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For the first time, Levy-type solution model and the state-space concept are employed to investigate the hygrothermal bending response of a cross-ply laminated plate on a three-parameter Kerr foundation subjected to a 2D magnetic field. The displacement field is established based on Shimpi's two-variable plate theory. Based on Maxwell's equations, the magnetic body force (Lorentz force) is established. In the present analysis, two opposite edges of the plate are simply supported. While, the other two edges have arbitrary boundary conditions. For more generality and reality, the mechanical load, temperature and moisture that are applied to the upper surface of the plate are assumed to be uniformly, linearly, exponentially, and sinusoidally varied. The principle of virtual displacements is employed to derive the governing partial differential equations based on the present theory, including Lorentz magnetic force. Levy procedure is employed to obtain the nonhomogeneous ordinary differential equations. The matrix method is utilized to get the homogeneous solution. While, the particular solution is obtained by employing the method of undetermined coefficients. The effects of Kerr foundation, loading type, boundary conditions, side-to-thickness ratio, plate aspect ratio, magnetic parameter, temperature, and moisture on deflection and stresses of Levy plate are investigated. It is noted that the magnetic field and hygrothermal loads reduce the structure's strength, which leads to an increment in the deflection and stresses. [ABSTRACT FROM AUTHOR]

The paper pursues the development of a novel methodology for the rapid identification of the diffuso-mechanical properties of polymer materials based on the employment of plates subject to asymmetric moisture concentration fields. The study is carried out on epoxy plate samples equipped with a thin aluminium foil on a surface exposed to the environment to promote asymmetric moisture absorption. The asymmetric moisture fields promote deformations of the plate. Mass gain and plate curvatures are measured as a function of time during conditioning. By using a weakly coupled diffuso-mechanical model: 1D Fick's diffusion model and 2D plane stress hygroelastic model the diffuso-mechanical properties of the material can be then identified. Due to the chosen size of the experimental samples the present study allows the identification of the coefficient of moisture expansion of the epoxy material. For the material under study, the following values can be identified for saturation mass gain, water diffusivity and coefficient of moisture expansion respectively: 1.67%, 0.025 mm2.h−1, 0.1628. [ABSTRACT FROM AUTHOR]

This study aims to combine, using a numerical tool, different phenomena of hygromechanical coupling in a unidirectional carbon/epoxy composite and to compare the results obtained with the cases where these couplings are considered separately. The first case of coupling considers the effect produced by the mechanical state on the diffusive behavior of the material. This was accomplished using the free volume theory, which links the trace of the matrix strain tensor to the moisture absorption capacity and the diffusion coefficient. The second case takes into account plasticization, that is, the effect of humidity on the mechanical properties of composites, without modifying the diffusion parameters. Finally, these two mechanisms are combined in a third configuration, which represents the original contribution of this present work. The results include the water content profiles, the diffusion coefficient, the transverse Young's modulus, the transverse hygroscopic expansion coefficient, as well as the induced local mechanical states. The interest of the work carried out is to pave the way for the extension to more complex materials, such as plant fiber biocomposites, in which the water absorption by the hydrophilic fibers should not be neglected anymore. [ABSTRACT FROM AUTHOR]

In this work, two functional superfine polyester yarns were selected as face yarns, three conventional yarns were selected as ground yarns, and 18 fabrics were designed by using a combination of three different plating structures. Then, through contact angle measurements, moisture management performance, thermal management performance, and breathability tests, we evaluated the effects of raw material, structure, and pore characteristics on the fabric's hygrothermal comfort, and furthermore assessed the prioritization of the three factors using a range analysis. The results show that fabrics with face yarn of 75 D/288 F have better hydrophilicity, and fabrics with face yarn of 50 D/216 F have a better temperature control effect. The fabric with spandex/polyester covered yarn or spandex/nylon covered yarn has the best moisture transmission, and the unidirectional transfer index can reach 300%. The microstructure has a great influence on air permeability, and the surface porosity is positively correlated with air permeability. Combined with the heat and humidity division of the sports body, the development of efficient zonal positioning of heat and moisture management sports undershirts can provide certain theoretical support for the design of weft-knitted seamless sports products. [ABSTRACT FROM AUTHOR]

The objective of this study is to examine through the finite element method the impacts of employing two-dimensional (2D) properties grading on the behaviors of piezoelectric sensors/actuators due to their significance. These structures are modeled as variable thickness discs and are assumed to be exposed to simultaneous asymmetric loading conditions (thermal, hygral, electrical, and mechanical loads). Results demonstrate that the 2D grading is superior compared to the conventional one-dimensional grading for reducing the von Mises stress. The reduction reached, for instance, 8.3% allowing further increase of loading and/or safety. Also, the change of the displacement is varied between −4.5% and 31% depending on the considered grading pattern, and thus can be controlled to a desired value which helps to improve the sensing and actuating functionality for certain requirements. The study also examines the effects of porosity, and the results are compared to nonporous discs. Reductions of the maximum compressive tangential stress and von Mises stress reached 79.75% and 33.6%, respectively at specific porosity distribution patterns and volume fractions. These findings have significant implications for the manufacturing of smart structures, enabling them to operate in severe working conditions with better sensing and actuating capabilities than previously possible. [ABSTRACT FROM AUTHOR]

Free vibration of the porous functionally graded magneto-electro-elastic (FGMEE) microbeams in hygrothermal environment is investigated. Four kinds of distributions of porosities including uniform porosity, "O,""X," and "V" type porosities are assumed in this paper. For the functionally graded microbeam, the physical neutral surface is considered. The modified couple stress theory is adopted to capture the size effect. The equations of motion for the porous FGMEE microbeam are derived and solved by differential transformation method. In the numerical examples, the effect of electric and magnetic loadings, material length scale parameter, the temperature rise, the moisture concentration, material gradient index, and porosity volume fraction on the natural frequency are analyzed and discussed in detail. The results indicate that different porous distribution modes have different effects on natural frequency. Moisture concentration/temperature rise can reduce the natural frequency regardless of what the temperature and moisture modes is. These results will be useful for the design of the porous FGMEE structures. [ABSTRACT FROM AUTHOR]

