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The objective of this study is to investigate the impact of hygrothermal and thermal aging on adhesive bonding joints of similar and dissimilar specimens. The research focuses on the single lap joint (SLJ) configuration using Aluminum/Aluminum and CFRP/CFRP for similar bonding and Aluminum/CFRP for dissimilar bonding. Understanding the behavior of such joints over time and eventual failure can enhance their durability, reliability, and safety in structures. The study submerged SLJ specimens in tap water at a temperature of 53°C for 20 days to assess hygrothermal aging and kept another group of joints in an oven set at the same temperature for thermal aging. The research evaluated the strength of samples that underwent no aging, hygrothermal and thermal aging, tested through three-point bending tests. Various load levels were tested utilizing a recently designed fixture, including 70%, 60%, and 50% of the static load level. Results showed the highest joint strength in Aluminum/Aluminum SLJs and reduced strength following thermal and hygrothermal aging. The failure patterns and number of cycles leading to failure also varied with load percent and aging. Ultimately, the study aimed to evaluate and contrast the strength of samples that underwent different aging processes. [ABSTRACT FROM AUTHOR]

This document provides a comprehensive overview of the integration of civil structural health monitoring and machine learning in the field of concrete structures. It discusses the importance of monitoring infrastructure condition and the challenges of manual inspection. The document highlights the increasing use of machine learning algorithms, such as computer vision methods, in optimizing maintenance and repairs. It presents case studies and applications of machine learning in civil engineering, including damage detection and load assessment. The document also emphasizes the challenges and limitations of using machine learning in this context and recommends further research and interdisciplinary collaboration. Additionally, it addresses ethical and privacy concerns, the importance of open data sharing, and aligning machine learning applications with sustainability efforts. The document includes a list of academic articles related to machine learning techniques in concrete structures, covering topics such as crack detection and structural health monitoring. It also compiles various studies and research papers on machine learning for structural health monitoring in concrete structures, exploring different methods and highlighting the potential of deep learning models and image processing techniques for crack detection. Overall, the document provides a comprehensive overview of the application of machine learning in the field of structural health monitoring for concrete structures. [Extracted from the article]

Mass timber has gained increasing focus as a sustainable alternative to concrete structures, and recent innovations have allowed timber buildings as high as 25 stories. However, although critical factors such as fire safety have been studied thoroughly, other facets, such as long-term material performance, have been neglected. Thorough assessments of sustainability must consider the full service life of a building, including its time-dependent behavior. Deformations in timber elements undergoing these time-dependent effects, namely creep, will have notable implications for the serviceability of a building. This study proposes a comprehensive model for predicting moisture-dependent creep in timber, based on the theory of microprestress in partially saturated porous materials. The model is implemented numerically using a Kelvin-chain approximation for basic creep and midpoint integration for mechanosorptive effects, resulting in a computationally efficient approach. Results show the model is able to fully capture the effects of moisture cycling, including effects of hygrothermal gradients. Using both calibrated and estimated parameters the model also predicts with reasonable accuracy the long-term moisture-dependent creep in structural-scale mass timber elements. [ABSTRACT FROM AUTHOR]

In reinforced concrete structures, GFRP bars are becoming acceptable as internal reinforcement subject to compressive load and hygrothermal environments. The paper presents an experimental study on the compressive behavior, thermodynamic properties, and degradation mechanism of the glass fiber‐reinforced polypropylene (GFRPP) bars after aging in distilled water (DW), alkaline solution (AS) and seawater and sea sand concrete (SWSSC) solution at 21, 40, and 60°C up to 120 days. The effect of specimen assembly methods, and slenderness rations (Lu/Db) on the compressive behavior was evaluated on the control GFRPP bars. After immersion, the compressive strength of the GFRPP bars was significantly affected by the type of solution, immersion time, and temperature. Typically, the compressive strength retention was decreased by 25.8%, 30.0%, and 33.0% at 60°C in DW, AS, and SWSSC solutions, respectively. The degradation mechanism of the compressive behavior of GFRPP bars was revealed through SEM images and FTIR spectroscopy analysis, and the debonding of fiber‐resin interfaces, chemical etching of glass fibers, and changes in polypropylene functional groups were confirmed or discovered. Finally, based on the Arrhenius theory, the long‐term life prediction of compression strength in three typical service environments was conducted to provide the design guideline for reinforcement concrete. Highlights: Effect of specimen assembly and Lu/db on compressive behavior of GFRPP barsThermodynamic behavior of the GFRPP bars under different aging environmentsRevealed the degradation mechanism of GFRPP bars under hygrothermal environmentsPredicted the service life of GFRPP bars in typical service environments [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of hygrothermal loads on the nonlinear free vibrations of a porous bi-directional functionally graded Timoshenko beam with a Winkler–Pasternak foundation. The corresponding governing equations were established according to Hamilton's principle and von Kármán nonlinearity assumption. Using the differential quadrature and iterative methods, the nonlinear fundamental frequencies were determined. A numerical example was presented, and we showed that the discretization of nonlinear items considerably decreased the number of iterations. A series of parametric studies were performed, and we determined that (1) all the vibration mode shapes were significantly affected by the axial functionally graded index, while they were almost unchanged by the thickness-wise functionally graded index. Moreover, compared to the thickness-wise graded index, the axial functionally graded index played a more important role in the higher-order mode shapes. (2) The geometric nonlinearity considerably influenced the critical temperature rise value of the beams. Increasing the maximum deflection value increased the critical temperature rise value. (3) The influence of increase in temperature and moisture on the nonlinear fundamental frequency became stronger with increase in the functionally graded index, but it weakened with increase in the maximum deflection value. [ABSTRACT FROM AUTHOR]

The composite interlamination is the key part of load transfer and plays a decisive role in the overall mechanical performance of composite structures. The interlaminar property is predominantly influenced by the matrix resin which is easily affected by the hygrothermal environment. This paper delved into the effect of hygrothermal aging duration on the interlayer debonding behavior of unidirectional (UD) laminates. The pre‐cracked specimens were treated by hygrothermal aging with a period of 0, 15, 30, 60, 90, and 120 days. The double cantilever beam (DCB) tests were employed to evaluate the interlaminar property. The effect of hygrothermal aging on load–displacement responses, R‐curves, crack growth speed, and fracture surface topography was analyzed. The results revealed that the load‐bearing capacity of aged specimens presented a reduction of 18.6%–29.0% compared with unaged ones. The interlaminar fracture toughness of specimens subjected to 15 days of treatment decreased significantly compared with that of unaged specimens due to the increase of water absorption caused by hygrothermal aging. With the increase in hygrothermal aging time, the interlaminar fracture toughness peaked at 60 days because of the post‐curing effect, followed by a declining trend influenced by the dominant hygrothermal aging effect. The fiber bridging of aged samples was increasingly obvious, became the most prominent at 60 days, and then gradually reduced. The fiber bridging diminished the crack propagation speed, hindered interlaminar debonding, and contributed to the interlaminar toughening. Highlights: The samples underwent hygrothermal aging for 0, 15, 30, 60, 90, and 120 days.Load ability of aged samples was at least 18.6% lower than that of unaged ones.R‐curves rose before the crack length of 79 mm and then tended to stabilize.Fracture toughness first decreased, then increased and reduced with aging time.Fiber bridging could hinder crack growth and improve the interlayer property. [ABSTRACT FROM AUTHOR]

