Uniform Temperature Change Research Articles

Exact solutions for thermally induced electromechanical fields of PN junctions in centrosymmetric semiconductors

PN junctions play important roles in semiconductor devices. Flexoelectricity, an electromechanical coupling between strain gradient and electric polarization, has non-negligible contributions in nano-devices. The thermoflexoelectric effect is a phenomenon in which temperature gradients generate inhomogeneous strains and further induce flexoelectric polarizations. Therefore, temperature gradients can affect carrier transport in PN junctions through the thermoflexoelectric effect. In this paper, a one-dimensional model of the PN junction under a uniform temperature change is established. Exact solutions for the electromechanical fields in the PN junction are obtained for the first time. The effects of the temperature gradient, doping level, and flexoelectric coefficient on the electromechanical behaviors of the PN junction are numerically analyzed. The results indicate that carrier concentrations in the p and n regions are sensitive to temperature gradients because of the screening effect of the mobile charge on the flexoelectric polarization induced by the temperature gradient. Meanwhile, the flexoelectric field and the initial built-in electric field in the depletion region jointly determine the magnitude of the potential barrier, and thus, the temperature-gradient-induced flexoelectric field can tune the switching characteristics of the PN junction. This study provides a theoretical basis for the tuning of the electromechanical behavior of the PN junction by thermally induced flexoelectric fields.

Nonlinear torsional buckling of corrugated core sandwich toroidal shell segments with graphene-reinforced coatings in temperature change using the Ritz energy method

An investigation on the nonlinear torsional buckling of corrugated core sandwich toroidal shell segments with functionally graded graphene-reinforced composite (FG-GRC) laminated coatings in temperature change is mentioned in this paper using the Ritz energy method. The complex configuration of sandwich toroidal shell segments with double curvatures and the combination of the corrugated core and the FG-GRC coatings create the special behavior of structures. A homogenization model for corrugated structures and the extended Halpin-Tsai model can be applied to estimate the stiffnesses of shells. The effects of uniform temperature change are taken into account by supplementing the thermal forces into the total forces of shells. The Donnell shell theory and Pasternak's foundation model are used to establish the total potential energy of the structures. Ritz energy method is applied, and the closed condition and circumferential stress are taken into account, the postbuckling curve expressions of torsion-deflection and torsion-twist angle are obtained in explicit forms. The numerically obtained examples can show the significantly beneficial effects of FG-GRC laminated coatings and corrugated core on nonlinear buckling responses of structures.

Numerical study of thermomechanical delamination mechanisms in segmented high-temperature coatings

This work addresses the thermomechanical delamination mechanisms in segmented multilayered high-temperature coatings system using computational fracture mechanics approach. A representative unit cell model is presented, where the thermomechanical load is generated by combining uniform temperature changes and boundary-loaded displacements. The model is used to analyze coatings over a broad range of material properties, geometries, and loads. The findings suggest that, for a given coatings system, the mechanical load carried by the top-coat layer is the only force that drives delamination developing along the top-coat/bond-coat interface. The introduced multiple vertical cracks lead to stiffness release over a limited region, resulting in reductions in stress and delamination driving forces within that region. An empirical equation is established using multiple regression analyses to evaluate the delamination driving forces. Accordingly, the importance of the influential factors on the delamination is ranked, and design maps are constructed to facilitate the development of durable coatings.

Stability analysis of hybrid laminated cylindrical shells reinforced with shape memory fibers

Laminated composite structures are widely used in various industries. Body and cape of high-speed flight vehicles are exposed to aerodynamic heating so that causes thermal buckling and dynamic instability. Shape memory alloys (SMAs) have extraordinary mechanical and physical properties which made them suitable for application in laminated structures. In this paper, stability analysis of hybrid laminated cylindrical shells reinforced with SMA fibers is investigated. Utilizing the principle of virtual displacement, governing equations and associated boundary conditions are determined based on the first-order shear deformation theory of shells considering Von- Kármán form of geometrical non-linearity and Love's first approximation. Material properties of SMA fibers and composite vary due to temperature. Variation of thermo-mechanical properties for SMA fibers due to uniform change of temperature are determined through the one-dimensional form of Brinson's constitutive law. Also, different types of loading conditions consist of axial load, pure lateral pressure and hydrostatic pressure are considered. Eventually, the effect of material properties, boundary supports and temperature on the critical buckling axial load, pure lateral pressure and hydrostatic pressure of the laminated cylindrical shells are studied. Investigations indicate that volume fraction and pre-strain of SMA fibers have significant effect on the stability of the laminated cylindrical shells.

