Hygrothermal Environment Research Articles

Determination of specific heat capacity of bio-fibre earth mortars stabilised at different relative humidities using Differential Scanning Calorimetry

Understanding the relationship that earth-based mortars have with both water and temperature is imperative to optimise moisture buffering properties. Specific Heat Capacity (Cp) is a key factor to understand the benefits in terms of thermal mass and latent heat. This paper presents the results of bio-based earth mortars (with fibres consisting of two varieties of sheep wool: Wool 1 (W1), Wool 2(W2) and Saw Mill Residue (SMR)) stabilised at 53% and 75% Relative Humidity (RH). Differential Scanning Calorimetry (DSC) according to ISO 11357–4 was used to calculate Cp of the aforementioned mortars. The temperature range of this experiment was that of 0–50 °C with a particular focus on values at 20 °C as this best represented a suitable indoor temperature. From these experiments, the results demonstrate that when stabilised at different RH, the difference in Cp was bio-fibre dependant and had a range between 0.71– 1.01 kJ/kg.K at 53% RH and 0.85–1.14 kJ/kg.K at 75% RH. These differences could potentially be attributed to the materials ability to readily accept water molecules. This emphasised that incorporating bio-fibres to a plain mixture (PL) can increase the Cp by up to 60%; significantly improving the thermal inertia of the building material. By reducing this temperature differential, it will reduce the heating requirements of a building which as consequential carbon reduction and thermal comfort benefits. Overall, SMR has the largest Cp for 75% at 20 °C was 1.141 kJ/kg.K, therefore specifically, this fibre would be the most effective to implement within a building. It also demonstrates the differences of the samples adsorption and absorption of water in differing hygrothermal environments.

The hygro-thermo-electro-mechanical coupling edge-based smoothed point interpolation method for the response of functionally graded piezoelectric structure under hygrothermal environment

In this paper, we analyze the hygro-thermo-electro-mechanical (HTEM) coupling problem of functionally graded piezoelectric (FGPE) structure based on edge-based smoothed point interpolation method (ES-PIM). The basic equations for FGPE structure are derived in the multi-physical field. Triangular elements adopted in ES-PIM can be generated automatically and suitable for complicated structures. The responses for the HTEM coupling problem are calculated by ES-PIM and finite element method (FEM) under different hygrothermal conditions. Through the numerical examples, the factors related to the temperature and moisture fields are explored. The exponential factor and the hygrothermal effect on the responses of the FGPE structure are also studied. Besides, the advantages of proposed method for HTEM coupling problems are also validated by several numerical examples. These solutions also indicate that the increase of temperature and moisture concentration decreases the structural stiffness when empirical constants are set to negative numbers, leading to the decrease of frequency and variation of displacement. This article proposes an excellent numerical method and provides a reference for the design and application of piezoelectric structures.

Nonlocal and surface effects on the bending analysis of flexoelectrically actuated piezoelectric microbeams in hygrothermal environment

Nonlocal and surface effects on the bending analysis of flexoelectrically actuated piezoelectric microbeams in hygrothermal environment

Effect of hygrothermal and alternating load coupled aging on CFRP/Al bonded joints

The fracture failure of bonding structures is closely related to aging environment, so it is of great significance to study the effect of hygrothermal and alternating load coupled aging on bonding structures. Referring to the actual service environment of the vehicle, we formulated three kinds of artificial accelerated aging conditions, including temperature cycle, high temperature and high humidity and hygrothermal cycle. CFRP (Carbon Fiber Reinforced Plastic)/Al butt joints were selected as research object. Under these conditions, after aging for 0 day, 5 days, 10 days, and 15 days, respectively, quasi-static tensile tests were carried out to analyze the failure strength and failure modes of the joint. Through FTIR (Fourier Transform Infrared Spectroscopy) and DSC (Differential Scanning Calorimeter) tests of the CFRP and adhesive before and after aging, the change law of material chemical properties after environment aging was studied, and the influence mechanism of hygrothermal environment on joint was discussed. All three environmental aging conditions were coupled with alternating load, and the accelerated aging tests of joints were carried out to obtain the aging law. Combined with the two factors analysis of variance, the influence degree of different factor on joint strength in coupled aging was quantitatively studied respectively. The results showed that the failure strength of the joint will decrease rapidly and then slowly as aging time went by. Furthermore, with the introduction of alternating load, the decrease of joint failure strength became faster, which was mainly due to the degradation of the adhesive layer and the damage of the adhesive/substrate interface. Under the conditions of hygrothermal coupled with alternating load, the damage mainly occurred in the adhesive layer. Among these three coupled aging conditions, the condition of hygrothermal cycle coupled with alternating load has the worst influence on the joint strength, followed by the high temperature and high humidty coupled with alternating load, and the temperature cycle coupled with alternating load has the least influence on the joint strength.

