• Computers and Concrete
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• v.2 no.3
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• pp.189-202
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• 2005

This paper presents an analysis of some experimental results concerning micro-structural tests, permeability measurements and strain-stress tests of four types of High-Performance Concrete, exposed to elevated temperatures (up to $700^{\circ}C$). These experimental results, obtained within the "HITECO" research programme are discussed and interpreted in the context of a recently developed mathematical model of hygro-thermal behaviour and degradation of concrete at high temperature, which is briefly presented in the Part 2 paper (Gawin, et al. 2005). Correlations between concrete permeability and porosity micro-structure, as well as between damage and cracks' volume, are found. An approximate decomposition of the thermally induced material damage into two parts, a chemical one related to cement dehydration process, and a thermal one due to micro-cracks' development caused by thermal strains at micro- and meso-scale, is performed. Constitutive relationships describing influence of temperature and material damage upon its intrinsic permeability at high temperature for 4 types of HPC are deduced. In the Part II of this paper (Gawin, et al. 2005) effect of two different damage-permeability coupling formulations on the results of computer simulations concerning hygro-thermo-mechanical performance of concrete wall during standard fire, is numerically analysed.

• Structural Engineering and Mechanics
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• v.92 no.2
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• pp.163-172
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• 2024

This paper intends to analyze the nonlinear forced vibrations of functionally graded material (FGM) beams with initial geometrical defects in hygro-thermal ambiences. For this purpose, we assume that the correlation properties of the material alter along the thickness direction in succession and the surface of the beam is subjected to humid and thermal loads. Based on the Euler Bernoulli beam theory and geometrical non-linearity, we use the Hamiltonian principle to formulate a theoretical model with consideration of the hygrothermal effects. Galerkin's technique has been proposed for the control equations of discrete systems. The non-linear primary resonances are acquired by applying the modified Lindstedt-Poincare method (MLP). Verify the reliability of the data obtained through comparison with literature. The non-linear resonance response is reflected by amplitude-frequency response curves. The numerical results indicate that the resonances of FGM beams include three non-linear characteristics, namely hard springs, soft springs and soft-hard spring types. The response modalities of the structure may transform between those non-linear characteristics when material properties, spring coefficients, geometric defect values, temperature-humidity loads and even the external stimulus generate variations.

• Structural Engineering and Mechanics
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• v.84 no.6
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• pp.783-798
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• 2022

This study attempts to investigate the impact of thickness stretching and nonlinear hygro-thermo-mechanical loading on the bending behavior of FG beams. Young's modulus, thermal expansion, and moisture concentration coefficients vary gradually and continuously according to a power-law distribution in terms of the volume fractions of the constituent materials. In addition, the interaction between the thermal, mechanical, and moisture loads is involved in the governing equilibrium equations. Using the present developed analytical model and Navier's solution technique, the numerical results of non-dimensional stresses and displacements are compared with those obtained by other 3D theories. Furthermore, the present analytical model is appropriate for investigating the static bending of FG beams exposed to intense hygro-thermo-mechanical loading used for special technical applications in aerospace, automobile, and civil engineering constructions.

• Advances in nano research
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• v.8 no.4
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• pp.293-305
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• 2020

In the current research, the free vibrational behavior of the FG nano-beams integrated in the hygro-thermal environment and reposed on the elastic foundation is investigated using a novel integral Timoshenko beam theory (ITBT). The current model has only three variables unknown and requires the introduction of the shear correction factor because her uniformed variation of the shear stress through the thickness. The effective properties of the nano-beam vary according to power-law and symmetric sigmoid distributions. Three models of the hygro-thermal loading are employed. The effect of the small scale effect is considered by using the nonlocal theory of Eringen. The equations of motion of the present model are determined and resolved via Hamilton principle and Navier method, respectively. Several numerical results are presented thereafter to illustrate the accuracy and efficiency of the actual integral Timoshenko beam theory. The effects of the various parameters influencing the vibrational responses of the P-FG and SS-FG nano-beam are also examined and discussed in detail.

• Structural Engineering and Mechanics
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• v.65 no.6
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• pp.645-656
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• 2018

Importance of procuring adequate knowledge about the mechanical behavior of double-layered graphene sheets (DLGSs) incensed the authors to investigate wave propagation responses of mentioned element while rested on a visco-Pasternak medium under hygro-thermal loading. A nonlocal strain gradient theory (NSGT) is exploited to present a more reliable size-dependent mechanical analysis by capturing both softening and hardening effects of small scale. Furthermore, in the framework of a classical plate theory the kinematic relations are developed. Incorporating kinematic relations with the definition of Hamilton's principle, the Euler-Lagrange equations of each of the layers are derived separately. Afterwards, combining Euler-Lagrange equations with those of the NSGT the nonlocal governing equations are written in terms of displacement fields. Interaction of the each of the graphene sheets with another one is regarded by the means of vdW model. Then, a widespread analytical solution is employed to solve the derived equations and obtain wave frequency values. Subsequently, influence of each participant variable containing nonlocal parameter, length scale parameter, foundation parameters, temperature gradient and moisture concentration is studied by plotting various figures.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.5
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• pp.400-407
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• 2011

