Face Layers Research Articles

Natural frequency, damping and forced responses of sandwich plates with viscoelastic core and graphene nanoplatelets reinforced face sheets

The free and forced vibration analysis of a sandwich plate with the viscoelastic core and face layers reinforced functionally with multilayered graphene nanoplatelets is presented. Different graphene nanoplatelet distributions are considered through the thickness, and the effective properties of the graphene reinforced nanocomposite are obtained by the rule of mixture. The equations of motion are extracted using Hamilton’s principle and assuming the classical thin plate theory for face layers and the first-order shear deformation theory for the thick viscoelastic core. Assuming the simply-supported boundary condition for all edges, the displacement components are proposed by Fourier series and the complex eigenvalue problem is solved to obtain the natural frequencies as well as the loss factors. The results are validated with available investigations, and effects of some important parameters on the free and forced responses of the sandwich plate are studied.

Strain measurements along zero-strain trajectories as possible structural health monitoring method for debonding initiation and propagation in aircraft sandwich structures

This paper investigates a strain-based structural health monitoring (SHM) method for damage detection and propagation assessment in composite sandwich structures. As case example, an idealized Airbus A-340 spoiler is considered. Critical failure modes of such sandwich structures composed of fiber reinforced polymer (FRP) face layers and a honeycomb core are, e.g., face layer delamination and debonding from the core. The latter challenges today’s non-destructive evaluation methods, and thus, shall be addressed in the present work. For investigation an idealized spoiler model in the scale 1:2 composed of glass fiber reinforce polymer (GFRP) face layers and a honeycomb core is considered. The damage assessment is realized by static strain measurements along so-called zero-strain trajectories (ZST) at the loaded structure. A zero-strain direction exists for every spatial strain state with major strain directions with opposite signs (tensile and compression). Connecting zero-strain directions at various points of a structure yields a ZST. This allows the monitoring of a ZST by, e.g., a distributed fiber optical sensor (FOS) or fiber Bragg grating sensors (FBG). However, for the undamaged pristine state and defined loading there would be no strain measured along these trajectories. A structural change, i.e., damage initiation and propagation would influence the strain state and therefore yield a strain value along the ZST of the pristine structure. Consequently, strain measurements along a ZST represent a most sensible feature for damage assessment. The work investigates the use of strain measurements along ZST for the monitoring of debonding initiation and propagation at the edge of the spoiler model sandwich structure by means of numerical and experimental analysis. The considered face layer debonding is semicircular and located at the trailing edge of the idealized spoiler. For damage propagation analysis it is increased step-by-step. As load case, a true wind-load condition of the A-340 spoiler is considered. An in-depth numerical FEM investigation is performed to calculate the ZST for the pristine structure and the changes in the strain states caused by the damage. The experimental validation of the FEM model is realized by strain measurements via a digital image correlation system (DIC) at the statically loaded idealized spoiler. Finally, the possible application of strain measurements along a ZST for debonding initiation and growth will be demonstrated and its potential and issues for real online monitoring will be discussed.

Performance of Composite Filters Assembled from Multiple Layers of Basic Filtration Media

There is a severe shortage of face masks and N95 respirators due to the current COVID-19 pandemic, particularly in countries that were not well prepared in advance. In order to help ease the supply demands of these resources, a strategy of using multiple layers of basic filtration media to construct a composite filter that can match the particle collection efficiency offered by a N95 filtering facepiece respirator (FFR) is proposed. In this study, the filtration performances of four face masks and one N95 respirator using the same test protocol (as a reference) were first compared. Composite filter samples composed of multiple layers of basic face mask and MERV13 furnace media were then constructed and the filter performance of the composite filters was investigated. As expected, the minimum particle collection efficiency of the N95 respirator media sample was higher than 95% and the efficiency of the samples from the four tested face masks varied from 71.8% to 83.6%. The Figure of Merit (FOM) values of the face mask samples were generally half that of the N95 media sample. It was found that a N95-comparable collection efficiency can be achieved by combining two/three layers of face mask media but at the expense of a higher media pressure drop. Additionally, the composite filter samples made up of three/five layers of MERV13 furnace media could approach the FOM offered by the N95 media without the increased pressure drop. It was also found that the measured collection efficiency of multiple-layered filter media was not equal to the calculated in the test particle size range. Further studies are required to identify the reason(s).

