Hygrothermal Effects Research Articles

Hygrothermal vibration of a laminated sandwich plate with magnetostrictive faces and a homogeneous core

AbstractHygrothermal forced vibration and damping analyses of a simply supported symmetric laminated composite plate with homogeneous core and magnetostrictive layers are examined using the exponential displacement model in this article. Three hygrothermal environment distribution types are investigated: uniform, linear and nonlinear rises in the present analysis. The equations of motion for laminated rectangular plates subjected to hygrothermal loads and in‐plane forces in x and y directions are developed through Hamilton's principle. The closed‐form solution is arrived at based on Navier's technique to analyze the hygrothermal effect on the vibrational behavior of the structure. Some parametric examples are presented to discuss the effects of the smart layer location, lamination schemes, mode number, aspect ratio, thickness ratio, feedback gain control value, in‐plane forces, core thickness‐to‐fiber reinforced layer thickness ratio, magnetostrictive layer thickness to fiber‐reinforced layer thickness ratio, temperature and moisture changes on vibration response of the proposed model. The study results illustrate that the high hygro ratio weakens the plate stiffness, and accordingly, the amplitude of the deflection increases with raising the moisture and/or temperature. The numerical results emphasize the strong role of the feedback control gain values and the smart layer position in controlling the system vibration. The largest deflections and highest damping time interval happen in the uniform temperature distribution and moisture concentration case. Moreover, the vibration frequencies of the thin smart plates are smaller than the thick ones.

Neural network-based prediction of the long-term time-dependent mechanical behavior of laminated composite plates with arbitrary hygrothermal effects

Neural network-based prediction of the long-term time-dependent mechanical behavior of laminated composite plates with arbitrary hygrothermal effects

Hygrothermal environment effect on the critical buckling load of FGP microbeams with initial curvature integrated by CNT-reinforced skins considering the influence of thickness stretching

Abstract Due to the need for structures with refined properties to bear against different loading conditions, recently, carbon nanotubes (CNTs) have been used widely to reinforce them. The extremely high stiffness of CNTs makes them significant as one of the best reinforcements to improve the mechanical behaviors of structures. This work focuses on microbeam buckling response with an initial curvature that includes three layers. The mid-layer that is known as the core is constituted of functionally graded porous (FGP) materials and two CNT-reinforced composite skins are bonded to the core to integrate it. The whole structure is affected by the hygrothermal environment and springs and shear layers are put below it. For the first time, for such a structure, a refined shear deformation theory (RSDT) as a higher-order theory that considers thickness stretching effect in polar coordinates is used that presents more accurate results, especially for deeply curved beams. Modified couple stress theory (MCST) in combination with the virtual displacement principle is utilized to establish the governing equations. The obtained results demonstrate the significance of porosity percentage and CNTs’ addition to the skins on the critical nanotubes buckling load. Also, the different behaviors of the microstructure at various temperatures are analyzed and discussed in detail.

Hygrothermal effects on the translaminar fracture toughness of a highly toughened aerospace CFRP: Experimental characterisation and model prediction

The translaminar fracture toughness and its dependence on the environmental condition are key considerations in designing aerospace-grade composites with a high damage tolerance to severe service conditions in terms of temperature and moisture. The present work characterises and models the hygrothermal effects on the translaminar fracture toughness of an interlaminar toughened aerospace carbon/epoxy composite under six environmental conditions: −55 °C, 23 °C, and 90 °C, for both ‘dry’ (i.e. moisture free) and ‘wet’ (fully moisture-saturated) specimens. Cross-ply compact-tension experiments show that the translaminar fracture toughness increases with the rise of temperature for both dry and wet conditions with the latter exhibiting a much greater increase. A model to predict the effect of moisture and temperature on the translaminar fracture toughness is here proposed and developed. This approach yields good agreement with experimental results, and it allows an improved understanding of the complex synergistic effects of interfacial properties on the overall translaminar toughening mechanisms.

Experimental study of hygrothermal ageing effects on failure modes of non-crimp basalt fibre-reinforced epoxy composite

Turbine blades form the main component for energy generation in renewable energy generation technologies such as wind and tidal energy. Non-crimp fabric (NCF) based fibre reinforced composite materials, with E-glass and carbon fibres have been widely used as the main materials for blades. However, sustainable composites using naturally derived fibres such as basalt, are being developed to reduce environmental impact. Basalt fibres require no chemical additives, solvents or hazardous materials for production and are recyclable. However, little information is available in the literature on the moisture ageing effects on failure modes of NCF based basalt fibre reinforced epoxy composites. Ageing is particularly important for applications in coastal wind and tidal turbine installations, which are exposed to high humidity. The current study analyses the effect of moisture ageing on flexural, interlaminar shear and in-plane shear properties and associated failure modes of NCF based basalt fibre reinforced epoxy composite at different stress levels. The results showed no significant impact on flexural stiffness of the composite, but in-plane shear stiffness and strength (flexural, interlaminar shear and in-plane shear) of the composite demonstrated a significant reduction following moisture absorption. Similar failure modes were observed in both dry and wet conditions.