• Analytical solution of viscoelastic laminated beams in hygro-thermo-mechanical condition is proposed. • The proposed solution is more accurate than simplified solutions and is efficient over finite element counterpart. • A superposition principle for viscoelastic laminated beams in hygro-thermo-mechanical condition is derived. In order to predict the creep and recovery behaviors of for viscoelastic laminated beam in hygro-thermo-mechanical (HTM) coupled condition, an exact analytical solution is proposed. This solution considers two effect mechanisms: temperature and humidity, including the expansion difference and the variation of viscoelastic properties. In the analytical model, the stresses and displacements of each lamina are described based on the hygro-thermo-elasticity theory combined with the Boltzmann superposition. By employing series expansion, the transfer matrix method, and Laplace transform, the solution is determined analytically. Notably, the entire process of Laplace inverse transformation is carried out analytically without relying on any numerical approximations. The comparison analysis indicates that the proposed solution is more computationally efficient than the finite element counterpart and is more accurate than the solutions based on transverse shear deformation assumption. By analyzing the components of the proposed solution, a modified superposition principle applicable to HTM coupled conditions and a superposition principle for creep recovery are derived. In the end, the HTM coupled behavior, the bending creep and recovery as well as the optimization of expansion coefficient are investigated in detail. [ABSTRACT FROM AUTHOR]

Turbulence parametrizations will remain a necessary building block in kilometer‐scale Earth system models. In convective boundary layers, where the mean vertical gradients of conserved properties such as potential temperature and moisture are approximately zero, the standard ansatz which relates turbulent fluxes to mean vertical gradients via an eddy diffusivity has to be extended by mass‐flux parametrizations for the typically asymmetric up‐ and downdrafts in the atmospheric boundary layer. We present a parametrization for a dry and transiently growing convective boundary layer based on a generative adversarial network. The training and test data are obtained from three‐dimensional high‐resolution direct numerical simulations. The model incorporates the physics of self‐similar layer growth following from the classical mixed layer theory of Deardorff by a renormalization. This enhances the training data base of the generative machine learning algorithm and thus significantly improves the predicted statistics of the synthetically generated turbulence fields at different heights inside the boundary layer, above the surface layer. Differently to stochastic parametrizations, our model is able to predict the highly non‐Gaussian and transient statistics of buoyancy fluctuations, vertical velocity, and buoyancy flux at different heights thus also capturing the fastest thermals penetrating into the stabilized top region. The results of our generative algorithm agree with standard two‐equation mass‐flux schemes. The present parametrization provides additionally the granule‐type horizontal organization of the turbulent convection which cannot be obtained in any of the other model closures. Our proof of concept‐study also paves the way to efficient data‐driven convective parametrizations in other natural flows. Plain Language Summary: Even though global simulations of the Earth system on monthly timescales reach now resolutions of 2.5 km, essential turbulent transport processes in the lowest part of the atmosphere still have to be modeled. Here, we implement a machine learning‐based mass‐flux parametrization of the subgrid‐scale heat flux for a shear‐free dry atmospheric boundary layer by a generative adversarial network. Training data and prediction capability of the algorithm are increased by incorporating the physics of boundary layer growth following from classical mixed layer similarity theory. Our model is compared successfully to standard mass‐flux parametrizations based on an equation model. It is additionally found to reproduce the intermittent fluctuations of the convective buoyancy flux and the horizontal organization of the transiently evolving turbulence correctly. Key Points: A generative adversarial network produces the subgrid‐scale buoyancy flux for a transiently growing dry convective boundary layerThe training data are enhanced by renormalizing simulation snapshots in correspondence with the self‐similar growth by mixed‐layer theoryThe algorithm generates data with the right spatial patterns and non‐Gaussian statistics, and agrees with standard parametrizations [ABSTRACT FROM AUTHOR]

Due to the advantage of strength enhancement without increasing the structural weight, stiffeners are commonly used in many engineering structures. However, during their service life, these stiffened structures are usually exposed to an extreme environment, which may cause damage. Most of the researchers have carried out the work to study the unreinforced plate's stability behaviour considering interlaminar skin debonding in the hygrothermal condition. However, in the current investigation, the buckling capacity of stiffened composite plates debonded at the contact of plate and stiffener under non-uniform edge loading in hygrothermal conditions is studied. The study is performed by developing a computationally efficient finite element formulation. In the present research, the plate and the flange of T-stiffener are formulated by adopting a 9-noded heterosis element preventing the shear locking. In contrast, a 3-noded isoparametric beam element is used to formulate the stiffener web by accommodating the torsion correction factor, considerably reducing the computational cost. In the current study, the debond is modelled by creating a dummy node, and further interpenetration of the nodes is prevented by introducing a fictitious spring in the debonded region. Due to the highly uneven stress variation, a dynamic approach is employed to estimate the buckling constant by utilizing two sets of boundary conditions. Three schemes of hygrothermally stable laminates (θ/(90-θ))s, (22.5/− 67.5)s, and (77.5/− 12.5)s are considered to identify the stiffened plate configuration with enhanced buckling capacity when subjected to various non-uniform loading patterns. Further, extensive parametric investigations are conducted on the obtained stiffened plate with improved performance under a hygrothermal environment by considering debond at the skin–stiffener interface. It is found that debonded plate's stability is substantially affected by moisture. On the other hand, depending on the stiffener position and hygrothermal load intensity, the stiffener's depth-to-width ratio substantially affects the debonded plate's stability. Therefore, this investigation can be considered as a benchmark study for the stability performance of the debonded reinforced composite panel, which partially reduces the 2-D problem to 1-D element, thereby improving the computational cost. [ABSTRACT FROM AUTHOR]

In this study, a fully coupled hygro-thermo-mechanical bond-based Cosserat peridynamic model is formulated to simulate the complex crack propagation and multi-field interaction process in concrete under fire. This model can consider the effect of the size and the independent rotation of cement particle. A numerical solution with a multi-rate explicit integration strategy is adopted for the complex multi-field interaction. The proposed model and the numerical solution are verified by the experimental results and finite element solutions. Numerical examples focus on the influence of fracture on mass transfer and heat conduction, and the effects of cement particle size on the temperature, water vapour pressure and crack propagation. Numerical results demonstrate the model's effectiveness in simulating the hygro-thermo-mechanical behaviours and crack propagation processes in concrete subjected to high temperatures. [ABSTRACT FROM AUTHOR]