The stress distribution and stress amplitude of a membrane are major factors to decide the mechanical fatigue life of PEMFC (Polymer Electrolyte Membrane Fuel Cell). In this paper, mechanical stresses under operating hygro-thermal condition of the membrane are numerically modelled. Contact analysis between gas diffusion layer (GDL) and the membrane is performed under various temperature-humidity conditions. The structural model has nonlinear material properties depending on temperature and relative humidity. Several geometric conditions are applied to the model. The numerical analysis results indicate that deformations of the membrane are strongly related with assembly conditions of the fuel cell. The fatigue life is predicted for practical operating condition through experimental data.

• Advances in materials Research
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• v.13 no.6
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• pp.431-462
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• 2024

The buckling mode of failure is very common in case of plates, especially when their aspect ratio is large. In the present study, an endeavour has been made to carry out the hygro-thermal-induced buckling-based study of sandwich functionally graded (FG) plates made up of different material variation laws. A comparative study has been carried out between FGM plates made up of power, exponential and sigmoidal law using higher order zigzag theory. Nine-noded C-0 finite element has been used. It has been observed that the buckling behaviour of sandwich FGM plates under hygrothermal conditions is widely influenced by the geometry of the plate and the value of the law coefficient.Also, the nature of boundary condition widely affects the behavior of the plate.

• Geomechanics and Engineering
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• v.38 no.4
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• pp.409-420
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• 2024

In this research the hygro-thermo-mechanical loading and micromechanical model effects on bending behavior of functionally graded material plates resting on Winkler and Pasternak elastic foundations, the higher order shear deformation theory is used here. The material properties of the plate: young's modulus, thermal coefficient and moisture expansion coefficient are assumed to be graded in the thickness direction according to various micromechanical models starting with the Voigt's model which is commonly used in most functionally graded plates studies to the Reuss's, LRVE's and Mori-Tanaka's models. The principle of virtual displacement is used to determine the equilibrium equations and the a several numerical results are given to validate the precision of the present method for bending behavior of FGM plates subjected to hygro-thermo-mechanical loading resting on elastic foundations. Afterwards, a parametric study is conducted to determine the effect of different parameters on the deflection of the FGM plates like micromechanical models, type of loading and plate geometry. In the lights of the present research, it can be concluded that the present theory is accurate and simple in predicting the deflection behavior of functionally graded plates under hygro-thermo-mechanical effects and micromechanical models.

• Smart Structures and Systems
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• v.18 no.4
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• pp.755-786
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• 2016

The hygro-thermo-mechanical bending behavior of sigmoid functionally graded material (S-FGM) plate resting on variable two-parameter elastic foundations is discussed using a four-variable refined plate theory. The material characteristics are distributed within the thickness direction according to the two power law variation in terms of volume fractions of the constituents of the material. By employing a four variable refined plate model, both a trigonometric distribution of the transverse shear strains within the thickness and the zero traction boundary conditions on the top and bottom surfaces of the plate are respected without utilizing shear correction factors. The number of independent variables of the current formulation is four, as against five in other shear deformation models. The governing equations are deduced based on the four-variable refined plate theory incorporating the external load and hygro-thermal influences. The results of this work are compared with those of other shear deformation models. Various numerical examples introducing the influence of power-law index, plate aspect ratio, temperature difference, elastic foundation parameters, and side-to-thickness ratio on the static behavior of S-FGM plates are investigated.

• Steel and Composite Structures
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• v.50 no.5
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• pp.563-581
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• 2024

This paper presents a novel finite element model for the free vibration analysis of variable-thickness functionally graded porous (FGP) microplates resting on Pasternak's medium in the hygro-thermal environment. The governing equations are established according to refined higher-order shear deformation plate theory (RPT) in construction with the modified couple stress theory. For the first time, three-node triangular elements with twelve degrees of freedom for each node are developed based on Hermitian interpolation functions to describe the in-plane displacements and transverse displacements of microplates. Two laws of variable thickness of FGP microplates, including the linear law and the nonlinear law in the x-direction are investigated. Effects of thermal and moisture changes on microplates are assumed to vary continuously from the bottom surface to the top surface and only cause tension loads in the plane, which does not change the material's mechanical properties. The numerical results of this work are compared with those of published data to verify the accuracy and reliability of the proposed method. In addition, the parameter study is conducted to explore the effects of geometrical and material properties such as the changing law of the thickness, length-scale parameter, and the parameters of the porosity, temperature, and humidity on the free vibration response of variable thickness FGP microplates. These results can be applied to design of microelectromechanical structures in practice.