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AbstractThis study investigates the behavior and reliability of CFRP-to-aluminum adhesive joints subjected to hygrothermal conditions under both natural and accelerated aging scenarios. Natural aging durations ranged from 1 to 3 years, while accelerated aging was performed over periods of 100–1200 h in 50-hour intervals. Fatigue life was evaluated using a three-point bending test, revealing a significant degradation in joint performance due to hygrothermal exposure. Key findings include a 25.98% reduction in fatigue life for samples naturally aged for three years and a comparable 27.33% reduction in samples subjected to 1000 h of accelerated aging. Hygrothermal conditions caused notable matrix degradation, transitioning failure modes from cohesive to mixed types (cohesive, adhesive, and fiber tear failures), with a direct impact on joint durability. Machine learning models, including artificial neural network (ANN), support vector regression (SVR), linear regression, polynomial regression, and random forest regression, were employed to predict natural aging durations based on accelerated aging data. Among these, the random forest regressor exhibited the highest predictive accuracy, effectively correlating accelerated aging durations to natural aging conditions. This study provides critical insights into the failure mechanisms and long-term performance of adhesive joints, offering a novel predictive approach to estimate natural aging effects from accelerated tests. These findings highlight the potential for optimizing joint designs to enhance durability and reduce failure risks in operational environments. [ABSTRACT FROM AUTHOR]

3D orthogonal woven composites (3DOWCs) are increasingly utilized in various engineering applications due to their superior mechanical properties. However, their mechanical properties and damage mechanisms could be significantly influenced by the environmental factors such as temperature and moisture. This study aims to investigate the mechanical behavior of 3DOWCs under hygrothermal conditions through meso-scale finite element (FE) simulations. The proposed FE model is validated using existing experimental results under standard temperature and humidity conditions, and subsequently applied to predict the performance in hygrothermal environments. The effects of temperature, humidity, and loading conditions on the mechanical properties of 3DOWCs are analyzed and the corresponding failure mechanisms are revealed. This study offers significant insights into the hygrothermal behavior of 3DOWCs, thereby facilitating their optimal design and implementation in various engineering applications. [ABSTRACT FROM AUTHOR]

Biosourced materials derived from agricultural by-products hold significant promise in both enhancing the hygrothermal performance of buildings and reducing their environmental footprint. We investigate the hygrothermal properties of green composites based on date palm fibers and lime. The eco-friendly building composites explored are manufactured using either trunk fiber (surface fiber) or rachi and petiole fiber (wood fiber). Through an experimental approach, for different fiber percentages, the hygrothermal characteristics of the explored composites were experimentally determined in terms of thermal conductivity, diffusivity, porosity, water vapor permeability, and sorption scanning isotherms. The results show that date palm fiber has a positive effect on the thermal properties of the composite material. Indeed, it significantly enhances the insulating capacity of the composites. Water vapor permeability exhibits significant variation depending on the fiber content, with samples containing higher fiber content exhibiting greater permeability. Furthermore, the effective moisture penetration depth (EMPD) model proved effective describing the experimental adsorption scanning isotherm curves. It was observed that the sorption process is significantly influenced by both the type and percentage of fibers. Finally, the observed results demonstrate that date palm fiber and lime composites could offer notable advantages for construction applications and serve as an effective, cost-effective insulation. [ABSTRACT FROM AUTHOR]

This study presents the findings from an in-depth study into the influence of hygrothermal aging on the material properties of a pultruded flat sheet composite composed of electrical-corrosion resistant (E-CR) glass fibers and an unsaturated polyester-based matrix. By discussing the impact of hygrothermal aging across 10 material properties, assessing the suitability of test procedures, and presenting a framework, this study evaluates the suitability of the experimental test results for use with two service life models. This study offers an open and critical evaluation of the currently accepted methods. Across 102 batches, which consist of 476 coupons, immersed in distilled water at 25°C, 40°C, 60°C, and 80°C, with exposure times of 28, 56, 112 and 224 days, the changes in tensile, compressive, in-plane shear, and pin-bearing properties are evaluated alongside mass changes. An understanding is discussed of the relationships that were obtained for moisture uptake and for material property retentions over time, which identified evidence termed nonconsistent fluctuating trends. This study highlights the possibility of misleading results that arise from the impact of the forced drying of coupons before coupon testing. For longitudinal tensile properties, a direct comparison is made between coupons termed Dried and Wet (to represent field conditions) coupons, which indicates the need for careful consideration in characterization work for the determination of the long-term material properties of composites. With the development of a framework for the evaluation of two service life prediction models, the quality of 11 sets of experimental results is evaluated. Using the four most reliable sets of predictions, the acceleration factors and service lifetimes are reported. From the evaluation of the experimental findings, testing methodologies, and the application of service life prediction techniques, this study puts forward an understanding of how to execute experimental programs with accelerated aging with the aim of obtaining meaningful test results for the long-term material properties of fiber–polymer composites. Practical Applications: The contribution of this study to the knowledge and understanding of how the mechanical properties of fiber–polymer composites might change over time due to the durability effects of moisture and temperature is important for the determination of adjustment factors for end-user conditions in North American standards and the conversion factors for moisture and temperature effects in the Eurocode standard. These factors are used in structural design codes to adjust the short-term material properties (characteristic values) so that the design values of material properties might be appropriate to the service lives of fiber–polymer composite structures of approximately 50 years. [ABSTRACT FROM AUTHOR]

This study presents a generalized two-dimensional model for evaluating the stationary hygro-thermo-mechanical response of laminated shell structures made of advanced materials. It introduces a generalized kinematic model, enabling the assessment of arbitrary values of temperature variation and mass concentration variation for the unvaried configuration at the top and bottom surfaces. This is achieved through the Equivalent Layer-Wise description of the unknown field variable using higher-order polynomials and zigzag functions. In addition, an elastic foundation is modeled utilizing the Winkler-Pasternak theory. The fundamental equations, derived from the total free energy of the system, are solved analytically using Navier's method. Then, the Fourier-based generalized differential quadrature numerical method is adopted to efficiently recover the through-the-thickness distribution of secondary variables in agreement with the hygro-thermal loading conditions. The formulation is applied in some examples of investigation where the response of panels of different curvature and lamination schemes is evaluated under external hygro-thermal fluxes and prescribed values of temperature and moisture concentration. In addition, this study investigates the effect of the hygro-thermal coupling due to Dufour and Soret effect. The present formulation is verified to be a valuable tool for reducing computational effort and determining the effect on the mechanical response of laminated structures in a thermal and hygrometric environment. [ABSTRACT FROM AUTHOR]

