Moisture Dependent Material Properties Research Articles

Free vibration analysis of a skew sandwich plate with bamboo biocomposite and polylactic acid core under temperature and moisture conditions

This article investigates the impact of moisture and temperature on vibration characteristics of bio-composite skew-laminated composite sandwich (SLCS) plates. The bio-composite SLCS plates with bamboo face sheets and polylactic acid (PLA) cores are biodegradable, radiolucent, lightweight, high strength, and withstand vibrations. The coupled thermo-elastic and hygro-elastic finite element (FE) model of the SLCS plate is derived using the higher-order shear deformation theory (HSDT). An initial stress stiffness matrix is developed using the nonlinear strain-displacement relations to incorporate the effect of temperature and moisture in FE modeling. Temperature and moisture-dependent material properties of bamboo fiber-reinforced biocomposite (BFB) and PLA core are employed for the analysis. A comprehensive investigation has been carried out to study the impact of moisture and temperature situations with different geometrical parameters and various skew angles on the frequency of the SLCS plate. The results indicate that the biocomposite sandwich material has excellent potential for structural applications under different environmental conditions in various applications like food processing, and biomedical applications, including MRI and CT scan beds.

Effect of moisture on the delamination properties of fractured PVB-laminated glass: A joint experimental and numerical study

In practical applications of laminated glass, local moisture exchange may occur through panel edges or glass cracks and leads to a significant impact on the post-fracture behavior of laminated glass. In this paper, the effect of moisture on the interfacial delamination properties of PVB-laminated glass is studied. At the experimental level, quasi-static uniaxial tensile tests on pure PVB and through-cracked tensile tests on PVB-laminated glass were conducted at room temperature, considering four initial moisture levels, i.e., 0.2%, 0.4%, 0.6%, and 0.8%, corresponding to relative humidity of 13.6%, 25.6%, 36.1%, and 44.5%, respectively. It is worth noting that for each laminated glass specimen used in the TCT tests, a controlled moisture content was uniformly introduced into the interlayer during the manufacturing process, which is different from traditional aging tests. This allowed for characterization of the moisture-dependent material properties of PVB and interfacial delamination properties of fractured PVB-laminated glass under controlled and uniform moisture conditions. At the numerical level, the moisture-dependent material behavior of the PVB interlayer was first calibrated with 5-parameter Mooney-Rivlin hyperelastic material laws. The moisture-dependent material laws and through-cracked tensile (TCT) test results were then used for an inverse determination of the cohesive strength and interfacial fracture energy at PVB-glass interface through a numerical cohesive zone approach. This study found that the moisture content can significantly affect the interfacial properties of the PVB-laminated glass, with the cohesive strength and interfacial fracture energy decreasing by approximately 70% and 50%, respectively, as the moisture content increases from 0.2% to 0.8%. The changes of the above interfacial parameters can be approximated by linear relationships. In addition, the energy absorption of fractured PVB laminated glass decreases significantly with increasing moisture content due to the degradation of PVB interlayer performance and reduced interfacial adhesion. Therefore, the effect of moisture content should be considered in the practical design of certain laminated glass applications to ensure post-fracture load-bearing capacity.

Free Vibration Analysis of Thick Annular Functionally Graded Plate Integrated with Piezo-Magneto-Electro-Elastic Layers in a Hygrothermal Environment

The present work aims at investigating the hygrothermal effect on the natural frequencies of functionally graded (FG) annular plates integrated with piezo-magneto-electro-elastic layers resting on a Pasternak elastic foundation. The formulation is based on a layer-wise (LW) theory, where the Hamiltonian principle is used to obtain the governing equation of the problem involving temperature- and moisture-dependent material properties. The differential quadrature method (DQM) is applied here as a numerical strategy to solve the governing equations for different boundary conditions. The material properties of FG annular plates are varied along the thickness based on a power law function. The accuracy of the proposed method is, first, validated for a limit-case example. A sensitivity study of the free vibration response is, thus, performed for different input parameters, such as temperature and moisture variations, elastic foundation, boundary conditions, electric and magnetic potential of piezo-magneto-electro-elastic layers and geometrical ratios, with useful insights from a design standpoint.