Smart laminated composite structures with piezoelectric patches are widely used in vibration control applications in several engineering fields. Precise mathematical models are required for the coupling of base structural and piezoelectric field variables. This paper presents the electro-structural analysis and optimization studies of piezoelectric energy harvester with laminated composite substrate plate subjected to base excitations. The coupled electro-mechanical equations are derived from recently proposed first-order shear deformation theory via the Hamilton's principle by considering hygrothermal effects. The coupled-field solution is obtained from Ritz-approximation and validated with three-dimensional finite element analysis. Effects of multiple piezoelectric patch topologies over the plate surface on the open-circuit voltage and displacement response are illustrated. Furthermore, the influences of piezoelectric-patch sizes, ply-orientation, size, and location of the tip mass are initially studied on the magnitude of output power and efficiency. An optimization study is conducted to identify the geometric and material variables for improvement of the harvester power output and efficiency. [ABSTRACT FROM AUTHOR]

Thermo-physiological comfort refers to the heat and moisture transport properties of clothing and how the clothing helps maintain the body's heat balance during various activities. To maintain the thermoregulation of the body, the resulting sweating should be absorbed by wicking fabrics close to the skin and evaporated to the ambient air. In this study, a mathematical model was developed considering evaporation during the capillary rise, based on the geometric configuration of a jersey-knitted fabric and taking evaporation into account. This model was used to calculate the evaporation coefficient. Based on the activities of the worker, sweat diffusion is controlled by capillary diffusion and moisture evaporation. The effect of air velocities of 0 m/s, 1 m/s, and 2 m/s, representing non-walking, walking, and running activities of a worker, respectively, was studied during capillary diffusion. The experiments were conducted at different relative humidities. The results show that the evaporation coefficient depends on the worker's activities and the relative humidity ratio. [ABSTRACT FROM AUTHOR]

In this study, nonlinear aeroelastic instability of a composite sandwich panel subjected to a supersonic airflow and thermal loading is investigated. The sandwich panel is composed of three-phase composites with polymer/Graphene platelet/fiber skins at the top and bottom surfaces and an auxetic honeycombs core layer with a negative Poisson's ratio. The motion equations of the panel within the framework of higher-order shear deformation theory (HSDT) and von Kármán nonlinearity are driven. In addition to Krumhaar's modified supersonic piston, unsteady aerodynamic pressure in the supersonic flow regime is considered. The governing equations of the sandwich panel are derived by implementing Hamilton's principle and solved by the generalized differential quadrature method (GDQM). Validation of the present formulation is assessed by comparing the numerical results with those available in the open literature. Then, the effects of several parameters such as geometric parameters, volume fraction, Mach number, different boundary conditions, yaw angle, and different inclined angles on the nonlinear aeroelastic stability of sandwich panels are examined. Finally, it was found that the ratio of core thickness, inclined angle, and Mach number have significant effects on aerodynamic pressure. [ABSTRACT FROM AUTHOR]

The vibration and stability of spinning viscoelastic Y-shaped bifurcated nanotubes conveying fluid in complex environments by considering additional concentrated masses and springs are studied based on the nonlocal strain gradient theory (NSGT). A detailed investigation is also performed to clarify the effect of influential parameters such as Knudsen number, magnetic nanoflow, scale parameter ratio, spin speed, fluid velocity, downstream bifurcation angle, viscoelastic coefficient, attached springs, localized masses, boundary conditions, and magneto-hygro-thermal environments on the system dynamics. The size-dependent dynamical equations of the system are derived utilizing Hamilton's principle. The Galerkin discretization scheme is adopted, and the eigenvalue problem is numerically solved. Campbell diagrams, forward and backward frequencies, divergence and flutter instability maps are acquired. Besides, the static instability threshold of the system is determined analytically. Results revealed that although the magnetic nanoflow has a decreasing effect on system vibrational frequencies, it delays the occurrence of the dynamical instability and prevents the buckling phenomenon. It is demonstrated that by considering simultaneous stiffness-softening effects induced by nonlocality and hygro-thermal environments, the flutter instability could occur instead of divergence condition in the system stability evolution. The present modeling and results could be applied as a benchmark for the performance improvement of innovative bi-gyroscopic nanofluidic devices. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer matrix composites during engineering applications can be influenced by critical environmental conditions (e.g., water and temperature), probably causing a negative impact on the mechanical performance. In this work, the hygrothermal aging behavior and flexural property of carbon fiber (CF)-reinforced polyethylene terephthalate glycol (PETG) composites were investigated at different aging temperatures and days. The CF/PETG composites were fabricated using the hot-press molding method. The mathematical fitting model and finite element analysis method were employed to reveal the hygrothermal aging behavior and the moisture absorption evolution. After 90 days of aging, the water uptakes of the specimens at 25°C, 45°C, and 60°C are 0.55%, 0.62%, and 1.67% for PETG and 0.47%, 0.54%, and 1.52% for CF/PETG, respectively. The flexural strengths of the CF/PETG composites at 25°C, 45°C, and 60°C after 90 days of aging decrease by 28.6%, 30.2%, and 32.2% as compared with the non-aging composites, respectively. The water uptakes of the CF/PETG composites tend to increase with the increase in cyclic aging time interval. The flexural strengths of the composites with the cyclic aging intervals of 2, 5, 10, and 15 days first decrease and then increase slightly. The knowledge gained in this study will benefit future design optimization of the CF/PETG composite material and lay the foundation for its engineering application. [ABSTRACT FROM AUTHOR]

The vibration analysis of an axially functionally graded material non-prismatic Timoshenko beam under axial thermal variation in humid environment is carried out using the harmonic differential quadrature method. In this modeling, the length and width of the beam remains constant whereas thickness of the beam is linearly varied along the axis of the beam. The material properties are temperature dependent and are assumed to be varied continuously along the axial direction according to power law distribution. Three types of temperature variations are considered in this study, that is, uniform temperature rise, linear temperature rise, and non-linear temperature rise. The temperature of the beam remains constant under uniform temperature rise condition and it is varied linearly and nonlinearly along the length of beam for rest of the conditions. The beam is subjected to uniform moisture concentration to impose humidity. Hamiltonian's approach is used to derive the governing equations of motion. The resultant governing equations are then solved using the harmonic differential quadrature method to obtain the natural frequencies of the axially functionally graded material non-prismatic beam. The results obtained using the harmonic differential quadrature method are compared with results obtained for special cases. The effects of thermal variation, humidity, non-homogeneity parameter, and end conditions on natural frequencies of the non-prismatic beam are reported. [ABSTRACT FROM AUTHOR]

