Hygrothermal Environment Research Articles

Hygrothermal dynamic behavior of fiber metal laminated structure under dual-ellipse distribution heat source

Refined plate theory could account for parabolic variation of transverse shear stress through the thickness, and satisfy the zero traction boundary conditions on the top and bottom surfaces of the plate without introducing shear correction factor, of which all displacement variables can be depicted in functions of shear and bending components. Based on three-dimensional transient thermal conduction theory and the refined plate theory, an analytical solution of fiber metal laminated (FML) plate under hygrothermal environment is presented. In present work, distinct from other literatures, the separate variable method and Newton-Cotes method is applied to solve the three-dimensional transient temperature field (subjected to moving dual-ellipse distribution laser heat source) firstly. Secondly, the constitutive equations and geometrical equations are derived. Subsequently, the governing equations in hygrothermal environment are obtained. Finally, the Newmark method and Galerkin method are used to solve the governing equations of which in terms of displacement functions. The results show that fiber orientation affects the bending stiffness, the selection of (45°/ 0°) fiber orientation is more resistance to deformation and normal stress, and bending part is more sensitive to shear factor between layers.

Interfacial Degradation of Calcium Silicate Hydrate and Epoxy under a Hygrothermal Environment: An Experimental and Molecular Model Study

The adhesion at the concrete/epoxy interface is crucial to the reinforcement of carbon fiber-reinforced polymer (CFRP) sheets. The multiscale mechanism of adhesion, particularly under a hygrothermal environment, yet remains largely unclear. This paper combines molecular dynamics (MD) and synthesis experiments of a novel single-phase calcium silicate hydrate (C-S-H) and epoxy composite to investigate the combined effects of aggressive chemicals and temperature on the bonding properties. MD models were constructed under various conditions on C-S-H/epoxy composites, whose equilibrium configuration, dynamic property, bond connection, interfacial interaction energy, and mechanical properties were quantified. In addition, the experiments were carried out under different temperatures and humidity conditions to explore the macroscopic splitting tensile property of the composites and further validate the MD results. The MD results suggest that the Ca ions on the C-S-H surface are crucial to the adhesion by forming Ca–O and Ca–N bonds with epoxy. However, these bonds were reduced in the presence of water molecules, with a reduction also of the interfacial energy. The degradation effects are exacerbated by the presence of NaCl solution, as Na ions gather around the interfacial region of C-S-H/epoxy, further accumulating water molecules by forming hydrated ion clusters. This process is accelerated by elevated temperature. The experiment results suggest that without the influence of NaCl solution, a moist C-S-H surface turns to gain a stronger bonding with epoxy when the curing temperature is higher (40, 60 °C). Meanwhile, the bonding properties of a dry C-S-H surface and epoxy are less sensitive to temperature. This work provides new insight into understanding the bonding mechanism on the C-S-H/epoxy interface and may benefit the engineering application of CFRP-concrete reinforcement.

Effect of graphene on the properties of epoxy in hygrothermal environment by molecular dynamics method

<abstract> <p>The physical and mechanical properties of graphene-reinforced epoxy (epoxy/graphene) in hygrothermal environment need to be comprehensively understood. This is because it is necessary to predict the durability of epoxy/graphene when epoxy/graphene is used in an aggressive environment with high humidity and high temperature. Based on the molecular dynamics method, the influences of water content (2, 4 and 6%) and temperature (298,333 and 368 K) on the physical and tensile properties of epoxy/graphene were studied in this research. The results showed that after the addition of graphene, the free volume fraction of epoxy and the diffusion coefficient of water molecules in the epoxy decreased, and the density, tensile strength and deformation performance of epoxy increased. In the hygrothermal environment, the tensile strength degradation rate of epoxy/graphene was lower than that of pure epoxy. The failure mechanism and mechanical response of epoxy/graphene during the tensile process in the nanoscale were revealed. The research results provide a reference for the design and performance optimization of epoxy/graphene composites in a hygrothermal environment.</p> </abstract>

Experimental and Numerical Investigations of Structural Performance of Slab Track under Hygrothermal Environment