Influence of Temperature and Moisture on Free Vibration Behavior of Skew Laminated Composite Sandwich Panels with CNTRC Core

This paper presents the influence of temperature and moisture on the free vibration characteristics of skew laminated composite sandwich (SLCS) panels. The face sheets of the panels are made of graphite–epoxy composite, while the core consists of carbon nanotube-reinforced composite. The coupled hygro-elastic and thermo-elastic relations for the SLCS shells/panels are formulated using first-order shear deformation theory. The nonmechanical stiffness matrices are represented by the initial stress stiffness matrix developed using nonlinear strain–displacement relations. The temperature and moisture-dependent material properties are considered to analyze the laminated composite sandwich spherical, hyperbolic, ellipsoid, cylindrical Shells, and flat plates. Several numerical examples are comprehensively studied to establish the influence of temperature, moisture, the volume fraction of carbon nanotubes in the core material, functional gradation types, skew angle, and edge constraints on the vibration responses of SLCS shells. Further exploration is devoted to studying the combined effect of moisture, temperature, and the geometrical parameters such as length to width ratio, length to thickness ratio, radius-to-length ratio, and the core thickness to face sheet thickness ratios on the natural frequency of the skew laminated composite sandwich panels.

Experimental and numerical determination of the screw deformation in laminated beech veneer lumber as a result of moisture‐induced swelling

The strong hygroscopic behavior of wood can lead to severe moisture-induced swelling deformations, especially perpendicular to the grain direction. Fully threaded screws arranged in this direction can be used as reinforcement and to constrain those deformations. Depending on the wood moisture content increase, tensile stresses in the screws and compression stresses in the surrounding solid wood evolve. A sufficiently accurate prediction of the maximum stresses occurring is important for reliable structural designs. For this reason, moisture-induced swelling experiments for two different configurations of screw diameter and specimen dimensions were performed within this work. Due to its homogeneity and its high swelling rate perpendicular to the grain, beech laminated veneer lumber (LVL) was used. A moisture content increase from oven-dry to about 7% led to screw tensile stresses in the magnitude of the yield strength and to highly nonlinear effects in the surrounding wood material. By means of a two-dimensional finite-element-based numerical simulation model, taking into account orthotropic plasticity and moisture-dependent material properties, the experiments could be simulated with high accuracy. The numerical results agree well with experimental observations. Based on a small parameter study, new insights into the complex interaction behavior between beech LVL and fully threaded screws could be gained.

Free vibration and modal stress analysis of FG-CNTRC beams under hygrothermal conditions using zigzag theory

The present study aims to carry out free vibration analysis of functionally graded single-walled carbon nanotube-reinforced composite (FG-CNTRC) beams under hygro-thermal conditions. The study is carried out using the recently proposed C-0 finite element-based higher-order zigzag theory. The study is carried out on five different CNTRC graded beams. Temperature and moisture-dependent material properties are used. Constant temperature or moisture distribution across the thickness of the beam is taken. Hamilton's principle has been used for defining the governing differential equations. Modal stresses are also studied for the first six mode shapes. Stresses at the higher mode of vibration are found to be more affected by temperature or moisture concentration as compared to the stresses observed for the fundamental mode of vibration. It is observed that the nature of stress distribution across the beam is widely affected by the gradation law along with moisture or temperature values to which the beam is subjected. FG-O beam is found to be least sensitive under thermal conditions whereas FG-X beam is found to be the most.

In-plane lateral cyclic behaviour of lime-mortar and clay-brick masonry walls in dry and wet conditions

This paper presents an experimental investigation into the structural and material response of ambient-dry and wet clay-brick/lime-mortar masonry elements. In addition to cyclic tests on four large-scale masonry walls subjected to lateral in-plane displacement and co-existing compressive gravity load, the study also includes complementary tests on square masonry panels under diagonal compression and cylindrical masonry cores in compression. After describing the specimen details, wetting method and testing arrangements, the main results and observations are provided and discussed. The results obtained from full-field digital image correlation measurements enable a detailed assessment of the material shear-compression strength envelope, and permit a direct comparison with the strength characteristics of structural walls. The full load-deformation behaviour of the large-scale walls is also evaluated, including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a notable effect on the main material properties, including the shear and compression strengths, brick–mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses, and can lead to a loss of more than a third of the stiffness and strength. For the large scale wall specimens subjected to lateral loading and co-existing compression, the wet-to-dry reduction was found to be up to 20% and 11% in terms of stiffness and lateral strength, respectively, whilst the ductility ratio diminished by up to 12%. Overall, provided that the key moisture-dependent material properties are appropriately evaluated, it is shown that analytical assessment methods can be reliably adapted for predicting the response, in terms of the lateral stiffness, strength and overall load-deformation, for both dry and wet masonry walls.