An ideal firefighter turnout system should be capable of releasing body heat to prevent heat stress, indicated by THL (total heat loss) and Ref (evaporative resistance) indexes, while maintaining high thermal protective performance (TPP). Our study found no correlations between THL and Ref, or between Ref and TPP. The results showed that, when tested in the mild condition as in the standard THL test method, turnout systems with bi-component moisture barriers exhibited an advantage in THL that did not translate to more thermally stressful hot environments. A physiological manikin was used to understand the effect of turnout clothing systems on heat strain in different environmental conditions and the value of utilizing Ref or THL to predict heat strain performance. We found no difference in heat strain performance between composites with one-layer and two-layer spunlace thermal liners in mild or hot conditions. It showed that both THL and Ref had their limitations: THL only predicted thermal burden in mild environments, while Ref was only correlated in hot conditions. Thus, the exclusive reliance on either index could increase the risk of heat stress, and we recommend incorporating the Ref heat strain index, along with THL, as dual metrics for certifying the heat strain performance of turnout suits in the NFPA 1971 standard. [ABSTRACT FROM AUTHOR]

The nonlocal strain gradient theory, when combined with the first-order shear deformation theory, provides many capabilities in size-dependent structures. The aim of the present study is evaluation of the free vibration behavior of two vertically aligned fluid-conveying single-walled boron nitride nanotubes in hygrothermal environments considering slip boundary condition based on Knudsen number. These two adjacent nanotubes are coupled in the context of linear deformation through van der Waals interaction according to Lennard–Jones potential function. Actually, the contribution of the present work, compared with those previously reported, is investigating the simultaneous effect of hygrothermal loading and slip boundary condition on the dynamic behavior of two vertically aligned fluid-conveying single-walled boron nitride nanotubes. As an additional step to achieve a more accurate model of low-scale structures, both hardening and softening effects of materials are taken as important variables in the nonlocal strain gradient approach. To derive the motion equations and associated boundary conditions, Hamilton's variational principle is used. The equations are then solved with the aid of differential quadrature method. Numerical studies are also performed to depict the effects of a number of parameters such as boundary conditions, size scale, aspect ratio, inter-tube distance, and temperature alteration on the variations of dimensionless eigenfrequency and critical flow velocity. [ABSTRACT FROM AUTHOR]

This paper aimed to evaluate hygrothermal aging effects on polymethyl methacrylate modified with TiO2, SiO2, and Al2O3 nanoparticles in 0.5, 1, and 2% weight fractions. The distribution of nanoparticles was characterized by the scanning electron microscopy (SEM) method. Moisture absorption behavior and mechanical properties of samples in terms of elastic modulus, tensile strength, impact strength, and hardness were investigated. Furthermore, the coefficient of hygrothermal expansion (CHE) for each sample was calculated thanks to experimental data. Finally, by applying the multi-criteria decision making (MCDM) technique, the optimum composition for superior performance was obtained in 0.5 wt% of nanoparticles, more specifically for SiO2. [ABSTRACT FROM AUTHOR]

This work aims to characterize the influence of hygrothermal conditioning on the mechanical and thermal behavior as well as the fractographic aspects of the interface of poly(ether imide) and glass fiber composite joints welded by electrical resistance using 400 mesh of AISI 304 stainless steel. The composites were mechanically characterized by Lap Shear Strength (LSS) and End Notched Flexure (ENF) testing to investigate maximum shear stress and energy from mode II interlaminar fracture toughness. Fractography was performed by SEM, while the influence on glass transition temperature and working temperature were evaluated by Dynamic-Mechanical Analysis and thermogravimetry. In the conditioned samples, the mechanical properties reduced 23% in the LSS test and 28% in the ENF test, while the fractography studies revealed elements of interlaminar and intralaminar fracture in both conditions. Thermal properties did not change significantly to disqualify this composite when applied to welding. [ABSTRACT FROM AUTHOR]

The present article deals with the vibration and damping characteristics of functionally graded carbon nanotubes reinforced hybrid composite skewed shell structure in different hygrothermal conditions. Carbon nanotube reinforced polymer as a matrix phase and carbon fibre as a reinforcing phase are used, and carbon fibre is graded with uniform distribution along the thickness direction for the shell panel according to the power law distribution. The Mori–Tanaka scheme and strength of materials are used to determine the mechanical properties of such functionally graded carbon nanotubes reinforced hybrid composite materials. Finite element modelling has been done by considering an eight-noded shell element with the transverse shear effect according to Mindlin's hypothesis, and an oblique coordinate system is used for the functionally graded carbon nanotubes reinforced hybrid composite skewed shell structures. Damping is incorporated into such carbon nanotube–based hybrid skewed shell structure based on the Rayleigh damping model. A MATLAB-based in-house computer code has been developed for the proposed formulation and verified with published research work before using for the present dynamic analysis of functionally graded carbon nanotubes reinforced hybrid composite skewed shell structure under hygrothermal conditions. The effect of the carbon nanotube, carbon fibre, material distribution as per power law index and hygrothermal conditions on the damping behaviour of such functionally graded carbon nanotubes reinforced hybrid composite skewed shell structures have been studied. Furthermore, parametric studies are carried out for the first resonant frequency, absolute amplitude, settling time and carbon nanotube impact on the vibrational behaviour of different functionally graded carbon nanotubes reinforced hybrid composite skewed shell structures under different hygrothermal conditions. [ABSTRACT FROM AUTHOR]

In the present study, the viscoelastic analysis is investigated for composite laminated plates using a smoothed finite element method called cell/element based smoothed discrete shear gap method. Moreover, the hygrothermal effects is considered on the viscoelastic responses of composite laminated plates. The first-order shear deformation theory is employed due to its simplicity and accuracy. With the help of the convolution theorem in Laplace transformation, the complex stress-strain relationship in integral form is simplified to linear in transformed domain. Therefore, all computing procedures are performed in the transformed domain and then, using inverse techniques (Fast Fourier Transform) to converted back to the real-time domain. The study provides an effective computational tool to analyze the viscoelastic response of laminated composite taking into account the influence of the time and hygrothermal effects. [ABSTRACT FROM AUTHOR]