This study presents a novel approach for improving the interfacial adhesion between Nd–Fe–B spherical magnetic powders and polyamide 12 (PA12) in polymer-bonded magnets using plasma treatments. By applying radio frequency plasma to the magnetic powder and low-pressure microwave plasma to PA12, we achieved a notable enhancement in the mechanical and environmental stability of fused deposition modeling (FDM)-printed Nd-Fe-B/PA12 magnets. The densities of the FDM-printed materials ranged from 92% to 94% of their theoretical values, with magnetic remanence (Br) ranging from 85% to 89% of the theoretical values across all batches. The dual plasma-treated batch demonstrated an optimal mechanical profile with an elastic modulus of 578 MPa and the highest ductility at 21%, along with a tensile strength range of 6 to 7 MPa across all batches. Flexural testing indicated that this batch also achieved the highest flexural strength of 15 MPa with a strain of 5%. Environmental stability assessments confirmed that applied plasma treatments did not compromise resistance to corrosion, evidenced by negligible flux loss in both hygrothermal and bulk corrosion tests. These results highlight plasma treatment's potential to enhance mechanical strength, magnetic performance, and environmental stability. [ABSTRACT FROM AUTHOR]

The purpose of this review is to report on the state-of-the-art on the interaction of moisture with natural materials and fabricated biomimetic functional materials, with an emphasis upon the hygro-responsive behaviour of wood. The primary objective is to examine how water sorption affects dimensional behaviour and how knowledge of this property in natural plant-based (mainly, but not exclusively wood) materials can be used to inform biomimetic design of moisture-responsive materials and devices. The study examines the literature on natural and bio-inspired materials, concentrating upon sorption kinetics, water migration and location of the sorbed water in the materials and their microstructure and mechanical response of the microstructure and how this affects molecular mobility of the sorbate translating to macrostructural changes. Also included within this review, it is an overview of the main experimental techniques which have been used to investigate the interaction of water with these materials at molecular length scales and how modern techniques can resolve the response of these materials at the cell wall level. [ABSTRACT FROM AUTHOR]

The nonlinear vibration response of rectangular plates made of functionally graded porous materials (FGPs) induced by hygrothermal loading is investigated in this article using a numerical approach. The effect of elastic foundation on the vibrations is taken into account according to the Winkler–Pasternak model. Hygroscopic stresses produced due to nonlinear rise in moisture concentration are also considered. The temperature-dependent material properties of plate are computed based on the modified Voigt's rule of mixture and Touloukian experiments for even and uneven distribution patterns of porosity. Within the framework of the first-order shear deformation plate theory and von-Kármán nonlinearity, Hamilton's principle is utilized in order to derive the equations of motions. To achieve the temporal evolution of maximum lateral deflection of hygrothermally-induced plates, the generalized differential quadrature (GDQ) and Newmark integration methods are employed. Selected numerical results are presented to study the influences of temperature distribution, porosity volume fraction, moisture concentration, geometrical parameters, elastic foundation parameters and FG index on the geometrically nonlinear vibrations of FG porous plates with various boundary conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a non-Fourier model of heat and a non-Fick model of moisture diffusion coupling in unification with hygrothermoelasticity theory within the framework of time-fractional calculus theory. The generalized two-temperature theory of hygrothermoelasticity has been used to develop the relevant linearly coupled partial differential equations system. In the context of time-fractional calculus theory, we investigate a hygrothermal elastic problem for a centrally symmetric sphere exposed to physical heat and moisture load at its surface within the limited spherical region. The integral transform approach produces analytical formulas for the transient response of temperature change, moisture distribution, displacement, and stress components in the sphere for pulsed and continuous heat-moisture flux at the sphere's surface. The Gaver–Stehfest procedure is used to invert the analytical hygrothermal variation solutions that were derived in the Laplace domain. The Kuznetsov convergence criterion has studied the problem's stability and bounded variations. The effects of fractional order on the hygrothermal fields and hygrothermoelastic stress response are graphically represented and calculated using numerical data. The specific heat and moisture connection, which abides by Fourier heat conduction and Fick's moisture diffusion, is recovered as a particular case when the fractional-order derivative reduces to the first-order derivative. The study reveals a significant coupling effect between temperature and moisture in composite material T300/5208, with a maximum discrepancy of up to 50%. [ABSTRACT FROM AUTHOR]

In the current study, the authors discuss a homogeneous hygrothermoelastic slab of thickness 2h sandwiched between two similar elastic half-spaces. The hygrothermoelastic slab is subjected to a mechanical source of constant magnitude. The source is applied along the interface of the slab and upper elastic half-space. The analytical expressions of the components of displacement, stresses, moisture concentration, and temperature field are obtained by the normal mode analysis technique. The analytical results are used to solve the problem numerically by taking a wood slab as a porous material. The graphical results elaborate the effect of the thickness of a slab on the physical quantities. The problem of hygrothermoelastic layers sandwiched between elastic half-spaces is a novel idea, which finds its applications in various engineering models. The results found are interesting in the context of the problem. It is observed that the thickness of a hygrothermoelastic slab affects the deformation in the medium and the values of physical quantities decrease with an increase in the thickness of the slab. [ABSTRACT FROM AUTHOR]

The differential swelling seen between softwood opposite wood (OW) and its neighbouring compression wood (CW) developed in branches prompts several engineering issues such as dimensional instability and cracking. For a more efficient use of resources, the inevitable CW and OW should not be discarded or used as fuel, but incorporated into engineered wood products. Swelling is a hygroelastic phenomenon, where both the swelling and elastic properties of CW and OW are needed in order to make proper structural predictions. In this paper, swelling coefficients and moisture dependent elastic moduli for both CW and OW in the three principal material directions are provided along with measurements of moisture content, density, and microfibril angle. The small deformations necessitate the use of precise X-ray micro-computed tomography for measurements. The results indicate that CW and OW from Norway spruce branches differ in swelling, especially in longitudinal direction at low moisture content. It is noted that CW is a wood type with less pronounced anisotropic behaviour than both OW and normal wood from the stem, with the elastic moduli less sensitive to moisture changes in both longitudinal and transverse directions. [ABSTRACT FROM AUTHOR]

The transient dimensional changes during hygro-expansion and hydro-expansion of freely and restrained dried, softwood and hardwood sheets and fibers is monitored, to unravel the governing micro-mechanisms occurring during gradual water saturation. The response of individual fibers is measured using a full-field global digital height correlation method, which has been extended to monitor the transient hydro-expansion of fibers from dry to fully saturated. The hygro- and hydro-expansion is larger for freely versus restrained dried and softwood versus hardwood handsheets. The transient sheet-scale hydro-expansion reveals a sudden strain and moisture content step. It is postulated that the driving mechanism is the moisture-induced softening of the so-called "dislocated regions" in the fiber's cellulose micro-fibrils, unlocking further fiber swelling. The strain step is negligible for restrained dried handsheets, which is attributed to the "dislocated cellulose regions" being locked in their stretched configuration during restrained drying, which is supported by the single fiber hydro-expansion measurements. Finally, an inter-fiber bond model is exploited and adapted to predict the sheet-scale hygro-expansion from the fiber level characteristics. The model correctly predicts the qualitative differences between freely versus restrained dried and softwood versus hardwood handsheets, yet, its simplified geometry does not allow for more quantitative predictions of the sheet-scale hydro-expansion. [ABSTRACT FROM AUTHOR]

