. The present density-based quality assurance (QA) apparatus and its procedures are not effective in measuring the resilient modulus of compacted pavement layers. However, the use of high-cost field apparatus such as nuclear density gauges (NDG) is also encouraging the search for an alternative procedure. This article aims at the measurement of pavement surface modulus directly in the field using a low-cost laboratory developed Indigenous Light Weight Deflectometer (ILWD). The developed ILWDs will be employed for pavement construction QA for interpreting the stiffness of compacted pavement layers. The study was performed on the National Highway-161 in Sivampet, Sangareddy district, Telangana state. The laboratory developed ILWD was validated using the available Light Weight Deflectometer (LWD), Dynatest make, and layer modulus was also computed using a Dynamic Cone Penetrometer (DCP). The DCP was also fabricated in the laboratory as per the Transportation Research Laboratory (TRL), UK. The ILWD and DCP were used to ensure the stiffness characteristics like elastic and dynamic modulus. The field and lab test results indicate that the calculated elastic modulus and stiffness characteristics are close to each other layer moduli for the different pavement layers considered in the study, like sub-grade and granular sub-base (GSB). It is also observed that the test results from the field and laboratory have a good measure of statical correlation among the different stiffness values, and hence the developed ILWD is suitable for pavement compacted layer investigation as quality control.

Vibration analysis of Non-uniform axially functionally graded beam resting on Pasternak foundation

Non-uniform beam with lengthwise material variation resting on Pasternak foundation is investigated for free vibration. A beam with its material properties and thickness varying linearly along its length is selected for investigation. Euler-Bernoulli beam theory along with Rayleigh-Ritz method is employed for the formulation and the equation of motion is derived by using Hamilton’s principle. Beams with two end conditions i.e., clamped on both ends and simply-supported on both ends are considered for investigation. The results of the current work are validated with established results in literature and new results which illustrate the effect various parameters have on the dynamic response of the beam are furnished. The study revealed that, the material variation, thickness variation and the stiffness of Winkler and shear layer significantly influence the dynamic characteristics of functionally graded beam with non-uniformity.

Predicting damage evolution in panel paintings with machine learning

Understanding the mechanical behavior and properties of works of art, such as panel paintings, is helpful for evaluating the failure mechanisms in play, especially during exhibitions in confined spaces. A panel painting is typically formed by a wooden panel and by layers of gesso, followed by paints and varnishes on the top. Induced by environmental changes, the mismatch in the moisture response of a stiff gesso layer and of the underlying wood panel produces risk of fracture in the pictorial layer. This happens because the gesso layer experiences tension which leads to cracking if the mechanical strain exceeds a critical level. The proposed contribution aims to develop a 3D simplified model for paintings, to detect the environmental conditions which may lead to exceeding the critical strain levels. To this aim, a penny-shaped crack has been simulated inside the gesso layer, centered along the symmetrical planes. To establish if the crack is in critical conditions, the failure criterion of the strain energy density (SED) method has been used: when the critical SED value is reached, the crack is assumed to be in unsafe conditions, otherwise it is in safe conditions. Several combinations of the geometric parameters describing the model have been checked, allowing to define whether the different conditions are likely to lead to a further damage development. Finally, the obtained results have been used to train a preliminary extreme gradient boosting machine (XGBoost) that may be able to classify and predict the two possible outcomes: safe and unsafe. This way, by exploiting the capabilities of machine learning, it could be possible to limit the need of numerical simulations and to introduce new rationales in the framework of work of arts conservation.

Effects of AC frequency on the capacitance measurement of hybrid response pressure sensors.

E-skins consisting of soft pressure sensors are enabling technology for soft robots, bio-integrated devices, and deformable touch panels. A well-known bottleneck of capacitive pressure sensors (CPS) is the drastic decay in sensitivity with increasing pressure. To overcome this challenge, we have invented a hybrid-response pressure sensor (HRPS) that exhibits both the piezoresistive and piezocapacitive effects intrinsic to a highly porous nanocomposite (PNC) with carbon nanotube (CNT) dopants. The HRPS is constructed with two conductive electrodes sandwiching a laminated PNC and a stiff dielectric layer. We have simplified the hybrid response into a parallel resistor-capacitor circuit, whose output depends on the AC (alternating current) frequency used for the capacitance measurement. Herein, through theoretical analysis, we discover a dimensionless parameter that governs the frequency responses of the HRPS. The master curve is validated through experiments on the HRPS with various doping ratios, subject to different compressive strains, under diverse AC frequencies. In addition, the relative contribution of piezoresistive and piezocapacitive mechanisms are also found to vary with the three parameters. Based on this experimentally validated theory, we establish a very practical guideline for selecting the optimal AC frequency for the capacitance measurement of HRPSs.