The coupled heat and moisture actions could easily cause deformation, cracking and corrosion problems in the slab ballastless track under operational conditions via China Railway Track System (CRTS) Ⅱ. In this paper, two one-quarter-scaled models of CRTS Ⅱ slab ballastless track under hygro-thermal environment were tested in a testing chamber, respectively. To study the effect of constrained conditions on the structural performance of track structure, temperature distribution, stress and displacement of two scaled models with constrained and free boundary conditions were also compared. Then, the temperature and stress field of the track structure was investigated by establishing a finite-element model. The results showed that the temperature transfer between layers has a temperature-lag effect. The positive and negative temperature gradients between the lower part of the track slab and the cement asphalt (CA) mortar layer of the constrained specimen are smaller than those of the free specimen. The longitudinal displacement of the track slab for the free specimen is significantly affected under the hygro-thermal environment and the longitudinal displacement of the concrete base and the track slab forms a displacement difference. Numerical-analysis results showed that the bottom of the concrete base is prone to produce a high-temperature core and that the temperature inside the track structure forms an agglomeration effect. KEYWORDS: Slab track, Hygro-thermal environment, Structural performance, Scale model, Finiteelement model.

Study of mechanical degradation of freestanding ALD Al2O3 by a hygrothermal environment and a facile protective method for environmentally stable Al2O3: toward highly reliable wearable OLEDs.

Al2O3 deposited via atomic layer deposition (ALD) has been used as an insulating and barrier film for thin-film transistors, organic electronics, and microelectromechanical systems. However, ALD Al2O3 films are easily degraded by hydrolysis under harsh hygrothermal conditions, owing to their poor environmental stability. In this study, the mechanical properties and water-vapor transmission rate (WVTR) of environmentally degraded Al2O3 films were investigated by varying the temperature and relative humidity (RH). The hygrothermal environment led to surface and pinhole-concentrated degradation based on aluminum hydroxide, which caused an increased WVTR and reduced elongation of the films in harsher environments. In particular, the elongation of the degraded Al2O3 films was reduced to 0.3%, which is one-third of that of as-deposited Al2O3, and their WVTR increased on the order of 10-1 g m-2 day-1, which is more than 1000 times that of as-deposited Al2O3. Therefore, we introduced a functional silane-based inorganic-organic hybrid layer (silamer) onto the Al2O3 films to improve their environmental stability. The silamer helped preserve the characteristics of Al2O3 films by forming a strong and continuous aluminate phase of Al-O-Si at their interface in hygrothermal environments. Furthermore, the silamer-capped Al2O3 was shown to be an environmentally stable encapsulation for application in wearable organic devices.

Method and Mechanism for Adhesion Recovery of Laser-Treated Aluminum Surface Exposed to Hygrothermal Environment

Laser treatment is used to improve the surface adhesion performance of metal materials, including aluminum alloy. However, the adhesion performance of laser-treated aluminum alloy is reduced after the hygrothermal exposure during storage before bonding, obtaining the reliable surface adhesion is a challenge. In this paper, the nanosecond laser-treated aluminum alloy was exposed in a hygrothermal environment with 80°C 95%R.H. for 48h. Scanning electron microscopy, transmission electron microscopy and adhesion strength testing were used to characterize the physical/chemical properties and adhesion reduction of the aluminum surface. Subsequently, a simple and effective method of heat treatment was proposed to recover the adhesion strength. Finally, molecular dynamics (MD) simulation was utilized to explore the underlying recover mechanism. The experimental results revealed a AlOOH layer with ~410 nm thickness was generated on the laser-treated aluminum surface after hygrothermal exposure, which reduced the adhesion strength by 38% (from 30.9MPa to 18.9MPa). After heating at 120 °C for 24 hours, the adhesion strength (30.4MPa) of aluminum surface recovered to the level before hygrothermal exposure. MD results suggested that there are two mechanisms for the adhesion recovery by heat treatment: 1) the atomic kinetic energy of AlOOH increased and the structural order decreased, which strengthened its electrostatic and hydrogen bond interactions with adhesive molecules; 2) the mechanical property of AlOOH were enhanced.