Simplified method for estimating restraint moment induced by vertical temperature gradient in continuous prestressed concrete bridges and verification using AASHTO BDS

Diurnal and seasonal temperature variations cause uniform temperature changes, vertical temperature gradients, and horizontal temperature gradients. Vertical temperature gradients occur when the bridge deck absorbs heat due to solar radiation more than the bottom parts of bridge girders. Consequently, the vertical temperature gradient causes redistribution of bearing reactions, and induces additional flexural stresses in continuous spans. Estimating the vertical temperature gradient effect on continuous concrete bridges requires knowledge of thermal analysis of statically indeterminate structures or advanced three-dimensional (3 D) finite element (FE) analysis. Therefore, this article focuses on developing a simplified analysis method for estimating vertical temperature variations effects on continuous prestressed concrete bridge girders, which is required for bridge design. Restraint moments induced by vertical temperature gradients are investigated using 3 D FE analysis. A total of 115 bridges with different configurations (number of spans, girder spacing, and girder type) were analyzed to estimate the positive thermal moments at support locations. Results from these analyses were then used to develop simplified equations for estimating the positive restraint moments due to vertical temperature gradients from AASHTO LRFD Bridge Design Specifications (BDS). The developed equations are validated using John James Audubon Bridge #2 field data, and for other AASHTO LRFD temperature zones.

On the curvature and internal stresses in a multilayer strip due to uniform heating, electric field, or hydration

An appealing matrix algorithm for calculating the curvature and internal stresses in isotropic multilayer strips subjected to a uniform temperature change is presented. An explicit representation of the effective stiffness matrix is constructed for any number of layers, which is of central importance in the development of the algorithm. Detailed results are given for bi-, tri-, quadra-, quinta-, and septalayers. Closed-form expressions are deduced for multilayer strips with equal thicknesses and equal elastic moduli of all layers. The algorithm is extended to piezoelectric multilayers subjected to an electric field, and hygromorph multilayers subjected to a uniform change of relative moisture. The presented analysis complements an alternative and more general analysis within the well-known anisotropic lamination theory.

ДОСЛІДЖЕННЯ ТЕМПЕРАТУРНОЇ ПОХИБКИ ДАТЧИКА АКСЕЛЕРОМЕТРА ДЛЯ ВИМІРЮВАННЯ ПАРАМЕТРІВ ВІДКОЧУВАННЯ СТВОЛА

The paper describes a methodical approach to building a mathematical model of the temperature error of an accelerometer based on a liquid sensor for measuring barrel recoil parameters. The effect of a uniform temperature change over the volume of the sensitive element is considered. Mathematical models of temperature error are presented in the form of expressions for evaluating changes in the informative parameters of the sensitive element. It is shown that with certain combinations of design parameters of the sensitive element, there is an effect of partial compensation of changes in the contact areas of the gas component with the upper and lower ends of the rotor cavity. Quantitative assessment of temperature error for cases of using traditional structural materials and liquids was carried out. The impact of uneven heating of the sensitive element due to point sources of heat generation, which leads to the appearance of a temperature gradient for its arbitrary intersection, is considered. Expressions for evaluating the change in the informative parameters of the sensitive element in the presence of a temperature gradient have been obtained. A quantitative assessment of the temperature error due to the temperature gradient of the use of traditional structural materials and liquids was carried out. Constructive methods of limiting the effect of temperature error based on thermostating and thermal insulation of the accelerometer sensor are proposed. The condition for choosing the ratio between the design parameters of the sensitive element, which provides a significant reduction in the influence of the temperature error, has been obtained. The method of stabilizing the temperature of the sensitive element, which is based on its simultaneous thermostating and thermal insulation, is substantiated. The requirements for the parameters of the temperature control system of the sensitive element are given.