AbstractFunctionally graded piezoelectric/piezomagnetic (FGPEPM) materials in a hygrothermal environment exhibit complex multi-physical field coupling effects when subjected to various loads such as mechanical, electric, magnetic, temperature, and moisture concentration. In this paper, a theoretical analysis of the electro-magneto-elasto-hygrothermal (EMEHT) coupling effects for a rotating FGPEPM hollow sphere is presented. By assuming that the properties of hygrothermo, electro-magneto-elastic, hygrothermal expansion, and density of the FGPEPM sphere obey different power laws along the thickness direction, the distributions of temperature, moisture, magnetic potential, radial displacement, electric potential, and stresses within the rotating FGPEPM sphere are determined. The present theoretical solutions are verified with existing analytical solutions for some related simplified problems. The FGPEPM hollow sphere exhibits complex multi-physical field coupling effects, containing positive/inverse piezoelectric, positive/inverse piezomagnetic, positive/inverse magnetoelectric, thermal/moist stress, pyroelectric/pyromagnetic, and hydroelectric/hydromagnetic effects under a hygrothermal environment. The influence of gradient parameters and other material properties on these EMEHT coupling effects is also investigated for FGPEPM hollow spheres under various types of loads. This theoretical research provides some reference for the optimal design for this type of functionally gradient multifield coupling material. [ABSTRACT FROM AUTHOR]

AbstractStiffened functionally graded (FG) folded plates are being widely used these days in aeronautical, automotive, and naval applications which are often exposed to extreme environmental conditions characterized by high temperature and moisture concentrations. However, a numerical model to estimate the dynamic response of such structures in hygrothermal environment is almost non-existent. It is from this perspective that, a MATLAB-based finite element (FE) model is developed to assess the free vibration characteristics of stiffened FG folded panels in hygrothermal environment and is presented for the first time in this article. The governing equation is derived following the first order shear deformation theory including hygro-elastic and thermo-elastic relations. Temperature and moisture concentrations are assumed to vary both linearly and uniformly through the plate’s thickness to numerically simulate hygrothermal environment. Non-linear strains are incorporated in the present FE model to consider the hygrothermal effect. Another FE model is also developed in COMSOL Multiphysics software for these structures and is compared with the MATLAB-based model. Numerical simulations reveal that the free vibration characteristics of stiffened FG folded plates are significantly affected by hygrothermal environment. The present FE models can be effectively utilized by engineers and researchers to analyze and optimize the dynamic behavior of stiffened FG folded plates. The results are also expected to serve as a benchmark for future research works. [ABSTRACT FROM AUTHOR]

The hygrothermal aging model, based on Fick's second law of diffusion, characterizes the degradation of engineering constants in T700 carbon fiber/epoxy resin composites. It focuses on changes in the tensile modulus, shear modulus, and transverse Poisson's ratio due to moisture absorption and temperature variations. The model validates through mass change observations before and after seawater immersion, along with surface morphology assessments and tensile experiments. The results reveal that the saturated moisture absorption rate for single-layer laminates in seawater immersion is 0.35%. Short-term seawater immersion at room temperature (≤60 days) does not induce cracks or defects (≥10 μm) on the composite's surface. The composite's modulus decreases as moisture absorption increases, with the longitudinal tensile modulus dropping by an order of 10−5%, while the other engineering constants decrease by an order of 10−3%. The modulus also decreases with rising temperature; the closer the temperature is to the matrix's glass transition, the faster the modulus declines, with the longitudinal tensile modulus decreasing by 0.84%, and the other engineering constants decreasing by 100%. This research provides valuable insights for the engineering applications of composite materials in marine environments. [ABSTRACT FROM AUTHOR]

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]

This article investigates the static and dynamic buckling behavior of a double-curved sandwich shell composed of two layers via improved first-order shear deformation theory without using the shear correction is utilized to model the sandwich shell. The sandwich two-layer shell are held together by elastic pins, each layer made from an ultra-light auxetic honeycomb core layer (negative Poisson's ratio) and is reinforced by a layer of tri-phase polymer, graphene nanoplatelets (GNP), and fiber. The double-curved sandwich shell is supported by a Kerr elastic medium in hygro-thermal environment assuming that temperature and humidity only cause forces to be applied tangentially to the shell and do not change the mechanical properties of the shell material. The motion equations of sandwich two-layer shell are derived by Hamilton's principle, then the finite element method and Bolotin method are used to derive the dynamic instability region of sandwich two-layer shell. The accuracy of these results is confirmed by a comparison with established statements within the specific conditions of the problem model. The influence of inputs on the static and dynamic stability of sandwich two-layer shell is fully explored and discussed. Additionally, this serves as a crucial foundation for the calculation and design of structures that can integrate a variety of materials with different properties with low cost and simplification. [ABSTRACT FROM AUTHOR]

Hygrothermal exposure significantly impacts polymer composite (PMC) performance, affecting various industries. This study evaluated the short-term hygrothermal effects on PMCs by examining interfacial shear strength (IFSS), water uptake, glass transition temperature (Tg), and morphology. Data-driven techniques minimized experimental time while analyzing multiple factors. Specimens were immersed in water at 25°C and 70°C for 3, 7, and 14 days. The IFSS between carbon nanotube yarns and carbon fiber with epoxy (EPON™ 862) was measured before and after exposure. Statistical analysis indicated that fiber type significantly influenced IFSS, while time had a marginal effect and temperature had no impact. The IFSS decreased by 4.14% for CF/epoxy and 14.9% for CNT/epoxy. Water uptake analysis revealed weight gains of 0.465% and 1.566% for epoxy after 14 days at 25°C and 70°C, respectively. Morphological studies showed moisture penetration between 7 and 14 days. Thermomechanical analysis (TMA) indicated that pristine epoxy expanded by 0.318% of its original height. After 14 days, the Tg of epoxy decreased by 6.4% at 25°C and 9.7% at 70°C. Dynamic mechanical analysis (DMA) on dried epoxy samples showed similar Tg but varied tan delta curves due to plasticization. Short-term hygrothermal evaluation revealed degradation in interface quality and viscoelastic properties. [ABSTRACT FROM AUTHOR]

A two-dimensional coupled hygrothermoelastic medium boundary problem using Finite difference method is discussed in the present work. Explicit and Implicit finite difference schemes for this problem are formed. The solutions of these schemes are carried out using numerical methods of finite difference. These solutions are compared of and analyzed and exciting similarities were found as result. [ABSTRACT FROM AUTHOR]

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A novelty FG honeycomb-reinforced laminate (FGHRL) with viscoelastic material is constructed for an industrial exoskeleton. The study examines how FGHRL dissipates energy under hygrothermal conditions. Low-velocity impacts on the exoskeleton's load-bearing structure are simulated using a spherical object. Parameters for the FGHRL, made of a two-phase material, are estimated using the Halpin-Tsai model and macroscopically uniform theory. In-plane deformations are determined using Reddy's HSDT, while the impact response is evaluated with Newmark-β and Wilson-θ methods. Energy dissipation properties are calculated using the energy balance model, validated through CUF-based FEM and LS-DYNA explicit solution, and factors influencing energy dissipation are investigated. [ABSTRACT FROM AUTHOR]