Hygro-thermo-mechanical based bending analysis of symmetric and unsymmetric power-law, exponential and sigmoidal FG sandwich beams

In the present work, an attempt has been made to carry out the bending analysis of sandwich FGM beams under combined hygro-thermo-mechanical loadings. Temperature and moisture-dependent material properties are used during the present study. A comparative study has also been carried out between the beams made up of different homogenization rules. The study has been carried out using recently proposed finite element-based HOZT. The present model satisfies the inter-laminar transverse shear stress continuity condition at interfaces and the zero condition at the top and bottom surfaces of the beam. The data is presented in the form of tables for displacement and stresses and graphs representing stress distribution across the thickness of the beam. For the first time, upward displacement of the sandwich FGM beam has been reported in the present work when subjected to hygro-thermo-mechanical loading. Several new results are also reported in the present work, which will serve as a benchmark for future studies in a similar direction.

Hygrothermal modeling of the buckling behavior of sandwich plates with nanocomposite face sheets resting on a Pasternak foundation

In this work we investigate the buckling response of sandwich plates with a polymeric core and two face sheets reinforced by carbon nanotubes (CNTs). The problem is tackled analytically by means of a higher-order sandwich plate theory, where the face sheets are modeled according to a classical plate theory and modified strain gradient theory with temperature-dependent and moisture-dependent material properties. A Mori–Tanaka method is applied to determine the mechanical properties associated with the face sheets, while considering the agglomeration effect of CNTs. The governing equations of the problem are derived from the Hamilton’s principle, whose solutions are recovered by means of a Navier–Stokes method. A thorough sensitivity study of the structural response to different parameters includes the agglomeration and volume fraction of CNTs, the material length scale parameter, the side and aspect ratios, together with the temperature variation and humidity conditions. The sandwich plates are assumed to be immersed within an orthotropic Pasternak foundation, whose normal and shear moduli can affect the overall buckling response of the structure. Numerical experiments show that sandwich plates with nanocomposite face sheets, resting on orthotropic elastic foundations, feature an increased stiffness, where the proposed formulation yields accurate results, due to the possibility of considering the variation in temperature, humidity and agglomeration of the reinforcing CNTs within the solution.

Multiphysics simulation of paper curl due to moisture transport

The moisture transport at the fuser nip of printers is postulated to be the main reason for paper curls. However, the fundamental mechanisms of paper curling remain unclear. Observing the moisture transport inside a sheet of paper through experiments is difficult because moisture transport rapidly occurs in a micro-scale thickness. Therefore, developing a theoretical model is crucial to understand the mechanisms of paper curling and to control the curls. In this study, we proposed a multiphysics model that includes the moisture and heat transport and mechanical deformation. The elasticity, plasticity, viscosity, and expansion caused by moisture were considered in the mechanical model to describe the complex material characteristics of paper. The curvature of curls was calculated using an effective two-spring model. The mechanisms of curling in printers and the direction of curls were understood through finite element simulations. The proposed model can qualitatively predict the paper curls observed in experiments. The temperature- and moisture-dependent material properties of paper will be studied in the future to improve the proposed model.

Biomechanical testing of a polycarbonate-urethane-based dynamic instrumentation system under physiological conditions

BackgroundPosterior dynamic stabilization systems are developed to maintain the healthy biomechanics of the spine while providing stabilization. Numerous dynamic systems incorporate polycarbonate urethane with temperature- and moisture-dependent material properties. In the underlying study, a novel test rig is used to evaluate the biomechanical performance of a system containing polycarbonate urethane. MethodsThe test rig is composed of two hydraulic actuators. An environmental chamber, filled with water vapor at body temperature, is included in the set up. The translational and rotational degrees of freedom of vertebrae and pedicle screws are measured using a magnetic tracking system. The Transition® device is tested in five lumbar spines (L2–L5) of human cadavers. Pure moment tests are performed for flexion-extension, lateral bending, and axial rotation. Three test conditions are compared: 1. native specimens, 2. dynamic instrumentation at L4–L5, 3. dynamic instrumentation with decompression at L4–L5. FindingsThe ranges of motion, the centers of rotation, and the pedicle screw loosening are calculated and evaluated. During daily motions such as walking, the loads on the lumbar spine differ from the standardized test protocols. To allow a reproducible data evaluation for smaller deformations, all moment-rotation curves are parameterized using sigmoid functions. InterpretationIn flexion-extension, the Transition® device provides the highest stiffening of the segment and the largest shift of the center of rotation. No shift in the center of rotation, and the smallest supporting effect on the segment is observed for axial rotation. In lateral bending, a mediate reduction of the range of motion is observed.