Understanding the moisture migration of unsaturated soil in response to temperature changes is essential in soil science and geosystems applications. The coupling of thermohydro (TH) processes is a result of changes in fluid density and viscosity; however, gravity can disrupt the moisture migration of unsaturated sand initiated by a thermal gradient when the sand is considerably porous. Moreover, the moisture redistribution caused by the gravity effect is influenced by the imposed boundary temperature and initial moisture content of the unsaturated sand. Therefore, this paper presents heating tests performed on sand specimens of different gradations and subjected to various thermal gradients in a modified and well-controlled soil testing cell to evaluate the coupling behavior of TH processes in unsaturated sand. Two sands were tested in the soil testing cell, which was equipped with thermocouples (TCs) to measure the temperature and time-domain reflectometry (TDR) sensors to measure the apparent dielectric constant (Ka); three temperature boundary conditions were imposed on the soil testing cell to create two thermal gradients. This study shows that gravity, thermal boundary conditions, initial moisture content, and matric suction influence the migration of moisture: the silty sand, as compared with pure sand, more properly displayed the phenomenon of coupled TH processes in unsaturated soil when tested at a temperature gradient of 200°C/m and initial moisture content of 6%. The study provides an advanced understanding of the paired migration of heat and moisture in porous media under various conditions, including thermal gradient, initial moisture content, and gradation. When unsaturated soils are under a temperature gradient, the pore water tends to move from the heat source to a cooler end in search of moisture equilibrium. Temperature-driven moisture flow is commonly investigated in soil science, agriculture, and geosystems. For example, the soil surrounding a geosystem (electrical cables and ground heat exchangers) experiences heating and cooling cycles when heat energy is exchanged from buildings to the soil via the geosystem. This heat exchange can effectively cool the buildings in the summer and heat the buildings in the winter. To maintain effective heat transfer in the soil, it is necessary to investigate the temperature-driven moisture flow, as it has been established that redistributed moisture also significantly impacts heat transport. At the same time, the moisture flow is also influenced by gravity, particularly for coarse sands. Moisture flow in coarse sands is more prone to the effect of gravity than that in fine sands. This paper evaluates how the physical and hydraulic properties of the soil, such as gradation and suction, can affect the coupled thermal and hydraulic processes. The gravitational effect can dominate the moisture redistribution depending on the direction of the temperature gradient. [ABSTRACT FROM AUTHOR]

This research represents the first theoretical investigation about the vibration behavior of circular organic solar cells. Therefore, the vibration response of asymmetric circular organic solar cells that represent a perfect renewable energy source is demonstrated. For this purpose, the differential quadrature method (DQM) is employed. The organic solar cell is modeled as a laminated plate consisting of five layers of Al, P3HT:PCBM, PEDOT:PSS, ITO, and Glass. This cell is rested on a Winkler–Pasternak elastic foundation and assumed to be exposed to various types of hygrothermal loadings. There are three different kinds of temperature and moisture variations that are taken into account: uniform, linear, and nonlinear distribution throughout the cell's thickness. The displacement field is presented based on a new inverse hyperbolic shear deformation theory considering only two unknowns. The motion equations including hygrothermal effect and plate–foundation interaction are established within the framework of Hamilton's principle. The DQM is utilized to solve these equations. In order to ensure the accuracy of the proposed theory, the present results are compared with those reported by other higher-order theories. A comprehensive parametric illustration is conducted on the impacts of different parameters involving the geometrical configuration, elastic foundation parameters, temperature, and moisture concentration on the deduced eigenfrequency of the circular organic solar cells. [ABSTRACT FROM AUTHOR]

Current exterior wall assembly designs for new low-rise residential buildings targeting low-energy demand in heating dominated countries include split-insulation wall and thick-wall assembly designs. Both have been shown to result in thermal efficiency gains compared to building-code minimum assemblies, however long-term hygrothermal performance can vary depending on boundary conditions and the presence of construction deficiencies. Future climate scenarios estimate many heating-dominated climates will experience a reduction in heating-degree day hours and an increase in annual rainfall. Using validated assembly performance data from a Passive House certified facility, a sensitivity analysis is performed to determine the impact of rainwater wetting, air exfiltration and insulation material properties on the hygrothermal response of a thick-wall assembly. Results show that rainwater leakage values of 0.50% and greater of the adhering rainfall on the exterior surface of the assembly results in the greatest risk for failure. The hygrothermal response of the assembly is then examined under a global temperature rise scenario of 3.5°C for five geographic locations across Canada. Results show that an increase in average annual total rainfall does not directly result in an increase in the failure rate of the assembly when a rainwater leak is present. Additional climatic factors, including outdoor air temperature, driving rain and solar radiation received will influence the hygrothermal response of the assembly and need to be considered when modelling the performance under future climate change scenarios. [ABSTRACT FROM AUTHOR]

Building materials are responsible for significant CO2 emissions and energy consumption, both during production and operational phases. Earth as a building material offers a valuable alternative to conventional materials, as it naturally provides high hygrothermal comfort and air quality even with passive conditioning systems. However, disadvantages related to high density, conductivity, and wall thickness prevent its effective inclusion in the mainstream. This research explores enhancing the thermophysical properties of compressed earth blocks (CEBs) by using locally sourced natural materials. The study is framed in the Portuguese context and the natural materials involved are wheat straw (WS) as a by-product of wheat harvesting, cork granules (CGs) from bottle caps, and ground olive stone (GOSs) residues from olive oil production. Blocks were produced with different mixtures of these materials and the thermal response was examined in a hot box apparatus. Best results include a 20 and 26% reduction in thermal conductivity for mixtures with 5v.% CG and 10v.% GOS, respectively, and an associated reduction in bulk density of 3.8 and 5.4%. The proposed approach therefore proves to be effective in improving the key thermophysical characteristics of CEBs. The article includes a comparative analysis of the experimental data from this study with those from the literature. The study contributes to the growing knowledge of sustainable materials, providing insights for researchers and practitioners looking for innovative solutions for low-carbon and energy-efficient materials. [ABSTRACT FROM AUTHOR]

Cubic boron nitride (cBN) has been used as a tool material for several decades due to its high hardness and thermal stability. Various binders are commonly added to cBN to synthesise cBN composites for better cutting performance. However, most studies have only investigated properties such as hardness and bulk modulus, without comprehensively studying elastic properties through experiments. In this study, the sound velocities and elastic properties of cBN with AlN binder were determined by using the ultrasonic interferometry technique. The bulk and shear moduli with their pressure dependence were determined as B 0 = 351 (3) GPa, G 0 = 344 (3) GPa, B 0 ′ = 4.32 (4) and G 0 ′ = 1.74 (2) using the finite strain equation-of-state approaches. Elasticity-related thermal properties, such as Debye temperature, Grüneisen parameter, thermal conductivity and coefficient of thermal expansion were also estimated. The results show that the elastic properties of the cBN composite with vol. 8.8% AlN-binder are comparable to the pure cBN compact. Additionally, the thermal conductivity and coefficient of thermal expansion have little effect on cBN composite with AlN binder compared to pure cBN. [ABSTRACT FROM AUTHOR]

