Cover Layer Thickness Research Articles

Efficiency of insulation layers in fire protection of FRP-confined RC columns-numerical study

This paper addresses the efficiency of thermal insulation layers applied to protect structural elements strengthened by fiber-reinforced polymers (FRP) in the case of fire event. The paper presents numerical modeling and nonlinear analysis of reinforced concrete (RC) columns externally strengthened by FRP and protected by thermal insulation layers when subjected to elevated temperature specified by standard fire tests, in order to predict their residual capacity and fire endurance. The adopted numerical approach uses commercial software includes heat transfer, variation of thermal and mechanical properties of concrete, steel reinforcement, FRP and insulation material with elevated temperature. The numerical results show good agreement with published results of full-scale fire tests. A parametric study was conducted to investigate the influence of several variables on the structural response and residual capacity of insulated FRP-confined columns loaded by service loads when exposed to fire. The residual capacity of FRP-confined RC column was affected by concrete grade and insulation material and was shown to improve substantially by increasing the concrete cover and insulation layer thickness. By increasing the VG insulation layer thickness 15, 32, 44, 57 mm, the loss in column capacity after 5 hours of fire was 30%, 13%, 7% and 5%, respectively. The obtained results demonstrate the validity of the presented approach for estimation of fire endurance and residual strength, as an alternative for fire testing, and for design of fire protection layers for FRP-confined RC columns.

Evaluation of the effect of cover layer on radon exhalation from building materials

Radium, which is naturally present in many building materials, decays to the radioactive gas radon, which is exhaled from the surface of concrete block and is a major source of human exposure to radioactivity. In this study, an experimental evaluation of radon exhalation was conducted on a concrete block covered with mortar and acrylic render. Factors such as sand aggregates content and water content of the mortar cover layer, the thickness of the double cover layer were considered. Results showed that the radon exhalation rate was increased with an increase of sand content in mortar cover layer, and the radon exhalation rate was reduced with an increase of the thickness and water content. Besides, indoor radon concentration and effective dose estimation involving concrete block with cover layer were evaluated. The calculated indoor radon concentration was reduced from 234.9 to 201.1 Bq m−3 as the thickness of the cover layer was increased from 15 to 35 mm, and the effective dose was reduced by 0.61 mSv y−1. Therefore, the addition of a cover layer on the indoor walls, floors and ceilings could reduce the indoor radon concentration and the radon dose on exposure to occupants.

Integrated system of geophysical methods for shallow loose covering stratum exploration in the granite region in the northwest of Zhejiang Province, China

The major triggering factor of the collapses, landslides, and debris flow in the northwest region of Zhejiang Province in China is the shallow loose covering stratum with a thickness of dozens of centimeters to dozens of meters generated by the intensive physical weathering process of granite. Therefore, accessing a three-dimensional model of the slope structure covering by the shallow loose stratum and quantifying its thickness and spatial distribution are very important in deepening one’s understanding of the failure mechanism and distribution features and improving the efficiency of geohazard prevention and mitigation. This study applies high-density electrical method, microtremor survey, artificial transient surface wave method, and ground-penetrating radar to explore the slope structure covered by the loose stratum. By validating and comparing the results obtained through engineering geological drilling, an integrated system of the geophysical methods for the shallow loose covering stratum is proposed herein with greater precision and suitability for the granite region in the northwest of Zhejiang Province. This integrated system of methods consists of geophysical exploration, followed by drilling for validation. Each individual method in the system can be applied with suitability evaluation and recommended parameters. The proposed system could also properly void shortage when only an individual method is used. The major conclusions obtained in this study are as follows: (1) the accuracy of the high-density electrical method in the dry condition could reach 85% or above, and in the rainy season, the test should be conducted 48 h after the rainfall; (2) the microtremor survey and artificial transient surface wave methods can achieve good results in the case of a complex climate condition or a large-area detection; (3) the ground-penetrating radar method can be used to discover the loose covering layer thickness with good precision (less than 5 m); and (4) the integrated method system is more applicable when the ground slope is less than 30°.