The durability of flexible eddy current array (FECA) sensors in harsh service environments

Sensors for structural health monitoring (SHM) need to be permanently integrated on structures and withstand the harsh service environments, which has been a big challenge for the application of SHM in aircrafts. This paper focuses on the durability of flexible eddy current array (FECA) sensors in harsh service environments of aircrafts, including vibration environment and several typical exposed environments. First, a kind of FECA sensor is illustrated and its integration method is proposed. Moreover, in order to study the durability of the sensor in vibration environment, the modal analysis is performed by the finite element method. According to the simulation results, the durability experiment in vibration environment is carried out under the fourth order vibration mode, which makes the sensor suffer the harshest vibration loads. During the vibration experiment, output signals of the sensor keep stable and the sensor is well bonded to the structure, which shows the integrated sensor has high durability in vibration environment. Finally, the durability of integrated sensors is separately tested in three exposed environments, including salt fog corrosion environment, fluid immersion environment, as well as hygrothermal and ultraviolet-radiation environment. After these environmental exposure experiments, all sensors are well bonded to structures and can effectively monitor fatigue cracks, which shows great durability. Therefore, FECA sensors can survive in harsh service environments of aircrafts, which provides important support for the engineering applications of FECA sensors.

Hygrothermal aging effects on the mechanical properties of 3D printed composites with different stacking sequence of continuous glass fiber layers

The present work studied the effects of hygrothermal aging on the flexure behaviors of 3D printed composites reinforced with continuous glass fibers. Composites filled with different stacking sequence of continuous glass fiber layers were prepared. Printed laminated composites were subjected to the hygrothermal environment for up to 30 days. Moisture absorption processes and the corresponded microstructure changes were monitored along with the flexural responses of specimens. Multi-scale morphological investigation was applied to reveal the underlying deformation and failure mechanisms of the specimens under flexion with the consideration of different staking sequence of continuous glass fiber layers. The results showed that the evolution of mechanical properties induced by hygrothermal aging was influenced by the competition of different mechanisms. Polyamide matrix crystallization and the elimination of partial residual stress provided the strengthening effect, while the loss of intralayer and interlayer bonding as well as breakage of glass fiber and matrix weakened the mechanical properties of printed composites. The flexural behaviors of composites with separated distribution of continuous glass fiber layers exhibited higher hygrothermal stability in the early stage of aging. However, this advantage weakened with increasing aging time due to gradual delamination between glass fiber layer and matrix layer.

Hygrothermal aging behavior and aging mechanism of carbon nanofibers/epoxy composites

In this study, carbon nanofibers (CNFs)/epoxy composites incorporating different contents of CNFs were fabricated and immersed in distilled water for 180 days. Water absorption test, tensile tests, scanning electron microscopy (SEM) observation, dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR) spectroscopy were performed to evaluate the effect of CNFs content on hygrothermal aging behavior of CNFs/epoxy composites, and to reveal the hygrothermal aging mechanism of such composites. Test results showed that the addition of CNFs into pure epoxy resin could obviously improve its hygrothermal aging behavior. The CNFs/epoxy composites had better resistance to water absorption than pure epoxy because CNFs improved the water barrier properties of the composites. The improvements of glass transition temperature and the storage modulus of the composites before and after aging were attributed to the fact that the addition of CNFs limited the loosening of molecular chains and increased the second cross-link density of epoxy resin. FTIR spectroscopy showed that the number of –OH functional groups of CNFs/epoxy composites was decreased, which revealed that CNFs inhibited the hydrolysis of epoxy resin and water absorption. This study demonstrates that adding appropriate amount of CNFs into epoxy resin has potential to improve the long-term durability of epoxy-based composites in hygrothermal environment.