A mesoscopic representative volume element (RVE) model of carbon fiber reinforced polymers (CFRP) laminate with 15 plies was established based on the principle of fiber random disturbance. The RVE model was validated by comparing the elastic parameters calculated by the RVE model, Chamis model, and Bridge model. Wet stress and thermal stress were coupled using a sequential method. Macroscopic and microscopic subroutines were developed to calculate the stress–strain field of CFRP laminate and RVE model. A multiscale numerical simulation of three‐point bending of moisture‐saturated CFRP laminate was conducted. Failure process and failure modes of CFRP laminate were discussed based on the multiscale simulation and SEM observations. The results show that the RVE model and the multiscale simulation strategy presented in this work can predict the coupled hygrothermal stress and the strength degradation due to moisture absorption very well. The maximum error between the simulated and experimental averaged force of the moisture‐saturated CFRP laminate subjected to three‐point bending is about 3.4%. Multiscale simulation demonstrated that uneven distribution of fibers can result in the fiber/matrix interfaces bearing a larger transverse stress in the fiber's dense distribution area. It is the main reason that results in fiber/matrix interface failure of CFRP laminates working in hygrothermal environments. Highlights: A RVE model of CFRP laminate was presented using fibers random disturbance.Coupled hygrothermal stress of single fiber and surrounded matrix was obtained.A multiscale simulation of the strength change of the CFRP plate due to wet‐thermal stress was conducted.Failure modes of CFRP laminate are discussed based on the multiscale simulation. [ABSTRACT FROM AUTHOR]

Gold-plated substrate is widely used in sintering with silver paste because of its high conductivity, stability, and corrosion resistance. However, due to massive interdiffusion between Ag and Au atoms, it is challenging for sintered Ag-Au joints to maintain high reliability. In order to study the effect of grain structure of gold plating layer on the environmental reliability of sintered Ag-Au joints, we prepared four substrates with different gold structures. In addition to the original gold structure (Au substrate), other gold structures were obtained by heat treatment at temperatures of 150 °C (Au-150 substrate), 250 °C (Au-250 substrate), and 350 °C (Au-350 substrate) for 1 h. Compared with the other three gold substrates, the sinter jointed on the Au-350 substrate obtained the highest shear strength. By analyzing the grain structure of the gold plating layer, it is found that the average grain size of the Au-350 substrate is the largest, and the proportion of low-angle grain boundaries is less. Few grain boundaries have a positive impact on inhibiting the excessive diffusion of Ag atoms and improving the bonding performance of the joint. Based on the above study, we further evaluated the environmental reliability of sintered joints. In 150 °C high-thermal storage, the interdiffusion of Ag and Au in the sintered joint on the Au-350 substrate was restricted, retaining stronger bonding until 200 h. In a hygrothermal environment of 85 °C/85% RH, the shear strength of the sintered Ag-Au joint with the Au-350 substrate maintained above 40.2 MPa during 100 h aging. The results indicated that the sintered Ag-Au joint on the Au-350 substrate with the largest grain size has superior high thermal reliability and hygrothermal reliability. [ABSTRACT FROM AUTHOR]

In order to investigate the durability of fiber-reinforced polymer composites in hygrothermal environments, hygrothermal accelerate aging tests, for 360 days at 70 °C, RH70%; 70 °C, RH85%; 85 °C, RH70%; and 85 °C, RH85% and natural storage for 2 years in Guangzhou, China, were carried out for composite laminates. Then, the moisture absorption and interlaminar shear strength were measured. The hygrothermal damage mechanism of the composite was studied by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FSEM). A dual stress storage life prediction model and the equivalent relationship between natural storage and hygrothermal acceleration were established. The results show that the order of moisture absorption rates, moisture absorption contents, and the severity effect order on the interlaminar shear strength is RH85%; 85 °C > 70 °C; RH85% > 85 °C; RH70% > 70 °C; and RH70%. The time to achieve an effective moisture absorption balance is opposite to this. The moisture absorption rate meets Fick's law before the effective moisture absorption balance, and then shows a linear trend. The interlayer shear strength still decreases exponentially with aging, which is mainly caused by the resin plasticization and interface weakening. Hygrothermal accelerated aging for 13.4831 days at 85 °C; RH85% is equivalent to that for one-year actual storage in Guangzhou. According to the failure criterion of shear strength decreasing to 77%, the storage life of T700/epoxy in Guangzhou is 14.4661 years. [ABSTRACT FROM AUTHOR]

Temperature and moisture are important environmental conditions governing the usage of carbon fiber‐reinforced plastics (CFRP). In this study, tensile, compression, and shear tests of woven CFRP composites were conducted in four composite environments: cold‐temperature dry state, room‐temperature dry state, elevated‐temperature dry state, and elevated‐temperature wet state. Fourier transform infrared (FTIR) spectroscopy was used to analyze the molecular composition and structure under these environments. The fracture morphology was also analyzed using scanning electron microscopy (SEM) to understand the deterioration mechanism of the material properties at the macro and micro scales. Finally, a two‐parameter Weibull statistical model was used to evaluate the scattering of the composites. The results demonstrate that the tensile, compressive, and shear properties of the material decrease under harsh conditions, and the degradation effect on the ultimate strength is much greater than that of the modulus. Cold‐temperature dry and elevated‐temperature wet conditions are particularly severe. Composite environments significantly affect the macroscopic failure process and ultimate failure mode of materials. In general, the temperature and humidity of the matrix system acts at the core of the deterioration mechanism of composites, affecting the properties of the fiber/matrix and orthogonal woven fiber interfaces, and eventually resulting in a loss of their constitutive strength and bearing capacity. The theoretical ultimate strength were consistent with the experimental values. Highlights: Comprehensive mechanical property testing in multiple composite environments.Degradation mechanisms were revealed from multiscale morphology analysis.Scattering of composites were evaluated using statistical analyses.Cold temperature dry and elevated temperature wet were the worst states.Deterioration effect of environment on matrix and interface is the core failure mechanism. [ABSTRACT FROM AUTHOR]

The effect of moisture on the photo-oxidative degradation of polyamide-6 (PA-6) was studied by analyzing the mechanical response after two different accelerated aging procedures. In the first aging procedure, the PA-6 was only exposed to ultra-violet (UV) radiation at 60 ∘ C. In the second procedure, the same duration of UV radiation was periodically interrupted while the relative humidity was raised to 100%. Diffusion-limited and nominally homogeneous degradation conditions were investigated using bulk and film specimens, respectively. Accelerated UV aging reduced the ductility of PA-6, but the additional hygrothermal exposure had no effect on the ductility or strength, indicating that humidity did not influence the photo-oxidation of PA-6. This finding contrasts with previous studies that found thermo-oxidation of PA-6 was accelerated by moisture. [ABSTRACT FROM AUTHOR]

New composites produced with recycled waste are needed to manufacture more sustainable construction materials. This paper aimed to analyze the hygrothermal and mechanical performance of plasterboard with a polymethylhydrosiloxane (PMHS) content, incorporating recycled PET microplastic waste and varying factors such as PMHS dose, homogenization time, and drying temperature after setting. A cube-centered experimental design matrix was performed. The crystal morphology, porosity, fluidity, water absorption, flexural strength, and thermal conductivity of plasterboards were measured. The results showed that incorporating recycled PET microplastics does not produce a significant difference in the absorption and flexural strength of plasterboards. However, the addition of recycled PET reduced the thermal conductivity of plasterboards by around 10%. [ABSTRACT FROM AUTHOR]