Based on three-dimensional transient thermal conduction theory, the refined plate theory and Hamilton variational principle, the constitutive equations, geometrical equations, and governing equations for fiber metal laminates with piezoelectric layer (PFMLs) under hygrothermal environment is presented. Subsequently, the Newmark method and Galerkin method are used to solve the governing equations which in terms of displacement functions. The results show that electric potential function, fiber orientation, external load as well as thickness ratio have great influence on the deflection as well as normal stress. The selection of (45°/0°) fiber orientation is more resistance to deformation and normal stress. [ABSTRACT FROM AUTHOR]

Understanding the gradual performance degradation of carbon fiber reinforced polymers (CFRP) is critical for the design of engineering structures that are expected to be affected by hygrothermal environments. This study aims to investigate the effects of hygrothermal aging on the degradation mechanisms of the mechanical properties and energy absorption of CFRP structures. An experimental database comprising tensile, compressive, and shear tests for CFRP composite laminates (in this study) and axial crushing tests for energy-absorbing structures (from the literature) was constructed, in which all CFRP samples were immersed in deionized water to achieve a saturated water-absorption state. A material constitutive model considering the effects of water absorption and temperature was developed and implemented via the user subroutine VUMAT of the ABAQUS software. The simulated results correlated well with the experimental measurements. Simulation results of axial crushing indicated that the degradation of the inter-layer properties tends to worsen the mismatch between the intra-layer and inter-layer properties, thus significantly degrading the load-carrying capability. Owing to degradation in compressive fracture toughness, the simulated results showed reduced post-crushing integrity, thus indicating a favorable effect on the load-carrying capability. [ABSTRACT FROM AUTHOR]

Stiffeners are frequently utilized in many engineering projects because they boost strength while adding only a small amount of weight to the overall structure. The environments that the stiffened composite constructions are typically exposed to are harsh, which can result in damage like interlayer delamination and debond at the plate-stiffener interface, which can cause catastrophic failure. As a result, it is necessary to examine these structures' dynamic behavior in addition to their stability performance. The current study attempts to investigate the free vibration response of stiffened composite plates with plate-stiffener interfacial debonding under hygrothermal circumstances using a robust finite element (FE) model. The skin and stiffener flange are simulated in the current work using a 9-noded heterosis element to prevent the shear-locking issue. Additionally, to considerably enhance computational performance, the stiffener web is formulated as a 3-noded isoparametric beam element with the torsion correction factor. Additionally, a dummy node is created to represent the debond, and a fictitious spring is added to stop the nodes from interpenetrating one another. 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 improved free vibration characteristics. Further, extensive parametric analyses are conducted on the obtained stiffened plate with improved performance in a hygrothermal environment by considering debond at the skin-stiffener interface. The vibrational behavior of the debonded plate is shown to be significantly more affected by moisture than by temperature. Additionally, the debond has a more obvious impact on the vibration characteristics in the plate with a centrally attached stiffener than in the plate with an eccentricity attached stiffener. As a result, the established FE formulation is anticipated to be trustworthy and computationally effective while effectively analyzing the debonded stiffened panel's free vibration behavior in a hygrothermal environment. HIGHLIGHTS: Developed a simplified finite element model to incorporate the interfacial debonding between the plate and stiffener. The current model reduces the computational cost by partially modeling the T-stiffener with the beam element. Investigates free vibration behavior of hygrothermally stable stiffened composite panels in hygrothermal conditions. Extreme environmental conditions significantly reduce the panel's natural frequency. Large stiffener depth debonded panel's frequency drops considerably at higher moisture concentration. [ABSTRACT FROM AUTHOR]

In this article, the application of an artificial neural network (ANN)-based machine learning (ML) strategy to predict the coupled frequency of geometrically skewed multiphase magnetoelectric (MME) composite plate exposed to hygrothermal environment is presented. The ANN model is trained using a dataset comprising more than one million simulations conducted using an in-house developed finite element formulation. The underlying multiphysics governing equations are derived using Hamilton's principle and higher-order shear deformation theory (HSDT). The influence of the hygrothermal environment on the elastic stiffness of MME composites is defined by the empirical constants in the constitutive relations. Four prominent combinations of the empirical constants leading to different elastic stiffness relations have been considered in this study. Alongside, the influence of geometrical skewness on the coupled fundamental frequency is also assessed. For the training of the ANN model, the Levenberg–Marquardt optimization algorithm with 30 neurons along with a tangent sigmoid activation function is used. The trained ANN model is tested on an unseen dataset, different from the training data, and it is shown to accurately predict the natural frequency of MME plate with a maximum error of 2.3%. Further, excluding the training time and considering the computational time alone, the ANN model is found to be 6.3 times faster than the FE simulations. It is anticipated that such ML-based reduced order models can be effective in the design process, especially in complex multiphysics problems, such as the one considered in the work, involving a multitude of geometric, loading and material parameters. [ABSTRACT FROM AUTHOR]

Highly transparent and mechanically robust thermoplastic composites have been developed by hot‐pressing PETG with E‐glass fabrics. The tow‐spreading technique facilitates the reduction of internal defects and fiber crimp angle in the composites, thereby significantly improving their optical and mechanical properties. The optimized composite containing 55.1 vol% glass fibers and 0.4 mm thickness has a high transmittance of 86.1%@616 nm and a low overall haze of 7.2%. Moreover, the 1 mm thick composites exhibit tensile strength of up to 340 MPa and impact strength of up to 86.3 kJ/m2. After 28 days of hygrothermal or UV aging, the composites show minimal changes in their glass transition temperature and thermal degradation temperature. The chemical structure also remains unchanged, with no observed crystallization. In comparison to UV aging, the composites demonstrate better resistance against hygrothermal aging. Specifically, the hygrothermal aged sample displayed a light transmittance retention rate of 93.5% and a bending strength retention rate of 94.3%, while these values were reduced to 73.3% and 90.5%, respectively, in the UV aged sample. The opto‐mechanical properties enhanced mechanism and aging degradation mechanism have been identified by microscopic morphological observation. This work provides an innovative and straightforward approach to fabricate transparent, recyclable, high‐strength thermoplastic composites. Highlights: Highly transparent, mechanically robust, recyclable glass‐fabric reinforced thermoplastic composites are fabricated.Composites with spread‐tow fabrics exhibits improved transparency.The fabrication route is scalable and cost‐effective.The mechanism for opto‐mechanical properties enhancement are proposed. [ABSTRACT FROM AUTHOR]