Deformation of a Three-Layer Rod with a Compressible Core in a Neutron Flow*

We studied the deformation of a three-layer elastoplastic rod with a compressible core in a neutron flow. To describe the kinematics of the sandwich asymmetric across the thickness, the broken line hypothesis are adopted: Bernoulli’s hypothesis for the thin face layers and Tymoshenko’s hypothesis with linear approximation of displacements over the thickness for the compressible core. The resistance of the core in the tangential direction is taken into account. The constitutive stress–strain relations correspond to the theory of small elastoplastic deformations. The system of differential equilibrium equations is derived using the variational method. The kinematic boundary conditions of the rod is free support of the ends by fixed rigid supports. The boundary-value problem is solved by determining four functions of deflections and longitudinal displacements of the midsurfaces of the face layers. The analytical solution is obtained on the basis of the method of elastic solutions. Its numerical analysis is carried out in the case of an evenly distributed load.

Hinged Brick Facade Systems for Seismic Regions of Russia

The results of experimental studies on the assessment of seismic resistance of various structural solutions of hinged facade systems with a facing layer of brickwork under the action of dynamic loads on the structure, simulating seismic effects in earthquakes of 7-9 points on the scale of MSK-64 are presented. Dynamic tests were carried out with the use of an installation developed at Moscow State University of Civil Engineering, which included a metal stand with special movable supports, hydraulic cylinders (Actuator) and modern measuring equipment. This equipment made it possible to evaluate during testing the force effects on the stand, accelerations, displacements and deformations in any element of the stand and the hinged facade system. Two design variants of the hinged facade system, in which different types of masonry fastening to the supporting substructures are applied, are considered. The factors affecting the seismic stability of the facing layer under the action of dynamic loads and excluding its destruction and the appearance of cracks in it are established. During the tests, accelerations and deformations of the structures of the hinged facade system at the specified points were obtained. On the example of the analysis of the results of experimental dynamic studies of the system of the ATS-450 type of "U-kon" Company of, the effectiveness of the use of special measures that ensure the monolithic masonry and, accordingly, its reliability under seismic influences is shown.

Technology for producing wear-resistant bimetal bearing based on cast aluminum

The paper presents the results of research the new technological process for producing bimetallic materials in the composition of “aluminum cast alloy - sintered iron powder” by the method of joint stamping of liquid metal. The purpose of this research is obtain parts with high wear-resistant properties, special sintered powder materials are used, which have an internal porosity to retain lubricant. However, such materials do not fit well with traditional aluminum alloys. This problem is may be solved by creating new bimetallic alloys, part of which is an outer casing, and the other materials is the functional bearing. To accomplish this task, we conducted a study of a new technology for joint stamping of liquid metal. In order to optimize and increase the reliability of the experiment, the pressing pressure, the pressure holding time, and the tooling temperature of the matrix were taken as quantitative factors. The effect of the applied pressure on the mechanical properties of the base material and the facing layer was determined on a longitudinal section of the obtained samples by the Vickers method. It was revealed that the gradient of increasing hardness is directed to the outer radius of the workpiece, that is, to the opposite crystallization front. The high level of bimetal adhesion is explained by the presence of a uniform moderate zone of mutual solubility, including due to the violation of the porous surface layer of the powder billet.

3-D magneto-electro-thermal analysis of layered nanoplate including porous core nanoplate and piezomagnetic face-sheets

In the present article, three-dimensional size dependent thermal analysis of three-layered nanoplate with porous graded core and two piezomagnetic face-sheets is studied based on nonlocal strain gradient theory considering thickness stretching effect. The sandwich nanoplate standing on an elastic foundation and face layers are exposed to electric/magnetic potentials. Porosity is evenly and unevenly repartitioned thorough thickness of the core. To predict both reduction and enhancement of stiffness in small scales, a nonlocal parameter and a strain gradient parameter is used for analysis. The governing equations are derived using the principle of virtual works based on sinusoidal shear and normal deformation theory. The small size effect is obtained exploiting Eringen’s nonlocal elasticity theory. The influences of the porosity coefficient, temperature parameters, electric/magnetic potential, boundary conditions (simply supported and clamped) and parameters of foundation on bending, electrical, and magnetic behaviors of the sandwich nanoplate are presented and discussed.

