Load-bearing Layers Research Articles

Investigation of the influence of the elastic medium on the dynamic behavior of a three-layer elliptical cylinder under non-stationary loading

Dynamic transient processes are studied and the results of evaluating the influence of an elastic medium on the behavior of a three-layer cylindrical shell structure of elliptical cross-section under non-stationary impulse loading are given. The used model of the theory of shells and rods by S. P. Tymoshenko, taking into account independent static and kinematic hypotheses for each layer of the structure. Numerical calculations of normal deflections and normal stresses of the load-bearing layers of the structure, which determine its stress-strain state (SSS), have been performed. Variants of the structure without a polymer aggregate and with a discrete-symmetric rib-reinforced aggregate are considered. A comparative analysis of the deflections and stresses of the load-bearing layers of the structure in the absence of light aggregate and in its presence is given.Numerical results regarding the dynamics of the three-layer structure were obtained using the finite element method.

GPR method for estimation of unbound load-bearing layers’ parameters using machine learning and interactive modelling

The demand for nondestructive testing techniques (NDTs) that can be implemented continuously and cost-effectively for large-scale study purposes is increasing. Ground penetrating radar (GPR) as an NDT method permits the estimation of pavement materials characteristics without disrupting the serviceability of the system. This research used typical pavement materials for constructing load-bearing layers (base and subbase) for the GPR laboratory tests. A 2 GHz GPR antenna was applied to execute the tests by changing three essential variables of the material: water content, compaction and clay content. Machine learning and interactive methods were innovatively utilised to model the collected data. As a result, a multivariate non-linear empirical function is proposed by the interactive procedure. Furthermore, the machine learning modelling (SVM method) with R2 of 0.91 indicates promising results to evaluate the pavement layers’ properties. Machine learning can enhance the speed and accuracy of analysis when faced with multi-variables and extensive data.

Mechanical Properties of the Materials Making up the Conveyor Belt Structure

Belt conveyors, equipped with belts designed for transporting materials and finished products are used in many industries. They allow to transport delicate items, for example made of glass, heavy products, such as canned food products and lightweight items, such as cardboard boxes. For this reason, the conveyor belts must, besides transferring power, ensure adequate conditions of transport for the conveyed materials without compromising the service life of the belt. Homogenous belts may not be capable of meeting all these requirements at a time. Composite belts, composed of the load-bearing layers and covering materials adhered thereon with the purpose to modify the surface properties, can be an option of choice in such cases. The described experiments were carried out on the respective materials making up composite belt joints as part of the research efforts related to the PhD thesis on adhesive bonding of composite belting materials. The strength tests were carried out on dumbbell-shaped specimens that were prepared from the load-carrying layer of synchronous polyurethane belting, the facing materials, namely polyamide fabric and polyurethane foam and the polyurethane adhesive used to join these layers. The differences in the parameters describing the surface properties, i.e. hardness and roughness were also checked. The experimental results were used to determine the material and strength properties of the components and the resulting differences were analysed.

Influence of Layer Motion in a Three-Layer Structure on Its Stress–Strain State

A refined calculation method is proposed for a three-layer (sandwich) structure in the edge-effect zones, taking account of how motion of the load-bearing (external) layers affects the stress–strain state. Functions approximating the stress distribution in the central layer (filler) are used to determine the stress–strain state of the three-layer structure. Those functions should correspond to the actual behavior of three-layer structures.

Повторное знакопеременное нагружение упругопластической трехслойной пластины в температурном поле

Axisymmetric deformation of a three-layer circular plate under repeated alternating loading from the plastic region by a local load is considered. To describe kinematics of asymmetrical on the thickness of the plate pack is adopted the hypothesis of a broken line. In a thin elastic-plastic load-bearing layers are used the hypothesis of Kirchhoff. A non-linearly elastic relatively thick filler is incompressible in thickness. It is taken to be a hypothesis of Tymoshenko regarding the straightness and the incompressibility of the deformed normals with linear approximation of the displacements through the thickness layer. The work of the filler in the tangential direction is taken into account. The physical relations of stress-strain relations correspond to the theory of small elastic-plastic deformations. The effect of heat flow is taken into account. The temperature field in the plate was calculated by the formula obtained by averaging the thermophysical parameters over the thickness of the package. The system of differential equations of equilibrium under loading of the plate from the natural state is obtained by the Lagrange variational method. Boundary conditions on the plate contour are formulated. The solution of the corresponding boundary value problem is reduced to finding the three desired functions: deflection, shear and radial displacement of the shear surface of the filler. A non-uniform system of ordinary nonlinear differential equations is written for these functions. Its analytical iterative solution is obtained in Bessel functions by the method of elastic solutions of Ilyushin. In case of repeated alternating loading of the plate, the solution of the boundary value problem is constructed using the theory of variable loading of Moskvitin. In this case, the hypothesis of similarity of plasticity functions at each loading step is used. Their analytical form is taken independent of the point of unloading. However, the material constants included in the approximation formulas will be different. The cyclic hardening of the material of the bearing layers is taken into account. The parametric analysis of the obtained solutions under different boundary conditions in the case of a local load distributed in a circle is carried out. The influence of temperature and nonlinearity of layer materials on the displacements in the plate is numerically investigated.