Vibration and damping characteristics of CNTR viscoelastic skewed shell structures under the influence of hygrothermal conditions

The vibration and damping characteristics of carbon nanotubes reinforced (CNTR) skewed shell structure under a hygrothermal environment have been investigated using the finite element method. CNT as reinforcing phase and polymer as matrix phase are considered for the nanocomposites (NCs) based viscoelastic skewed shell structure. Dynamic mechanical analysis is used to conduct the creep test for NCs samples which were fabricated, as per ASTM-D4065 standard, and obtained the viscoelastic properties in the frequency domain under different hygrothermal conditions. The shell geometry is defined by considering an arbitrary coordinate system for the skewed shell structure. Finite element modelling has been done with Serendipity element with five degrees of freedom in all eight nodes. The present formulation is based on Koiter’s shell theory and first-order shear deformation theory is considered to incorporate the transverse shear effect based on Mindlin’s hypothesis. The frequency dependant viscoelastic properties are directly used to obtain the frequency responses of the skewed shell panel using fast Fourier transform (FFT) whereas the transient responses are determined using inverse fast Fourier transform (IFFT). An in-house MATLAB code is developed for the numerical simulation and the accuracy of the proposed formulation is validated with available results in literatures and using ANSYS software. A parametric study has been carried out for the skewing angle and CNT volume fraction on the vibration behaviour of different thin and thick NC skewed shell structures under various hygrothermal conditions.

Wave propagation analysis of a ceramic-metal functionally graded sandwich plate with different porosity distributions in a hygro-thermal environment

Wave propagation analysis of porous functionally graded (FG) sandwich plate in a hygro-thermal environment is presented in this paper. The sandwich plates’ composing materials change through three layers that are either homogeneous ceramic, homogeneous metal, or power-law-based functionally graded ceramic–metal. Six different porosity models are considered in the analysis to express the porosities’ distribution factor and uniformity. The study is conducted using a simple four-unknown integral higher-order shear deformation theory (HSDT). The effect of moisture and temperature on wave propagation in porous FG sandwich plates is investigated by considering their role on the materials’ expansion. The governing equations are derived for the wave propagation problem based on the presented theory via Hamilton’s principle. A generalized solution for wave propagation is applied to formulate the stiffness and mass matrix that describes the dispersion relations. The numerical results are obtained by solving an eigenvalue problem. The effects of core-to-thickness ratio, FGM power index, porosity volume fraction, temperature, and moisture change are illustrated and discussed. The presented results can be utilized as a benchmark for further studies on wave propagation in FGM plates.

Semi-analytical static analysis of nonlocal strain gradient laminated composite nanoplates in hygrothermal environment

In this work, the bending behavior of nanoplates subjected to both sinusoidal and uniform loads in hygrothermal environment is investigated. The present plate theory is based on the classical laminated thin plate theory with strain gradient effect to take into account the nonlocality present in the nanostructures. The equilibrium equations have been carried out by using the principle of virtual works and a system of partial differential equations of the sixth order has been carried out, in contrast to the classical thin plate theory system of the fourth order. The solution has been obtained using a trigonometric expansion (e.g., Navier method) which is applicable to simply supported boundary conditions and limited lamination schemes. The solution is exact for sinusoidal loads; nevertheless, convergence has to be proved for other load types such as the uniform one. Both the effect of the hygrothermal loads and lamination schemes (cross-ply and angle-ply nanoplates) on the bending behavior of thin nanoplates are studied. Results are reported in dimensionless form and validity of the present methodology has been proven, when possible, by comparing the results to the ones from the literature (available only for cross-ply laminates). Novel applications are shown both for cross- and angle-ply laminated which can be considered for further developments in the same topic.

Experimental Study of Hygrothermal and Ultraviolet Aging on the Flexural Performance of Epoxy Polymer Mortar

This paper studies the effects of hygrothermal environment at different temperatures and ultraviolet (UV) radiation on the bending properties of epoxy polymer mortar (EPM). The microstructure changes of EPM during aging were studied by scanning electron microscopy, and the bending properties of EPM were predicted by the Arrhenius law. The results showed that the bending properties of EPM were greatly affected by the temperature in the hygrothermal aging, but not evidently affected by ultraviolet radiation in UV aging. The prediction of Arrhenius model shows that the EPM will steadily retain 92.8%, 89.1% and 79.4% of the original flexural strength after long-term hygrothermal aging at $$40^{\circ }$$ C, $$60^{\circ }$$ C and $$80^{\circ }$$ C, respectively.