The implementation of third order shear deformation theory using finite element method is presented in the current article to analyze the stability characteristics of porous magneto-electro-elastic (MEE) plates. This study aims to present the obscure behavior of FGMEE plate considering the loading to be hygrothermal in nature for buckling. Several temperature and porosity distribution are involved in this study in order to understand their influence on the buckling characteristics. The material properties of the porous MEE plate are assumed to vary continuously throughout its thickness according to rule of mixture. The porosity is considered as a locally distributed density estimated using the modified power law. The effect of temperature and moisture on buckling of MEE plates is of interest in this study. Skewness is incorporated through a transformation matrix to account for the angle. The stability characteristics of the porous FGMEE plate are examined under thermal, hygrothermal, electric, and magnetic loads to determine the critical buckling temperature. The influence of various variables, such as porosity, porosity distribution, and porosity volume, on the buckling behavior is extensively studied to realize that as porosity increases, the critical buckling temperature decreases in both load forms and noticed to be highest in Vo and Vx porosity distribution. Skew angle directly influenced the critical buckling temperature and was seen to be increasing with increase in skew angle between the plates. The study is also extended to assess the effect of geometrical parameters, such as aspect ratio, thickness ratio, and boundary conditions, on the stability characteristics that established an inverse relation between the parameters. [ABSTRACT FROM AUTHOR]

Highlights This study examines the failure mechanisms of fiber‐reinforced polymer (FRP) composites in hygrothermal conditions and develops a theoretical model for tensile strength prediction of FRP composites at various moisture and temperature levels. The model defines the function of water content in hygrothermal conditions and presents a physically‐based framework for temperature and moisture‐dependent tensile strength (TMDTS). It is based on the force‐heat equivalence energy density (FHEED) concept. The model considers how the tensile strength is affected by temperature, Young's modulus, and particularly the hygrothermal conditions. It is confirmed by contrasting the proposed model's reasonableness with the available experimental data. Additionally, the work examined the factors affecting the FRP composites' tensile strength in a range of temperature and moisture conditions, and offering insightful knowledge about their properties. Ultimately, this study not only presents a reasonable theoretical approach for forecasting FRP composites' tensile strength under hygrothermal conditions but also offers suggestions for material evaluation and composites enhancement. A physics‐based temperature and moisture‐dependent strength model is proposed. The model considers the effect of hygrothermal condition on the tensile strength. The temperature and moisture‐dependent tensile strength can be well predicted. This study deepens the understanding on the mechanical properties degradation. [ABSTRACT FROM AUTHOR]

We develop a computational framework to model damage and delamination in laminated polymer composite structures incorporating the effects of temperature and moisture content. The framework is founded on a recently developed comprehensive multi-layer thin-shell formulation based on Isogeometric Analysis, which includes continuum damage, plasticity and cohesive-interface models. To incorporate hygrothermal effects in the modeling, we propose a scaling law that is based on the Arrhenius equation and material glass transition temperature that establishes the dependence of the intra- and interlaminar material properties on the temperature and moisture content. We compute several classical test cases using a combination of environmental conditions and demonstrate that the resulting modeling approach shows a good agreement with the experimental data, both in terms of failure loads reached as well as failure modes predicted. [ABSTRACT FROM AUTHOR]

Carbon–glass hybrid fiber-reinforced epoxy polymer (C-GFRP) winding pipes integrated with the advantages of light weight, high strength, corrosion resistance, and cost-effectiveness offer immense potential to mitigate corrosion issues in oil, gas, and water transportation pipelines. In this study, C-GFRP winding pipes underwent accelerated aging tests through immersion in distilled water at temperatures of 25 °C, 40 °C, and 60 °C for 146 days. Water absorption tests were conducted to investigate the water absorption behavior of only CFRP- or GFRP-side absorbed water. Bending tests were performed to assess the evolution of the pipes' flexural properties in two directions (GFRP or CFRP in tension). The results showed that the single-sided water absorption behavior adhered to the two-stage diffusion model. The diffusion coefficient, activation energy, and 146-day water absorption were all higher for the CFRP-side absorbed water compared to the GFRP-side absorbed water. The flexural strength and modulus of C-GFRP pipes were influenced by post-curing and resin hydrolysis/debonding. Initially, the flexural strength of CFRP in tension was higher than that of CFRP in tension. After 146 days of aging, the flexural strength of CFRP in tension was lower than that of CFRP in tension. Utilizing Arrhenius theory, the long-term lives were predicted for the flexural strength at temperatures of 5.4 °C, 12.8 °C, and 17.8 °C. The predicted lives of GFRP in tension were higher than those of CFRP in tension. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Nanchang University (Engineering & Technology) is the property of Nanchang University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent decades, the aviation industry has increasingly adopted composite materials for various aircraft components, due to their high strength-to-weight ratio and durability. To ensure the safety and reliability of these structures, Health and Usage Monitoring Systems (HUMSs) based on fiber optics (FO), particularly Fiber Bragg Grating (FBG) sensors, have been developed. However, both composite materials and optical fibers are susceptible to environmental factors such as moisture, in addition to the well-known effects of mechanical stress and thermal loads. Moisture absorption can lead to the degradation of mechanical properties, posing a risk to the structural integrity of aircraft components. This research aims to quantify and monitor the impact of moisture on composite materials. A new formulation of the Bragg equation is introduced, incorporating mechanical strain, thermal expansion, and hygroscopic swelling to accurately measure Bragg wavelength variations. Experimental validation was performed using both uncoated and polyimide-coated optical fibers subjected to controlled hygrothermal conditions in a climate chamber. The results demonstrate that uncoated fibers are insensitive to humidity, whereas coated fibers exhibit measurable wavelength shifts due to moisture absorption. The proposed model effectively predicts these shifts, with errors consistently below 2.6%. This approach is crucial for improving the performance and reliability of HUMSs in monitoring composite structures, ensuring long-term safety in extreme environmental conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] Epoxy resin (EP) incorporating inorganic fillers has garnered significant attention in the electrical and electronic industries due to its enhanced dielectric and mechanical properties, but its long-term performance under harsh conditions remains a critical concern. This study investigates the effects of filler surface wettability on the durability of EP-SiO 2 composites. Micro-sized SiO 2 with hydrophilic (HP) and hydrophobic (HB) surfaces are prepared via surface treatment, before they are incorporated into epoxy resin and subjected to hygrothermal aging at 95 °C and 95 % relative humidity for up to 1200 h. Comprehensive characterizations of wettability, microstructure, mechanical properties, and dielectric performance are conducted. Results show that the composite with hydrophilic fillers, HP-SiO 2 -EP, exhibits superior dispersion and interfacial adhesion compared to its hydrophobic counterpart, HB-SiO 2 -EP. Consequently, HP-SiO 2 -EP demonstrates higher initial tensile strength, Young's modulus, and dielectric breakdown strength. Finite element simulations reveal the breakdown mechanism, highlighting that the hydrophobic SiO 2 filler with interfacial defects results in earlier mechanical and dielectric failure. Furthermore, HP-SiO 2 -EP shows better resistance to hygrothermal aging compared to HB-SiO 2 -EP, with smaller increases in dielectric constant (+13 % vs. +28 %) and dielectric loss (+234 % vs. +311 %), as well as lower decrease in volume resistivity (−89 % vs. −93 %). This study provides valuable insights into the relationship between filler surface wettability and long-term composite performance, contributing to the design of more reliable materials for advanced dielectric applications. [ABSTRACT FROM AUTHOR]