Anisotropic imperfect interface in elastic particulate composite with initial stress

The model of an anisotropic interface in an elastic particulate composite with initial stress is developed as the first-order approximation of a transversely isotropic interphase between an isotropic matrix and spherical particles. The model involves eight independent parameters with a clear physical meaning and conventional dimensionality. This ensures its applicability at various length scales and flexibility in modeling the interfaces, characterized by the initial stress and discontinuity of the displacement and stress fields. The relevance of this model to the theory of material interfaces and its applicability in nanomechanics is discussed. The proposed imperfect interface model is incorporated in the unit cell model of a spherical particle composite with thermal stress owing to uniform temperature change. The rigorous solution to the model boundary value problem is obtained using the multipole expansion method. The reported accurate numerical data confirm the correctness of the developed theory, provide an estimate of its accuracy and applicability limits in the multiparticle environment, and reveal significant effects of the interphase or interface anisotropy and initial stress on the local fields and overall thermoelastic properties of the composite.

Guided wave propagation of porous functionally graded plates: The effect of thermal loadings

Because there is no literature on the effect of thermal loadings on guided wave propagation in FG plates, the present paper is to fill the gap. In the present paper, the wave propagation analysis of porous FG plates with clamped ends in thermal environments based on first order shear deformation theory are presented. The plates are exposed to various types of thermal loading including uniform and non-uniform temperature changes, the material properties of FG plates are temperature- and porosity-dependent. Using the Galerkin method, we obtain the dispersion relation of thermoelastic waves in porous functionally graded plates. Compared with the previous results, the correctness of the present work is verified. In the end, the effects of the temperature changes, porosity as well as power law index on the phase velocity and group velocity of the guided wave are investigated.

Numerical modelling of spoolable thermoplastic composite pipe (TCP) under combined bending and thermal load

ABSTRACT Spoolable thermoplastic composite pipe (TCP) consisting of fibre-reinforced laminate with inner and outer liners is an ideal candidate to replace steel counterparts in deepwater. In this paper, a 3D finite element (FE) model is developed to analyse stresses in TCP under combined bending and uniform temperature change illustrative of spooling in different environments. Thermal load causes deviation from the stress symmetry expected at the top/bottom of the pipe in simple bending. Maximum stress, Tsai–Hill and Hashin failure responses are analysed for [±55]4, [±42.5]4, [±30]4 and [(±55)2/(±30)2] laminates at low and high temperatures. The [±42.5]4 configuration displays superior spooling capacity as layers orientated at ±55° and ±30° exhibit high utilisation of relatively weak transverse tensile and fibre compressive strengths, respectively. The failure criteria are in closest agreement at the top of the pipe (under axial tension) but differ more significantly at the bottom (axial compression).

Nonlinear buckling analysis of stiffened FG-GRC laminated cylindrical shells subjected to axial compressive load in thermal environment

The main aim of this paper is to investigate the postbuckling and buckling of functionally graded graphene-reinforced composite (FG-GRC) laminated cylindrical shells strengthened by stiffeners under axial compression with the uniform temperature change effect. The stiffener design option for FG-GRC cylindrical shells under axial compression is presented and a suitably smeared stiffener technique for GRC laminated stiffener system is developed. Basing on the von Kármán Donnell shell theory, the Galerkin’s procedure, and the three-term solution of deflection, the explicit forms of critical buckling and expression of load-deflection postbuckling curves relation are obtained. Effects of the GRC laminated stiffeners, the environment temperature, the graphene-reinforced parameters on the compressed buckling behavior are validated.

Size effect on the bandgap change of quantum dots: Thermomechanical deformation

The size effect on the optoelectronic behavior of semiconductor crystals has attracted great interest for the applications of semiconductor nanocrystals in photonics, bioimaging, energy harvesting etc. In this work, we study the size effect on the bandgap change of spherical semiconductor nanocrystals under concurrent action of mechanical pressure and uniform temperature change and incorporate the theory of surface elasticity in the analysis. Using Taylor series expansion to the first order of approximation, we obtain an analytical relationship between the bandgap change of the spherical semiconductor nanocrystal, the volumetric strain, the maximum shear strain and the temperature change. The thermal expansion due to the temperature increase causes the decrease of bandgap. The effect of surface energy/elasticity on the bandgap change exhibits similar size dependence to the effect of the Coulomb interaction, and the effect of the volumetric strain on the bandgap change is equivalent to the pressure (hydrostatic stress) effect.