Cost-Effectiveness Evaluation of Nearly Zero-Energy Buildings for the Aging of Red Wine

Achieving the best energy performance has become an important goal. The European Union has consequently developed legislative measures that introduce the concepts of nearly zero-energy buildings and cost-effectiveness during life-cycle. We use these concepts, looking for the design of energy-efficient wineries, while reducing wine production costs. The research method is based on the monitoring of temperature and humidity of 12 red wine aging rooms of representative construction designs with almost zero energy consumption that together with the economic data obtained from construction cost update, determine a parameter that has been called “construction effectiveness”. This parameter allows the evaluation of the cost–benefit ratio of each of the analyzed constructions. The results obtained demonstrate that adequate conditions can be achieved for the wine aging with zero-energy buildings, although there are notable differences in cost, damping effectiveness, and resulting hygrothermal environment depending on the type of building. The correlation between performance and construction costs shows large differences in cost per unit of damping achieved: 0.5–2.7 €/m2 for temperature and 0.6–5 €/m2 for relative humidity. With a correct design, the differences between typologies can be reduced or even non-existent. The results obtained can be a valuable tool to promote the design of zero-energy warehouses.

Hygro-Thermal Vibrations of Porous FG Nano-Beams Based on Local/Nonlocal Stress Gradient Theory of Elasticity.

In this manuscript the dynamic response of porous functionally-graded (FG) Bernoulli–Euler nano-beams subjected to hygro-thermal environments is investigated by the local/nonlocal stress gradient theory of elasticity. In particular, the influence of several parameters on both the thermo-elastic material properties and the structural response of the FG nano-beams, such as material gradient index, porosity volume fraction, nonlocal parameter, gradient length parameter, and mixture parameter is examined. It is shown how the proposed approach is able to capture the dynamic behavior of porous functionally graded Bernoulli–Euler nano-beams under hygro-thermal loads and leads to well-posed structural problems of nano-mechanics.

Studies about aging and corrosion of galvanized steel and polyvinyl chloride shielded cable caused by fireproof mud

Fireproof mud is a widely-used sealing and plugging material in power and construction industry, yet it may cause aging/corrosion problems to its directly contacted materials, leading to high safety risk. However, studies about the aging/corrosion behavious caused by fireproof mud are surprisingly rare. To fill in such a research gap, aging and corrosion of galvanized steel and polyvinyl chloride (PVC)-shielded cable caused by fireproof mud under simulated hygrothermal environment have been systematiclly investigated, based on which the mechanisms of these processes have been proposed. The results show that the corrosion of galvanized steel is mainly influenced by chloride anions from the fireproof mud, which can be aggravated/ alleviated if the fireproof mud is acidic/alkaline. For the aging of PVC shielded cable, one main reason is acidic/alkaline chemical corrosion caused by acidic/alkaline fireproof mud, the other is radical chain reaction of the PVC polymer in hygrothermal environment. These discoveries can offer important guidance for correct and safe use of fireproof mud in industries, thus ensure safe industrial production.

Exact solutions of steady-state dynamic responses of a laminated composite double-beam system interconnected by a viscoelastic layer in hygrothermal environments

The current paper is the first to study the steady-state dynamic problem of a laminated composite double-beam system (LCDBS) under hygrothermal environments, in a systematic manner. The LCDBS consists of two laminated composite beams connected by a uniformly distributed viscoelastic layer and is supported on the Winkler-Pasternak elastic foundation. The governing equations of LCDBS are derived based on the Euler–Bernoulli beam hypothesis considering the free expansion caused by temperature variation and moisture concentration. Exact solutions for steady-state dynamic responses of the LCDBS are obtained by employing the Green's functions method and superposition principle. In the meantime, the implicit equation calculating the natural frequency of the LCDBS is proposed. The material properties are considered to be temperature- and moisture-dependent. Numerical calculations are performed to explore the influences of physical parameters of the connecting layer, foundation stiffness, fiber orientation angle, temperature variation, and moisture concentration on steady-state dynamic responses of the LCDBS. Outcomes reveal that the bond between the two beams can be strengthened by increasing the stiffness and damping coefficient of the connecting layer, and the increase of the temperature variation can significantly reduce the system stiffness and enhance the dynamic responses of the two beams.

