Hygrothermal Loading Research Articles

Environmental degradation and mechanical behavior of glass fiber reinforced polymer nanocomposites used in offshore applications

Present study aims at the variation of mechanical properties of glass fiber/epoxy composite under the effect of temperature, alkalinity, and rate of loading. Glass fiber reinforced polymer (GFRP) with plain epoxy and GFRP with 1–2% variation of Nanoclay were utilized for experimentation. Flexural testing of specimen at optimum percentage of Nanoclay in GFRP and epoxy was performed and after that pre-stretching of GFRP with plain epoxy and GFRP with optimum percentage of Nanoclay was conducted. Combined effect of moisture, alkali, and temperature on the degradation behavior of glass fiber reinforced polymers in different environments was studied. The macroscopic and microscopic behavior of the GFRP composite specimen and pure epoxy and Nanoclay reinforced epoxy exposed to varying hygrothermal loads has also been analyzed. Scanning electron microscope (SEM) was used to study the microscopic behavior of GFRP composites. X-Ray diffraction analysis of epoxy with 1%, 2%, and 3% Nanoclay addition was also performed. Tensile and flexural testing of specimen at different orientations such as 0°, 30°, 45°, 60°, and 90° were also studied. At 0° orientation, maximum average flexural strength of 295.04 MPa and 481.69 MPa was observed for plain glass fiber reinforced polymer and 2% Nanoclay/glass fiber reinforced polymer before hygrothermal loading. At 20% and 50% loading conditions the maximum flexural strength of 46.7 MPa for plain glass fiber reinforced polymer and 147.52 MPa for 2% Nanoclay/glass fiber reinforced polymer was observed before hygrothermal conditions. Maximum degradation in tensile strength (384.78 MPa at 50% loading) for 2% Nanoclay/glass fiber reinforced polymer after hygrothermal loading was observed in NaCl environment. Lower tensile strength observed for 1% of Nanoclay addition in pure epoxy as compared to the 0% and 2% mixing. There is decrease in tensile strength for specimen with 2% of Nanoclay in pure epoxy as compared to the 0% and 1% mixing. Tensile strength changed by moisture as well as mechanical loading of the glass composites. There is lesser degradation and significant increase in tensile strength of glass fiber reinforced polymer nanocomposite was observed when it exposed for lesser time period while tensile strength significantly reduced when specimen was exposed for longer time (3000 hr). After degradation in four different environments (four tanks) for 30 days intervals, SEM analysis of glass fiber reinforced polymer nanocomposite at pre-stretching of 20% and 50% loading was observed. At 20% loading there is lesser damage of glass fiber reinforced polymer nanocomposite with the formation of small irregular lumps were observed while at 50% loading there is significant damage of glass fiber reinforced polymer nanocomposite with the formation of voids of epoxy was clearly observed during SEM analysis.

Application of Galerkin iterative technique to nonlinear bending response of three-directional functionally graded slender beams subjected to hygro-thermal loads

In the view of some progressive devices such as shuttles in the aerospace field, the vessels in the marine engineering and reaction equipments in the nuclear field are exposed to super-high thermal or hygro-thermal loads simultaneously varied along the three directions in the operation, we propose the three-directional functional graded materials (3D FGMs) to carry out the composition of slender beams to meet the requirements of the hygro-thermal distribution in the multi-directions and improve the endural ability so that catastrophic failure is refrained due to large deflections. Built up on von Kármán geometric nonlinearity, one takes advantages of the principle of minimum total potential energy to derive the nonlinear governing equation of the structures subjected to hygro-thermal loadings of the uniform, linear and sinusoidal distributions. A novel analytical solution for the nonlinear bending response is presented based on the Galerkin iterative technique, which overcomes the shortcoming of finding difficultly the closed-form solution to antisymmetric nonlinear structures such as multi-directional FGMs. The generalized differential quadrature method (GDQM) is performed for validating the effectiveness of the presented methodology. Numerical simulations are implemented to reveal the effects of 3D FGMs indexes, mechanical and hygro-thermal loadings on the nonlinear bending response. Results exhibit the nonlinear behavior is profoundly dependent on the 3D FGMs and hygro-thermal properties, which is applied for optimizing the 3D FGMs structures in multiple physical fields.