THE SIMULATION ASSESSMENT OF THE VENEERING LAYERS OF PROSTHETIC CROWNS IN CONCENTRATED CONTACT

The aim of the study is to simulate and analyse the distributions of stresses and resultant displacements during concentrated loading of the layered material compositions used in prosthetic crowns in order to assess their resistance and demonstrate the impact of strength parameters of the veneer and framework on the transfer of external loads. The research materials are samples replicating the layered structure of prosthetic crowns. The load-bearing layers were made using CAD/CAM technology, and the dedicated veneering layers were fired or polymerized on the frameworks and constituted the top structure for cooperation during occlusion. If the material of the veneering layer differs from the material building the framework, for example, in the ceramic-metal type, spreading of the resultant displacements to the framework and high values of shear stress at the border of the veneering layer and the framework may be unfavourable and cause the veneer layer to chip off. This distribution of stresses and displacements may have a much smaller impact on the ceramic veneering of a ceramic or glass-ceramic framework, as both layers are much more homogeneous in terms of material.

Design of a Novel Road Pavement Using Steel and Plastics to Enhance Performance, Durability and Construction Efficiency.

Durability is one important problem that pavement engineers need to address in pavement’s long service life. Furthermore, easily recycled pavement materials, and safe and efficient pavement construction are also important areas for development in road engineering. For these reasons, a new asphalt steel plastic (ASP) pavement structure was proposed with an asphalt mixture forming the surface layer, and steel plate and plastic materials functioning as the main load-bearing layers. Based on a comprehensive performance review and cost-benefit analysis, stone mastic asphalt (SMA) is recommended to be used as the surface layer; and A656 steel plate and acrylonitrile butadiene styrene (ABS) plastic materials should be the main load-bearing layer, on top of a foundation layer made with graded crushed stones. A glass fiber reinforced polymer (GFRP) insulation layer is recommended for use between the steel plate and ABS. Mechanical properties of the ASP pavement were analyzed using the finite element method. Laboratory tests were conducted to verify the thermal insulation performance of GFRP, the high-temperature stability and the fatigue resistance of ASP pavement. Results show that some of the mechanical properties of ASP pavement (with a structure of 80 mm SMA asphalt mixture, 8 mm steel plate, 140 mm ABS and 200 mm crushed stones) are comparable with conventional long-life pavement (with 350 mm asphalt layer overlaying 400 mm graded crushed stones). Dynamic stability of the ASP slab specimens can reach 10,000 times/mm, and the fatigue life is about twice that of SMA. Besides, the ASP pavement can be prefabricated and assembled on-site, and thus can greatly improve construction efficiency. From the lifecycle perspective, ASP pavement has many advantages over traditional pavements, such as durability, lower environmental footprint and recyclability, making it is worth further research.

Dynamic characteristics of three-layer beams with load-bearing layers made of alumino-glass plastic

Aluminum-fiber-reinforced plastics (GLARE) are promising aviation materials with increased characteristics of specific stiffness and strength, fatigue strength, impact resistance, and residual strength after impact. Nowadays, GLARE are used for making elements of the fuselage of the long-haul passenger aircraft Airbus A380, as well as some other elements of aircraft structures. The results of experimental studies of eigenfrequencies and damping coefficients of three-layer beams made with face sheets of five-layer GLARE and with a core made of polyimide foam are presented. The tests were performed using the method of free bending vibrations of cantilever samples. The dynamic parameters of the three-layer beams were calculated based on the analysis of amplitude-frequency characteristics obtained by the fast Fourier transform method. Mechanical characteristics of GLARE and filler samples are preliminary determined in static and dynamic tests. The damping factor of the core is determined by the dynamic mechanical analysis method. The core shear modulus is determined by measuring the flexural rigidity of manufactured three-layer beams in a quasi-static three-point bending test. Based on a comparison of the design data and the results of the experiments, it is shown that in dynamic tests, the flexural rigidity of three-layer specimens is reduced in comparison with the estimated values, which may be due to the peculiarities of changing the characteristics of the foam core under dynamic loading. The value of the damping factor of GLARE samples was ~0.02, the foamed core was ~0.08 and three-layer beams were ~0.067 in the range of vibration frequency up to 60 Hz.