The risk of unintended consequences arising from the energy retrofit of buildings, especially concerning moisture movement through the building fabric, is well recognised. As highlighted by Publicly Available Standards (PAS) 2030 and 2035, this is particularly relevant to buildings of traditional construction, defined as those 'consisting of solid brick or stone external walls, or pre-1919 timber-framed external walls with any infill'. This paper focuses on this last construction typology, presenting ongoing research, funded by Historic England, monitoring the hygrothermal performance of four pairs of mock-up replacement infill panels for timber-framed walls. The chosen materials, informed by current guidance, are wattle and daub, expanded cork, wood fibre/wood wool, and hempcrete. Each pair of panels features two finishes: one with a natural hydraulic lime (NHL) 3.5-based render, and the other with a non-hydraulic lime/hemp mix. The panels are installed as the northern façade of a test cell, exposed to Cardiff's climate, with controlled internal conditions during the heating season. Since December 2019, moisture content (%) has been monitored by measuring electrical resistance every 30 minutes in a total of 60 positions. Previously published results from the initial 18 months of monitoring reported no evidence of interstitial condensation, with wetting and drying cycles directly corresponding only to wind-driven rain events. Following four years of monitoring, however, there now appears to be evidence to suggest that interstitial condensation is occurring within both the traditional wattle and daub and the composite wood fibre/wood wool infill panels. Although predicted by simulation and previous trials, this condensation might have previously been obscured by wind-driven rain. Its emergence in both traditional and retrofitted infill materials underscores the complex nature of moisture behaviour in this construction typology. This development is under ongoing review, and the monitoring of case study buildings is planned. The results will eventually inform best practice guidance for the energy retrofit of historic timber-framed buildings in the UK. [ABSTRACT FROM AUTHOR]

The paper is concerned with the impact of memory-dependent (MD) derivatives in the hygrothermal (HTE) three-phase-lag (3PL) hollow cylinder under thermal and moisture loading. We derive equations for temperature, moisture, displacement, and stress components. We solve these HTE field quantity equations using the variable separation method and Laplace transform. We then perform numerical calculations via Laplace transform inversion. We use Mathematica software to understand the hygrothermal behavior of fiber-reinforced 3PHL hollow cylinders. The model validity is assessed by comparing it to existing results. The analysis focuses on the effect of MD derivatives in the HTE 3PL model by examining their impact on heat and moisture field quantities in the presence of time delay parameters and singular kernel functions. This study further highlights the significant influence of employing various kernel functions on the behavior of the HTE hollow cylinder. The author believes that this research will help develop more robust and efficient methods for incorporating memory effects in mathematical models. [ABSTRACT FROM AUTHOR]

Highlights Glass fiber‐reinforced polymer composites are widely used in marine applications, including renewable energy devices and submarines, due to their strength‐to‐weight ratios and corrosion resistance. As sustainability becomes more important, recyclable thermoplastic composites are gaining attention in marine energy applications. These materials face harsh conditions such as high chloride water, UV radiation, pressurization, and thermal cycling, which can affect their durability and recyclability. This study examines the impact of hygrothermal aging on the recyclability of an Elium glass fiber (GF) composite. Samples were mechanically ground for recycling, and mechanical and thermal properties were compared between aged and unaged samples. After seawater aging, the tensile strength and modulus of the unaged composite dropped by 25% and 13% respectively, due to water ingress along the fiber‐matrix interface. The recycled composite showed reduced flexural strength as the long fiber composite was converted into short fibers during the process. Differential scanning calorimetry (DSC) revealed no change in glass transition temperature after aging. Weight loss (25%) was attributed to the thermal stability of the glass fibers. Dynamic mechanical analysis (DMA) showed that the storage modulus increased with aging, and fracture analysis confirmed a mixed mode of failure for aged composites. Hygrothermal aging lowers mechanical performance of Elium® GF composites. Failure mechanism tends to be matrix cracking and interface bonding. Glass transition temperature is not reduced by hygrothermal aging. Fractured composite was successfully recycled via thermoforming. Flexural strength of the recycled composite is lower. [ABSTRACT FROM AUTHOR]

Highlights Assessing the mechanical properties of CFRP and aluminum specimens exposed to hygrothermal aging is vital. Moreover, it is important to develop strategies to improve these properties. This study examines the influence of fullerene and Single‐Walled Carbon Nanotubes (SWCNT) on the fatigue life and static strength of bonded and bonded/bolted joints. The research concentrates on composite‐to‐composite and composite‐to‐aluminum substrates under three‐point bending tests, both prior to and after hygrothermal aging. The samples were classified into four groups: (1) neat specimens, (2) specimens with added fullerene, (3) specimens containing SWCNT, and (4) specimens with a blend of 50% SWCNT and 50% fullerene.The findings indicated that the optimal nanoparticle ratio for bonded joints differs from that for bonded/bolted joints. Incorporating nanoparticles into the adhesive enhanced the fatigue life of single lap joints (SLJs), particularly in samples with mixed particles and SWCNT. In some instances, nanoparticles intensified the effects of hygrothermal conditions, further increasing fatigue life. The incorporation of nanoparticles and the use of bonded/bolted joints significantly enhanced joint strength, with the combination of both yielding the best results. This study improves the understanding of aging in adhesive and hybrid joints, particularly in dissimilar configurations, and offers insights into their performance under various environmental conditions. Study examines fullerene and SWCNT impacts on CTC/CTA joint strength and fatigue. Optimal nanoparticle ratios differ for bonded and bonded/bolted joints. Nanoparticles reduce moisture absorption, aging damage, and increase failure load. Nanoparticles enhance fatigue life, varying by type, volume, load, and joint. Incorporating nanoparticles significantly improves joint strength. [ABSTRACT FROM AUTHOR]