Hygrothermomechanical creep and stress redistribution analysis of thick-walled FGM spheres with temperature and moisture dependent material properties and inelastic radius changes

In the present research, effects of the hygrothermal degradation of the material properties on rates of the creep strains and stresses and stress redistributions of thick-walled FGM spheres subjected to internal and external pressures, temperature rises, and diffusions are investigated. In this regard, the non-linear time-dependent governing equations of the sphere are derived based on the theory of elasticity, Prandtl-Reuss flow rule, and Norton's creep law and solved using a special iterative solution scheme. The main novelties of the present research are: (i) analyzing the FGM sphere as it is; without dividing it into isotropic homogeneous sub-spheres, (ii) considering the temperature and moisture dependencies of the elastic modulus of the FGM material, (iii) proposing a more general numerical procedure instead of the traditional successive elastic or Taylor's expansion procedures, and (iv) successively updating of the inner and outer radii of the vessel to consider the resulting inelastic creep deformations. Results reveal that the moisture absorption generally increases the maximum values of both the elastic and creep portions of the stresses, strains, and stress and strain rates. The creep process reduces the circumferential stresses in the interior regions and increases them in the outer regions, but even in presence of moisture absorption, the area beneath the radial distribution curve of the circumferential stress remains unchanged.

Wick action in mature mortars with binary cements containing slag or silica fume – The relation between chloride and moisture transport properties under non-saturated conditions

Moisture and ionic transport under non-saturated condition is an important, but poorly understood transport phenomena particularly for mature systems containing supplementary cementitious materials. This paper investigates the moisture and chloride profiles of 3-year old mortars containing Portland cement (OPC), slag and silica fume (SF) after long-term (30–48 months) wick action exposure in 1.09 M NaCl solution. Moisture profiles were measured with 1H NMR relaxometry and chloride profiles with microXRF. The measured profiles were discussed in relation to moisture dependent material properties such as chloride diffusion coefficients, moisture diffusion coefficients, and desorption isotherms. Results show that the combination of different cementitious materials, e.g. the cementitious binder, is the key factor affecting chloride penetration depth. The cementitious binder also strongly affects chloride diffusion coefficient, moisture diffusion coefficient and chloride binding properties, which are all important parameters for the prediction of chloride ingress.

Hygrothermal analysis of magneto-electro-elastic plate using 3D finite element analysis

In this article, the static response of magneto-electro-elastic (MEE) plate subjected to hygrothermal loads is investigated using the finite element (FE) method. A FE formulation is derived using the principle of total potential energy and linear coupled constitutive equations of MEE materials by taking into account the thermal and hygroscopic field effects. A uniform temperature rise and moisture concentration rise has been considered. The variations of static parameters are estimated along the MEE plate length by considering the temperature and moisture dependant elastic stiffness coefficients. The coupled FE equilibrium equations in terms of displacements, electric and magnetic potentials are solved directly using condensation procedure. Numerical examples of the FE results are presented and discussed in detail to understand the significant effects of hygrothermal loading, temperature and moisture dependent material properties, boundary conditions and aspect ratio on the direct (displacements, electric potential and magnetic potential) and derived quantities (stresses, electric displacement and magnetic flux density) of MEE plate.

Effect of Temperature and moisture dependent material properties on the Bending behavior of Laminated Cylindrical Shell under Hygrothermal Loads

The effect of temperature and moisture dependent material properties on the bending behavior of simply supported angle-ply composite laminated shells has been investigated. A 13 term accurate higher order shear deformation theory with zigzag function is used in this analysis in which the effects of transverse shear deformation are taken into account. A number of examples are solved to illustrate the numerical results concerning bending response of simply supported angle-ply composite shell subjected to hygrothermal effects. It is suggested that temperature-dependent and/or moisture-dependent material properties ought to be used in the analysis of laminated composite shell subjected to hygrothermal loads.