Limit support pressure on tunnel face at different construction line slopes by slip line method

Tunnels in urban areas typically have complex geological conditions, and sufficient support pressure is necessary to guarantee the safety of tunnel excavations and prevent damage to adjacent structures. In this study, the slip line method is employed to obtain the limit support pressure on the tunnel face and analyze the effects of the internal friction angle, cohesion of the soil, interface friction angle, cover layer thickness and tunnel construction line slope on tunnel face stability. The soil is idealized as a rigid plastic material. The slip line method assumes that the soil satisfies the plastic equilibrium state specified by the Mohr-Coulomb criterion. Moreover, a mathematical model of the static equilibrium with a solvable limit equilibrium boundary is established. The limit support pressure distribution and failure mechanism of the tunnel face are obtained by the finite difference method. The results show that the limit support pressure decreases when the internal friction angle and cohesion of the soil increase, whereas limit support pressure increases when the interface friction angle increases. When comparing the derived results with those found in related references, it is observed that the slip line method for calculating the limit support pressure on the tunnel face is reliable. Furthermore, it is particularly suitable when the interface friction angle and tunnel construction line slope are considered.

Linking tundra vegetation, snow, soil temperature, and permafrost

Abstract. Connections between vegetation and soil thermal dynamics are critical for estimating the vulnerability of permafrost to thaw with continued climate warming and vegetation changes. The interplay of complex biophysical processes results in a highly heterogeneous soil temperature distribution on small spatial scales. Moreover, the link between topsoil temperature and active layer thickness remains poorly constrained. Sixty-eight temperature loggers were installed at 1–3 cm depth to record the distribution of topsoil temperatures at the Trail Valley Creek study site in the northwestern Canadian Arctic. The measurements were distributed across six different vegetation types characteristic for this landscape. Two years of topsoil temperature data were analysed statistically to identify temporal and spatial characteristics and their relationship to vegetation, snow cover, and active layer thickness. The mean annual topsoil temperature varied between −3.7 and 0.1 ∘C within 0.5 km2. The observed variation can, to a large degree, be explained by variation in snow cover. Differences in snow depth are strongly related with vegetation type and show complex associations with late-summer thaw depth. While cold winter soil temperature is associated with deep active layers in the following summer for lichen and dwarf shrub tundra, we observed the opposite beneath tall shrubs and tussocks. In contrast to winter observations, summer topsoil temperature is similar below all vegetation types with an average summer topsoil temperature difference of less than 1 ∘C. Moreover, there is no significant relationship between summer soil temperature or cumulative positive degree days and active layer thickness. Altogether, our results demonstrate the high spatial variability of topsoil temperature and active layer thickness even within specific vegetation types. Given that vegetation type defines the direction of the relationship between topsoil temperature and active layer thickness in winter and summer, estimates of permafrost vulnerability based on remote sensing or model results will need to incorporate complex local feedback mechanisms of vegetation change and permafrost thaw.

Chemical, optical and transport characterization of ALD modified nanoporous alumina based structures

Nanoporous alumina-based structures (NPA-bSs) obtained by anodization of aluminum in sulfuric acid medium were coated by atomic layer deposition (ALD) of a thin conformal layer of different functional oxides (Al2O3, TiO2, Fe2O3 or ZnO), leading to samples with similar geometrical parameters but different surface materials. Morphological characterization of the NPA-bSs confirms a reduction of about 35% in pore size associated to the presence of the oxides of interest, while chemical surface analysis permits the estimation of cover layer purity and thickness. Additionally, ALD functionalization also modifies optical (band-gap, refractive index and dielectric constant) according to transmittance and spectroscopic ellipsometry results for visible and near-infrared regions, as well as electrolyte diffusive transport parameters (effective fixed charge, ion transport numbers or ionic permselectivity) of the NPA-bSs, both of which are dependent on the nature of the coating layer. Therefore, the suitability of ALD technique for geometrical and functional modification of nanoporous structures is demonstrated, thus broadening the potential application of these NPA-bSs platforms to optical sensing, nanophotonics, biosensing, microfluidics or drug delivery applications.