Assessment of the quality of abrasion-resistant plates welded joint

The article presents the analysis of the structure and properties of joints made of abrasion-resistant plates having the structure of chromium cast iron and welded with filler metals, the use of which aimed to provide the high abrasion resistance of the surface layer and good mechanical properties of the base material. The face layer of the joint was made using the MMA (Manual Metal Arc) welding method and the Fe-Cr-Nb-B type nanocrystalline filler metal. The root weld was welded using an austenitic filler metal, whereas the filling layer was welded using the MAG method with a low-alloy filler metal. The joints were subjected to non-destructive tests (visual tests and penetrant tests) as well as to mechanical properties tests. The research involved macro and microscopic metallographic tests, the determination of the grain size using an Xpert PRO X-ray diffractometer, and the EDS analysis of the chemical composition of the precipitates. The assessment of the operational properties of the joints based on hardness measurements, static tensile tests, bend tests as well as identifying the metal-mineral abrasive wear resistance were performed in accordance with ASTM G65 ? 04 standards. The results of the abrasion resistance tests were referred to the HARDOX 400 steel reference specimen. Considering the tests results it was concluded that the used filler materials can assure the appropriate operational properties of welded abrasion-resistant plates.

Analytical and numerical simulations of a pressurized functionally graded smart spherical cap

To measure changes in pressure, strain or force in pressurized spherical shells used in caps and nose of a spacecraft, piezoelectric layers as sensors are used. In this article, axisymmetric bending analysis of a hybrid piezoelectric layered functionally graded spherical cap is analytically investigated. The piezoelectric face layers behave as sensors. Using thin shell theory in a polar coordinate as well as a new decoupling method, the differential equations for the shell with electrical and mechanical coupling are exactly solved. The pressurized spherical cap is subjected to external pressure and properties of the functionally graded material are changed through the thickness of the shell. The displacement, stress, and electric potential of the hybrid piezoelectric layered functionally graded spherical cap are analytically derived and then, the accuracy and performance of these results are validated by a finite element model and literature. Finally, the effects of various parameters such as piezoelectricity, material grading index, thickness to radius and curvature ratios are examined.

Knowledge and practice regarding menstrual hygiene among physically disabled women in Kathmandu, Nepal

Background and Objectives: Disability is the condition of difficulty in carrying out daily activities normally and in taking part in social life due to problems in parts of the body and the physical system. Disability also carries stigma, so disabled people may face layers of discrimination when they are menstruating. The objective of the review is to assess the menstrual hygiene practice of disabled women, the barriers they face, and the available interventions to help them manage their menstruation hygienically and with dignity.
 Material and Methods: This was a cross-sectional descriptive study that was conducted among 151 physically disabled peoples.Self-structured questionnaire and face-to-face interview was used as data collection tools and techniques. Data entry and analysis was done using SPSS 16.0. The results of the study were presented with the help of tabular description using the same software along with Microsoft word and excel 2007.
 Results: Most of respondents knew the 26-30 days as normal cycle duration (80.13%). Majority of respondents had reported that they do not go to holy places (91.39%) and should not cook food (94.03%) during menstruation. Most of respondents had stayed (96.68%) and eat (98.01%) at same place and 31.38% of respondents had bath daily during menstruation. 83.44% of respondents used sanitary while 69.53 % of respondents changed pad twice a day. Maximum number of the respondents 91.39% disposed sanitary pad in dustbin. 87.41% of respondents learned about menstrual hygiene from parents.
 Conclusion: Good and satisfactory knowledge about menstrual hygiene was found among girls of age group 15-24years.

A new formulation of continuous transverse shear stress field for static and dynamic analysis of sandwich beams with soft core

SummaryThis article presents a novel formulation for sandwich beams with soft core based on a layerwise description of continuous transverse shear stress field. The transverse shear stress field is assumed to follow a quadratic distribution in thick face layers and a uniform distribution in soft core. Based on stress‐strain relations, transverse shear strain is obtained, and in‐plane displacement field is determined by taking the integral of the transverse shear stain. By enforcing interlaminar displacement continuity, an explicit displacement field expression containing only displacement variables is formulated. In this formulation, interlaminar continuity conditions of displacement and transverse shear stress are satisfied simultaneously, and transverse shear and crosssectional warping effects in thick face layers are accurately taken account. To show characteristics and advantages of the present model, some classical theoretical models are further developed under different kinematic assumptions. The governing equations are derived using Hamilton principle, and finite element solutions for static and dynamic analysis of sandwich beams are presented. Comparisons with exact solution and other well‐known solutions, well demonstrate high accuracy of the present model for sandwich beams with different features. Besides, numerical discussions further reflect accuracy advantages of the present model in static and dynamic analysis of sandwich beams.