In general, a double-skin façade has been used to reduce energy consumption as well as to improve thermal performance in buildings as a buffer space between indoors and outdoors. The goal of this study is to undertake pre-normative research to provide information for developing a comprehensive double-skin façade system under the climatic condition in Saudi Arabia. To pursue this goal, the characteristics associated with the double-skin façade system are identified. In addition, the impact of various configurations on the thermal performance of the double-skin façades is evaluated under the weather situation in Saudi Arabia. Computational double-skin façade models are created by computational fluid dnamics simulation to assess the thermal performance of the various configurations such as cavity geometry and the use of a shading device. As a result, the variation of the opening size has a significant impact on the temperature in the cavity of the double-skin façade. For the air velocity in the cavity, the variation of the opening size and cavity depth is less sensitive. Moreover, the use of a shading device has an impact on the temperature drop in the cavity of the double-skin façade. Practical application: Generally, many studies have investigated the efficiency of double-skin façade applications due to its beneficial aspects. However, a few buildings have adopted double-skin façades to their envelopes. With a substantial growing demand for building industry in Saudi Arabia, double-skin façade applications to building design can be a solution for reducing building energy consumption. The present study investigates the thermal performance of double-skin façades under hot climates in Saudi Arabia and it can provide information for building stakeholders to develop proper double-skin façade systems [ABSTRACT FROM AUTHOR]

Ultraviolet light cured-in-place pipe is a popular trenchless rehabilitation technology used to repair existing buried pipelines without soil excavation. A polymer composite liner is manufactured directly in the field. After curing is complete, the new liner is placed in service to convey flowing water. Long-term water exposure has the potential to degrade the fiber reinforced cured-in-place pipe liners. Like other composites, liner hygrothermal stability could be a major challenge, especially for undercured materials. The objective of this study was to investigate the effect of aggressive environmental conditions such as water, salt solution, and simulated concrete pore solution at 50℃ on cured-in-place pipe liner mechanical and thermo-mechanical performance. Liners were exposed to aqueous solutions ranging from a typical exposure environment to a very aggressive alkaline environment. Cured-in-place pipe liner samples were collected from New York storm sewer installation sites. Specimens were assessed for the degree of curing as determined by differential scanning calorimetry and TGA. Samples were then immersed in aforementioned solutions for investigating the stability of the liners as a function of degree of cure. Both interlaminar shear strength and thermo-mechanical properties significantly differed based on the degree of cure. Cured-in-place pipe liner mechanical and thermo-mechanical properties were significantly impacted by water, salt, and pore solutions exposure. Long-term exposure to salt and alkaline environments may have a detrimental effect on the performance of cured-in-place pipe liners and desires additional scrutiny. [ABSTRACT FROM AUTHOR]

The mechanical response of composite structures may be affected by harsh environments, particularly when the matrix has a major contribution, e.g. with off-axis plies. This study aims at investigating the influence of the winding pattern on the axial compressive behavior of filament wound composite cylinder under hygrothermal conditioning. Carbon fiber-reinforced epoxy cylinders were manufactured via filament winding with 1/1, 3/1, and 5/1 mosaic winding patterns and submitted to distilled and artificial seawater environmental conditioning. Water uptake for each hygrothermal conditioning was periodically monitored. The winding pattern influenced both compressive strength and stiffness, and the environmental conditioning decreased strength up to ≈10%. The winding pattern with three diamonds around the circumference of the cylinders provides the properties in term of compressive strength and stiffness. [ABSTRACT FROM AUTHOR]

This paper attempts to investigate the potential of courtyards in optimizing natural ventilation and improving comfort levels in the learning spaces of a naturally ventilated educational institution with courtyards in the warm-humid climatic region of Madurai. Field measurements and experimental studies were carried out to predict the indoor and outdoor environmental conditions. The numerical study was carried out using computational fluid dynamics-based simulations using Ansys Fluent as the solver. The main aim of the simulation is to understand the airflow pattern and air velocity fields inside the classrooms surrounding the courtyards for different wind directions. The computational fluid dynamics results were validated by comparing it with the experimental results obtained in the current study and numerical results from other studies. The major findings of the current study suggest that courtyards with an aspect ratio of 1:2, orientations of openings at an angle of 0–20° to the predominant wind directions and the overall percentage of openings between 15 and 30% in buildings in Madurai region can enhance natural ventilation and thus improve thermal comfort of the occupants. Practical application : Naturally ventilated buildings in warm-humid climates have difficulty in providing thermal comfort to the occupants. CFD tools have been used to predict the ventilation performance of a naturally ventilated educational building with courtyards. The CFD results were helpful in identifying the implication of building design on the indoor air flow pattern. The recommendations given in this paper are applicable to any building type which relies on natural ventilation for thermal comfort provided they have similar building configurations, boundary conditions and weather conditions. The study is intended to help architects and building designers in the effective design of naturally ventilated buildings with respect to its climatic conditions. [ABSTRACT FROM AUTHOR]

The performance of fiber reinforced polymer externally bonded to concrete is greatly influenced by the environmental conditions to which it is exposed during service. Temperature and humidity are the two common environmental factors that alter the bond behavior of externally bonded fiber reinforced polymer. This paper reviews the experimental and computational approaches used to evaluate the hygrothermal effects—that is, the effect of temperature and humidity—on the durability of the fiber reinforced polymer–concrete bond, as well as on the bond's performance under loading conditions. Some experimental testing conducted in the laboratory and in situ are critically reviewed and presented. Implemented approaches for improving bond performance under hygrothermal conditions and their modeling techniques are also presented. The paper concludes by discussing the review's salient issues. The ongoing wide application of externally bonded fiber reinforced polymer creates opportunities for new research on improving and predicting the bond strength of fiber reinforced polymer concrete under hygrothermal conditions. [ABSTRACT FROM AUTHOR]