Stability of solution for Rao-Nakra sandwich beam model with Kelvin-Voigt damping and time delay

This paper deals with stability of solution for a one-dimensional model of Rao?Nakra sandwich beam with Kelvin?Voigt damping and time delay given by ??1?1?????? ? ??1?1?????? ? ??(??? + ?? + ??????) ? ?????????? ? ??????????( ? , ?? ? ??) = 0, ??3?3?????? ? ??3?3?????? + ??(??? + ?? + ??????) ? ?????????? = 0, ????????? + ?????????????? ? ????(??? + ?? + ??????)?? ? ?????????? = 0. A sandwich beam is an engineering model that consists of three layers: two stiff outer layers, bottom and top faces, and a more compliant inner layer called ?core layer?. Rao?Nakra system consists of three layers and the assumption is that there is no slip at the interface between contacts. The top and bottom layers are wave equations for the longitudinal displacements under Euler?Bernoulli beam assumptions. The core layer is one equation that describes the transverse displacement under Timoshenko beam assumptions. By using the semigroup theory, the well-posedness is given by applying the Lumer?Phillips Theorem. Exponential stability is proved by employing the Gearhart-Huang-Pr?ss? Theorem.

Real-time multiscale prediction of structural performance in material extrusion additive manufacturing

The material extrusion additive manufacturing (AM) has been extensively used in fabricating structures with complex geometries. However, geometric defects often exist in an AM structure, which could compromise its final performance. In this paper, a real-time multiscale performance evaluation method is developed for material extrusion-based honeycomb structures. The representative cell boundary is extracted from three-dimensional (3D) point clouds obtained via an in-situ monitoring approach. The cell boundary is then used to generate the digital twin of the unit cell of the printed layer based on the finite element (FE) method. A physics-based multiscale modeling approach called mechanics of structure genome (MSG) is then employed to predict the effective material properties of the printed layer and plate stiffness matrix of the final structure. The proposed approach provides a highly efficient way to predict the real-time performance of the as-manufactured products. Moreover, the numerical example shows that the geometric defects could result in complex mechanical behaviors in the defected parts, which cannot be captured by the conventional approaches based on the shape deviations. The numerical results are validated by the three-point bending tests. The proposed method can be used in the closed-loop control of material extrusion-based manufacturing systems.

The Impact of Using Different Types of Soft Soils Treated by Stone Columns on Creep Behavior

The stone column technique is an effective method to increase the strength of soft cohesive soil, which results in a reduction in foundation settlement and an increase in bearing capacity. The topic of restraining creep settlement through the use of stone columns techniques has gained increasing attention and consideration; because stone columns are widely used to treat soft soil deposits, caution should be applied in estimating creep settlement. We discovered a reversible relation between shear parameters and the creep settlement in floating stone columns; while, in case of end-bearing stone columns shows a direct positive relation between shear parameters and the creep settlement, and the creep settlement began at the primary settlement. The shear parameters affected the improvement factor (n) of creep settlement in both floating and end-bearing stone columns. The standard creep coefficient’s n values in floating and end-bearing conditions were more significant than the low creep coefficient’s n values in forwarded geometric conditions. The stress in both floating and end-bearing stone columns was increasing and uniformly distributed along the length of the floating stone column and in the case of end-bearing stone column was limited to the stiffness layer; the maximum vertical stress was in the central point of the embankment. The embankment’s maximum horizontal displacement occurred on the edge.

Effect of surface residual stress and surface layer stiffness on mechanical properties of nanowires

Effect of surface residual stress and surface layer stiffness on mechanical properties of nanowires

Stress Intensity Factors for a Non-Circular Hole with Inclusion Layer Embedded in a Cracked Matrix

The failure analysis of a non-circular hole with an inclusion layer embedded in an infinite cracked matrix under a remote in-plane uniform load is presented. In this study, a series solution of stress functions for both the matrix and inclusion layer is obtained using the complex variable theory in conjunction with the method of conformal mapping. The stress intensity factor (SIF) can then be determined numerically by solving the singular integral equation (SIE) for the interaction among different crack sites, material properties, and geometries of irregular holes with an inclusion layer. In particular, the failure behavior of composite structures associated with an approximately triangular hole and an approximately square hole with inclusion layers, such as those of oxides, nitrides, and sulfides, is examined in detail. The results demonstrate that a softer layer would enhance the SIF and a stiffer layer would restrain the SIF when a crack is near the inclusion layer. It can be concluded that crack propagation would be suppressed by a stiffer layer even when a micro-defect such as a hole resides in the inclusion layer.