Hygro-thermo-mechanical vibration of two vertically aligned single-walled boron nitride nanotubes conveying fluid

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

Influence of temperature and humidity on the fatigue behaviour of adhesively bonded CFRP/aluminium alloy joints

ABSTRACT To further promote the use of composite bonded structures in engineering applications, it is necessary to understand the change law of the fatigue performance in the long-term server process. This paper investigated the effect of temperature and humidity on the fatigue behaviour of adhesively bonded CFRP/aluminium alloy joints using an experimental method. The quasi-static tensile and fatigue tests of CFRP/aluminium alloy butt joints were carried out at 20 °C, 40 °C, 60 °C and 80 °C, as well as at different ageing times of the 60 °C/95% RH hygrothermal environment. The results demonstrate that with increasing test temperature, the fatigue performance of the adhesive joints decreases substantially, especially when the temperature is close to or higher than Tg of the adhesive (similar to the static failure strength). In the 60 °C/95% RH environment, the fatigue performance of the joint decreases as the ageing time increases, and the fatigue strength decreases more obviously in the early ageing stage. In the single logarithmic coordinate system, the S-N curves at different temperatures/ageing times both conform to the linear law. The function of the stress-temperature/ageing time-number of the cycles to failure was established to help understand the influence law of the environment on the fatigue characteristics of joints and provide a reference for the prediction of the fatigue performance of adhesively bonded joints exposed to a hygrothermal environment.

Porosity-dependent vibration analysis of FG microplates embedded by polymeric nanocomposite patches considering hygrothermal effect via an innovative plate theory

The sandwich structures contain three or more layers attached to the core. In the current research, a three-layered sandwich microplate containing functionally graded (FG) porous materials as core and piezoelectric nanocomposite materials as face sheets subjected to electric field resting on Pasternak foundation is chosen as a model to investigate its vibrational behavior. To make the face sheets stiffer, they are reinforced by carbon nanotubes (CNTs) via different distribution patterns which result in changing their properties along the thickness direction. An innovative quasi-3D shear deformation theory with five unknowns, Hamilton’s principle, and modified couple stress theory are hired to gain equations of motion related to the abovementioned microstructure. Eventually, the evaluation of materials’ properties, geometry specifications, foundation moduli, and hygrothermal environment on vibrational behavior of such structures became easier using the presented results of the current study in figure format. As an instance, it is revealed that CNTs’ volume fraction elevation causes mechanical properties improvement, and in the following, natural frequency increment. Besides, considering the hygrothermal environment causes significant effects on the results.

Buckling analysis of axially compressed CFRR cylindrical shell with damaged porous microcapsule coating in hygrothermal environments

This paper shows an analytical approach to investigate buckling behavior of a carbon fiber reinforced resin (CFRR) cylindrical shell covered with a damaged porous microcapsule coating subjected to axial compressed loads under hygrothermal environment. The formulas are in view of the Donnell’s shell theory considering the von Kármán geometric nonlinearity. The material parameters of microcapsule coating are predicted with the self-consistent model and Mori-Tanaka model. By utilizing Galerkin approach, the buckling behavior for simple-support damaged double-layered cylindrical shell are determined. The influence of temperature and moisture, interface debonding damages, material properties, geometry parameters of microcapsules and porosity upon the buckling behavior of the double-layered cylindrical shell are investigated. Results show moisture and geometry size of microcapsules are propitious to the critical buckling and post-buckling compressive load. In addition, the micro-structure damage greatly affects temperature and moisture. The geometric parameters of microcapsules significantly affect the buckling and post-buckling behavior of double-layered cylindrical shell.

Dynamic Response of the Piezoelectric Materials Based on Cell-Based Smoothed Finite Element Method in Hygrothermal Environment

In this paper, the dynamic response of piezoelectric structures under hygrothermal environment is studied by using cell-based smoothed finite element method (CS-FEM). Ignoring the influence of temperature and moisture on the response of elastic matrix, we derive the basic equations of the piezoelectric materials under hygrothermal environment. Then the CS-FEM equations of piezoelectric problem are deduced based on the constitutive equation of the material. The improved Newmark scheme is used to solve the transient response of this problem. Several numerical examples are given to illustrate the advantage of CS-FEM in dealing with piezoelectric materials in hygrothermal environment. Results of this study provides some ideas for the design and manufacture of piezoelectric smart structures in hygrothermal environment.