Hygrothermal effects on buckling behaviors of porous bi-directional functionally graded micro-/nanobeams using two-phase local/nonlocal strain gradient theory

Rapid development of technology puts forward higher performance requirements for advanced materials with multi-field coupling stability. The porous functionally graded materials, which is well developed with mature design, tools, can be customized according to specific application through nanostructures. In this work, the influences of hygro-thermo-mechanical coupling loadings on buckling behaviors of porous bi-directional functionally graded (2D FG) Timoshenko nanobeam is investigated through the numerical study. The governing equation and boundary conditions are derived on the basis of two phase local/nonlocal strain gradient theory employing the principle of virtual work, and a processing method for Clamped-Free (C–F) boundary condition is proposed. By employing generalized differential quadrature method (GDQM), the theoretical solution of buckling behavior of the Timoshenko nanobeam is obtained, with the implementation of comparison and convergence studies to demonstrate the accuracy and effectiveness. On the best of the authors’ knowledge, it is novel to investigate the buckling response of 2D FG Timoshenko nanobeam under hygrothermal environment using the two local/nonlocal strain gradient theory. Herein, the influence of nonlocal parameter, strain gradient theory, aspect ratio, axial gradient index, thickness gradient index, hygrothermal loadings and local volume fraction on the critical buckling load under various natural boundary conditions are acquired and discussed. The numerical results indicate that the present model can capture the buckling response of porous 2D FG Timoshenko nanobeams under hygrothermal environment, exhibiting consistent softening/hardening effects under all boundary conditions and modes.

Hygrothermoelastic response of a finite hollow circular cylinder

In this paper, a hollow circular cylinder of finite length with finite extent occupying the space is considered. Based on the hygrothermoelasticity theory, the transient response of a hollow circular cylinder subjected to the hygrothermal loading at the surface is analyzed. The analytical solution for the coupling and uncoupling effects of temperature, moisture, and thermal stresses is obtained by using the integral transform technique. The numerical results of the transient response of the hygrothermoelasticity field are presented graphically for a graphite fiber–reinforced epoxy matrix composite material (T300/5208).

Transient Response of a Hollow Functionally Graded Piezoelectric Cylinder Subjected to Coupled Hygrothermal Loading

In this paper, transient response of a simply supported finite length hollow cylinder made of functionally graded piezoelectric material (FGPM) subjected to coupled hygrothermal loading was investigated. The coupled equations of heat conduction and moisture diffusion as well as motion equations and the electrostatic equation of FGPM were solved employing the Fourier series expansion method through the longitudinal direction, the differential quadrature method (DQM) along the radius and Newmark method for time domain. Finally, the distribution of temperature, humidity, electric potential, stresses and displacements was achieved. The effect of coupled and uncoupled hygrothermal loading, grading index and hygrothermal loading was illustrated in the numerical examples. The results show that using the coupled model is vital for analysis of transient response of the cylinder subjected to hygrothermal loading.

Condition Assessment of a Reinforced Concrete Residential Building using Non-destructive Testing Methods - A Case Study

The present study deals with both experimental and numerical investigation on buckling effects of laminated composite plates subjected to varying temperature and moisture. A simple laminated plate model is developed for the buckling of composite plates subjected to adverse hygrothermal loading. A computer program based on FEM in MATLAB environment is developed to perform all necessary computations. The woven fiber Glass/Epoxy specimens were hygrothermally conditioned in a humidity cabinet where theconditions were maintained at temperatures of 300K-425K and relative humidity (RH) ranging from 0-1% for moisture concentrations. All the investigations are made with a symmetric cross-ply laminates. The present study deals with both experimental and numerical investigation on buckling behavior of laminated composite plates subjected to varying temperature and moisture concentration. Quantitative results are presented to show the effects of geometry, material and lamination parameters of woven fiber laminate onbuckling of composite plates for different temperature and moisture concentrations with simply supported boundary conditions with different aspect and side-to-thickness ratios. Experimental results show that there is reduction in buckling loads in KN with the increase in temperature and moisture concentration for laminates with clamped-free-clamped-free boundary conditions

A unified modeling method for dynamic analysis of GPLs-FGP sandwich shallow shell embedded SMA wires with general boundary conditions under hygrothermal loading

In this research, the dynamic analysis of graphene platelets (GPLs) reinforced functionally graded porous (FGP) sandwich shallow shell embedded shape memory alloy (SMA) wires with general boundary conditions under hygrothermal loading is conducted. Four different porosity distributions of FGP reinforced with four various GPLs dispersion patterns are considered. Based on the Brinson formulation, the constitutive equation of the SMA is established. The energy functional of the sandwich shallow shell is constructed by employing the Hooke’s law and the first-order shear deformation theory (FSDT). Ultimately, the dynamic characteristics of the sandwich shallow shell are obtained by solving the energy functional with the Rayleigh-Ritz method. After the verification of accuracy and reliability, parametric studies on the effects of material properties, geometrical parameters, and boundary conditions are investigated.

Thermomechanical Buckling Analysis of the E&P-FGM Beams Integrated by Nanocomposite Supports Immersed in a Hygrothermal Environment.