For the first time, the dispersion of elastic waves in natural fiber-strengthened composite high-order beam rested on an elastic substrate is probed in the current article. Furthermore, a theoretical damage model is used to describe the mechanical degradation of natural fiber-strengthened composite beam during hygrothermal aging. Different three types of Winkler foundations are considered as a linear layer of the elastic foundation. To derive the equations of motion of natural fiber-strengthened composite beam, principle of Hamilton is implemented. In addition, the analytical solution is utilized to solve the derived governing equation of natural fiber-strengthened composite beam rested on Winkler–Pasternak substrate. The accuracy of using methodology is verified by those reported in the literature. The impacts of various parameters, i.e., wave number, aging time, fiber content, different types of Winkler foundation, Winkler and Pasternak parameters, α parameter and slenderness ratio on the variation of wave propagation of natural fiber strengthened composite beam are explored. Some tables and figures are provided to illustrate the obtained outcomes. The obtained results indicate that elastic foundation coefficient and wave number have an increasing effect and slenderness ratio and α parameter have decreasing effect. Furthermore, the effect of fiber content on change in wave propagation behavior depends on aging time. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to contribute novel insights into the analysis of thin functionally graded material (FGM) plates with variable thickness, considering both temperature-dependent and independent material properties, focusing on critical linear buckling temperature rise and the effect of critical linear moisture for various moisture concentrations. Design/methodology/approach: The study derives stability and equilibrium equations for thin rectangular FGM plates under hygrothermal loading, employing classical plate theory (CPT). Buckling behavior is examined using Galerkin's method to obtain pre-buckling force resultants. Findings: The findings highlight significant increases in critical buckling temperature with aspect ratio, distinct temperature sensitivity between materials and increasing moisture susceptibility with larger aspect ratios. These insights inform material selection and design optimization for FGM plates under hygrothermal loading, enhancing engineering applications. Research limitations/implications: This research primarily focuses on hypothetical scenarios and mathematical model development and analysis. Originality/value: This paper presents original contributions in the field by addressing the hygrothermal buckling analysis of thin FGM rectangular plates with variable thickness, utilizing CPT, thereby enriching the understanding of structural behavior in varying environmental conditions. [ABSTRACT FROM AUTHOR]

The aim of this work is to analyze the effect of water absorption on the mechanical properties and damage mechanisms of polyester/glass fiber/jute fiber hybrid composites obtained using the compression molding and vacuum-assisted resin transfer molding (VARTM) techniques with different stacking sequences. For this purpose, the mechanical behavior under tensile stress of the samples was evaluated before and after hygrothermal aging at different temperatures: TA, 50 °C, and 70 °C for a period of 696 h. The damage mechanism after the mechanical tests was evaluated using SEM analysis. The results showed a tendency for the mechanical properties of the composites to decrease with exposure to an aqueous ambient, regardless of the molding technique used to conform the composites. It was also observed that the stacking sequence had no significant influence on the dry composites. However, exposure to the aqueous ambient led to a reduction in mechanical properties, both for the molding technique and the stacking sequence. Damage such as delamination, fiber pull-out, fiber/matrix detachment, voids, and matrix removal were observed in the composites in the SEM analyses. [ABSTRACT FROM AUTHOR]

Nanomechanical properties of bio‐compatible polymers play crucial roles in tissue engineering scaffolds and filtration devices. The hygro‐mechanical properties of those fibers have been mostly studied from a very coarse perspective, reaching a micrometer‐scale. However, at the nanoscale the mechanical response of polymeric fibers becomes more challenging due to both experimental‐theoretical limitations. In particular, the environment‐mediated mechanical response of polymer‐fibers demands advanced models that consider sub‐nanometric changes in the local structure of water‐intercalated with single‐polymer‐chains. Herein, atomic force‐microscopy (AFM) experiments, analytical theory, and simulations are combined to determine the elastic properties of the nanofibers as a function of relative humidity. The effect of morphological changes from the adsorbed water‐layer, and an ensemble of inter‐chain interaction strength and morphological changes at peak‐forces are explored. For the polyvinyl‐alcohol (PVA) nanofibers, considerable differences are found, which are strongly dependent on the molecular signatures of hydration‐adsorption at a polymer‐chain level. Here, the semi‐empirical model plays a key role in properly interpreting experiments by evaluating only a few observables, the height, phase (dissipation), and alternatively the force‐distance curves. Beyond the semi‐empirical model, an analytical approach to calculate the peak‐forces of hygroscopic materials is featured, which enables on‐the‐fly characterization of the samples, and thus the interactive adjustment of operational‐parameters. [ABSTRACT FROM AUTHOR]

This work aims to study the cutting behavior of biocomposites under different controlled hygrothermal conditions. This investigation choice is motivated by the fact that natural plant fibers such as flax are characterized by their hydrophilicity which makes them able to absorb water from a humid environment. This absorption ability is intensified by increasing the conditioning temperature. The moisture diffusion process affects considerably the mechanical properties of the resulting composite, which causes many issues during the machining operations. In this paper, moisture diffusion, chip form, cutting and thrust forces, and scanning electron microscope (SEM) observations are considered to explore the cutting behavior of flax fiber-reinforced polylactic acid (PLA) depending on the hygrothermal conditioning time. Results reveal that moisture content in the biocomposite is significantly influenced by the conditioning temperature and the fiber orientation. Moisture content and fiber orientation affect both the curling behavior of the removed chip as well as the tool/chip interaction in terms of friction. The machinability of flax fiber-reinforced PLA biocomposites depending on hygrothermal conditioning time is then investigated using SEM analysis in addition to analytical modeling. An analysis of variance is used finally to quantify the observed results. [ABSTRACT FROM AUTHOR]

The search for environmentally friendly and low-carbon-footprint construction materials continues progressively. Researchers are now interested in innovative materials that connect with the principles of sustainable construction, and materials such as hemp concrete prove to be promising. This article presents the results of a study that aimed to evaluate the hygrothermal performance of hemp concrete integrated into the building envelope using the hygrothermal tool WUFI Pro 6.2. The simulation model was compared and verified with existing models before its utilization for this study. The results of this verification were in good agreement, which gave us more confidence in its application for further parametric studies of building envelopes in hot climate zones. Three wall systems were simulated: (i) a wall system with hemp concrete, (ii) a compressed earth block wall, and (iii) a cement block wall. The most important variables used in the simulations were the hygrothermal properties of the materials or wall components and the incident solar radiation. The simulation results showed that hemp concrete has good thermal performance and temperature and humidity regulation capabilities of the building envelope. The interior surface temperatures of the hemp concrete walls were between 22.1 °C and 24.6 °C compared to the compressed earth block and cement block walls, where the surface temperatures were between 22.0 °C and 27 °C and between 21.2 °C and 28.7 °C, respectively, and between 23 °C and 45 °C for the exterior temperatures. These values remain the same with the increase in exterior temperatures for hemp concrete walls. In conclusion, hemp concrete could be a great alternative material for use in construction for hot climate zones. [ABSTRACT FROM AUTHOR]