Nonlinear vibration analysis of CFRP spherical shell panel under hygrothermal effects

Based on the nonlinear static stability analysis, this paper establishes the governing equations of the nonlinear dynamic stability of a spherical shell panel of carbon fiber-reinforced polymer (CFRP) under the hygrothermal effects; the Galerkin method is used to solve the governing equations. Then, for the free vibration of CFRP spherical shell panel, the analytical expression of the ratio of nonlinear vibration frequency to natural frequency is obtained by employing the multiscale method; for forced vibration, the analytical expression of the ratio of excitation frequency to natural frequency is obtained by considering the harmonic excitation load. Finally, the effects of geometric parameters, boundary conditions, loads, and the hygrothermal effects on the amplitude-frequency response curves of the CFRP spherical shell panel are discussed.

Numerical modeling of hygrothermal effect on the dynamic behavior of hybrid composite plates

Numerical modeling of hygrothermal effect on the dynamic behavior of hybrid composite plates

Dynamic instability zone analysis of laminated piezoelectric cylindrical shell with delamination under hygrothermal effects

To use effectively the shell in high-performance applications, analyzing the effect of hygrothermal effects on a piezoelectric delamination event is necessary. A laminated piezoelectric cylindrical shell with delamination is first established under hygrothermal effects, followed by an internal force analysis and an energy analysis of the shell. Then, a parametric vibration equation of the Mathieu for the shell is obtained by using the energy variation of the Rayleigh-Ritz method; later on, the harmonic balance method is employed to solve this equation. Finally, the effects of delamination parameters, geometric parameters, hygrothermal effects, and piezoelectric materials on the shell under uniformly distributed axial load are discussed.

Micro-structure characteristics of unsaturated polyester resin modified concrete under fatigue loads and hygrothermal environment

To explore the evolution characteristics about the microstructure of unsaturated polyester resin modified concrete (UPMC) for bridge deck pavement under two regimes: the single-load action and the interaction of hygrothermal effect and fatigue load, the four-stage experimental programs were arranged. The micromorphological characteristics of micro-crack and pore structure and the micromechanical properties of interfacial transition zone (ITZ) corresponding to the cementitious composites were quantitatively characterized and evaluated through micro-structure analysis approaches and digitized image manipulation. The experimental results demonstrated that the addition of hygrothermal effect would profoundly aggravate the deterioration of crack and pore structure and expedite the ITZ expansion concerning bridge paving concretes under the action of fatigue load. Furthermore, with regard to the concrete microstructure under external action, the incorporation of unsaturated polyester resin (UPR) might restrain crack propagation and depress cracks irregularities, exert a refinement and homogenization effect on the porous structure and reduce the expansion thickness of ITZ.

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.

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.

Nonlinear hygrothermal effects on the vibrations of a magnetostrictive viscoelastic laminated sandwich plate resting on an elastic medium

In engineering applications, composite structures supported by elastic foundations are being vastly utilized in various operating environmental conditions. The nonlinear hygrothermal effect on vibration analysis of a magnetostrictive viscoelastic laminated composite sandwich plate rested on two-parameter Pasternak’s foundations is studied in the present article. The material properties of the viscoelastic plate’s layers are considered based on the Kelvin–Voigt model. The governing equation system is derived according to Hamilton’s principle. The analytical solution is obtained to study influences of the hygrothermal change, half wave number, magnitude of the feedback control gain, aspect ratios, thickness ratio, and structural viscoelastic damping coefficients on vibration damping characteristics of the plate including the frequencies, the damping rate, and the deflection. The obtained results indicate that the natural frequency and deflection reduce with increasing the structural viscoelastic damping value. The plate takes a long time for suppressing its vibration due to increasing the hygrothermal factor.

Nonlinear vibration behavior of CNTRC plate with different distribution of CNTs under hygrothermal effects

Hygrothermal effects and periodic loading often occur in carbon nanotube-reinforced composite (CNTRC) during their service life. For the effective use of such materials for high-performance applications, their nonlinear vibration behavior under hygrothermal effects should be clearly understood. Firstly, this paper establishes a nonlinear vibration mechanical model of the CNTRC plate with different distributions of carbon nanotubes (CNTs). Then, ordinary differential equations of nonlinear vibration are given by using the Galerkin method and solved by using the harmonic balance method; additionally, a primary resonance and stability of the CNTRC plate under transverse harmonic loads are analyzed by employing the multi-scale method. Finally, for a fixed shear deformation function, effects of geometric size, volume fraction, CNT distribution, and damping coefficient on the nonlinear vibration behaviors of the CNTRC plate are discussed.