Influence of approach of layers of a three-layer structure on its stress-strain state

A refined method for calculating three-layer structures (TLS) in the zones of edge effects is considered, taking into account the influence of the approach of load-bearing layers on the stress-strain state (SSS) of the TLS. To determine the SSS of TLS, approximating strain distribution functions in the filler are used, which should correspond to the actual work of three-dimensional structures. Keywords: three-layer structure, load-bearing layer, approach of layers, approximating function, filler. hairulla213@mail.ru

Technology for Strengthening Earth Mound’s Foundations, Reinforced with Geosynthetic Materials

Technology of strengthening subgrade foundations, using geosynthetic material at a specific object is described in the article. The use of the proposed geosynthetic material as a reinforcing element is effective, creating load-bearing layers of the earth mound’s foundations, slopes or other types of support structures. Soil base reinforcement of the earth mound with geosynthetic woven material “Stabilenka®” allows increasing the bearing capacity of weak silty clay soils of soft plastic and fluid consistencies to fluid from 1.5 to 5 times, depending on the strength of the material, reduce deformability by 20% and can be considered as the most optimal. We can consider, that the use of a new progressive material allows increasing bearing capacity of the subgrade and reducing the cost and labor intensity of its construction in comparison with traditional methods and the duration of the mound preparation on weak areas is reduced by up to 5 times, using such technology.

Wear Morphology on the Surfaces of CoCrMo Unicompartmental Knee Joint Endoprostheses as Elements of Metal-Metal Friction Nodes.

The article assesses the strength and structural parameters of load-bearing layers of metal biobearings made of CoCrMo alloy. The research material consisted of unicompartmental knee joint endoprostheses used in the human body, removed due to excessive wear. No patient participated in the examinations. The endoprostheses used as research material underwent the liquidation procedures in the hospital, which has all necessary permissions and certifications to perform endoprosthetic procedures. Endoprostheses selected for the examinations had been used for 6 to 12 years at similar load conditions as declared by the patients, i.e., body weight of F = 835 N, declared activity expressed as the number of load cycles up to 100 thousand/year, and no artificial joint infections. To assess the homogeneity of the research material, the analysis of chemical composition using a Joel scanning electron microscope with EDS (Energy-dispersive X-ray spectroscopy) was made to exclude endoprostheses with various alloying additives. Microscopic examinations were performed using the Phenom XL microscope, while the wear surface was examined using a Keyence VHX-900F microscope. Several experimental tests were also carried out on load-bearing surfaces to assess changes in strength parameters of the base material after a known life cycle and load conditions. Material hardness using the Vickers method, yield point, critical value of stress intensity coefficient, and the coefficient of friction µ were evaluated. The examinations allowed for the systematization of wear in the knee and femoral components of unicompartmental hip endoprostheses. The statistical evaluation of the number and costs of hip joint replacement surgeries in Poland was also made.

Effective Model of Load-Bearing Layers for Layer-by-Layer Analysis of the Stress-Strain State of Three-Layer Cylindrical Irregular Shells of Revolution

The use of effective approximations that increase the rate of convergence of numerical results when constructing a finite element model of bearing layers for a more accurate layer-by-layer analysis of the stress-strain state of three-layer irregular cylindrical shells is considered. It is believed that the carrier layers are sufficiently thin and rigid, and two-dimensional finite elements of natural curvature, constructed on the basis of the classical theory of moment shells, are used to simulate the stress-strain state. It is assumed that the aggregate layer can be modeled in thickness by the required number of three-dimensional finite elements, which allows one to take into account the change in geometric and physical-mechanical characteristics, as well as the parameters of the stress-strain state, not only along the meridional and circumferential coordinates, but also along the thickness of the shell and the aggregate layer. The finite element approximations considered allow one to reduce the order of systems of equations, i.e. to reduce the dimensionality of the problems being solved in comparison with the traditionally used approximations, which is especially important for layer-by-layer analysis of layered-heterogeneous structures. The high convergence rate of the numerical results obtained using the considered finite element model of the bearing layers is confirmed by a comparison with other known finite elements.

