Calculation of the moisture concentration field in a multilayered plate

Conclusion Thus, we have developed an algorithm and program to calculate fields of moisture concentration in a laminated plate for steady external temperatures and moisture contents. A test calculation and comparison of some of the findings with previous results demonstrated the accuracy of the program for solving a number of diffusion problems. For example, the program can be used to evaluate the life of the moisture-protective properties of polymer products, as well as to model moisture absorption in fiber composites.Curves of moisture concentration were calculated for a unidirectionally reinforced (with organic fibers) plastic at different relative humidities. We also calculated sorption curves and isotherms, which were shown to agree satisfactorily with previous empirical curves. It was shown that it is possible to approximately evaluate the sorption behavior of a unidirectionally reinforced fiber composite by means of a three-layer model and to analyze the stability of the result against an increase in the number of layers. For the two-component composite examined here, sorption behavior deviates from the classical behavior described by Fick's law — although the components of the composite obey this law.The algorithm and program that were developed make it possible to evaluate the kinetics of moisture absorption in complex composite systems and determine the distribution of moisture among and within the components.The study described here was conducted under grant 93.176 from the Latvian Science Council.Translated from Mekhanika Kompozitnykh Materialov, Vol. 30, No. 4, pp. 502–511, July–August, 1994.     

Study of moisture absorption by an organoplastic

Conclusion A complex experimental study of the state of sorbed moisture in a unidirectionally reinforced organoplastic was conducted. The methods of TG, DSC, DTA, and NMR showed that moisture absorption in OP is reversible up to 8%, the sorbed moisture does not crystallize in the temperature range from –70 to 0 °C, it is finely dispersely distributed and is in the strongly and weakly bound state, and there is almost no free moisture. The results of the sorption experiments conducted on OP and its structural components: microplastic and EDT-10 binder, in a wide range of temperature-humidity conditions and the data from physical studies showed that moisture absorption in the materials basically takes place by diffusion and is satisfactorily described by a phenomenological model based on the Fick equation.A method of accelerated determination of the sorption characteristics of anisotropic composite materials was developed, using the introduced concept of the fictitious diffusion coefficient and the extrapolation method of determining the limiting moisture content. The features of migration of moisture on the interface in a multiphase system were investigated, and the possibility of successive calculation estimation of the sorption characteristics of an organoplastic at different structural levels was demonstrated: components—unidirectionally reinforced composite—model laminated article. The tested phenomenological model of the sorption process and the experimentally obtained values of the characteristics of the material were the basis for a method of calculation determination of the resource of moisture-proofing properties of a model multilayer article of CM in nonstationary external conditions.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 624–632, July–August, 1990.     

A comparative analysis of moisture transport models as applied to an epoxy binder

The results of experimental and theoretical investigations into the kinetics of moisture sorption by a neat epoxy resin obtained from RAE Industries (Reapox 520, D523) are reported. The sorption process was realized in atmospheres with a constant relative humidity of 33, 53, 75, 84, and 97% and a temperature of 50°C. The results obtained showed that the diffusion behavior of epoxy resin did not obey Fick’s law under the experimental conditions considered. Consequently, the application of a non-Fickian diffusion model was necessary. For this purpose, two-phase moisture sorption models, a model with a time-dependent diffusivity, a two-phase material model, as well as relaxation and convection models of anomalous diffusion, were considered. The model parameters were obtained from the approximation of experimental sorption data. A comparative analysis of the sorption models was performed, and the specific features of their applications were estimated. The two-phase material model and the model with varying diffusivity were found to be the most suitable ones due to a good agreement between calculation results and experimental data and the rather small (three or four) number of parameters, which make them more flexible and physically more justified than the classical Fick’s model with its two parameters. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 4, pp. 555–570, July–August, 2007.     

Effects of Moisture and Stresses on the Structure and Properties of Polyester Resin

The results of a complex study of structural changes in a cured Norpol 440 polyester resin under the action of damp environment and mechanical loading are presented. A considerable effect of absorbed moisture on the structure and some characteristics of the material is revealed by using thermophysical methods and X-ray diffractometry. The joint effect of moisture and mechanical stress is estimated by investigating the creep in stationary and nonstationary moisture conditions. The anisotropy of the material structure formed during creep is evaluated from the results of dilatometric measurements. It is found that the degree of anisotropy of the material after creep accompanied by moisture sorption is higher than that after creep in the conditions of moisture equilibrium with atmosphere. It is established that the aftercure and relaxation of the residual creep deformation come to an end at heating to 80-85°C. At a further rise in temperature and repeated heating, changes in the material structure are not observed.     