The 3D Design of Multifunctional Silver Nanoparticle Assemblies Embedded in Dielectrics

Many applications as optical spectroscopy, photothermal therapy, photovoltaics, or photocatalysis take advantage of the localized surface plasmon resonance of noble metal nanoparticles (NPs). Among them, AgNPs are multifunctional nano‐objects that can be used not only as efficient plasmonic antennae but also as electron reservoirs for charge transfer or ion reservoirs with strong biocide activity. Herein, the 10 years’ efforts on the safe‐by‐design synthesis of multifunctional nanocomposites consisting of 3D patterns of small AgNPs embedded in dielectrics are presented by coupling low‐energy ion implantation and stencil masking techniques. Their multifunctional coupling with different objects deposited on top of the dielectric surface is also presented through three examples. The twofold role of this single plane of AgNPs as the embedded plasmonic enhancer and charge carrier reservoir is first tested on few‐layer graphene deposited in specific areas at a controlled nanometer distance from the AgNPs. These buried AgNPs are also coupled to light emitters coimplanted in the dielectric matrix in specific regions, showing light emission enhancement. Finally, these AgNPs also provide an efficient biocide activity on green algae when submerged in water, with the amount of Ag+ release simply controlled by the thickness of the silica cover layer.

Influence of vocal fold cover layer thickness on its vibratory dynamics during voice production.

The influence of vocal fold cover layer thickness on the flow-induced vibration and voice production was studied by using a continuum-mechanics based computational model. The cover-body thickness ratio of a three-layer vocal fold was systematically varied. The effect on the vocal fold stiffness, eigenfrequencies and eigenmodes, fundamental frequencies, glottal flow rate, vocal fold vibratory dynamics, and synchronization of the eigenmodes were analyzed by using the structure eigen analysis and flow-structure interaction simulations. It was found that the cover-body layer thickness ratio significantly affected the strength and synchronization of the eigenmodes during flow-structure interactions, and ultimately affected the fundamental frequency and vibration pattern. With the increasing cover-body thickness ratio, the strength of the wave-type higher-eigenfrequency modes increased, and that resulted in a nonlinear bifurcation of the system in which the system evolved from a regular periodic vibration to a periodic doubling vibration and then back to a regular periodic vibration with increased fundamental frequencies. During the transition, the system vibrated chaotically. Because of the increased strength of the wave-type modes, the maximum divergent angle of the glottis was also increased with the increasing cover-body thickness ratio.

Effects of external confinement on steel reinforcement corrosion products monitored by X-ray microcomputer tomography

Rebar corrosion destroys the bond interface between concrete and the original rebar and, thus, affects their collaborative performance. External confinement, such as a concrete cover or fiber reinforced polymer (FRP) jackets, is a promising method to solve this problem since both can improve the bond properties between corroded rebars and concrete. However, existing tests results have shown the expected bond performance between rebars and its external concrete surroundings to be unstable for corrosion condition, and much of the bond strength data of corroded specimens is highly discrete. Traditional test methods such as cutting specimen are difficult to explain the instability of bonding phenomenon since it likely to destroy the rebar’s bonding interface during processing the specimen. In this study, X-ray microcomputed tomography (X-ray μCT), a new type of non-destructive testing method, was adopted to scan the inside of the corroded specimens and perform a three-dimensional reconstruction enabling a complete understanding of corrosion development. This paper also presents a thorough research analysis that focuses on the effects of variation in corrosion rates as well as the thickness of the concrete cover and FRP layers on the distribution of rust products and the volume change of rust products on the bond interface. Test results indicate that the distribution of corrosion products in 2D/3D is directly related to the location of cracks in the concrete cover, and increasing confinement (concrete cover thickness, FRP layer number) leads to a more uniform distribution of corrosion products. In addition, by using X-ray μCT, the “hollow volume,” defined as the volume between the surface of the uncorroded steel bar and the inside of the concrete cover, could be accurately obtained. Most importantly, this hollow volume was found to be the main factor affecting the bond performance of corroded reinforced concrete.