The effect of long‐time moisture exposure and low temperatures on mechanical behavior of open‐hole Cfrp laminate

AbstractCarbon fiber composite laminates (CFRP) used in aerospace are operating under various environmental conditions. Parts are often exposed to moisture which slowly diffuses into the laminate and forms internal stresses. During the flight, the aircraft is also exposed to low or elevated temperatures. The result is negative impact on composite performance due to formation of hygrothermal stresses. Understanding this phenomenon helps with prediction of the damage development which is vital for increasing the components service life. The open‐hole CFRP laminates were conditioned in humid air at 70°C/85% RH for 33,800 h and the effect of low temperatures on quasi‐cyclic tension properties and fracture behavior was investigated. The mechanical tests on two types of CFRP laminate with different number and orientation of plies were performed under − 55°C. The material behavior during the testing was monitored by acoustic emission technique. The light optical microscopy and scanning electron microscopy were used for the identification of failure mechanisms. The study showed that the hygrothermal effect has significant impact on materials toughness reduction. The damage mechanisms and characteristic morphologic features are changing due to the matrix degradation and weakened fiber/matrix interface.

Hygrothermal effect on high-velocity impact resistance of woven composites

The woven glass fiber reinforced composites (GFRP) subjected to high-speed impact is investigated to identify the hygrothermal aging effect on the impact resistance. Both the hygrothermal aged and unaged glass/epoxy laminates are subjected to different impact velocities, which is confirmed as a sensitive factor for the failure modes and mechanisms. The results show the hygrothermal aging effect decreases the ballistic limit by 14.9%, but the influence on ballistic performance is limited within the impact velocity closed to the ballistic limit. The failure modes and energy dissipation mechanisms are confirmed to be slightly influenced by the hygrothermal aging effect. The hygrothermal aging effect induced localization of structural deformation and degradation of mechanical properties are the main reasons for the composite undergoing the same failure modes at smaller impact velocities. Based on the energy absorption mechanisms, analytical expressions predict the ballistic limit and energy absorption to reasonable accuracy, the underestimated total energy absorption results in a relatively poor agreement between the measured and predicted energy absorption efficiency.

Hygrothermal environmental effect on free vibration of laminated plates using nth-order shear deformation theory

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

Sepiolite-zeolite powder doped with capric acid phase change microcapsules for temperature-humidity control

A composite material with temperature-humidity control functions was prepared by using sepiolite-zeolite powder as humidity control matrix and capric acid phase change microcapsules as temperature control material. The micromorphology, thermal conductivity, compressive strength, hygrothermal effect were studied by environmental scanning electron microscope (ESEM), thermal conductivity test, strength test and hygrothermal effect test, respectively. The results showed that the phase change temperature of capric acid phase change microcapsule is between 31 °C ~ 32 °C, the phase change enthalpy is 123.91 J/g, and it has good thermal stability. The humidity control performance is the best and the maximum humidity absorption rate is 6.28% when sepiolite-zeolite powder ratio is 9:1. The humidity control matrix@CAM (Capric acid microcapsules) can control the relative humidity of the environment at 51.74 ~ 58.54% and reduce the temperature fluctuation range by 2 °C ~ 3 °C. Capric acid phase change microcapsules are embedded in the interlaced sepiolite and zeolite powder to form a frame space body which produce capillary condensation adsorption and surface adsorption, absorb and desorb heat through phase changes, thus giving humidity control matrix@CAM a good temperature-humidity control performance.

RETRACTED: Influence of hygrothermal effect on dynamic buckling of composite slender column

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/about/our-business/policies/article-withdrawal ). This article has been retracted at the request of the authors. The authors have recognised that the equation 32 in Ref. [1] is incorrect and its modification will affect the equation of the axial motion in Reference [1] as a consequence. Additionally, this will affect the solution of the equation which will result in a revision of the comparison between average wavelengths and fragment lengths being required. The results and discussions presented cannot therefore be appropriately justified. In addition, the authors note that Ref. [51] in Fig. 6 should be Ref. [50]. The authors apologise for these inaccuracies.

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.

Analytical model for the estimation of the hygrothermal residual stresses in generally layered laminates

Delamination tests are commonly used for the evaluation of the fracture toughness. The analytical formulation used for the tests is derived for homogeneous symmetric laminates with a crack propagating in the middle plane. The difference between manufacturing and operating temperature and moisture conditions is neglected. The present paper considers geometries with asymmetric generic stacking (asymmetric and unbalanced) that are under the influence of hygrothermal effects. Explicit formulas are derived for the parameters associated with delamination tests that are of practical interest for in-situ monitoring. The results depict a good agreement with Finite Element analyses.