Highlights This study investigates how carbon fiber reinforced polymer (CFRP)‐to‐aluminum adhesive joints behave under accelerated aging conditions with hygrothermal exposure and compares these findings against naturally aged samples to evaluate material reliability in challenging environments. The CFRP‐to‐aluminum adhesive joints were manufactured and subjected to natural aging for durations ranging from 1 to 3 years with 6‐month intervals, as well as accelerated aging (hygrothermal) for periods ranging from 100 to 1200 h, with intervals of 50 h. Subsequently, the mechanical properties of the joints were evaluated using a three‐point bending test. To forecast natural aging times from accelerated aging data, five machine learning models were utilized: artificial neural network, support vector regression, linear regression, polynomial regression, and random forest regression. Hygrothermal aging significantly degraded the matrix, causing a shift in failure modes from cohesive to mixed types (cohesive, adhesive, and fiber tear failures), leading to a notable decline in bending strength. The study observed a 23.13% strength reduction in samples aged naturally for 3 years and a 24.33% decrease in those subjected to 1000 h of accelerated aging. The random forest regressor demonstrated superior accuracy in predicting natural aging times across different accelerated aging periods. Through the application of machine learning models, this study introduces a novel approach to forecast natural aging durations using data from accelerated aging experiments. This method shows potential for optimizing joints and composite structures, ultimately improving their durability and minimizing the likelihood of failures during operational use. Studied hygrothermal effects on accelerated aging of carbon fiber reinforced polymer/Aluminum (AL) adhesive joints. Noted strength reduction from hygrothermal aging. Used five machine learning models; random forest regression had the highest accuracy. Analyzed correlation between natural and accelerated aging of dissimilar adhesive joints. [ABSTRACT FROM AUTHOR]

In this study, the deflection and stress field of perfect and imperfect (with and without porosities) functionally graded (FG) cylindrical panels are determined following the first-order shear deformation theory (FSDT). The panel rested on the twoparameter elastic foundation (Pasternak foundation) under pressure loads and worked in a hygro-thermal environment. Navier's solution has been used for simply supported cylindrical panels to analyze the effects of porosity, geometrical and foundation parameters, as well as temperature and humidity on deflection and stress field. The validated examples demonstrate the reliability of the solution and the self-written Matlab program. Numerical investigations show a significant hygro-thermal effect on the static response of the FG panel. [ABSTRACT FROM AUTHOR]

The 13th Nordic Symposium on Building Physics (NSB 2023) was held at Aalborg University in Denmark, attracting participants from around the world to discuss topics such as heat, air, and moisture transport in buildings, energy performance, and indoor environmental quality. The conference featured keynotes, paper presentations, and workshops, with selected papers published in the Journal of Building Physics. Notable research topics included using Nuclear Magnetic Resonance to measure moisture distribution in building materials and investigating air entrapment effects on water transfer in porous materials. [Extracted from the article]

Due to the heritage value of historical buildings, external facades can often not be modified. Therefore, in heritage buildings interior insulation is often considered when undergoing an energy renovation. However, interior retrofitting drastically changes the hygrothermal behaviour of a wall and can potentially cause moisture-related problems. Besides an interior retrofit, a changing climate might also trigger some of these damage mechanisms as parameters such as temperature and precipitation will change over time. Hygrothermal models can provide relevant insights into the risk of deterioration associated with these damage phenomena. However, these Heat, Air and Moisture (HAM) tools are commercially available but rarely used in the building industry to study deterioration risks. Translating research into practical tools and guidelines is a challenge across the whole field of building renovation. This paper aims to tackle that challenge, by means of creating a hygrothermal risk assessment tool based on 48,384 HAM-simulations for the climate of Brussels, Belgium. Seven different performance criteria are addressed and discussed: freeze-thaw damage, mould growth, wood rot, corrosion, moisture accumulation, salt efflorescence and bio-colonisation. Subsequent to a sensitivity analysis, the study further explains how these results can be translated into practice, providing building practitioners the most suitable insights and recommendations. The development of an interactive web tool to assess hygrothermal risks is demonstrated and its use and benefits are further elaborated. [ABSTRACT FROM AUTHOR]

This paper investigates the nonlinear dynamic deflection, natural frequency, and wave propagation in functionally graded (FG) porous piezoelectric microscale tubes under periodic load, hygrothermal conditions, and an external electric field. The piezoelectric material used to make the smart microtubes has pores that may be smoothly changed or uniformly distributed over the tube wall. Here, three types of porosity distribution are taken into consideration. The nonlinear motion equations are constructed using a novel shear deformation beam theory and the modified couple stress theory (MCST). The nonlinear motion equations are solved using the fourth-order Runge–Kutta technique and the Galerkin approach. The effects of various geometric parameters, porosity distribution type, porosity factor, periodic load amplitude and frequency, material length scale parameter, moisture, and temperature on the nonlinear dynamic deflection, natural frequency, and wave frequency of FG porous piezoelectric microtubes are explored through a number of parametric investigations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Carbon fiber reinforced polymer (CFRP) laminates are widely used to strengthen and retrofit deteriorated concrete structures, yet their long‐term performance and durability under varied environmental conditions remain critical areas of investigation. This study comprehensively examined the behavior of small concrete beams externally bonded with CFRP laminates under three distinct hygrothermal regimes: immersion in water at 23, 45, and 60°C for up to 112 days. The experimental program encompassed direct tension pull‐off testing of the CFRP–concrete assembly and four‐point bending tests on the beams. Pull‐off tests revealed complex failure modes, with bonding epoxy failure (43%) and concrete substrate cohesion failure (39%) being dominant. Notably, pull‐off strength exhibited nonmonotonic trends across all environments, suggesting that environmental degradation is not solely time‐dependent. Flexural capacity increased by 20%, 49%, and 11% for room temperature (RT), moderate temperature (MT), and high temperature (HT) conditions, respectively, after 112 days, highlighting the synergistic effect of CFRP strengthening and ongoing concrete curing. A calibrated three‐dimensional finite element model, developed using Abaqus, accurately replicated the experimental results and facilitated parametric studies on factors influencing CFRP‐strengthened beam performance. This included concrete compressive strength, number of CFRP layers, laminate thickness, and FRP type. The study elucidates the complex interplay between environmental exposure, material properties, and structural performance, contributing valuable insights for enhancing durability predictions and design guidelines for CFRP‐strengthened concrete structures in diverse climatic conditions. [ABSTRACT FROM AUTHOR]

This paper presents a comparative assessment of hygrothermal effects on the mechanical and thermomechanical properties of resin‐infused thermoplastic E‐glass fiber‐reinforced composites (FRC) in the marine environment. The thermoplastic FRCs were immersed in seawater at two different aging temperatures, that is, 35 and 70°C. The quasi‐static tests were conducted on unaged and aged FRCs, followed by scanning electron microscopy (SEM) to determine the effect of the marine environment on the mechanical properties and damage progression. The specimens immersed at 70°C showed a significant drop of 46.7%, 39.7%, 22.6%, and 16% in mechanical properties (tensile, compression, flexural, and ILSS) mainly due to plasticization, matrix cracking, and fiber/matrix debonding. The specimens immersed at 35°C showed a reduction in tensile, compressive, and flexural strength of 10%, 14.7% and 1.9% respectively, with no significant effect on ILSS. In addition, dynamic mechanical analysis (DMA) reveals that prolonged aging induces an increase in glass transition temperature Tg due to polymerization reactions. This work is intended to reveal the effect of extreme marine environment on the resin‐infused thermoplastic FRC and to provide a useful reference for their potential structural applications in the marine industry. Highlights: Influence of aging conditions on the long‐term performance of FRCs.Hygrothermal aging leads to an increase in the glass transition temperature.The marine environment degrades mechanical properties of FRCs by up to 50%.Matrix cracking and fiber‐matrix debonding evolved as dominant failure modes. [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]