Influence of Test Configuration on Bond Strength of GFRP Bars

It is well-known that test configuration affects bond behaviour of steel reinforcement, but this effect has not yet been sufficiently quantified when using FRP reinforcement. This paper presents partial results from an ongoing experimental programme that deals with the bond strength of GFRP bars with concrete, with regards to the effect of the surface treatment of the rebars and test configuration. A modified beam test is presented in this study along with a pull-out test with an eccentric bar placement. The bond strength of GFRP reinforcement with sand-coated treatment using silica sand and ribbed type with milled ribs was tested. The sand-coated bars exhibit different bond behaviour compared to the ribbed ones due to different forces transfer from the reinforcement to the concrete. Thickness of the concrete cover layer also has a significant effect on the bond behaviour of the reinforcement.

Dynamic analysis of multilayer ceramic capacitor for vibration reduction of printed circuit board

Owing to their high permittivity and volumetric efficiency, the demand for multilayer ceramic capacitors (MLCCs) has increased rapidly in recent times. Because of the electromechanical characteristics of BaTiO3, MLCC vibrates, resulting in printed circuit boards (PCBs) generating acoustic noise. To construct an accurate finite element model of an MLCC, piezoelectric and electrostrictive coefficients were extracted and verified through experiments. The top cover layer thickness and bandwidth were chosen as design parameters to reduce the vibration of PCB. The simulation results indicate that the bandwidth and top cover layer thickness are highly related to the vibration in the top direction and the rotational moment generated from the head surface, respectively. Based on the analysis results, a novel MLCC was suggested and it exhibited reduced vibrational characteristics of PCB about 75 % compared with that of commercial MLCCs.

The influence of dielectric environment on the localized surface plasmon resonance of silver-based composite thin films

Ag-based thin films with different topography were prepared by annealing process and laser irradiation, respectively. The tunability of localized surface plasmon resonance (LSPR) was realized by adjusting the cover layer thickness of ITO or TiO2. The effect of dielectric environment of Ag-based composite thin films on structure, surface morphology and optical property was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), UV-VIS-NIR double beam spectrometer and Raman system, respectively. With the thickness of dielectric layer increasing, the topography of as-irradiated Ag-based thin films became smoother while the as-annealed Ag-based thin films had a rougher surface. LSPR absorption of both ITO/Ag and TiO2/Ag bilayers showed red shift with the thickness of dielectric layer increasing. The electromagnetic field coupling between dielectric layers and Ag thin films contributed to increase significantly the sensitivity of surface enhanced Raman scattering (SERS). Additionally, the result of finite-difference time-domain (FDTD) simulation was in good agreement with that of the experiment.

Experimental tests on the underwater abrasion of Engineered Cementitious Composites

The abrasion of Engineered Cementitious Composites (ECC) due to waterborne materials in hydraulic structures was investigated using the ASTM C1138 abrasion test method. The test specimens were divided into two groups, the first was directed to study the effect of the PVA fiber content, while the second investigated the effect of the ECC covering layer thickness. The tests were conducted at ages of 3, 7 and 28 days. The test results showed that the abrasion resistance increases as PVA content increase. At an age of 28 days, incorporating low PVA contents (0.5% and 1.0%) increased the abrasion resistance by approximately 20%, while the inclusion of high PVA contents (1.5% and 2.0%) improved the abrasion resistance significantly with percentage improvements ranging from 50 to 95%. The percentage abrasion weight losses after 72 testing hours at this age were 7.6, 5.9, 4.7, 3.6 and 2.4% for fiber contents of 0, 0.5, 1.0, 1.5 and 2.0%, respectively. The test results also showed that covering of normal concrete with 1 cm layer of ECC is not effective during the early age of this material, while a layer of 3 cm thickness showed good abrasion resistance at early and mature ages.