Investigation of premature failure mechanism in pavement overlay of national highway of Bangladesh

Roadway is the economic lifeline of Bangladesh. Maintenance of this roadway is main challenge of Roads and Highways Department (RHD). Overlay is the most common maintenance practice for National Highways, which design life is five years. However, it’s been reported, the overlay failed prematurely with cracking and rutting within one year even 6 to 9 months in some cases. This study aiming to investigate the premature failure mechanism of national highway pavement. Several field investigations were done on national highway namely N2. A numerical parametric study was also conducted with variable interfacial bond condition, overloading and layers stiffness. To investigate the pavements failures, conventional fatigue and rutting criteria were considered. Laser crack measurement system showed that alligator cracking is dominant failure mode followed by rutting. Alligator crack pattern indicated about slippage failure and overloading induced fatigue failure. Core cutting confirmed that interface de-bonding and cracking are strongly related. Bitumen samples were found highly temperature susceptible which could be correlated slippage failure. Moreover, Base layer stiffness variation was observed from Dynamic Cone Penetration test. Numerical analysis revealed that poor interfacial bonding significantly affects horizontal and vertical strain distributions; subsequently reduce pavement life but only it is not enough to fatigue and rutting failure of N2 within one year. Overloading found more significant than de-bonding especially for rutting. Analysis also suggested that fatigue and rutting failure within one year should be associated by coupling effect of poor bonding and overloading. Variation of base layer stiffness might be exacerbated the coupling effect in N2.

Evaluation of inverted pavement by structural condition indicators from falling weight deflectometer

Inverted pavement has been a potential alternative to the conventional flexible pavement structure due to its cost-efficient usage of asphalt, comparable performance and durability. For increasing utilization of the inverted pavements, appropriate structural evaluation is necessary. The Falling Weight Deflectometer (FWD) test has been widely accepted for evaluating the structural condition of conventional pavements through pavement deflection basin parameters (DBPs). As a special type of pavement, inverted pavement relies on the stress-dependence of the unbound stone interlayer to withstand the heavy traffic loads, which typically affects a relatively larger pavement area. So far, there have been few systematic studies on the effectiveness of utilizing FWD to evaluate the structural conditions of inverted pavements. This study used a DBPs-based inverted pavement structure assessment system to assess an inverted pavement constructed in Georgia, USA. A nonlinear stress-dependent finite element model of the inverted pavement coupled with the impulse loading mode was built to simulate the realistic FWD loading process and investigate the effect of layer stiffness on the DBPs evaluation system. Furthermore, a full-scale inverted pavement section in Knoxville, TN, USA, was tested by the FWD method to obtain the corresponding deflection basin parameters. The DBPs data were used to evaluate this practical inverted pavement project based on the aforementioned DBPs-based assessment system. The analysis results show that the DBPs-based pavement evaluation method can provide a quick and comprehensive assessment for each layer in the inverted pavement structure without knowing the detailed properties of the layers. The evaluation results were consistent with the data from the testing vehicle equipped with the laser crack measurement system. Thus, the DBPs-based evaluation system is a promising method to assess the condition of the inverted pavement structures, contributing to the Inverted Pavement Management System (IPMS).

Hydraulic fracture height growth in layered rocks: Perspective from DEM simulation of different propagation regimes

A propagating fluid driven fracture in a rock mass is expected to interact with geological interfaces on a wide variety of length scales. The vertical growth of hydraulic fractures in layered rocks is of pivotal importance for the successful stimulation in reservoir development. In this study, 2D discrete element modeling is used to investigate the influence of the stiffness and toughness ratio, as well as stress contrast between layers on the hydraulic fracture height growth. In particular, the ultimate goal is to better understand mechanisms of the fracture height containment by contrasts of different rock properties and to quantitatively determine which parameters provide a stronger influence. In addition, the analysis is performed in the context of hydraulic fracture regimes, whereby the dominant dissipation mechanism in the system can either be associated with fracture toughness or viscous fluid flow. As a starting point, we investigated the propagation of a plane strain hydraulic fracture from a low stiffness layer to a high stiffness layer and vice versa, while keeping the stress constant. The influence of stress on hydraulic fracture propagation in layered rocks is investigated afterwards. The numerical results demonstrate that the hydraulic fracture can either directly pass through the geological interface, be arrested at the interface, or stop before reaching the interface. The interface itself is assumed to be perfectly bonded, therefore no slippage is considered. Ability of the hydraulic fracture to approach the interface is first determined by the elastic modulus ratio of the two adjacent layers. Once reached the interface, the further growth is then affected by the toughness ratio between the layers. After that, if the fracture crosses the interface, then it is affected by the stress contrast. The propagation regime has an important influence on the fracture propagation in layered rocks. If the propagation regime is closer to the viscosity dominated, the hydraulic fracture is likely to cross the interface. In contrast, it is more difficult for a fracture to cross the barrier if the propagation regime is near the toughness dominated. A map of fracture crossing behavior versus propagation regime and contrast in properties has been constructed, that can be used to quantify strength of mechanical barriers and to deduce hydraulic fracture height growth behavior for various scenarios.