Highlights Composite structures are frequently exposed to varying hygrothermal environments, which can lead to the deterioration of their mechanical properties. This study explores the effects of hygrothermal aging on the mechanical behaviors of twill‐woven carbon fiber composite laminates, with a particular focus on laminates with flame‐retardant epoxy resin (CF_FR)—a relatively underexplored area. The findings reveal several key insights: (1) CF_FR exhibit more pronounced aging damage compared to those with general epoxy resin (CF_G), primarily due to higher moisture absorption, which results in increased surface swelling and internal delamination. (2) Hygrothermal aging enhances the impact resistance of both types of laminates by increasing peak force, particularly at higher temperatures, thereby reducing impact‐induced damage. (3) CF_FR suffers greater reductions in compressive and compression after impact (CAI) strength following aging, with CAI strength decreasing by 36.3% for flame‐retardant laminates and 14.8% for CF_G after immersion at 70°C. (4) Significant local buckling is observed in the swollen regions of CF_FR under compressive loading, indicating an heightened vulnerability to structural instability after aging. These findings offer valuable insights into the performance of composite materials under prolonged moisture exposure, particularly in safety‐critical applications where both flame retardancy and mechanical integrity are crucial. More aging damage is captured from laminates with flame‐retardant epoxy resin Aging temperatures alleviate LVI induced damage and improve the peak force Compressive and CAI strength are affected after prolonged aging conditions CAI strength of CF_FR decreases by 36.3% after exposure to the 70°C water bath Significant local buckling is observed in CF_FR under compressive loading [ABSTRACT FROM AUTHOR]

The influence of hygrothermal aging on the mechanical properties of flax fiber‐reinforced polymer (FFRP) composites was studied by examining the mechanical properties and failure mechanism of the composite laminates exposed in distilled water at different temperatures. The resin transfer molding (RTM) process was used to manufacture FFRP laminates, which were then subjected to accelerated aging tests in distilled water at different temperatures. The moisture absorption characteristics of FFRP were analyzed by a water absorption test. Tensile, bending, and low‐velocity impact tests of laminates after different aging conditions were performed. Combined with DSC and FTIR tests, the failure mechanism of FFRP exposure to hygrothermal aging was analyzed. The result indicated that the increase in temperature will accelerate the moisture absorption process of FFRP, and the hygroscopic behaviors at different temperatures conform to Fick's law. In the early stage of hygrothermal aging, the composites undergo post‐curing, and the tensile and bending strengths increase. After that, the tensile and bending strengths are decreased because of the thermo‐oxygen aging of materials and fiber/matrix interface damage. After hygrothermal aging, the impact peak force of FFRP decreases obviously while the absorbed energy increases due to the increase of internal defects and plasticization of composites. The increase of hygrothermal aging temperature aggravates the aging of materials, resulting in a more obvious decline in the tensile, bending, and impact properties of the composites. Highlights: The effect of hygrothermal aging on the mechanical properties of FFRP is investigated.With the increase of hygrothermal aging time, the tensile and bending strength of FFRP increased at the early stage of aging and then decreased.After hygrothermal aging, the impact peak force of FFRP decreases and the absorbed energy increases due to the increase of internal defects and plasticization of composites. [ABSTRACT FROM AUTHOR]

This study investigates the hygrothermal aging effect on the tensile and impact behavior of flax/PLA biocomposites. Specimens underwent up to four weeks of conditioning at 40°C in a climate chamber with water. Analysis covered porosity, moisture diffusibility, and transversal microstructure, enabling assessment of tensile strength, tensile modulus, and impact performance in relation to moisture uptake and fiber orientation. The study of tensile properties revealed that at approximately 12% moisture content, stiffness and yield stress decrease, while strength remains constant. Moisture diffusivity is higher in warp and weft yarn directions than the out‐of‐plane direction. Tensile testing at environmental equilibrium moisture reveals greater stiffness in the weft direction, correlated with lower crimp percentage and yarn angle. The main contribution of the paper is the study of the influence of moisture on the impact behavior, the results show that energy absorption capability of flax/PLA biocomposite increases with moisture content. Highlights: Fully biodegradable composite material by heat‐compression molding subjected to hygrothermal aging conditions for up to four weeks.The moisture diffusivity in both the warp and weft yarn directions registered higher values in comparison to the out‐of‐plane direction.Tensile testing at environmental equilibrium moisture revealed that the stiffness in the weft direction presented higher values.At 12% of moisture uptake, the stiffness and yield stress reached their lowest values, while strength remained constant.However, the low‐velocity impact properties of the composites exhibited improvement with moisture. [ABSTRACT FROM AUTHOR]

THIS STUDY DEALS WITH THE VIBRATION RESPONSE of porous functionally graded (FG) nanobeams under hygro-thermal loadings. The FG nanobeam model is developed based on the Euler-Bernoulli beam theory, in which the doublet mechanics is implemented to account for the size effect. The material properties of the FG nanobeam are assumed to vary along the thickness direction of the beam according to the power-law form with the temperature dependent and porosity phases. The approximate Ritz method is employed to obtain the natural frequencies of porous FG nanobeam models for various boundary conditions. The influences of several parameters such as temperature rise, moisture concentration, porosity volume fraction, material gradient index, material length scale parameter and mode number on the free vibration response of the porous FG nanobeams under hygro-thermal environments are examined in detail. It is explicitly shown that the proposed approach can provide accurate frequency results of FG nanobeams as compared to existing studies in open literature. These study's results may be useful for the optimal and safety design of nano-electro-mechanical systems. [ABSTRACT FROM AUTHOR]

Purpose: The influence of the temperature discrepancy parameter and higher order of the time-derivative is discussed. Classical coupled and generalized hygrothermoelasticity models are recovered by considering the various special cases and illustrated graphically. Design/methodology/approach: The theory of integral transformations has been used to study a new hygrothermal model that includes higher-order time derivatives with three-phase-lags and memory-dependent derivatives (MDD). This model considers the microscopic structure's influence on a non-simple hygrothermoelastic infinitely long cylinder. The generalized Fourier and Fick's law was adopted to derive the linearly coupled partial differential equations with higher-order time-differential with the two-phase lag model, including memory-dependent derivatives for the hygrothermal field. The investigation of microstructural interactions and the subsequent hygrothermal change has been undertaken as a result of the delay time and relaxation time translations. Findings: These two-phase-lag models are also practically applicable in modeling nanoscale heat and moisture transport problems applied to almost all important devices. This work will enable future investigators to gain insight into non-simple hygrothermoelasticity with different phase delays of higher order in detail. Originality/value: To the best of my knowledge, and after completing an intensive search of the relevant literature, the author could not learn any published research that presents a general solution for a higher-order time-fractional three-phase-lag hygrothermoelastic infinite circular cylinder with memory memory-dependent derivative. [ABSTRACT FROM AUTHOR]