Acoustic radiation efficiencies of laminated composite structure under mechanical excitation and hygrothermal loading: Numerical analysis

In this research, the sound radiation efficiencies of multi-layer composite flat as well as curved structure under harmonic mechanical excitation in hygrothermal environment is numerically investigated using a coupled micromechanical finite element and boundary element scheme. The higher-order mid-plane kinematics including the stretching effect is equipped for the structural modeling and the Hamilton’s principle is utilized to evaluate the hygro-thermo-elastic natural frequencies alongside corresponding modes of the structures lying on an infinite rigid-baffle. An isoparametric Lagrangian element with zero order Hermitian interpolation function (ten degrees of freedom per node) is utilized for transforming the continuous structural equations into discrete counterparts. The effective composite material properties due to combined hygrothermal loading are considered via a micromechanical model. Then, an indirect boundary element method is employed to attain the structure-surrounding coupling and the sound radiation efficiencies are computed by solving the Helmholtz wave equation. The effectiveness of the model is established by converging it with the similar results available in the open literature for vibrational as well as sound radiation efficiencies and the results reveal the confirmation of the model accuracy. Upon solving diverse numerical illustrations, the sound radiation efficiency found to decrease with intensity of hygrothermal loads and the cross-ply spherical panels with less volume fraction of fiber depicted the least RE values over the entire frequency range considered.

Effects of biophilic design on hygrothermal environment and human sensation in a large artificial garden of a public building

Biophilic design is aimed at creating a good habitat for people by enhancing the connectedness between people and nature in the urban environment; its effects on promoting psychological health are well known, but further studies are required to quantify the effects on physical and physiological aspects to provide a holistic view to support design practice. In this study, we focused on the physical aspect and quantitatively analyzed the effects of biophilic design on the thermal environment and occupants' thermal sensations. Field measurements and questionnaire surveys were conducted at a multifloor indoor garden in a public building in Kumamoto, Japan, with an artificial waterfall, pond, plants, and natural light as biophilic elements. Predicted mean vote was calculated using field measurement results as an objective indicator to assess thermal comfort. Questionnaires were used to verify the psychological effects and clarify the occupants' thermal sensations by comparing with field measurement results. The effects of the waterfall were studied when it was switched on and off. The results suggest the rationality behind incorporating biophilic design inside buildings, in terms of the physical aspect, highlighting the psychological effectiveness, especially during winter, and the benefits of thermal comfort, especially during summer.

Development of an intelligent envelope system with energy recovery ventilation for passive dehumidification in summer and solar collection in winter

With the aim of establishing a zero-energy housing (ZEH), an intelligent envelope system composed of a passive dehumidification and solar collection system (PDSC system) based on thermodynamic energy theory and an energy recovery ventilation (ERV) unit has been developed, abbreviated as PSE (PDSC & ERV) system, which can be expected to control the indoor hygrothermal environment by using renewable energy further to reduce the heating and cooling demand for the HVAC system. In this study, the measurement experiments were conducted in a wooden house equipped with a PSE system, and the temperature and humidity distributions in the rooms were assessed using thermohygrometer sensors. The field comparison experiments for the three systems (exhaust-only ventilation system, ERV system, and PSE system) were performed separately under various meteorological conditions in summer and winter. The measurement results in summer showed that the PSE system has a significant dehumidification effect compared to the exhaust-only and ERV-only ventilation systems and could effectively reduce the latent heat load caused by ventilation. The measurement results in winter indicated that the PSE system has the effect of heat collection and humidity control as well as reducing the sensible heat load originating from ventilation.

Evaluation of Hygrothermal Environments in Traditional Houses with Patio: Case of an Old Mediterranean City

Evaluation of Hygrothermal Environments in Traditional Houses with Patio: Case of an Old Mediterranean City

Effect of loading rate on the failure of BFRP-Aluminum alloy single lap joints after hygrothermal aging

With the increasing scale of the automotive industry, the mixed application of multiple materials and bonding technology have become indispensable means to achieve lightweighting. In this paper, accelerated aging experiment and tensile test were developed to study the effect of loading rate (1 mm/min–100 mm/min) on the failure of BFRP-Aluminum alloy single lap joint after hygrothermal aging (0 days–28 days). The aging mechanism of the adhesive and BFRP in the hygrothermal environment was also analyzed by Fourier transform infrared and differential scanning calorimetry. The test results showed that the joint failure strength varied with the hygrothermal aging time and loading rate, with the former showing a negative correlation and the latter a positive correlation. Combined with the joint failure surface, it was found that the joint strength decrease was mainly caused by the hydrolysis reaction of the adhesive and the interfacial failure of the joint. A regression model was developed to characterize the failure strength of the joints under different loading rates in the hygrothermal environment, and it was concluded that the aging time was more significant than the loading rate on the strength of the joints.