The present work deals with the hygrothermal aging of the bolt joints prepared from glass fiber reinforced plastics. To investigate the effect of nanoclay on joint performance, nanoclay content was varied from 0 to 5 wt%, with laminates prepared from 3 wt% of nanoclay content demonstrating the best mechanical properties. Nanoclay acts as a mechanical interlock between the fiber and the epoxy and thus improves the interfacial bonding. A good dispersion of nanoclay also improves moisture barrier properties which in turn reduces the degradation of the composite material hygrothermal conditions. Bolt joints were prepared from woven glass fiber reinforced laminates incorporating 3 wt% of nanoclay content. To design the bolt joint, ASTM D5961 was used and the geometric parameters, i.e. edge distance to hole diameter (E/D) ratio and width to hole diameter (W/D) ratio were fixed to 5 and 6, respectively. Three different temperatures, i.e. 25℃, 50℃ and 75℃ were considered for the aging to three different duration of exposure, i.e. 1, 2 and 3 weeks. The effect of different levels of bolt torque, i.e. 0, 2 and 4 Nm were considered for the failure analysis of the joint. A full factorial design of experiment was conducted on important control factors, i.e. water temperature, exposure time, bolt torque and material variation. It was found that the hygrothermal conditions degraded the material with temperature as the most contributing factor. [ABSTRACT FROM AUTHOR]

In this research, nonlinear free and forced vibration behaviors of the multiscale doubly curved composite shells have been investigated. By using Reddy's third-order shear deformation theory (TSDT) and von-Karman type nonlinearity the strains and stresses are obtained. Three-phase composites shells with polymer/carbon nanotube/fiber and polymer/graphene platelet/fiber and shape-memory alloy (SMA)/matrix according to the Halpin–Tsai model have been analyzed. The governing equations of composite shell have been derived by implementing Hamilton's principle, and according to the multiple scales perturbation method have been solved. The obtained results are validated through the comparison with the available results. Finally, the effects of different parameters such as volume fraction of SMA, temperature rise, various distributions pattern, aspect, and curvature ratio considered on nonlinear frequency have been studied. The results indicate that the changes of the fundamental vibrational mode shape have a significant influence on the nonlinear frequency of the composite shell. [ABSTRACT FROM AUTHOR]

This research studied large amplitude vibration behaviors of multiscale composites doubly curved shells with piezoelectric layer. By using Reddy's third-order shear deformation theory, the strains and stresses are obtained. According to the Halpin–Tsai model three-phase composites layers are considered. The governing equations of the multiscale doubly curved shell are derived by implementing the Hamilton's principle and are solved via homotopy perturbation method. For investigating correctness and accuracy, this article is validated by other previous studies. Finally, the influence of different parameters such as temperature rise, various distributions pattern, applied voltage, magnetic potential, and aspect and curvature ratio are observed in this article. It is found that these parameters have significant influence on nonlinear frequencies. [ABSTRACT FROM AUTHOR]

This paper is devoted to the buckling problem of the composite cylindrical shell subjected to hydrostatic pressure. Both analytical and numerical methods are applied to investigate the buckling behavior. Based on the study of analytical formulas, it is found that the composite cylindrical shells with the same length-to-diameter ratio, diameter-to-thickness ratio, and type of layup have the same buckling pressure. Thus, a scale model experiment method is then proposed, which uses the scale model to replace the full-scale model in pressure test experiment to reduce the manufacturing cost of the test specimen. The feasibility of this method is verified by numerical calculation. The influences of ply orientation angle and length of shell on buckling shape and critical buckling pressure have been investigated numerically and demonstrated by several examples. Based on the study of the influence of shell length on critical buckling pressure, a modified finite element model, which can overcome the conservatism of optimization result due to the stress concentration caused by boundary conditions, is combined with the genetic algorithm to optimize the laminations for mass reduction. [ABSTRACT FROM AUTHOR]

The origin of fiber print-through is commonly based on the influence of temperature during cure and post cure thermal treatments on polymeric matrix systems due to chemical and thermal shrinkage. Furthermore, it is proven that especially polymeric matrices are hygroscopic and therefore, have a disposition to soak up water in surroundings with a high level of humidity. Currently, to characterize influences like these on coated surfaces of carbon fiber reinforced plastics short and long wave values are applied which are actually developed to describe waviness of coating film structures of conventional materials like aluminum or steel. A fitted value regarding the phenomenon of fiber print-through is missing today to consider various influences on the surface topography. This investigation delivers a novel approach with a specific value to determine averaged altitudes caused by fiber print-through. For this purpose, the used confocal chromatic sensor by Fries Research and Technologies creates 3D images of surface topography and fiber print-through. This elaboration allows to correlate the change of mass of carbon fiber reinforced plastics due to thermal and hygrothermal post curing treatments with the characteristic of fiber print-through. Mass increase of 0.25% due to hygrothermal influence leads to a rise of print-through effect of about 210% and a decrease of mass of 0.5% due to thermal influence rises the characteristic of print through of about 75%. [ABSTRACT FROM AUTHOR]

For the application of continuous fibre-reinforced thermoplastics in car body structures it has to be ensured that they can pass through the automotive paint shop. There are substantial chemical, hygroscopic and thermal impacts throughout this process that can affect the shape of such components. The aim of this study is to model the deformation behaviour of continuous fibre-reinforced thermoplastics under hygrothermal loading. Relaxation tests were performed to assess temperature-dependent and viscoelastic behaviour. Input parameters for temperature and moisture distribution were determined experimentally and computed using finite difference method. A straightforward approach based on classical laminate theory is presented that comprises anisotropic viscoelasticity as well as hygroscopic, thermal and polymer-chemical effects. The introduced phenomenological model was successfully used to describe the deformation of five different laminate layups both dry and fully saturated with moisture. [ABSTRACT FROM AUTHOR]

In this article, free vibration of functionally graded (FG) viscoelastic nanobeams embedded in viscoelastic foundation exposed to hygro-thermal loading is investigated based on nonlocal strain gradient elasticity theory and a higher order refined beam theory which captures shear deformation influences without the need for any shear correction factor. Also, the exact position of neutral axis is determined. The visco-Pasternak foundation is consists of parallel springs and dashpots as well as a shear layer. Temperature-dependent material properties of FGM beam are graded across the thickness based on the power-law form. Hamilton's principle is used to obtain nonlocal governing equations of embedded strain gradient viscoelastic nanobeam which are solved analytically for various boundary conditions. The results are validated with those available in the literature. The impacts of visco-Pasternak foundation parameters, structural damping coefficient, hygrothermal loading, nonlocal stress parameter, nonlocal gradient parameter, power-law exponent, mode number, boundary conditions and slenderness ratio on the damping frequency of nanoscale viscoelastic FG beams are evaluated. [ABSTRACT FROM AUTHOR]