Effects of Tree Species and Wood Fiber Size in the Core Layer on the Formaldehyde Emission of Three-Layers Fiberboard

Three-layered medium density fiberboards (MDFs) were produced using fine wood fibers in the face layers and coarse wood fibers in the core layer. The core layer were produced from pine wood fiber or beech wood fibers while the face fibers were produced pine fibers. The length of the beech fibers in the core layer increased from 4.3 mm to 28.2 mm while it increased from 4.9 to 29.1 mm for the pine fibers. The shelling ratio and panel thickness were 50/50 and 10 mm, respectively. Based on EN 120-method, the formaldehyde emission released from the MDFs were identified. The formaldehyde emission considerably declined with increasing fiber size at the same manufacturing parameters such as resin content, density, pressing parameters, and mat moisture content. Furthermore, MDF specimens having beech fibers in the core layer showed lower formaldehyde emission than that of the MDFs having pine fibers in the core layer.

Buckling and vibration of FG graphene platelets/aluminum sandwich curved nanobeams considering the thickness stretching effect and exposed to a magnetic field

This paper studies the buckling and vibration analyses of a new model composed of a homogeneous ceramic curved nanobeam sandwiched between two reinforced composite layers. The face layers are made of an aluminum matrix reinforced with functionally graded (FG) graphene nanosheets (nanoplatelets) (GNShs). The present model is assumed to be embedded in an elastic substrate, exposed to an axial magnetic field and axial compressive external loads. Moreover, various boundary conditions are considered. The faces contain multi-composite nanolayres. Each nanolayer is composed of an aluminum matrix reinforced with uniformly distributed GNShs. The material properties of each face layer as a whole are graded through the thickness according to a piecewise micromechanical model. A refined higher-order curved beam theory is introduced in the polar coordinates considering the thickness stretching effect. Based on the proposed theory, four motion equations are presented containing Lorentz magnetic force and beam-foundation interaction. These equations are analytically solved to obtain the mechanical buckling load as well as the natural frequencies of the sandwich curved nanobeam. Since the general form of the strain-displacement relations is considered in the polar coordinates, the present formulation gives precise results for both shallow and deep curved beams. The effects of the different parameters such as arc angle, magnetic field parameter, elastic substrate parameters, boundary conditions, graphene wight fraction and core thickness on the buckling load and free vibration of the sandwich curved composite beams are investigated.

THE ANALYSIS OF DEFECTS AND REPAIR METHODS OF THE FRONT LAYER OF BRICKWORK OF MULTILAYER WALLS ON THE EXAMPLE OF A RESIDENTIAL BUILDING IN PERM

The article discusses the problem of defects in the front layer of brickwork of multilayer walls. At many facilities constructed using the technology of laminated masonry with brick facing, after several years of operation, defects such as vertical cracks in the masonry face layer and destruction of the bricks of the face layer begin to appear. These defects violate the aesthetic appearance of the building, reduce the thermal characteristics of the external walls, and, in some cases, can lead to the collapse of certain sections of the brick cladding layer. This problem is considered on the example of a 10-storey residential building with external multilayer walls, located in Perm. The building was commissioned in 2005, but already in 2010, many defects of the front layer of masonry were discovered. The article provides data obtained during surveys carried out in 2010 and 2019. The main defects of the external masonry verst are described, among which one can distinguish the destruction of the masonry face layer, vertical cracks, the absence of stitching along the supporting corner of the masonry, and the absence of expansion joints. The main causes of damage are associated with numerous deviations from the project. The results of calculating the outer verst of brickwork for eccentric compression are presented. As measures aimed at eliminating defects, the article describes possible methods of repairing the face masonry: the installation of vertical and horizontal expansion joints, longitudinal reinforcement and anchoring with BIT rods to prevent the development of vertical cracks and destruction of the masonry.

Influence of layered structure of composite timber floor boards on their hardness

The possibility of using composite elements of flooring pine veneers with knotholes for the production of supporting layers has been determined. This assessment was made on the basis of the Brinell hardness measurement of the face layer of five-layer composites with empty spots in their structure imitating knotholes of various diameters (10, 20 and 50 mm). The dependencies obtained from empirical determinations were supported by numerical analysis. It was found that it is possible to use veneers with defects (empty spots) with a diameter of up to 20 mm to produce composites of three and more layers of wood (counting from the face layer). The anatomical section of the exposed wood on the face (radial cross-section, tangential section) of the layered composite does not affect the obtained hardness values.