How Thick Should Cover Layer be for Radioactive Waste Disposal Facility? The Case of the Yamin Plain, Israel

Two main natural processes which control the migration of radioactive contaminants to the biosphere were studied in the Yamin Plain in order to evaluate the thickness of a cover layer needed for near-surface radioactive waste disposal facility. The first is the natural erosion of the cover layer, and the second is the infiltration during rain and runoff events. The erosion rate of the soil surface was studied by optical stimulation luminescence technique. It was found that during the last 14,000 years, the erosion rate was 0.3 mm/y which are 3 m for 10,000 years. The infiltration depth assessment was based on water content measurements and numerical modeling. It shows that under the most extreme rain event having an equivalent rain of 84 mm, infiltration depth was limited to 4.5 m. Taking into account the two processes, the effective cover layer thickness over 10,000 years should be at least 7.5 m thick.

Modeling viscous dissipation during vocal fold contact: the influence of tissue viscosity and thickness with implications for hydration.

The mechanics of vocal fold contact during phonation is known to play a crucial role in both normal and pathological speech production, though the underlying physics is not well understood. Herein, a viscoelastic model of the stresses during vocal fold contact is developed. This model assumes the cover to be a poroelastic structure wherein interstitial fluid translocates in response to mechanical squeezing. The maximum interstitial fluid pressure is found to generally increase with decreasing viscous dissipation and/or decreasing tissue elasticity. A global minimum in the total contact stress, comprising interstitial fluid pressure and elastic stress in the tissue, is observed over the studied dimensionless parameter range. Interestingly, physiologically reasonable estimates for the governing parameters fall within this global minimum region. The model is validated against prior experimental and computational work, wherein the predicted contact stress magnitude and impact duration agree well with published results. Lastly, observations of the potential relationship between vocal fold hydration and increased risk of tissue damage are discussed based upon model predictions of stress as functions of cover layer thickness and viscosity.

Stability assessment of tunnel face in a layered soil using upper bound theorem of limit analysis

Underground tunnelling is one of the sustainable construction methods which can facilitate the increasing passenger transportation in the urban areas and benefit the community in the long term. Tunnelling in various ground conditions requires careful consideration of the stability factor. This paper investigates three dimensional stability of a shallow circular tunnel in a layered soil. Upper bound theorem of limit analysis was utilised to solve the tunnel face stability problem. A three dimensional kinematic admissible failure mechanism was improved to model a layered soil and limiting assumptions of the previous studies were resolved. The study includes calculation of the minimum support pressure acting on the face of the excavation in closed-face excavations. The effects of the characteristics of the layers on the minimum support pressure were examined. It was found that the ratio of the thickness of cover layers particularly when a weak layer is overlying a stronger layer, has the most significant influence on the minimum tunnel support pressure. Comparisons have been made with the results of the numerical modelling using FLAC3D software. Results of the current study were in a remarkable agreement with those of numerical modelling.

Effect of landfill cover layer modification on methane oxidation.

Levels of methane (CH4) oxidation in materials used for landfill cover attained in the laboratory are not often replicated in the field due to effects from the surrounding environment. This study investigates the three dominant factors affecting CH4 oxidation in the cover layer, namely, the thickness of cover layer, the methanotroph spraying manner, and the osmotic coefficient of the cover material. Results show that improved CH4 emission performance of the cover layer can be realized if methanotroph are introduced, meaning that a thinner cover layer is required. The highest CH4 emission reduction can be realized by spraying methanotroph into the top, middle, and bottom layers of a 30-cm thick cover layer with an osmotic coefficient of 7.76×10-5cms-1. Comparing results on cover layer thickness, methane monooxygenase (MMO) activity was much lower with increasing thickness meaning that the thicker cover could reduce O2 availability, thus inhibiting MMO activity. This suggests that MMO may be responsible for differences in CH4 emission reduction and/or oxidation making the osmotic coefficient an important factor for cover layer material.