Premature local failure of web/flange junctions of the majority of unstiffened commercially produced pultruded fiber-reinforced polymer composites profiles is inescapable due to lack of fiber continuity at the resin-dominated junction zones. This paper focuses on evaluating both short- and long-term behavior of such junctions when subjected to axial tensile stresses. In this study, the axial mechanical behavior of web/flange junctions of pultruded bridge deck components before and after hygrothermal aging effect is investigated. In the experimental phase, axial tensile tests were performed on six different types of pultruded web–flange junctions to assess axial characteristics of each web/flange junction type. In order to evaluate the hygrothermal behavior of such junctions, axial tensile tests were conducted on web/flange junction specimens that were exposed to both fresh water and artificial seawater environments at temperatures of 40℃, 60℃, and 80℃. Several controlling parameters affecting both strength and stiffness of pultruded fiber-reinforced polymer junctions were identified and discussed that include: (i) Junction's web and flange thicknesses, (ii) fillet radius, and (iii) variation of hygrothermal exposure environments. Results of this study indicated that the axial tensile capacity of a pultruded profiles is increased as the thickness of both web and flange increases. Also, it was found that the larger fillet radius of the pultruded fiber-reinforced polymer profile may contribute to a larger axial tensile capacity of pultruded profiles. However, due to variable size and geometry of the resin-rich junction zones and the common manufacturing defects in the form of folded fabric and other fibers misalignment effects, it is difficult to generalize the preceding results. Experimental results also showed that the degradation of web/flange junctions axial tensile strength increases when junctions are exposed to higher temperatures. Also, it was found that the axial tensile characteristics for junctions specimens exposed to freshwater environment are slightly different than those that were exposed to artificial seawater environments. [ABSTRACT FROM AUTHOR]

Non-destructive test technique for monitoring delamination failure under complex load and environments is still not mature until now. The purpose of this paper is to study mixed-mode delamination failure properties of carbon fiber/epoxy composite laminates under hygrothermal environment using acoustic emission. Different water-saturated composite specimens with initial intralaminar and interlaminar defects are tested. Two loading modes including single-leg and over-leg three-point bending are applied under hygrothermal environment. By analyzing the responses of acoustic emission parameters including amplitude and energy, the effects of the hygrothermal environment, layup pattern and initial defect on the delamination behaviors of composite specimens are studied. Besides, different failure modes are observed through scanning electron microscope. Quantitative acoustic emission results show hygrothermal environment and load mode affect the delamination properties of composites remarkably. [ABSTRACT FROM AUTHOR]

Fibre metal laminates are high strength materials made up of alternating layers of metal alloy and composite materials. Commercially available fibre metal laminates include CARALL, ARALL and GLARE. Other than the commercially available fibre metal laminates, number of researches have been performed with the alternate metal alloys such as stainless steel, Ti, Mg alloys and polymer matrices based on polypropylene, polyimide, polyester, etc. In this study, various factors affecting the mechanical properties of fibre metal laminates have been addressed along with the different types of failure modes observed by various researchers in their experiments. Hygrothermal conditioning which involves the subjection of fibre metal laminates to moisture and temperature (80℃ and 90% humidity as per ASTM standard 5229), their behaviour and influence on mechanical properties has also been reported in this study based on the results from the various researchers. [ABSTRACT FROM AUTHOR]

Bamboo fibers reinforced with non-woven fabric polypropylene composites were prepared via compression molding. Three types of bamboo fibers were used in the research: untreated, treated with a sodium hydroxide solution and treated with a sodium hydroxide solution followed by three-aminopropyltriethoxysilane. The effects of the preformed structures and chemical treatments on the composite performances were investigated. The results showed that the composite attained optimum mechanical properties at an alkali concentration of 5% and at a silane coupling reagent concentration of 3%. The preformed structure composed of materials with bamboo fiber/polypropylene mass ratios of 50/50 and 70/30 exhibited ideal mechanical properties. The moisture absorption behavior of the composites with different bamboo fiber contents exhibited good agreement with Fick’s law. Scanning electron microscopy showed that the composites prepared using alkali-silane-treated fibers demonstrated better bonding between the fibers and matrix and had fewer voids in the composites. We also confirmed that the modifications of the bamboo fibers improved the hygrothermal properties of the composites because of the improved interfacial adhesion between the fiber and matrix. [ABSTRACT FROM AUTHOR]

Analytical and numerical results on transverse shear stresses of angle-ply composite plates subjected to hygrothermal loadings are scarce in literature. Thus, a higher order global-local model a priori satisfying the continuity condition of transverse shear stresses is proposed for hygrothermal analysis of angel-ply composite plates. Based on the higher order global-local model, a triangular element is developed by using the refined element approach. Comparing the results from available three-dimensional elasticity solution, the proposed model can produce promising transverse shear stresses directly from constitutive equations without any smoothing technique. By analyzing hygrothermal response of composite plates with general configurations, the effects of material properties, lamination angles, boundary conditions, transverse normal strain, and hygrothermal expansion coefficients on the hygrothermal response have also been studied. Differing from previous work, the corrected hygrothermal expansion coefficients are used for hygrothermal analysis of composite plates. [ABSTRACT FROM AUTHOR]

Exposure to hygrothermal environments affects mechanical properties of laminated composites through two principle mechanisms, namely, moisture absorption and the structural deterioration due to it. Previous studies have indicated that moisture plays a positive role in carbon fiber reinforced polymer composites by alleviating their damage under impact. In this study, carbon fiber reinforced polymer composites were exposed to long-term hygrothermal ageing to investigate the possibility of the initiation of structural defects due to it and their influences on the various behaviors of the laminated composites. A major type of observable structural defects was identified and the related initiation mechanism was proposed. It was found for the first time that the structural defects formed during hygrothermal ageing in turn changed the moisture uptake profile of the laminated composites. The effects of structural defects on the impact resistance of carbon fiber reinforced polymer composites were exclusively evaluated after removing the absorbed moisture. Tensile testing on vacuum-oven-dried laminates was conducted to assist the understanding of the mechanical strength of the carbon fiber reinforced polymer composites exposed to the hygrothermal environments. [ABSTRACT FROM AUTHOR]