Analyses and design of steep slope with GeoBarrier system (GBS) under heavy rainfall

A GeoBarrier system (GBS) is a combination system of reinforced soil walls to stabilize near-vertical cut slopes and capillary barrier principles to protect the wall from the effect of rainfall infiltration. Singapore requires construction materials that are cost-effective to support sustainable urban development. Therefore, recycled materials are utilized as GBS materials to avoid the use of high-cost materials, such as steel or concrete. GBS consists of planting geobags with unique geosynthetic pockets for sustainable plant growth as a facing layer of GBS. The negative pore-water pressure (suction) within the reinforced soil behind GBS was assured to be constant during rainfall since GBS is designed specially to minimize the rainfall infiltration into the reinforced soil. This paper presents the practical design and stability analysis of the GBS, considering the presence of suction within the reinforced soil body. The monitoring of GBS performance in the field was carried out via field instrumentation. Finite element analyses of the GBS under extreme rainfalls were also performed for evaluation of the GBS performance. The field instrumentations and numerical analysis results showed that GBS was able to protect the slope from rainfall infiltration; therefore, the stability of the slope retained by GBS was not affected by the rainfall. Results from the analytical calculation showed that the most critical mode of failure is sliding along the base, followed by the global and local slope stability. The GBS is not susceptible to local instability.

Free and forced vibration of sandwich plates with electrorheological core and functionally graded face layers

The free and forced vibration of a sandwich plate with functionally graded face layers and electrorheological fluid core is presented in this article. Assuming classical thin plate theory for face sheets and first order shear theory for the core layer, the equations of motions are derived using Hamilton’s principle. The simply-supported boundary condition is considered for all edges and the generalized Fourier series are employed to represent the displacements of the sandwich plate. The natural frequencies and loss factors are obtained by solving the complex eigenvalue problem. The results of free and forced responses are compared and validated with the previous articles and effects of electric field, geometric aspect ratio, functionally graded component ratios and core layer thickness on the dynamic behavior of the sandwich plate are studied.

Effects of a Chipboard Structure on Its Physical and Mechanical Properties.

The paper evaluated the possibility of manufacturing wood-based boards from the material left over from sawmill processing of wood. The boards were made from chips created during cant preparation for cutting and sawdust generated during further sawnwood preparation. They were made as one- and three-ply boards with face layers containing industrial microchips. Mechanical properties determined for one-ply boards in a bend test were used as guidelines for manufacturing three-ply boards. The outcomes were much better when the core layer comprised a mix of chips and sawdust than the chips alone. The study also showed that for the assumed technological parameters it is possible to produce three-ply boards with properties meeting the criteria for P2 furniture boards.

An effect of fabrics thickness and structure on moisture management properties of 3D spacer fabrics

PurposePolyester multifilament is used to produce the face and back layer of warp knitted spacer fabric (WKSF) and these two layers are connected by polyester monofilament as a middle layer. This fabric has unique and extraordinary characteristics, and different possibilities of fabric structure and the middle layer thickness are tried to find out the moisture management properties. The paper aims to discuss these issues.Design/methodology/approachThis study investigates the influence of fabric thickness and structure on moisture management properties.FindingsPolyester monofilament quickly up takes the water molecule from the water reservoir and transfers it by capillary action. The gravitational force and the availability space between the two outer surface layers restrict the movement of water molecules, although the pressure develops to push the molecules from the water reservoir. As a result, all the spacer fabric samples attain the equilibrium state very quickly. WKSF and the hexagonal net structure prove to be better in vertical wicking.Originality/valueThe liquid movement is quick in the front side of the spacer fabric, and the rate of wicking is higher in open structure than in the closed structure. It confirms that the hexagonal net structure produces high pore size on fabric and it reaches maximum wicking values. Fabric thickness does not have much influence on the vertical wicking properties of all fabric samples, and the rate of liquid movement produces a similar trend. In in-plane wicking, the polyester monofilament in the middle layer of spacer fabric plays a major role rather than the outer surface layers of fabric.

Free vibration and buckling analysis of laminated composites and sandwich microbeams using a transverse shear-normal deformable beam theory

In this paper, the free vibration and buckling responses of laminated composite and sandwich microbeams with arbitrary boundary conditions are investigated. The governing equations based on the modified couple stress theory are derived by using the total potential energy of a microbeam and employing a transverse shear-normal deformable beam theory. Extensive analysis results in terms of dimensionless fundamental frequencies and dimensionless critical buckling loads are introduced for various boundary conditions, aspect ratios, orthotropy ratios, fiber orientation angles, thickness to material length scale parameter ratios, and core thickness to face layer thickness ratios.