A favorable environment for fungi colonization in building materials' surfaces can emerge when certain hygrothermal conditions occur. Thus, reducing fungal growth susceptibility is of major interest. Furthermore, if the integration of bio-wastes is performed in parallel with the development of innovative materials for this purpose, a more sustainable and environmentally friendly material can be obtained. In this study, the fungal susceptibility of lime mortars incorporating almond-shell powder (ASP) microparticles (2 and 4%, wt.–wt. in relation to the binder content) was evaluated. The particle-dispersion technique was employed to prepare the bio-waste introduced in the mixtures. The fungal susceptibility of ASP samples was compared with nanotitania (n-TiO2) with recognized antifungal properties. Mechanical strength, water absorption, and wettability tests were also performed for a better characterization of the composites. Although the addition of 2% ASP led to mechanical properties reduction, an increase in the compressive and flexural strength resulted for 4% of the ASP content. Difficulties in fungal growth were observed for the samples incorporating ASP. No fungal development was detected in the mortar with 2% of ASP, which may be correlated with an increase in the surface hydrophobic behavior. Furthermore, mortars with ASP revealed a reduction in water absorption by capillarity ability, especially with 4% content, suggesting changes in the microstructure and pore characteristics. The results also demonstrated that an improvement in the physical and mechanical properties of the lime mortars can be achieved when ASP microparticles are previously subjected to dispersion techniques. [ABSTRACT FROM AUTHOR]

With increasing attention being paid to environmental issues, the application of natural fibers in fiber-reinforced composites has attracted more and more attention. Composite materials with basalt fibers (BFs) as reinforcement have excellent properties and are widely used in many fields. Hydrothermal aging crucially influences the durability of basalt fiber/epoxy resin composites (BF/ERCs). In this study, BFs were used as reinforcing materials, whose surfaces were modified with a rare earth modification solution (CeCl3). The density, mechanical performance, and chemical properties of BF/ERCs subjected to hygrothermal aging were analyzed by the weight method, static mechanical performance testing, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The effects of the modification solution with different Ce concentrations on the water absorption, tensile, bending and interlaminar shear strength (ILSS) of BF/ERCs were investigated. The test results showed that the water absorption of BF/ERCs treated with a modification solution that contained Ce 0.5 wt % as the minimum value and the retention rate of the mechanical properties of BF/ERCs reached maximum values after hygrothermal aging. [ABSTRACT FROM AUTHOR]

Membrane electrode assemblies (MEAs) have been subjected to alternating hygrothermal conditions, and frequent load changes significantly reduces the proton exchange membrane fuel cells (PEMFCs) lifetime. PEMs with a reinforced layer of e-PTFE have gained widespread application with the PEMFC development. However, the fatigue mechanism beyond the glass transition temperature remains to be elucidated. In this study, two accelerated stress tests (AMFT-85 and AMFT-95) are designed to investigate the PEM response to humidity under varying operating temperatures. In-situ fatigue experiments are conducted to comprehensively examine the fatigue mechanism of MEAs through the integration of electrochemical property characterization, mechanical property evaluation, and surface morphology analysis. The polarization curve results indicate that the AMFT-95 condition accelerates output performance degradation. The catalyzer-coated membrane displays a diminishing trend regarding of final strain, ultimate tensile strength, fracture toughness, and glass transition temperature due to the formation of cracks and delamination induced by cyclic stresses during physical fatigue. This decreasing trend becomes more pronounced with higher operating temperatures. Furthermore, elevated temperatures decreased the viscoelastic properties of the membranes, rendering catalyzer-coated membranes more susceptible to creep-fatigue failure and microstructural damage. This study proposes an experimental approach to enhance the understanding of physical fatigue in PEMs, contributing to mitigate fatigue failure and enhance PEMFC service life. • These paper focus on the temperature on CCM mechanical degradation mechanism. • The results confirm the relationship between temperature and cracks. • Elevated temperature degraded CCMs have lower glass transition temperatures. • Mechanical degradation is more severe above glass transition temperature. [ABSTRACT FROM AUTHOR]

The textile industry now produces thousands of tons of waste worldwide, and the total amount of discarded material waste increases yearly. Hygrothermal aging of cotton/E-glass (hybrid) fiber reinforced with various proportions of graphene oxide (0%, 1%, 3%, 5%, 7%, and 9%) was performed. Epoxy and vinyl ester (50:50) have been chosen because of the Interpenetrating Polymer Networks (IPNs) concept. Laminates were subjected to 50, 60, and 70°C temperatures for 180 days. Further, Tg and the degree of cross-linking have been determined by using differential scanning calorimetry (DSC). DSC analysis proves that a hot water bath enhances the cross-linking of the polymer. IPN laminates were also intermittently weighed for water uptake, and their consecutive mechanical properties like tensile, flexural, and impact strength were obtained. From this work, it was observed that the addition of 5 w.t% graphene oxide in cotton/E glass fiber vinyl ester/epoxy resin hybrid IPN composites showed a tensile strength of 375.61 MPa, flexural strength of 393.54 MPa, Interlaminar shear strength (ILSS) of 49 MPa and the impact strength of 22.54 MPa. Moreover, the lowest inclusion of particulate addition exhibits better mechanical properties than (up to 5% of GO) the highest particulate loading into the matrix. SEM study was conducted on the broken specimens to know the impact of diffusion characteristics on the physical properties of the IPN composites. Highlights • Natural and synthetic fibers are used as reinforcements. • Waste cotton/E glass fiber vinyl epoxy composites are fabricated. • Laminates were subjected to diverse temperatures for 180 days. • The moisture diffusion coefficient is proportional to water temperature. • Bathtub temperature affects the tensile strength of the laminate. [ABSTRACT FROM AUTHOR]

The investigation of the reflection issue in a hygrothermal medium in nonlocal elasticity is the focus of the current research project. The velocity equation is created by formulating and solving the governing equations of a hygro-thermoelastic material. The solution for plane waves predicts three incorporated plane waves, including longitudinal displacement, P-wave, thermal diffusion TD-wave and moisture diffusion mD-wave and shear vertical SV wave propagate in the medium. The velocity of P, TD, mD and SV waves are computed for the hygrothermal medium. Expressions for the energy ratio and reflection coefficient are developed for the incidence of a hygrothermal plane wave. The effect of hygrothermal parameters and nonlocal parameter on velocity, the reflection coefficient and energy ratio are displayed on a graph. [ABSTRACT FROM AUTHOR]

The hygroscopic and moisture-dependent mechanical characteristics of small-leaved lime wood (Tilia cordata) were investigated experimentally. This study includes sorption, swelling and shrinkage experiments, as well as tension and compression tests in the three principal anatomical directions at four relative humidity levels. Four sample groups from trees of three different locations in Germany were used. The findings are comparable to those of earlier studies. The hygro-expansion anisotropy is relatively small. Young's moduli at tension/compression decreased by about 52 %/64 % in radial, 19 %/48 % in tangential and 16 %/58 % in longitudinal direction for an increase of moisture content from 10 % (65 % RH) to 20 % (95 % RH). Tension strengths/compression yield stresses decreased by about 25 %/45 % in radial, 9 %/42 % in tangential, and 32 % (compression) in longitudinal direction, respectively. These parameters increased with an increasing density. Based on the mechanical tests, Young's modulus, tension strength and compression yield stress were derived as density- and moisture-dependent material model parameters. Shear modulus and shear strength were estimated by a theoretical approach. The experimental and modelling study was accompanied by a literature survey on characteristics of lime wood relevant for hygro-mechanical material modelling. [ABSTRACT FROM AUTHOR]