In this study, the effects of hygrothermal aging on the mechanical properties and impact behavior of glass-epoxy composites were investigated experimentally. The vacuum-assisted resin infusion molding was used to manufacture composites. In manufacturing of composites, unidirectional E-glass fabrics with areal density of 300 g/m2 and a resin system (Araldite LY 564/Aradur 3487 BD) were used. In order to determine mechanical properties such as modulus of elasticity, longitudinal and transverse strengths, shear strength, and Poisson’s ratio, the composite samples were prepared according to the ASTM standards. Then, the samples were conditioned at a constant temperature (95℃) and a constant humidity (70%) for different periods of times, ranging from 0 h to 1200 h. The conditioning temperature was chosen due to the glass transition temperature (Tg) of the intact composites which is determined as 78℃. It is noted that the most affected mechanical property via material degradation is modulus of elasticity in transverse direction (E2) while the least affected one is shear modulus (G12). The perforation threshold of the composite materials also decreases with increase of conditioning time. [ABSTRACT FROM AUTHOR]

In the present study, the influence of temperature and moisture concentration on the bending characteristics of delaminated rotating composite conical shells has been investigated. The shells with initial twist are considered for moderate rotational speeds wherein Coriolis effect is assumed to be absent. The effects of rotary inertia and transverse shear deformation have been incorporated in the present finite element formulation along with the multi-point constraint algorithm for modeling the delamination. Graphical results have been presented depicting the contours of deflection and relative moment along the planform of the conical shell resulting from centrifugal and hygrothermal forces taking into account the influence of twist angle, stacking sequence, rotational speed, and size of delamination present inside the laminate. [ABSTRACT FROM AUTHOR]

CCF300/5228A aero composite stiffened panels achieved absorbing saturation in hygrothermal condition (70℃ distilled water), whose absorbing process followed the Fick law. Many debonding and gaps of matrix to fibers could be observed after hygrothermal exposure by scanning electron microscope (SEM). Compressive experiments were conducted on unaged and aged composite stiffened panels. Failure modes of the two types of specimens are quite similar with several major ways, including the debonding and fracture of stiffeners together with the splitting and ripping of panel. Buckling patterns for both types of specimens are similar and characterized by buckling of panels between stiffeners and buckling of the middle two stiffeners. However, the bending direction of buckling mid-panel for aged specimens is opposite to that of the unaged at same position panel, which shows that hygrothermal condition influences the bending direction of buckling mid-panels seriously. There still exists a post-buckling process for aged specimens under axial compression, whose average buckling load and failure load decrease by 3.1% and 22.2% respectively, comparing to that of unaged specimens. [ABSTRACT FROM AUTHOR]

Low-velocity impact testing was conducted on carbon/epoxy composite laminates exposed to hygrothermal environments. Besides normal laminates, staggered lay-up structures were made from unidirectional prepreg materials. The specimens were immersed in water at 80℃ for different durations before impact testing. Experimental data showed that moisture played a positive role by improving the impact resistance of composite laminates. Laminates with higher moisture level could behave elastically up to higher strain levels and retain their resistance to the striking impactor to larger deflections. After absorbing moisture, more of the impact energy was dissipated by the specimen through elastic deformation and less damage was induced to the laminate. Little degradation in the fiber/matrix interface was observed from SEM graphs. It is postulated that absorbed moisture improved the ductility of the epoxy resin by promoting chain segmental mobility of the polymer molecules, which eventually lead to the better impact response of laminates with higher moisture content. [ABSTRACT FROM PUBLISHER]

Since flax is the most promising plant for the reinforcement of polymer-based composites in structural applications, we have chosen to investigate its hygrothermal characteristics which can be useful for the understanding of the behaviour of other plant fibres. The flax fibres were exposed to different hygrothermal conditions: in an oven at various controlled temperatures (–40 to 140℃) and measured relative humidity, in a climate chamber at 50% relative humidity for define temperatures between 25℃ and 85℃, or different determined aging conditions. The correlation of these hygrothermal conditions to the evolution of the mechanical properties gives evidence of the prominent influence of water over temperature on the microstructural changes of flax fibres. The mechanical parameters drastically decrease in usually prescribed hygrothermal aging conditions for organic matrix composite materials, the strength being particularly sensitive to the presence of water. These evolutions were correlated to the fibre microstructure modifications induced by water absorption as revealed by electron microscopy analyses. These findings could be useful for understanding the behaviour of polymer matrix biocomposites in severe hygrothermal conditions. [ABSTRACT FROM PUBLISHER]

This paper investigated the effect of porosities, environmental factors and impact energies on the impact resistance properties of Carbon Fiber Reinforced Polymer/Plastic (CFRP) laminates. Impact tests on the CFRP laminates with three porosity levels were subjected to five energy levels from 3 J to 15 J at the room temperature. The damage area was assessed with combined effects of different impact energies and porosity levels. The damage area was evaluated by visual inspection and ultrasonic C-scan measurement. The thermal deply technique was used to evaluate the damage evolution behavior. Three-point bending tests were conducted on the non-impacted and impacted specimens that were exposed to the room temperature, the hygrothermal and the drying environments. The curves of the impact resistance of the tested laminates mutate at the impact energy of 9 J. The thermal deply technique reveals the failure mechanism of the impact damage mutation of the tested laminates when the impact energy exceeds the threshold 9 J. [ABSTRACT FROM AUTHOR]

The tensile test of a multidirectional laminate of strip geometry is analysed assuming that the clamping system imposes elastic restrictions to the rotations at both ends. The problem has five redundant unknowns that are determined by applying Engesser’s second theorem. Thus, the stress field can be obtained including clamping effects. The displacement field is determined by applying Engesser’s first theorem in conjunction with the unit load method. Hygrothermal effects are also included in the analysis. A method for determining the end compliances based on longitudinal strain and out-of-plane displacement measurements is proposed. Experiments are simulated by numerical results corresponding to AS4/3501-6 carbon/epoxy composite. Finally, two examples concerning multidirectional laminates with general coupling are analysed. [ABSTRACT FROM AUTHOR]