Investigation of the Influence of the Cutout Dimensions on the Stress-strain State of Three-layer Shells with Load-bearing Layers of Composite Materials

The description of the model for investigation of the influence of rectangular dimensions in terms of cutouts on the stress-strain state (SSS) in the layers of three-layer conical shells is given. The finite element model is based on the layer-by-layer analysis approach and allows to perform calculations of SSS in shell layers in a wide range of changes in the physical and mechanical characteristics of the layers in the presence of cut-outs. The equations of the classical theory of shells at reception of effective approximations (leading to high speed of convergence of received results) and construction of finite-element model of moment bearing layers are used. The approach with application of the elasticity theory relations for a three-dimensional body in curvilinear coordinates and obtained approximations for construction of a finite element model of the filler layer is described. Influence of the cut-out mortar angle on the parameters of the three-layer shell with load-bearing layers of composite materials is investigated.

Stability and Initial Post-Buckling Behavior of Orthotropic Cylindrical Sandwich Shells with Unidirectional Elastic Filler

The problem of the stability and initial post-buckling behavior of sandwich shells with transversely elastic light-weight filler is solved. The governing system of nonlinear equations is derived with allowance for structural discreteness that allows independent deformation of load-bearing layers. The system is solved with the asymptotic Koiter–Budiansky method. Structures composed of two cylindrical carbon-fiber shells interacting through a spring-type filler are analyzed. It is shown that the critical load under axial compression with like forces falls between the critical loads for the inner and outer shells. In the post-buckling state, the bending modes may be different. It is rational to increase the filler stiffness to a certain level.

Deformation of an Elastoplastic Three-Layer Circular Plate in a Temperature Field

A boundary-value problem on axisymmetric deformation of a circular elastoplastic plate, asymmetric across its thickness, in a temperature field is formulated. The physical equations of state used correspond to the theory of small elasticoplastic strains. The effect of a temperature field on the stress-strain state of the plate is considered. The intensity of thermal flow is constant. To describe the kinematics of the plate package, the hypotheses of a broken line are accepted: in the thin load-bearing layers, the Kirchhoff hypotheses are valid; in the rigid core, incompressible across it thickness, the Tymoshenko hypothesis is valid. The work of core in the tangential direction is taken into account. The equilibrium equations are derived by the variational method. An analytical solution of the boundary-value problem is obtained by the method of elastic solutions. A numerical analysis of the stress-strain state of a plate with a hinged contour is carried out.

Topological design, permeability and mechanical behavior of additively manufactured functionally graded porous metallic biomaterials

Recent advances in additive manufacturing (AM) have enabled the fabrication of functionally graded porous biomaterials (FGPBs) for application as orthopedic implants and bone substitutes. Here, we present a step-wise topological design of FGPB based on diamond unit cells to mimic the structure of the femoral diaphysis. The FGPB was manufactured from Ti-6Al-4V powder using the selective laser melting (SLM) technique. The morphological parameters, permeability and mechanical properties of FGPB samples were measured and compared with those of the biomaterials with uniform porous structures based on the same type of the unit cell. The FGPB exhibited a low density (1.9 g/cm3), a moderate Young’s modulus (10.44 GPa), a high yield stress (170.6 MPa), a high maximum stress (201 MPa) and favorable ductility, being superior to the biomaterials with uniform porous structures in comprehensive mechanical properties. In addition, digital image correlation (DIC) and finite element (FE) simulation were used to unravel the mechanisms governing the deformation and yielding behavior of these biomaterials particularly at the strut junctions. Both DIC and FE simulations confirmed that the deformation and yielding of the FGPB occurred largely in the load-bearing layers but not at the interfaces between layers. Defect-coupled FE models based on solid elements provided further insights into the mechanical responses of the FGPB to compressive loads at both macro- and micro-scales. With the defect-coupled representative volume element model for the FGPB, the Young’s modulus and yield stress of the FGPBs were predicted with less than 2% deviations from the experimental data. The study clearly demonstrated the capabilities of combined experimental and computational methods to resolve the uncertainties of the mechanical behavior of FGPBs, which would open up the possibilities of applying various porosity variation strategies for the design of biomimetic AM porous biomaterials. Statement of SignificanceFunctionally graded bone scaffolds significantly promote the recovery of segmental bone defect. In the present study, we present a step-wise topological design of functionally graded porous biomaterial (FGPB) to mimic the structure of the femoral diaphysis. The Ti-6Al-4V FGPB exhibited a superior combination of low density, moderate Young’s modulus, high yield stress and maximum stress as well as favorable ductility. The biomechanical performance of FGPB was studied in both macro and micro perspectives. The defect-coupled model revealed the significant yielding in the load-bearing parts and the Young’s modulus and yield stress of the FGPBs were predicted with less than 2% deviations from the experimental data. The superiority of combined experimental and computational methods has been confirmed.