The present project investigated the hygrothermal performance and risk of mould growth in solid masonry walls retrofitted internally with three diffusion-open bio-based insulation materials (two loose-fill cellulose and one hemp fibre), installed in test containers with controlled indoor climate. Focus was on bio-based insulation materials, as these are upcoming due to necessary CO2 reductions and because the hygroscopic properties of bio-based materials are different from traditional insulation materials like mineral wool therefore, some manufacturers claim a vapour barrier is unnecessary, even in relatively cold climates. The project was a large experimental study in two reefer containers with reconfigured facades, in which solid masonry walls with embedded wooden elements were constructed. The study focused on the conditions in the masonry/insulation interface and in the embedded wooden elements. The effect of hydrophobization and different indoor moisture loads were also investigated. Moreover, the bio-based insulation systems were compared with a wall insulated with the traditional mineral wool and vapour barrier system. Relative humidity and temperature were measured at several locations in the test walls for 1 year and 9 months. Measurements show that exposed masonry walls retrofitted internally with diffusion-open bio-based insulation materials resulted in unacceptably high moisture levels (>80% RH over longer periods). Lower moisture levels were observed when the internal insulation was combined with hydrophobization against wind-driven rain, but unacceptably high moisture levels still occurred (60%–70% in summer and 95%–100% in winter in the interface). Hydrophobization reduced the moisture levels in the interface and embedded wooden elements only in walls facing southwest, which is the direction with the most wind-driven rain. Mould growth tests showed no growth in the interface in walls insulated with cellulose insulation (mycometer surface value <25). Meanwhile growth was found in all four walls insulated with hemp fibre matts (mycometer surface value >400). [ABSTRACT FROM AUTHOR]

Concrete exposed to fire can experience spalling when the pore pressure increases due to water evaporation resulting in damage to part of the concrete cross-section which causes the loss of the initial cross-sectional symmetry, both thermal and geometrical. This may lead to what is, in essence, a biaxial bending problem in reinforced concrete columns. This study does not deal with the prediction of the occurrence of spalling for which a fully coupled hygro-thermo-mechanical analysis would be required. This work evaluates the consequences that corner spalling and surface spalling have on the fire resistance of reinforced concrete columns and presents a methodology based on the determination of a modified fire resistance time. An advanced fiber based numerical model for evaluating the fire resistance of RC sections exposed to fire is used as a tool to analyse the effect that spalling has on the performance of the columns. The model is able to generate the interaction surfaces of the columns subjected to uniaxial or biaxial bending and 4-sided exposed to the standard fire curve ISO 834. After a parametric analysis, it is observed that the negative effect of spalling can be quantified by means of an additional fire exposure time, which ranges between 0–35 min and depends on the column cross-section configuration, dimensions and load level. Finally, a proposal for the calculation of the modified fire resistance time for the effect of spalling is presented, which may be beneficial for practitioners in design. [ABSTRACT FROM AUTHOR]

Yellow tea (YT), a slightly-fermented tea originated from Ming Dynasty with distinctive "Three yellows," mild-sweet smell, and mellow taste attributed to the unique yellowing process. Based on current literature and our previous work, we aim to comprehensively illustrate the key processing procedures, characteristic chemical compounds, health benefits and applications, as well as the interlocking relationships among them. Yellowing is the most vital procedure anchored on the organoleptic quality, characteristic chemical components, and bioactivities of YT, which is influenced by temperature, moisture content, duration, and ventilation conditions. Pheophorbides, carotenoids, thearubigins and theabrownins are the major pigments contributing to the "three yellows" appearance. Alcohols, such as terpinol and nerol, are attributed to the refreshing and sweet aroma of bud and small-leaf YT, while heterocyclics and aromatics forming during roasting result in the crispy rice-like large-leaf YT. Hygrothermal effects and enzymatic reactions during yellowing result in the decline of astringent substances. Meanwhile, multiple bioactive compounds such as catechins, ellagitannins, and vitexin, endow YT with antioxidant, anti-metabolic syndrome, anti-cancer, gut microbiota regulation, and organ injury protection effects. Future studies focusing on the standard yellowing process technology, quality evaluation system, and functional factors and mechanisms, possible orientations, and perspectives are guaranteed. [ABSTRACT FROM AUTHOR]

Lately, metal foams have been widely used in various engineering structures due to their exceptional mechanical properties, including their lightweight. However, scientists have proposed adding nano-fillers like graphene nanoplatelets (GNPs) to overcome the issue of low stiffness caused by increased porosity. Hence, aerodynamic stability and vibrational behaviors of nanocomposite metal foams (NCMF)-reinforced GNPs sector microplate with piezoelectric/metallic face sheets are provided in this work. The microstructure is sited on Kerr elastic substrate and also is in a hygro-thermo-electrical media, subjected to supersonic flow based on first-order piston's theory (FPT). Gaussian random field (GRF), Halpin-Tsai, and extended rule of mixture (ERM) in conjunction with Gurtin-Morduch, modified strain gradient theories, and Hamilton's principle are used to derive the governing equations and linked boundary conditions. Generalized differential quadrature (GDQ) scheme is chosen to attain the results. By validating the results' precision, the effects of different parameters on the natural frequencies (NFs) and critical aerodynamic pressures (CAPs) are observed. It is perceived that adding GNPs enhances both NFs and CAPs significantly, and increasing porosity up to seventy percent, leads the results to drop. Various industries use simpler models to evaluate the microstructure, therefore the present model can pave the way for future uses and push the boundaries of knowledge in these industries based on the results it produces. [ABSTRACT FROM AUTHOR]

This research employs a multiple scales perturbation approach to evaluate the nonlinear wave propagation behaviors of a doubly curved sandwich composite piezoelectric shell with a flexible core in a hygrothermal environment. Stress and strain calculations for the flexible core and face sheets are carried out using Reddy's third-order shear deformation theory (TSDT) and third-order polynomial theory, respectively. The study explores the synergistic effects of a multilayered shell, flexible core, and magneto-rheological layer (MR) in revealing the nonlinearity of both in-plane and vertical moment within the core. The Halpin–Tsai model is employed to derive the properties of polymer/carbon nanotube/fiber (PCF) and polymer/graphene platelet/fiber (PGF) three-phase composite shells. The governing equations for the multiscale shell are derived using Hamilton's formulation. The research investigates temperature variations, diverse distribution patterns, curvature ratios, and magnetic fields through numerical analysis, presenting the results graphically and prior research has demonstrated the accuracy of these methods. Notably, these factors exert significant influence on the frequency-amplitude curves of the smart structure. [ABSTRACT FROM AUTHOR]