The hygrothermal effect on the flexural, interfacial and glass transition behaviors of 977-2A carbon/epoxy composites cured in an autoclave and by using Quickstep were evaluated in the previous paper. This article concerns with the hygrothermal effect on the mode I and mode II delamination resistance of the samples cured in an autoclave and by Quickstep. It was observed that the mean initiation and propagation GC values (i.e. GIC and GIIC) of both autoclave and Quickstep 60 cured specimens were apparently reduced after hygrothermal conditioning; however, the data obtained from both autoclave and Quickstep 60 cured specimens in dry and wet states were not statistically significant. The scanning electron micrograph confirmed the enhancement of matrix ductility; however, no effect of this matrix ductility was observed in the GIC and GIIC data. [ABSTRACT FROM PUBLISHER]

The effect of moisture and temperature on the strength of composite single-lap bonded joints were extensively investigated. Secondary bonded-joint specimens were immersed in tap water and 3.5% salt water at 71°C for different durations up to a maximum of 300 days. A total of 160 specimens were tested under six different moisture contents and two different temperature environments. Test results showed that while the strengths of the joints with 2.1% or more tap water moisture content decreased compared with those of dry joints, the strengths of pre-saturated joints with up to 1.0% moisture content increased at both room and elevated temperature. However, the strengths of saturated joints at 2.5% moisture content decreased by 34% (room temperature) and 44% (71°C) compared with those of the dry joints. In the joints with 1.0% or lower moisture content, the higher temperature environments resulted in slightly increased strengths, whereas the elevated temperature degraded the strengths in the joints with 2.1% or greater moisture content. The major failure modes of the joints were delamination and intralaminar failure of the composite adherend; the joints with high moisture content tested under elevated temperature showed cohesive failure of adhesive. The strengths and failure modes of the joints that were immersed in salt water did not show a remarkable difference from the joints that absorbed tap water. [ABSTRACT FROM AUTHOR]

In this article, the effect of hygrothermal aging on the painted surface finish of unidirectional and fabric carbon fibre composite laminates, with and without surfacing film was investigated. The results highlighted the importance of ensuring that the composite surface directly beneath the paint layer is made from a uniform material with a consistent thickness in order to minimise surface defects from occurring during aging. The surfacing film was found to minimise the print through development on the painted unidirectional and twill composite surfaces. However, the surfacing film layer was found to intermingle with the carbon fibre plies during cure, which resulted in an uneven film thickness that caused increased levels of orange peel. The twill laminate painted surface produced high levels of print through and surface waviness that was caused by the large resin rich regions located within the tow intersections at the surface which enlarged due to thermal expansion and swelling of the matrix with hygrothermal aging. It was also noted that the small resin rich regions between the individual carbon fibres on the unidirectional composite surface were sufficiently large to print through the painted surface. [ABSTRACT FROM AUTHOR]

This article focuses on the calculation of transient and cyclical hygrothermal fields in laminated composite plates. Water diffusion is simulated by employing Fick’s law, while thermal fields are assumed to be uniform: temperature and water concentration are coupled through the coefficient of hygroscopic diffusivity, which follows a classical Arrhenius law. Relative humidity and temperature at the plate boundary vary in a transient/cyclic way, reproducing real complex environmental conditions. Analytical solutions of the cyclical hygrothermal fields in laminated plates can be employed as benchmark for numerical calculations and for evaluating the induced hygrothermal stress, therefore, for structural, design and optimisation purposes. [ABSTRACT FROM PUBLISHER]

The present study deals with both experimental and numerical investigation on the free vibration behavior of laminated composite plates subjected to varying temperature and moisture. A simple laminated plate model is developed for the vibration of composite plates subjected to hygrothermal loading. A computer program based on finite element method in the MATLAB environment is developed to perform all necessary computations. The woven fiber glass/epoxy specimens were hygrothermally conditioned in a humidity cabinet where the conditions were maintained at temperatures of 300–425 K and relative humidity ranging from 0% to 1.0% for moisture concentrations. Quantitative results are presented to show the effects of geometry, material and lamination parameters of woven fiber laminate on the free vibration of composite plates for different temperature and moisture concentrations. The numerical and experimental results show that there is reduction in natural frequency in Hz with the increase in temperature and moisture concentration for laminates with simply supported and clamped boundary conditions with different aspect ratio and side-to-thickness ratios. [ABSTRACT FROM PUBLISHER]

The article presents hygrothermally induced buckling of geometrically linear laminated composite plates resting on two parameters Pasternak elastic foundation subjected to moisture and temperature-independent and -dependent material properties with random system properties. System properties such as elastic moduli, shear moduli of the constituent materials, hygroscopic contraction coefficients, thermal expansion coefficients, and foundation stiffness parameters are modeled as independent basic random variables. A computationally efficient C 0 finite element method combined with Taylor series based mean-centered first-order perturbation technique via higher order shear deformation plate theory is used to solve the random eigenvalue problem. Typical numerical results for dimensional mean and coefficient of variance of hygrothermally induced buckling load of laminated composite plate subjected to uniform hygrothermal loadings are examined with uniform moisture concentration and temperature rise, plate thickness and aspect ratios, total number of plies, fiber orientations, elastic foundations, and different boundary conditions with random system properties. The numerical results obtained by the present solution approach are validated with those available in the literatures and independent Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

This article deals with the durability of 2D woven mat carbon/polyester, glass/isopolyester, and gel-coated glass/isopolyester reinforced composites under hygrothermic conditions with regard to marine applications. The test coupons were exposed to 60°C and 70°C at 95% RH for a maximum duration of 100 h. The samples were periodically withdrawn and weighed for moisture absorption and tested for the degradation in the mechanical properties such as ultimate tensile strength, flexural strength, interlaminar shear strength, and Young’s modulus and flexural modulus. Carbon/isopolyester-based specimens showed greater stability with respect to degradation in the mechanical properties than the glass/isopolyester/gel coat- and glass/isopolyester-based specimens. Glass/isopolyester exhibited the maximum moisture absorption, whereas the minimum moisture absorption was found in glass/isopolyester/gel coat. Diffusion coefficient (D) was found to be the highest for glass/isopolyester and the lowest for glass/isopolyester/gel coat, based on the Fick’s law of diffusion. Diffusion coefficient increases with the increase in temperature for all the specimens. Microstructure study of fractured specimens was carried out using scanning electron microscope to compare matrix/fiber debonding and matrix-degradation of fiber-reinforced polymer composites. [ABSTRACT FROM AUTHOR]