Performance development of polyurethane elastomer composites in different construction and curing environments

This study addresses the performance development law of polyurethane elastomer in different construction environments to promote its popularization and application. The ultra high molecular weight polyethylene (UHMWPE) micropowder/polyurethane elastomer composites were prepared. Different types of construction and curing environments during the actual application of materials were simulated. The mechanical strength, flexibility, energy absorption state and cushion property of polyurethane elastomer at different environment conditions and curing time were studied systematically. The interactive development law of each performance was analyzed. The environmental adaptability of polyurethane elastomer was clarified. The results show that after curing at normal room temperature for 7 days, the index values of various performances for polyurethane elastomer at this time reached 95 % of the final value. And the various indexes were as follows. Tensile strength was 12–12.5 MPa, and elongation at break was 590 %-600 %. Tear strength was 78–80 N/mm. Absorbed energy was 1.7–1.8 J. The minimum buffer factor was 8–8.2. The hygrothermal environment accelerated the development of mechanical properties, but the cold environment greatly reduced the performance growth rate. These two environments damaged some performances of the material. Among them, mechanical strength and toughness decreased 45–60 %. In the performance forming process, the three indexes of mechanical strength, flexibility and energy absorption state had interactive relationship.

Effect of hygrothermal acid rain environment on the shear bonding performance of CFRP-concrete interface

In this study, forty-five carbon fiber-reinforced polymer (CFRP)-concrete single shear specimens were designed to investigate the effect of hygrothermal acid rain environment. At first, the hygrothermal acid rain environment was simulated through a mechanical high-temperature dry-wet cycle and by artificially preparing acid rain solution with a pH value of 1.5. Subsequently, the effects of concrete strength and corrosion times on the interface failure mode, bond shear capacity, ultimate displacement, load–displacement behavior, and strain distribution in bonding interval were studied through the single shear test of CFRP-concrete. Then, the interface constitutive relation model was built based on the influence coefficient of hygrothermal acid rain. Finally, a reference method was proposed to divide the corrosion degree in hygrothermal acid rain environment, and the interface failure mechanism was expounded using a scanning electron microscope (SEM) for detection. The results indicated that the interface bonding performance was enhanced with the increase of the concrete strength, and the interface peeling position tended to change to the adhesive layer. The interfacial bonding performance increased first and then decreased with the increase of the corrosion times. When the corrosion number reaches ten cycles, the interfacial bond performance gets the best, the interfacial peel load and ultimate displacement of the three types of strength concrete(C30\\C40\\C50) were examined as 3.04 %, 3.50 %, 5.78 %, and 0.50 %, 0.49 %, 0.95 % higher than those of the uncorroded specimens, respectively. The SO42- ions in the acid rain invaded the surface of the concrete to synthesize an expansive substance CaSO4·2H2O, thus temporarily enhancing the interfacial bonding performance at the early corrosion stage. The load–displacement curve comprised four stages, including rising, oscillating, strengthening, and falling. In this study, an interface constitutive model was proposed based on the influence coefficient of hygrothermal acid rain, which is well consistent with the existing experimental data and exhibits high accuracy and safety. The relevant research results can provide theoretical support and design guidance for CFRP reinforcement projects in high-humidity and high-heat acid rain areas.

Effects of recycling and hygrothermal environment on mechanical properties of thermoplastic composites

Recyclability of nine types of composites including natural and mineral fillers in polypropylene and nylon matrix have been studied through injection molding and mechanical grinding. No significant degradation in mechanical properties of natural fiber composites occurred after recycling or water absorption tests. In contrast, glass fiber composites showed decrease in tensile strength and modulus by up to 45% and 40%, respectively after five rounds of recycling mainly due to severe fiber attrition. Glass bubbles breakage occurred after recycling, which diminished its ability to provide lightweighting. Only glass fiber reinforced nylon composites were affected by hygrothermal conditioning, which were characterized as a function of recycling. At saturation point, water absorption for nylon composites was 7.7% by wt. after 45 days of immersion, which significantly affected the mechanical properties. Tensile strength and modulus of glass fiber nylon composites reduced from 88.4 MPa and 5.6 GPa to 36.2 MPa and 1.8 GPa, respectively.

