Exact solution for thermal vibration of multi-directional functionally graded porous plates submerged in fluid medium

An analytical method for analyzing the thermal vibration of multi-directional functionally graded porous rectangular plates in fluid media with novel porosity patterns is developed in this study.Mechanical properties of MFG porous plates change according to the length,width,and thickness directions for various materials and the porosity distribution which can be widely applied in many fields of engineering and defence technology.Especially,new porous rules that depend on spatial coordinates and grading indexes are proposed in the present work.Applying Hamilton's principle and the refined higher-order shear deformation plate theory,the governing equation of motion of an MFG porous rectangular plate in a fluid medium(the fluid-plate system)is obtained.The fluid velocity potential is derived from the boundary conditions of the fluid-plate system and is used to compute the extra mass.The GalerkinVlasov solution is used to solve and give natural frequencies of MFG porous plates with various boundary conditions in a fluid medium.The validity and reliability of the suggested method are confirmed by comparing numerical results of the present work with those from available works in the literature.The effects of different parameters on the thermal vibration response of MFG porous rectangular plates are studied in detail.These findings demonstrate that the behavior of the structure within a liquid medium differs significantly from that within a vacuum medium.Thereby,they offer appropriate operational approaches for the structure when employed in various mediums.

Thermal vibration of functionally graded porous nanocomposite beams reinforced by graphene platelets

The thermal vibration of functionally graded(FG)porous nanocomposite beams reinforced by graphene platelets(GPLs)is studied.The beams are exposed to the thermal gradient with a multilayer structure.The temperature varies linearly across the thickness direction.Three different types of dispersion patterns of GPLs as well as porosity distributions are presented.The material properties vary along the thickness direction.By using the mechanical parameters of closed-cell cellular solid,the variation of Poisson’s ratio and the relation between the porosity coefficient and the mass density under the Gaussian random field(GRF)model are obtained.By using the Halpin-Tsai micromechanics model,the elastic modulus of the nanocomposite is achieved.The equations of motion based on the Timoshenko beam theory are obtained by using Hamilton’s principle.These equations are discretized and solved by using the generalized differential quadrature method(GDQM)to obtain the fundamental frequencies.The effects of the weight fraction,the dispersion model,the geometry,and the size of GPLs,as well as the porosity distribution,the porosity coefficient,the boundary condition,the metal matrix,the slenderness ratio,and the thermal gradient are presented.

Effects of Thermal Lattice Vibration on the Effective Potential of Weak-Coupling Bipolaron in a Quantum Dot

Based on the Huybrechts' linear-combination operator,effects of thermal lattice vibration on the effective potential of weak-coupling bipolaron in semiconductor quantum dots are studied by using the LLP variational method and quantum statistical theory.The results show that the absolute value of the induced potential of the bipolaron increases with increasing the electron-phonon coupling strength,but decreases with increasing the temperature and the distance of electrons,respectively;the absolute value of the effective potential increases with increasing the radius of the quantum dot,electron-phonon coupling strength and the distance of electrons,respectively,but decreases with increasing the temperature;the temperature and electron-phonon interaction have the important influence on the formation and state properties of the bipolaron:the bipolarons in the bound state are closer and more stable when the electron-phonon coupling strength is larger or the temperature is lower;the confinement potential and coulomb repulsive potential between electrons are unfavorable to the formation of bipolarons in the bound state.

Thermally Induced Vibration Analysis of Flexible Beams Based on Isogeometric Analysis

Spacecraft flexible appendages may experience thermally induced vibrations(TIV)under sudden heating loads,which in consequence will be unable to complete their intended missions.Isogeometric analysis(IGA)utilizes,in an isoparametric concept,the same high order and high continuity non-uniform rational B-splines(NURBS)to represent both the geometry and the physical field of the structure.Compared to the traditional Lagrange polynomial based finite element method where only C0-continuity across elements can be achieved,IGA is geometrically exact and naturally fulfills the C1-continuity requirement of Euler–Bernoulli(EB)beam elements,therefore,does not need extra rotational degrees-of-freedom.In this paper,we present a thermally induced vibration analysis framework based on the isogeometric method where thermal and structural behaviors are coupled.We fully exploited the higher order,higher continuous and geometric exactness of the NURBS basis with both benchmarks and sophisticated problems.In particular,we studied the thermally induced vibrations of the Hubble Space Telescope(HST)solar panel where main factors influencing thermal flutters are studied,and where possible improvements of the analytical reference methods are discussed.Additionally,thermally induced vibrations of the thin-walled lenticular tubes are studied and two new configurations of the tube are proposed to effectively suppress the thermally induced vibrations.Numerical examples of both benchmarks and sophisticated problems confirm the accuracy and efficiency of the isogeometric analysis framework for thermally induced vibration analysis of space structures.

High-Fidelity Hugoniots of α Phase RDX Solid from High-Quality Force Field with Thermal,Zero-Point Vibration,and Anharmonic Effects

It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in predict- ing the densities for the α phase crystalline hexahydro-1,3,5-trinitro-l,3,5-triazine （RDX）, and derivation of its high-fidelity Hugoniot locus and Mie-Grfineisen equation of state covering a very wide range of pressures and temperatures. This work can be used to efficiently and accurately predict the thermophysical properties of solid explosives over the pressures and temperatures to which they are subjected, which is a long-standing issue in the field of energetic materials.