Reduction of multilayer ceramic capacitor vibration by changing the cover thickness

Vibration of multilayer ceramic capacitors (MLCCs), caused by the piezoelectricity of the dielectric material, BaTiO3, can generate acoustic noise in electronic devices. To reduce the vibration of MLCCs, the relationship between the cover layer thickness and vibration of the MLCC was analyzed in this study. A numerical model using a finite element method was constructed for a parameter study of the cover layer. The results indicated that increasing the cover layer thickness reduced the vibration. Especially, thicker head and side covers largely reduced vibrations at the head and side surfaces of the MLCC. Increasing the thickness of the top cover reduced the entire vibration of the MLCC, while thickening the head and side covers increased top surface vibration.

3D FINITE ELEMENT METHOD MODELING AND SIMULATION OF THE TEMPERATURE OF CRYSTALLINE PHOTOVOLTAIC MODULE

The temperature reached by solar cells/modules during operation has been simulated to have information about the temperature distribution in the solar cell/module. A finite element (FE) model of the solar cell/module was created in COMSOL Multiphysics environment. The simulations enable visualization of the temperature distribution in crystalline silicon solar cell. The effect of different encapsulating materials, Ethylene-vinyl Acetate (EVA) and silicone on cell temperature are also investigated. An unwanted side-effect of the encapsulation of solar cells into a PV module is that the encapsulation alters the heat flow into and out of the PV module, thereby increasing the operating temperature of the PV module. These increases in temperature have a major impact on the PV module by reducing its voltage, thereby lowering the output power. A finite element (FE) model representing a real crystalline silicon solar cell/module in terms of size, mechanical and material properties is created. An in-depth study of the FE software used, COMSOL Multiphysics is done in other to get the best output in terms of solver configuration and memory considerations. Four different geometries of the solar cell/module are created for these simulations; each representing a stage or variant in the solar module assembly. At first, the models are validated comparing results from simulations such as the effect of changes in solar irradiance, wind velocity and incident angle of solar irradiance on temperature with those in literature. The effect of the type of protective cover used in the encapsulation, either glass-glass or glass-Tedlar on cell temperature is analyzed. The thickness of the protective cover layers and its optical properties are also investigated based on their effects on cell/module temperature. All the simulations leading to the conclusions drawn about the cell/module temperature and its distribution were performed by varying wind velocity, irradiance, material sizes and incident angle among other model modifications. The color maps and graphs are presented in this study.

Multifunctional poly(ester urethane) laminates with encoded information

Solvent-cast films from shape memory poly(ester urethane) (PEU) containing different weight contents of microencapsulated thermochromic pigments (T-PIGs) were prepared by drying in air. Spectrophotometric investigations unveiled that gradual loading with T-PIG black resulted in continuous darkening of the films up to filler contents of 20 wt%, accompanied by a steady enhancement of thermochromic properties. Taking this composition as standard, PEU films equipped with T-PIG black, blue and red were deposited atop PEU plaques to obtain laminate structures. Herein, the cover layer thickness (100 ± 5 μm) and the good dispersion of T-PIGs inside the polymer matrix were verified by scanning electron microscopy. Machine-readable information carriers were prepared by laser engraving quick response (QR) codes into the cover layer of the laminates and subsequently cutting cuboidal samples therefrom. Finally, thermo-mechanical programming of the QR code carriers was applied to randomly distort the code patterns, thus rendering them unreadable. Upon heating, surface decolorization and shape recovering occurred; during the ensuing cooling, the surface color and contrast reappeared whereupon the QR codes could be read out. Spectrophotometric, calorimetric and thermo-mechanical investigations gave evidence that the color switching temperature of the T-PIGs roughly coincided with the melting temperature of the ester-based switching segment and thus with the activation temperature of the shape memory effect. Apart from that unique functionality, manifold design concepts may render information carriers difficult-to-copy. Therefore, we anticipate tremendous potential as anti-counterfeiting technology.