Due to the widespread use of sandwich structures in many industries and the importance of understanding their mechanical behavior, this paper studies the thermomechanical buckling behavior of sandwich beams with a functionally graded material (FGM) middle layer and two composite external layers. Both composite skins are made of Poly(methyl methacrylate) (PMMA) reinforced by carbon-nano-tubes (CNTs). The properties of the FGM core are predicted through an exponential-law and power-law theory (E&P), whereas an Eshelby–Mori–Tanaka (EMT) formulation is applied to capture the mechanical properties of the external layers. Moreover, different high-order displacement fields are combined with a virtual displacement approach to derive the governing equations of the problem, here solved analytically based on a Navier-type approximation. A parametric study is performed to check for the impact of different core materials and CNT concentrations inside the PMMA on the overall response of beams resting on a Pasternak substrate and subjected to a hygrothermal loading. This means that the sensitivity analysis accounts for different displacement fields, hygrothermal environments, and FGM theories, as a novel aspect of the present work. Our results could be replicated in a computational sense, and could be useful for design purposes in aerospace industries to increase the tolerance of target productions, such as aircraft bodies.

Influence of local stiffeners and cutout shapes on the vibration and stability characteristics of quasi-isotropic laminates under hygro-thermo-mechanical loadings

Abstract s The perforated stiffened panel is generally found as a sub-component of sophisticated structures. The fundamental purpose of this panel is to withstand against buckling under complicated loading and environmental conditions. Hence, an accurate knowledge of critical buckling behaviour of stiffened panels is very much essential for a reliable and lightweight structural design. In this paper, the focus is on quasi-laminated panels with different cutout shapes of various sizes and their responses to hygrothermal environments under nonlinearly varying edge loads and is compared with the locally stiffened panels. Towards this, the modelling of the panel and stiffener is done by adopting nine-noded heterosis plate elements and three noded beam elements respectively. The stiffener formulation is suitably modified in order to take the torsional effect also into consideration along with the effect of shear deformation. Initially, the plate and the stiffener elements are treated separately, and then the displacement compatibility is maintained between them by using the transformation matrix. For a given loading and geometric discontinuity, the stress distribution within the perforated panel is highly non-uniform in nature and hence a dynamic approach has been used to calculate buckling loads by adopting two sets of boundary conditions, one set for pre-buckling stress analysis and the second set for buckling analysis. Four different quasi-isotropic stacking sequences are deliberated in this work by varying different ply-orientation in each scheme. The study also addresses the effect of various parameters such as nonlinear loads, hygro-thermal loads, cutout size and shapes, position of cutout, stiffener parameters, stacking sequences, thickness of plate and boundary conditions.

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.

Nonlocal vibration analysis of spinning nanotubes conveying fluid in complex environments

In the current paper, hygro-thermo-magnetically induced vibrations of small-scale viscoelastic tubes containing flow with a spin motion under gravity and tangential loads are analyzed by including surface effects. The dynamic equations are derived in the framework of the modified nonlocal elasticity theory (NET) and Rayleigh beam model. The Galerkin method and Laplace transformation are implemented to solve model equations. Vibration frequencies, stability boundaries, and Campbell diagrams of the system are acquired. Impacts of influential parameters such as scale rotary inertia factor, scale parameter, viscoelastic materials, gravity and tangential loads, flow and spin velocities, geometrical properties, and environmental conditions on the stability of the structure are examined. Also, the obtained results are compared for the Rayleigh and Euler-Bernoulli (EB) beam models. The golden results of this work are that by fine-adjusting the scale parameter and magnetic intensity in the system, destructive effects of hygro-thermal loads can be dampened. Besides, the increment of the rotary inertia factor and nanotube thickness induces destabilizing effect on the system.

Dynamic Response of Multilayered Polymer Functionally Graded Carbon Nanotube Reinforced Composite (FG-CNTRC) Nano-Beams in Hygro-Thermal Environment.

This work studies the dynamic response of Bernoulli–Euler multilayered polymer functionally graded carbon nanotubes-reinforced composite nano-beams subjected to hygro-thermal environments. The governing equations were derived by employing Hamilton’s principle on the basis of the local/nonlocal stress gradient theory of elasticity (L/NStressG). A Wolfram language code in Mathematica was written to carry out a parametric investigation on the influence of different parameters on their dynamic response, such as the nonlocal parameter, the gradient length parameter, the mixture parameter and the hygro-thermal loadings and the total volume fraction of CNTs for different functionally graded distribution schemes. It is shown how the proposed approach is able to capture the dynamic behavior of multilayered polymer FG-CNTRC nano-beams under hygro-thermal environments.