Size-dependent vibration and buckling of porous functionally graded microplates based on modified couple stress theory in thermal environments by considering a dual power-law distribution of scale effects

In this study,the thermodynamic behaviors of the intrinsic frequency and buckling temperature of rectangular plates of functionally graded materials(FGMs)are explored based on the modified couple stress theory(MCST)and the novel dual powerlaw scale distribution theory.The effects of linear,homogeneous,and non-homogeneous temperature fields on the frequency and buckling temperature of FGM microplates are evaluated in detail.The results show that the porosity greatly affects the mechanical properties of FGM plates,reducing their frequency and flexural temperature compared with non-porous plates.Different temperature profiles alter plate frequencies and buckling temperatures.The presence and pattern of scale effect parameters are also shown to be crucial for the mechanical response of FGM plates.The present research aims to provide precise guidelines for the micro-electro-mechanical system(MEMS)fabrication by elucidating the complex interplay between thermal,material,and structural factors that affect the performance of FGM plates in advanced applications.

Zero thermal expansion in metal-organic framework with imidazole dicarboxylate ligands

Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion.Metal-organic framework(MOF)with unique structure flexibility is an ideal material to study the thermal expansion.This work adopts the high-resolution variable-temperature powder x-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF([Sr(DMPhH_(2)IDC)_(2)]_n).It has the unique honeycomb structure with one-dimensional(1 D)channels along the c-axis direction,the a-b plane displays layer structure.The thermal expansion behavior has strong relationship with the structure,ZTE appears in the a-b plane and large PTE along the c-axis direction.The possible mechanism is that the a/b layers have enough space for the transverse thermal vibration of polydentate ligands,while along the c-axis direction is not.This work not only reports one interesting zero thermal expansion material,but also provides new understanding for thermal expansion mechanism from the perspective of the structural model.

Effects of Intermolecular Interactions on Luminescence Property in Organic Molecules

The organic solid-state lightemitting materials have attracted more and more attention owing to their promising applications in displays,lasers and optical communications.In contrast to isolated molecule,there are various weak intermolecular interactions in organic solids that sometimes have a large impact on the excited-state properties and energy dissipation pathways,resulting in strong fluorescence/phosphorescence.It is increasingly necessary to reveal the luminescence mechanism of organic solids.Here,we briefly review how intermolecular interactions induce strong normal fluorescence,thermally activate delayed fluorescence and room-temperature phosphorescence in organic solids by examining changes in geometry,electronic structures,electron-vibration coupling and energy dissipation dynamics of the excited states from isolated to aggregated molecules.We hope that the review will contribute to an in-depth understanding of the excited state properties of organic solids and to the design of excellent solid-state light-emitting materials.

NON-LINEAR DYNAMIC BEHAVIOR OF THERMOELASTIC CIRCULAR PLATE WITH VARYING THICKNESS SUBJECTED TO NONCONSERVATIVE LOADING

The non-linear dynamic behaviors of thermoelastic circular plate with varying thickness subjected to radially uniformly distributed follower forces are considered. Two coupled non-linear differential equations of motion for this problem are derived in terms of the transverse deflection and radial displacement component of the mid-plane of the plate. Using the Kantorovich averaging method, the differential equation of mode shape of the plate is derived, and the eigenvalue problem is solved by using shooting method. The eigencurves for frequencies and critical loads of the circular plate with unmovable simply supported edge and clamped edge are obtained. The effects of the variation of thickness and temperature on the frequencies and critical loads of the thermoelastic circular plate subjected to radially uniformly distributed follower forces are then discussed.

Stochastically driven vibrations of single-layered graphene sheets

Thermal vibration of single-layered graphene sheets (SLGSs) is investigated using plate model together with the law of equi-partition of energy and the molecular dynamics (MD) method based on the condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field.The in-plane stiffness and Poisson ratio of SLGSs are calculated by stretching SLGSs.The effective thickness of SLGSs is obtained by the MD simulations for the thermal vibration of SLGSs through the natural frequency.The root-mean-squared (RMS) amplitudes for SLGSs of differing temperatures and boundary conditions are calculated by the MD,and are compared with the results calculated by the thin plate model together with the law of equi-partition of energy.At the center of SLGSs,the thin plate theory can predict the MD results reasonably well.For the difference of bonding structure of the edge atoms,the deviation between the MD results and plate theory becomes more readily apparent near the edges of SLGSs.

A thermal-flutter criterion for an open thin-walled circular cantilever beam subject to solar heating

The flexible attachments of spacecraft may undergo Thermally Induced Vibration(TIV)on orbit due to the suddenly changed solar heating. The unstable TIV, called thermal-flutter, can cause serious damage to the spacecraft. In this paper, the coupled bending-torsion thermal vibration equations for an open thin-walled circular cantilever beam are established. By analyzing the stability of these equations based on the first Lyapunov method, the thermal-flutter criterion can be obtained. The criterion is very different form that of closed thin-walled beams because the torsion has great impact on the stability of the TIV for open thin-walled beams. Several numerical simulations are conducted to demonstrate that the theoretical predictions agree very well with the finite element results, which mean that the criterion are reliable.

WAVE PROPAGATION IN A TRANSVERSELY ISOTROPIC THERMOELASTIC SOLID CYLINDER OF ARBITRARY CROSS-SECTION

The wave propagation in an infinite, homogeneous, transversely isotropic solid cylin- der of arbitrary cross-section is studied using Fourier expansion collocation method, within the frame work of linearized, three-dimensional theory of thermoelasticity. Three displacement po- tential functions are introduced, to uncouple the equations of motion and the heat conduction. The frequency equations are obtained for longitudinal and flexural （symmetric and antisymmet- ric） modes of vibration and are studied numerically for elliptic and parabolic cross-sectional zinc cylinders. The computed non-dimensional wave numbers are presented in the form of dispersion curves.