Varied thermo-rheological structure, mechanical anisotropy and lithospheric deformation of the southeastern Tibetan Plateau

To investigate the lithospheric structure and deformation of the Tibetan Plateau, we present thermo-rheological models for two transects across the southeastern Tibetan Plateau (SE Tibet), showing strong lateral heterogeneity. The geodynamic implications are also investigated in relation to GPS motions, seismic anisotropy, seismicity distribution and crustal isostatic state. The unmatched pattern between Pms and SKS splittings which even intersect at right angles to the south of 26°N, suggests the crust-mantle decoupling. Constrained by a brittle load-bearing layer at the uppermost mantle beneath the Indochina block, the decoupling may occur below the uppermost mantle. The strong crust beneath the South China plate and Indochina block implied by the seismicity distribution, has two thick brittle load-bearing layers, indicating a coupled system. The crust beneath the Emeishan large igneous province (ELIP) also has two brittle load-bearing layers, but the brittle deformation is restricted to the topmost 10 km of the upper and lower crust. Only one brittle load-bearing layer resides in the upper crust in the other part of the Chuandian block. Combining with GPS and Pms splitting, we can infer that the weak crust with seismicity restricted into the depth of <30 km beneath the Chuandian block becomes decoupled. The heterogeneous rheological behavior under SE Tibet is further supported by different crustal isostatic states among the blocks. Through the comparison with observations in the central-northern Tibetan Plateau and Chuandian block, we suggest that the layers with aqueous fluids and (or) partial melting are distributed only in some place/channels of the weak middle-lower crust.

Study of Transverse Bending of a Honeycomb Three-Layer Panel with a Circular Axis

The model of transverse bending of a honeycomb three-layer panel with a circular axis is reduced to the design scheme of a three-layer beam with a circular axis and a shear-responsive core. Differential equations are obtained from the condition of stationarity of the functional from displacements of the three-layer beam; these equations allow one to investigate transverse bending while taking into account the variability of shear deformations along the thickness of the core. Transverse forces in load-bearing layers (shells) were found from the equilibrium condition of the selected beam element. The limits of the applicability of the proposed method are estimated.

Influence of Maximum Particle Size, Fines Content, and Dust Ratio on the Behavior of Base and Subbase Coarse Aggregates

Unbound aggregate base and subbase layers are the main load-bearing layers in a pavement structure. Size and shape properties of these aggregate materials should be controlled to ensure proper workability during construction and improved performance for pavement longevity. The effects of gradation, maximum particle size, fines content (percentage passing the No. 200 sieve), and dust ratio on the quality of aggregates were investigated by performing many soaked California bearing ratio tests on a crushed limestone material. The dust ratio represents the amount of fines content divided by the amount of minus No. 40 sieve material. The dust ratios studied were 0.4, 0.6, and 1.0. Two gradations commonly used in Illinois, with maximum particle sizes of 1 in. and 2 in., were studied to analyze the effect of fines content with respect to maximum particle size in the gradation. A typical range of fines contents (i.e., 5%, 8%, and 12%) was also considered. The results show that the gradation, dust ratio, and fines content should be taken into account in the selection of aggregate properties for stability requirements. Aggregates with larger maximum size particles provide high strength, and they are not affected as much as aggregates with smaller maximum size particles by an increase in fines content. The aggregates with smaller maximum size particles provide lower strength. It was also concluded that samples with a dust ratio of 1.0 do not necessarily result in an aggregate material with low strength.

Developing a 'thick skin': a paradoxical role for mechanical tension in maintaining epidermal integrity?

Plant aerial epidermal tissues, like animal epithelia, act as load-bearing layers and hence play pivotal roles in development. The presence of tension in the epidermis has morphogenetic implications for organ shapes but it also constantly threatens the integrity of this tissue. Here, we explore the multi-scale relationship between tension and cell adhesion in the plant epidermis, and we examine how tensile stress perception may act as a regulatory input to preserve epidermal tissue integrity and thus normal morphogenesis. From this, we identify parallels between plant epidermal and animal epithelial tissues and highlight a list of unexplored questions for future research.