A finite element model for hygrothermal analysis of masonry walls with FRP reinforcement

Modeling of moisture migration and heat transfer in fiber reinforced polymer (FRP) composite upgraded masonry structures is of great importance, since the interfacial adhesive between the reinforcing FRP laminate and the host masonry is prone to moisture damages. In this paper, a generic theoretical formulation was first developed to model moisture and heat transport in a layered structure consisting of distinct materials. This formulation was based on the framework of the hygrothermal model presented by Philip and De Vries for a monolithic porous medium. Finite element implementation of the formulation was subsequently used to model moisture and heat transport in an FRP reinforced masonry block. Analytical results were then compared with experimental data to validate the model. Parametric studies were then performed for a concrete block with a reinforcing FRP laminate partially covering one surface. The results showed that changing temperature gradient affects the moisture distribution considerably. This effect was found particularly significant at the concrete/FRP interface where a drastic change in local temperature gradient is present.     

Sorption Characteristics of Polymer Concrete during Long-Term Exposure to Water

The moisture sorption characteristics of polymer concrete and its components (polyester resin, unfilled and filled with diabase flour) on long-term (up to 15-year) exposure to water at different temperatures are studied. It is established that, during the long-term sorption and subsequent desorption at 20°C, the ratio of diffusion coefficients of the polymer concrete and the corresponding resin is equal to the value of time-moisture reduction function, which characterizes changes in the creep compliance of the materials. The evaluation of the diffusion coefficient of the composite from the properties of its components, by using various known heat-and-mass-transfer models, shows that most acceptable is the Kerner model. With account of volume content of pores, an estimate for the limiting moisture content in the composite is proposed. An analysis of sorption curves of the composite and the corresponding resin reveals that Fick's law does not describe the experimental results in the range of large times and/or elevated temperatures. In the case of polyester resin filled with diabase flour, the composite effect is expressed in a linear increase in the specimen mass (the rate of the increase is temperature-dependent. In the case of polymer concrete, the composite effect is expressed in mass losses, which can be described by Fick's law with a diffusion coefficient and a limiting moisture content both depending on temperature.     

Formation of Saddle-Shaped Composite Sheets

Based on the deformation model of an unbalanced multilayer composite, changes in bending curvatures of sheet-type composites with nonsymmetric structure relative to the midplane of the sheet, depending on the moisture of layers, are predicted. The bending curvatures of saddle-shaped sheets of wood-based composites are calculated with regard to the physical and mechanical properties, geometrical dimensions, orientation, and distribution of layers. The analytical results are compared with the bending curvatures found experimentally for a four-layered unbalanced composite made of birch veneer. The applied calculation model enables us to determine the values of bending curvatures of saddle-shaped wood composite sheets, which can be used in elaborating the technological recommendations.     

Influence of Modifiers on the Physicomechanical Properties of Sawdust-Polyethylene Composites

Polymer-wood composites based on recycled polyethylene (RPE) are investigated. Dispersed alder sawdust was utilized as a filler. To improve the compatibility between the nonpolar matrix and the polar wood fibers as a reinforcement, two types of modifiers were used, which differed in their chemical nature and mechanical interaction with the constituents of the composites. The modifiers of the first type (paraffin and OP) improved the dispersibility of sawdust (SD), and those of the second type (Exxelor 1015 and OREVAC) contained groups of maleic anhydride, which interacted with the OH-groups of SD. The effect of the modifiers on the moisture sorption by SD, the dispersibility of the filler in the matrix, and the strength characteristics (ultimate strengths and moduli in tension and bending) of dry and moist RPE–SD composites and on their moisture sorption is estimated. The best results were obtained for the composites modified with paraffin, which is due to the more efficient employment of the strength and rigidity of well-dispersed SD fibers. In their strength characteristics, the RPE-based composites investigated are comparable to composites based on low-density polyethylene.     

A quasilinearization approach to heat transfer in MHD visco-elastic fluid flow

The paper deals with the study of the flow of an incompressible electrically conducting visco-elastic fluid referred to as Walter’s liquid B over a porous non-isothermal stretching sheet using quasilinearization technique adopting a numerical approach. The sheet is assumed to stretch uni-directionally and the fluid above the sheet is at rest if there were no stretching. The temperature profiles are obtained numerically and these are displayed through graphs for diverse values of Prandtl number, visco-elastic parameter, magnetic parameter, source/sink parameter, wall temperature parameter and wall heat flux parameter. The results are compared with those available in literature obtained through analytical procedures and are seen to be in good agreement.     