Biaxial thermo-mechanical buckling of orthotropic auxetic FGM plates with temperature and moisture dependent material properties on elastic foundations

Thermo-mechanical buckling analysis of the orthotropic auxetic plates (with negative Poisson ratios) has not been performed so far, especially, in the hygrothermal environments. The complexity increases when the auxetic plate is fabricated from functionally graded orthotropic materials and surrounded by an elastic foundation. The aforementioned analyses are carried out in the present research, for the first time. The buckling loads may be uniaxial or biaxial ones. Moreover, temperature and moisture dependent material properties are considered. The pre-buckling effects are also considered in the paper. The high-order shear-deformation governing differential equations are solved based on a new differential quadrature method (DQM). The resulting solution may cover many practical simpler applications. A comprehensive parametric study is accomplished for a wide range of geometric and material properties parameters and various boundary conditions. Results reveal that the hygrothermal conditions lead to degradations in the material properties and buckling strengths, especially for higher gradation exponents, the elastic foundation may enhance the buckling behavior through monitoring the buckling pattern, the buckling load decreases as the orthotropy angle increases, and the auxeticity has reduced the buckling strength for the employed material and environmental information.

Simplified Theory for Hygrothermal Response of Angle-Ply Composite Plates

A simplified four-unknown shear and normal deformation plate theory is proposed. It is used to study the response of multilayered angle-ply composite plates due to a variation in temperature and moisture concentrations. The effects of temperature and moisture concentrations on the material properties and the hygrothermal response of multilayered angle-ply composite plates are studied. A number of examples are solved to illustrate the numerical results concerning bending response of multilayered angle-ply composite plates subjected to hygrothermal effects. It is suggested that temperature-dependent and/or moisture-dependent material properties ought to be used in the analysis of laminated plates subjected to hygrothermal loads. Additional comparisons between the present theory and the classical, uniform, and parabolic shear deformation plate theories are made to show how the effect of transverse normal strain is highly significant.

Hygrothermal effects on the bending of angle-ply composite plates using a sinusoidal theory

The sinusoidal shear deformation plate theory is presented to study the response of multilayered angle-ply composite plates due to a variation in temperature and moisture concentrations. The classical, uniform and parabolic shear deformation plate theories are also considered. The effects of temperature and moisture concentrations on the material properties and the hygrothermal response of multilayered angle-ply composite plates are studied. A number of examples are solved to illustrate the numerical results concerning bending response of multilayered angle-ply composite plates subjected to hygro-thermo-mechanical effects. Hygrothermal response due to a variation in temperature and moisture concentrations has been investigated for different material types sensitive to changing hygrothermal environment conditions. Numerical results suggest that temperature-dependent and/or moisture-dependent material properties ought to be used in the analysis of laminated plates subjected to hygrothermal loads.

Numerical Simulation of Vacuum Drying by Luikov's Equations

A two-dimensional mathematical model was developed to simulate coupled heat and mass transfer in apple under vacuum drying. Luikov's equations are the governing equations in analyzing heat and mass diffusion problems for capillary-porous bodies. The model considers temperature- and moisture-dependent material properties. The aim of this study is to analyze the influence of some of the most important operating variables, in particular, pressure and temperature of drying air, on the drying of apple. The resulting system of unsteady-state partial differential equations has been solved by a commercial finite element method (FEM) package called FEMLAB (COMSOL AB, Stockholm, Sweden). Simulations, carried out in different drying conditions, showed that temperature is more effective than air pressure in determining the drying rate. A parametric study was also carried out to determine the effects of heat and mass transfer coefficients on temperature and moisture content distributions inside apple during vacuum drying. A comparison between the theoretical predictions and a set of experimental results reported in the literature showed very good agreement, especially during the first 4,200 s, when experimental data and theoretical predictions overlapped and relative errors never exceeded 2%.

Environmental degradation of the interfacial fracture energy in an adhesively bonded joint

The mixed mode flexure and notched coating adhesion tests have been carried out in order to characterise interfacial fracture for a range of environmental exposure conditions and to find a meaningful interfacial strength parameter using a fracture mechanics approach. The moisture uptake of the adhesive was accelerated using an open-faced configuration. The critical loading to cause interfacial fracture was measured and was used in conjunction with finite element analysis (FEA) to determine the fracture energy under various exposure conditions. Moisture dependent material properties were incorporated in the FEA. Scanning electron microscopy was used to characterise the nature of the failure surface. Significant degradation of the fracture energy of the interface was found and this was matched by observed changes to the failure surface. The fracture energies were found to be largely independent of test method, exposure environment and time and was primarily related only to the moisture concentration.