Optimizing pea protein fractionation to yield protein fractions with a high foaming and emulsifying capacity

Specific pea protein fractionation steps can be used to control foaming and emulsifying properties of three pea protein fractions at pH 7.0. Mild fractionation, involving dispersion of the flour at pH 8.0, subsequent centrifugation, and drying of the supernatant yielded a pea protein concentrate (PPC). Further fractionation was achieved by applying isoelectric precipitation on the supernatant, followed by centrifugation, and re-dispersion, resulting in the globulin-rich fraction (GLB-RF); the supernatant – which could be considered a by-product – was diafiltrated to obtain the albumin-rich fraction (ALB-RF). Size exclusion chromatography showed that PPC contained mostly globulins and some albumins, whereas GLB-RF and ALB-RF indeed contained either globulins or albumins. The smaller and less charged albumins displayed strong in-plane interactions at the air-water interface, thereby forming a stiff and cohesive interfacial layer which led to high foam overrun (258%) and stability (272 min). PPC- and GLB-RF contained larger and highly charged globulins, showing substantially lower foam overruns (<81%) and stability (<70 min), which can be attributed to the formation of weaker and more mobile interfacial layers than ALB-RF. For the emulsifying properties, it was found that the larger size and higher net charge of globulins resulted in the formation of oil droplets that were stable against coalescence and flocculation, while albumin-stabilised oil droplets flocculated due to lower surface charges. The functionality of the fraction is largely determined by the protein composition. We have demonstrated how targeted fractionation can be used to control this composition, and hence the functionality of pea protein fractions.

Microstructural effects on the response of a multi-layered elastic substrate

The size dependent response of a multi-layered elastic substrate under surface loading is investigated in the present work. The effect of material microstructure is modeled using the generalized continuum theory of couple stress elasticity. In the formulation, the displacement field is chosen as a primary unknown and the generalized Navier’s equation is established for a generic material layer. The Fourier integral transform method is directly applied to derive the general solution of the elastic field for the generic layer, and such solution is subsequently utilized to form the layer stiffness equation in the transform space. Boundary conditions together with the field continuity across the material interfaces are enforced, via the standard assembly procedure, to obtain a system of linear algebraic equations governing all unknowns of the multi-layered system. An efficient quadrature is adopted to carry out all involved integrals arising from the integral transform inversion. Detailed results are reported that confirm the validity of our results through the comparison with well-known solutions and demonstrate the capability of the proposed model to simulate various scenarios of layered media including those made of functionally graded materials. The important role of the material length scale effect on the predicted response is also elucidated.

Sliding ferroelectricity in 2D van der Waals materials: Related physics and future opportunities

Near the 100th anniversary of the discovery of ferroelectricity, so-called sliding ferroelectricity has been proposed and confirmed recently in a series of experiments that have stimulated remarkable interest. Such ferroelectricity exists widely and exists only in two-dimensional (2D) van der Waals stacked layers, where the vertical electric polarization is switched by in-plane interlayer sliding. Reciprocally, interlayer sliding and the “ripplocation” domain wall can be driven by an external vertical electric field. The unique combination of intralayer stiffness and interlayer slipperiness of 2D van der Waals layers greatly facilitates such switching while still maintaining environmental and mechanical robustness at ambient conditions. In this perspective, we discuss the progress and future opportunities in this behavior. The origin of such ferroelectricity as well as a general rule for judging its existence are summarized, where the vertical stacking sequence is crucial for its formation. This discovery broadens 2D ferroelectrics from very few material candidates to most of the known 2D materials. Their low switching barriers enable high-speed data writing with low energy cost. Related physics like Moiré ferroelectricity, the ferroelectric nonlinear anomalous Hall effect, and multiferroic coupling are discussed. For 2D valleytronics, nontrivial band topology and superconductivity, their possible couplings with sliding ferroelectricity via certain stacking or Moiré ferroelectricity also deserve interest. We provide critical reviews on the current challenges in this emerging area.