Flow and heat transfer of double fractional Maxwell fluids over a stretching sheet with variable thickness

This paper presents research on the fractional boundary layer flow and heat transfer over a stretching sheet with variable thickness. Based on the Caputo operators, the double fractional Maxwell model and generalized Fourier's law are introduced to the constitutive relationships. The governing equations are solved numerically by utilizing the finite difference method. The effects of fractional parameters on the velocity and temperature field are analyzed. The results indicate that the larger is the fractional stress parameter, the stronger is the elastic characteristic. However, fluids show viscous fluid-like behavior for a larger value of fractional strain parameter. Moreover, the numerical solutions are in good agreement with the exact solution and the convergence order can achieve the expected first order. The numerical method in this study is reliable and can be extended to other fractional boundary layer problems over a variable thickness sheet.     

Biomagnetic viscoelastic fluid flow over a stretching sheet

Of concern in this paper is an investigation of biomagnetic flow of a non-Newtonian viscoelastic fluid over a stretching sheet under the influence of an applied magnetic field generated owing to the presence of a magnetic dipole. The viscoelasticity of the fluid is characterised by Walter’s B fluid model. The applied magnetic field has been considered to be sufficiently strong to saturate the ferrofluid. The magnetization of the fluid is considered to vary linearly with temperature as well as the magnetic field intensity. The theoretical treatment of the physical problem consists of reducing it to solving a system of non-linear coupled differential equations that involve six parameters, which are solved by developing a finite difference technique. The velocity profile, the skin-friction, the wall pressure and the rate of heat transfer at the sheet are computed for a specific situation. The study shows that the fluid velocity increases as the rate of heat transfer decreases, while the local skin-friction and the wall pressure increase as the magnetic field strength is increased. It is also revealed that fluid viscoelasticity has an enhancing effect on the local skin-friction. The study will have an important bearing on magnetic drug targeting and separation of red cells as well as on the control of blood flow during surgery.     

Modelling of thermal printers

This paper is concerned with the temperature field produced by a thermal printer head. Such heads are used to provide high quality prints of electronically stored images. In this system, a thin dye-layer, sandwiched between two copolymer sheets, is heated by a thermal head and dye diffuses into the receiver sheet producing a small dye-dot. The picture is made up of a large number of such dots. The basic aim is to determine the amount of dye which is eventually diffused into the receiver sheet when the heating is turned off and the system has cooled down. However, the amount of dye which diffuses into the receiver sheet depends on the temperature field because the diffusion coefficient is a sensitive function of temperature. In the thermal printer system, each head is heated by an electric current which is carried by gold leads. In this paper, we show that the heat loss through these leads has an important effect on the temperature field produced by the head and therefore, strongly influences the amount of dye transferred.     

A numerical study of boundary layer flow of viscous incompressible fluid past an inclined stretching sheet and heat transfer using nonpolynomial spline method

In the present paper, we study the boundary layer flow of viscous incompressible fluid over an inclined stretching sheet with body force and heat transfer. Considering the stream function, we convert the boundary layer equation into nonlinear third-order ordinary differential equation together with appropriate boundary conditions in an infinite domain. The nonlinear boundary value problem has been linearized by using the quasilinearization technique. Then, we develop a nonpolynomial spline method, which is used to solve the flow problem. The convergence analysis of the method is also discussed. We study the velocity function for different angles of inclination and Froude number with the help of various graphs and tables. Then using these in heat convection flow, we obtain the expression for temperature field. Skin friction is also calculated. The various results have been given in tables. At last, we calculated the Nusselt number.     

Diffusion Moisture Sorption by an Isotropic Polymer Material in Atmosphere with Stationary and Nonstationary Humidity

Solutions to the Fick's diffusion equation with stationary and nonstationary boundary and nonequilibrium initial conditions for describing the moisture sorption under actual operational conditions are presented. The cases of stepwise and harmonic changes in the environmental humidity are considered. Generalized criteria for comparing the moisture sorption under nonstationary and stationary conditions are developed. A possibility of accelerated computer simulation of natural periodic changes in the atmospheric humidity is shown. The solutions obtained are approbated on a polyester resin.     