Epoxy resins are used in electronic packaging. However, its low thermal conductivity is a disadvantage and the high moisture absorption leads to defects such as cracking and delamination. In this work, the effect of thermo‐mechanical properties of epoxy resins under moisture‐heat coupling is investigated by molecular dynamics (MD) simulations. The diglycidyl ether of bisphenol A (DGEBA) and polyetheramine D230 are used as epoxy resin matrix and curing agents, respectively. The degree of cross–linking is set from 0% to 98% and the moisture mass fraction is set from 0 wt.% to 10 wt.%. The radius distribution function(RDF) shows that water molecules tend to appear ≈2.75 Å from the epoxy resin. The thermal conductivity of the epoxy resin increases by 54.55% for the maximum cross–linking degrees studied. And it increases by 19.23% when the moisture mass fraction is increased from 0 wt.% to 10 wt.%. The deformation of the epoxy resin is calculated which includes the coefficient of thermal expansion(CTE), coefficient of moisture expansion(CME), and coefficient of linear expansion. It is found that moisture expansion predominated at low temperatures and thermal expansion dominates at high temperatures. The analysis provides a theoretical basis for the study of hygrothermal coupling effects. [ABSTRACT FROM AUTHOR]

A case of underground long-term hot water storage is investigated numerically. The study is based on the unsteady two-dimensional Navier-Stokes equations in Boussinesq approximation applied to a closed cavern with time-dependent temperature boundary conditions on the walls. The problem formulated in a vorticity-stream function statement is solved by finite difference method (FDM) for high values of the Rayleigh number and for the Prandtl number of water. Streamlines, velocity and temperature fields are presented graphically for given moments of time. The evolution of the thermocline thickness in the mid-section of the cavern is slow and illustrates that the hot water zone occupies more than the half of the cavern even after 6 months period. The Nusselt number on the walls shows that the convective thermal losses are small and after certain period of time tend to decrease due to the diminished temperature difference at the walls. The influence of the fluid convection on the thermal losses is evaluated quantitatively, showing high seasonal thermal efficiency of the insulated hot water storage. [ABSTRACT FROM AUTHOR]

In order to investigate the durability of two kinds of fiber-reinforced composite materials, and obtain the degradation mechanism and failure model in a hygrothermal environment, E-glass- fiber-reinforced composite materials, glass fiber-reinforced epoxy vinyl ester and glass fiber-reinforced unsaturated polyester (named GF/VE and GF/UP, respectively) were chosen to suffer rigorous hygrothermal aging. Their mechanical performance was monitored during the aging process to evaluate their durability. The cause of deterioration of the composite was comprehensively analyzed. Based on the analysis results of attenuated total-reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), the change mechanism of chain structure of the resin molecule was proposed. SEM (scanning electron microscopy), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to analyze the microstructure and degradation mechanism of the fiber and the interface between fiber and matrix. The degradation mechanism of the composite system, including the resin, the fiber and the interface, was obtained, and it was found that the deterioration of the matrix resin caused by the hygrothermal environment was the main factor leading to the decline in composites performance. [ABSTRACT FROM AUTHOR]

The main advantage of green composites is their biodegradability, but this biodegradability can also be considered a drawback if the degradation appears during the service life of the component. Therefore, the study of the mechanical behavior of green composites after hygrothermal aging tests is necessary to analyze their degradation process. This study aims to comprehensively analyze the hygrothermal aging behavior and aging mechanism of flax-fiber-reinforced polylactic acid (PLA) biocomposites. The fully biodegradable composites are manufactured by compression molding. In addition, the influence of atmospheric-pressure plasma treatment on the mechanical properties of the biocomposite is studied. Specimens are exposed to water vapor and 40 °C environmental conditions in a stove for up to 42 days. Several specimens of each type are taken out at regular intervals and tested to examine the water absorption, mechanical properties, and thermal characterization. The results show that the stiffness was significantly reduced after 24 h due to matrix degradation, while the strength was reduced only after three weeks. [ABSTRACT FROM AUTHOR]

The formulation of the nth-order shear deformation theory was modified to discuss the hygrothermal response of free vibration of laminated composite plates. Current theory has four unknown variables. Besides, this theory does not require a shear correction factor and gives a parabolic distribution of shear stresses across the thickness of the plate. The properties of the plate are affected by temperature and humidity. The equations of motion are established from Hamilton's principle. The Navier-type solution procedure is applied to determine analytical solutions for free vibration of simply-supported laminated plates. The numerical results obtained by the present analysis of the free vibrations of composite plates are discussed to present the influence of the temperature, humidity, proportion of the aspect, and the orientation of the fiber orient on the characteristics of the vibration of the laminated plate. [ABSTRACT FROM AUTHOR]

In this work, the nonlinear vibrations of functionally graded (FG) porous circular plates under hygro-thermal loading is studied utilizing a numerical approach. Hygroscopic stresses generated due to the nonlinear rise in moisture concentration, even and uneven porosity distributions, and temperature dependency of material properties are all taken into account. Modified Voigt's rule of mixture is applied to obtain the hygro-thermo-mechanical properties of the FG circular plate. All material properties are assumed to be temperature-dependent using the Touloukian formula. In order to obtain the equations of motion, the first-order shear deformation theory, von-Kármán geometrical non-linearity assumption, and hygro-thermal strains are considered concurrently. After deriving the equations of motion using Hamilton's principle, the differential quadrature method and the Newmark-beta time integration scheme are employed in conjunction with an iterative approach to solve the set of nonlinear governing differential equations of motion. The effects of various parameters including temperature distribution, plate's thickness, porosity volume fraction, moisture concentration, and FG index are studied on plate's maximum non-dimensional lateral deflection. [ABSTRACT FROM AUTHOR]

Thermal power units play a crucial role in the deep peak regulation of power generation. During deep peak regulation, the load of the unit changes significantly, causing fluctuations in the inlet water temperature of the cooling tower and the water temperature in the filler. Therefore, in cold regions in winter, cooling towers have a high risk of freezing, which threatens the economic and safe operation of the unit. This paper establishes a three-dimensional numerical model based on constant heat dissipation and explores the average and minimum water temperatures at the bottom of filler under different water distribution methods, crosswind velocities, and ambient temperatures. The results show that the water distribution method has a significant impact on the water temperature at the filler bottom. Reducing the water distribution area can significantly increase the minimum water temperature at the filler bottom and reduce the risk of freezing. Although the presence of crosswind is not conducive to the cooling performance of the cooling tower, the higher the crosswind velocity, the higher the minimum outlet water temperature at the filler bottom and the lower the risk of freezing. The minimum water temperature at the filler bottom is approximately linearly related to the ambient temperature and is less affected by the unit load at the same temperature. [ABSTRACT FROM AUTHOR]