Large deflection bending analysis of variable-thickness tapered plates under three-dimensionally hygrothermomechanical loads

This paper aims at large deflection bending analysis of variable-thickness tapered plate under three-dimensionally hygrothermal stresses based on Kirchhoff-love assumptions with von Kármán strains. Three dimensionally hygrothermal loads on plate are researched with different heat and moisture boundaries which seems to be overlooked in previous studies. The formulation of varying tapered thickness is further amended by eliminating singular sharp edges in previous literatures. The highly coupled and nonlinear variable-coefficient governing partial differential equations for the variable-thickness plate in hygrothermomechanically bending with arbitrary tapering thickness profiles have been derived and solved by a unified wavelet solving methodology, which overcomes the limitations of additional Neumann boundary of plate thickness in previous homotopy-based work. Numerical convergence is performed to verify the formulation and highly accurate wavelet solutions are given in excellent agreement with published results, while the ultimate deflection to thickness can be up to over 10 rarely obtained by other methods. Parametric studies are carried out to investigate the large deflection behavior of tapered plates with different geometric parameters. It is concluded that the largely deformed characteristics of variable-thickness tapered plate in hygrothermal environment is highly influenced prominently by effects of tapered ratios and profiles’ polynomial orders.

Characterization of microcracking of NCF composites under accelerated hygrothermal cycles: Influence of the stitching yarn and the style of biaxial NCF

In this paper, an analysis of the evolution of microcracking of Non-Crimp Fabric (NCF) polymer matrix laminates under hygrothermal loading is presented. These composites are reinforced with biaxial NCF styles ([+45/-45], [0/90], etc.) and manufactured by Liquid Resin Infusion (LRI). The samples are subjected to accelerated hygrothermal cycles that cause microcracks in specific resin-rich areas (RRA). Three types of microcracks were found to occur in the heterogeneous morphology of NCF. An experimental method based on 2D microscopic observations was adapted for the characterization of microcracking in several NCF laminates. 3D tomographic X–ray observations were performed to investigate the propagation and location of microcracks in the NCF volume. The influence of humidity on microcracking was investigated. The impact of several parameters on microcracking was discussed, in particular the stitching yarn size and styles of biaxial NCF used in laminates.

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.

Nickel-Aluminum Thermal Spray Coatings as Adhesion Promoter and Susceptor for Inductively Joined Polymer-Metal Hybrids.

Hybrid joints of metal- and fiber-reinforced-polymer offer great potential for lightweight applications. Thereby, a fast and reliable joining process is mandatory for mass-production applications. To this end, this study assesses inductive spot-joining in combination with prior thermal spray coating of the metal adherent. A nickel–aluminum 95/5 coating was applied to achieve high adhesion through mechanical interlocking and to act as susceptor for the inductive joining process. The joint strength was assessed with lap shear specimens consisting of EN AW-6082 aluminum alloy and glass fiber reinforced polyamide 6 or polypropylene, respectively. The joints were further investigated in terms of heating time and hygrothermal cyclic loading. The results showed that significant time savings for the joining process as well as strong adhesion were achieved due to the coating. Moreover, the high strengths were even preserved under hygrothermal cyclic loading.

Design and Analysis of Cng Pressure Vessel Using Natural Fibre Composites

Bio composites comprise one or more phases derived from a biological origin; these may be reinforcements (cotton, hemp, flax, sisal, jute, and kenaf or recycled wood and paper) or organic matrices, for example, polylactic acid (PLA) and soybean resins. Use of natural fibers has been in existence for many generations, however, the discovery and subsequent commercialization of synthetics such as glass, aramids, and carbon fibers in early and mid-twentieth century resulted in the reduced preference for natural fibers in a number of applications. However recent advancement in manufacturing methods and a shift towards environmental protection shifted the focus back to biodegradable composite. This paper deals with the generation of MATLAB script files that assists the user in the design of a biodegradable composite CNG pressure vessel to operate within safe conditions. The inputs of the program are the material properties, ply strength, applied loading, cure and room temperature and fiber orientation. Classical Laminate Analysis (CLA) is a widespread theory in engineering for analyzing the stress/strain behavior of orthotropic laminates under mechanical and hygrothermal loading. CLA is an orthotropic adaptation of Kirchoff’s thin plate theory. The output of the program is extension, coupling and bending stiffness matrices, equivalent elastic constants, thermal, moisture, mechanical and total strain vector, total strains and stresses at ply Interfaces and mid planes. The calculation also predicts the minimum reserve factors with the occurrences of failure at various points in the ply interface.

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.

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.

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

In this work, the hygrothermal effect on the behavior of hybrid laminated composite plate has been investigated using high-order shear deformation theory and finite element analysis. The equation of motion of the laminated plate is obtained using Hamilton's principle, and the mathematical expressions are obtained using Navier's solution for different boundary conditions. The engineering moduli for the different cases: non-hybrid composite and hybrid composite are calculated using the law of mixtures. The mechanical properties of hybrid composite plate are considered as temperature and humidity dependent. The results obtained with finite element analysis using Abaqus and analytical approach show a good agreement in predicting the fundamental frequencies of hybrid cross-ply laminated plates under hygrothermal loading.