Hygrothermal conditions for the aging of red wine from experimental data

Despite the importance of the aging process, there is great disparity in the hygrothermal conditions in which to carry it out. The aim of this work is to propose contrasted data, based on successful cases and millions of experimental data, which can be taken as a reference for the climate control of aging rooms. For this purpose, the hygrothermal environment of 19 red wine aging rooms with multiple construction designs was monitored and statistically characterized. The results showed a great variability in the hygrothermal environment. Frequency histograms and psychometric diagrams revealed the true hygrothermal environment of red wine aging rooms. There were large differences in stability and uniformity depending on the construction design (up to four times). The indoor hygrothermal environment was not kept within the comfort ranges mentioned by a wide list of authors (2–65% of time out of range). A contrasted psychometric diagram establishing monthly comfort intervals and other useful data (stability, uniformity …) were proposed, based on the hygrothermal environment of wineries with quality wines. The results should be a valuable tool for the wine sector, in order to control the evolution of aging, set the programming of air conditioning equipment and simulate the behavior of new wineries.

Magneto-Electric Influence on a Functionally Graded Porous Hollow Structure in Hygrothermal Environment

Magneto-Electric Influence on a Functionally Graded Porous Hollow Structure in Hygrothermal Environment

Hygro-magneto-thermally induced vibration of spinning viscoelastic Y-shaped bifurcated tubes containing magnetic fluid based on nonlocal strain gradient theory

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

Effect of hygrothermal aging on moisture diffusion and tensile behavior of CFRP composite laminates

Carbon Fiber Reinforced Polymer (CFRP) composites are widely used in aircraft structures, because of their superior mechanical and lightweight properties. CFRP composites are often exposed to hygrothermal environments in service. Temperature and moisture can affect the material properties of composites. In order to make clear the moisture diffusion behavior and the properties degradation of composites, the TG800/E207 composite laminates with four stacking sequences [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s are designed and manufactured. Moisture absorption tests are carried out at 80 ℃, 90 %RH. It is shown that the moisture absorption curves of composite laminates present a three-stage. A modified Fickian model was proposed to capture the diffusion behavior of TG800/E207 composite laminates. The relationships among the non-Fickian parameters, the environmental parameters and the stacking sequences of CFRP were correlated and compared. Results showed that the modified Fickian curve is sensitive to the diffusivity of Stage I and Stage II. Compared with unaged specimens, the maximum tensile stress for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s decreased by 14.94 %, 28.15 %, 11.96 %, and 26.36 %, respectively. The strains at failure for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s decreased by 55.38 %, 62.65 %, 46.41 %, and 31.71 %, respectively. The elastic modulus for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s increased by 90.93 %, 94.57 %, 49.22 %, and 8.22 %, respectively. [90]16 sample has the minimum saturated moisture content and the maximum strength degeneration.

Influence of circular cutouts and elastic foundation on vibration characteristics of porous sandwich FGM plates under hygro-thermal environments

The present article investigates the effect of cutouts, porosity inclusion, and hygro-thermal environment on the vibrational characteristics of sandwich functionally graded material (FGM) plates resting on Pasternak elastic foundation. The governing equations for the sandwich FGM plates have been developed using the finite element method (FEM) with the conjunction of non-polynomial-based higher-order shear deformation theory (HSDT). The trigonometric shear-strain shape function has been used for the first time for sandwich FGM plates. The effective material properties with porosity inclusions have been computed using modified power–law distribution. The present results have been acquired by employing a C0 continuity isoparametric finite element (FE), using 4-noded elements with 7-DOF's per node. The accuracy of the current solution has been confirmed by convergence and validation studies. The influence of circular cutout, elastic foundations, hygro-thermal conditions, and geometric and boundary conditions on the vibrational frequency of porous sandwich FGM plates have been discussed in detail.

A characteristic curve including hygrothermal effects for predicting the failure of composite multi-bolt joints

A characteristic curve that considers hygrothermal effects was developed based on the traditional characteristic curve. A nondimensional temperature was introduced to represent the severity of seven hygrothermal conditions experienced by primary aircraft structures. The tensile characteristic lengths and compressive characteristic lengths under the seven conditions were determined using a numerical strategy. Expressions between the characteristic lengths and the nondimensional temperature were established by fitting the data with exponential functions. Consequently, an equation of the characteristic curve formulated as a function of the nondimensional temperature and the angle, was established. The developed characteristic curve can be used to predict the failure of composite multi-bolt joints under any hygrothermal environment.