Heat transfer in MHD viscoelastic boundary layer flow over a stretching sheet with non-uniform heat source/sink

This paper presents the study of momentum and heat transfer characteristics in a hydromagnetic flow of viscoelastic liquid over a stretching sheet with non-uniform heat source, where the flow is generated due to a linear stretching of the sheet and influenced by uniform magnetic field applied vertically. Here an analysis has been carried out to study the effect of magnetic field on the visco-elastic liquid flow and heat transfer over a stretching sheet with non-uniform heat source. The non-linear boundary layer equation for momentum is converted into ordinary differential equation by means of similarity transformation and is solved exactly. Heat transfer differential equation is also solved analytically. The effect of magnetic field on velocity, skin friction and temperature profiles are presented graphically and discussed.     

Numerical Solution of the Kiessl Model

The Kiessl model of moisture and heat transfer in generally nonhomogeneous porous materials is analyzed. A weak formulation of the problem of propagation of the state parameters of this model, which are so-called moisture potential and temperature, is derived. An application of the method of discretization in time leads to a system of boundary-value problems for coupled pairs of nonlinear second order ODE's. Some existence and regularity results for these problems are proved and an efficient numerical approach based on a certain special linearization scheme and the Petrov-Galerkin method is suggested.     

Moisture permeability of a polymer nanocomposite containing unmodified clay

Results of an investigation into the kinetics of moisture sorption by an unfilled styrene-acrylate copolymer and a nanocomposite containing unmodified montmorillonite clay are reported. The sorption tests were performed at 25°C and different levels of the relative humidity of air up to 80%. The moisture diffusivity was calculated using Fick's equation for one-dimensional diffusion. Data on the influence of montmorillonite concentration on the coefficients of diffusion, solubility, and permeability are obtained. The experimental values of the permeability coefficient are compared with those calculated by using a model taking into account the increased path of a diffusing water molecule caused by the shielding effect of plate like filler particles. Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 5, pp. 723–736, September–October, 2008.     

广义线性模型在汽车延保风险保费测算中的应用

基于保险公司2010年1月—2019年3月的实际保单数据样本,分别运用广义线性模型中的泊松模型和伽玛模型测算出险频率和案均赔款,构建风险保费测算模型,对影响风险保费的因素进行定量研究及分析.结果表明:该方法能够构建多个变量与风险保费的数值关系,减少了信息的损失,得到的费率表可作为实际应用的参考.最后,通过该方法测算结果与市场定价的实例比较对方法的合理性与优越性进行了说明.     

A finite element model for the fire-performance of GRP panels including variable thermal properties

A finite element study is conducted to determine the thermal response of a widely used glass reinforced plastic panel exposed to fire. This study is performed based on a formulation developed previously by the authors and improved by including the moisture and temperature-dependent thermal properties and a newly developed time-dependent non-linear mixed boundary condition at the unexposed surface of the panel. In addition, the influence of non-zero final resin mass is considered according to a recently performed thermal gravimetric analysis. In order to derive the appropriate element equations, a mixed explicit–implicit Bubnov–Galerkin finite element approach is adopted. Results of this study are presented for a standard, 10.9 mm, thickness of single-skinned polyester-based glass reinforced plastic panel and comprise temperature profiles, density distributions and moisture profiles. Comparisons are made between the predicted results and those obtained experimentally. The predicted temperatures agreed with the experimental results with an average difference of 21.41°C. A simple comparison of the present value with that of the authors’ previous model, 29.66°C, indicates a considerable improvement of 38.53% in the fire-performance prediction of the material.     

Nonlinear flexural response of laminated composite plates under hygro-thermo-mechanical loading

The paper deals with Chebyshev series based analytical solution for the nonlinear flexural response of the elastically supported moderately thick laminated composite rectangular plates subjected to hygro-thermo-mechanical loading. The mathematical formulation is based on higher order shear deformation theory (HSDT) and von-Karman nonlinear kinematics. The elastic foundation is modeled as shear deformable with cubic nonlinearity. The elastic and hygrothermal properties of the fiber reinforced composite material are considered to be dependent on temperature and moisture concentration and have been evaluated utilizing micromechanics model. The quadratic extrapolation technique is used for linearization and fast converging finite double Chebyshev series is used for spatial discretization of the governing nonlinear equations of equilibrium. The effects of Winkler and Pasternak foundation parameters, temperature and moisture concentration on nonlinear flexural response of the laminated composite rectangular plate with different lamination scheme and boundary conditions are presented.