Multi-Objective Optimization of Functionally Graded Beams Using a Genetic Algorithm with Non-Dominated Sorting

A mixed layer-wise (LW) higher-order shear deformation theory (HSDT) is developed for the thermal buckling analysis of simply-supported, functionally graded (FG) beams subjected to a uniform temperature change. The material properties of the FG beam are assumed to be dependent on the thickness and temperature variables, and the effective material properties are estimated using either the rule of mixtures or the Mori–Tanaka scheme. The results shown in the numerical examples indicate the mixed LW HSDT solutions for critical temperature change parameters are in excellent agreement with the accurate solutions available in the literature. A multi-objective optimization of FG beams is presented to maximize the critical temperature change parameters and to minimize their total mass using a non-dominated sorting-based genetic algorithm. Some specific forms for the volume fractions of the constituents of the FG beam are assumed in advance, such as the one- and three-parameter power-law functions. The former is used in the thermal buckling analysis of the FG beams for comparison purposes, and the latter is used in their optimal design.

Effective stiffness and thermal expansion of three-phase multifunctional polymer electrolyte coated carbon fibre composite materials

Multifunctional composites including polymer electrolyte coated carbon fibres and polymer matrix systems gained recent interest in light-weight design related research areas. Compared to classical fibre reinforced plastics, the interphase, made by electropolymerisation on the fibre surface, represents a new, third material phase. The coating serves as ion-conducting separator in structural batteries and as insulating layer in energy transmitting multifunctional composites. The importance of this study is related to the fact, that multifunctional applications, based on such composites, are exposed to temperature changes in many cases. The coating material, acting as thin interphase, shows a significant temperature dependant Young’s modulus, determining the overall macroscopic behaviour under thermal loads. The new influences on the effective elastic properties of the composite are determined in this work in a 3D microstructural simulation approach based on a unit cell geometry. For the first time, the resulting effective properties are discussed towards the state of research and future work. First, the effective elastic stiffness is computed by isothermal virtual material testing, applying unit strain modes on the unit cell. Second, a uniform temperature change is applied and the effective thermal expansion coefficients are computed. The results show that a change of stiffness in the coating domain has a great influence on the effective stiffness in the transversal isotropic plane. The effective thermal expansion of the composite is also highly sensitive to the thermal expansion behaviour of the coating phase. Main conclusions are drawn towards multiphysical material simulation: Influences of the coating material properties have to be taken into account to compute effective properties. In particular, it is necessary to include the temperature dependant stiffness and the coefficients of thermal expansion of the interphase, which affect effective properties significantly. A thermo-mechanic coupled microscale model is needed to represent in-situ properties of such composites for applications with heat exposure.

Decomposing the Drivers of Polar Amplification with a Single-Column Model

AbstractThe precise mechanisms driving Arctic amplification are still under debate. Previous attribution methods compute the vertically uniform temperature change required to balance the top-of-atmosphere energy imbalance caused by each forcing and feedback, with any departures from vertically uniform warming collected into the lapse-rate feedback. We propose an alternative attribution method using a single-column model that accounts for the forcing dependence of high-latitude lapse-rate changes. We examine this method in an idealized general circulation model (GCM), finding that, even though the column-integrated carbon dioxide (CO2) forcing and water vapor feedback are stronger in the tropics, they contribute to polar-amplified surface warming as they produce bottom-heavy warming in high latitudes. A separation of atmospheric temperature changes into local and remote contributors shows that, in the absence of polar surface forcing (e.g., sea ice retreat), changes in energy transport are primarily responsible for the polar-amplified pattern of warming. The addition of surface forcing substantially increases polar surface warming and reduces the contribution of atmospheric dry static energy transport to the warming. This physically based attribution method can be applied to comprehensive GCMs to provide a clearer view of the mechanisms behind Arctic amplification.

Effects of temperature changes on voided slab integral abutment bridge

Integral Abutment Bridges (IABs) are joint-less bridges whereby the deck is monolithic with the abutment walls. IABs are outperforming their non-integral counterparts in economy and safety. Thermal effects introduce significantly complex and nonlinear soil-structure interaction into the response of abutment walls and piles of the IB. This paper carried out comprehensive study on voided slab system with five spans bridge each span is 17m long. The bridge has been modelled using SAP software. The abutments and pile foundations are modeled taking into consideration the soil-structure interaction. The study covered a design uniform temperature change of (10, 20, 30, 40 and 50) °C. To gain a better understanding of the mechanism of load transfer due to thermal actions, a 3D frame anal¬ysis is carried out on the above mentioned IABs. The results showed wide range of different linear and lightly non-linear relationships between temperature range, deformations and moments. The paper highlighted the serious effect of the deformations resulting from the repeated temperature change which causes drop in soil or bombing at the abutments ~ embankment contact zone.

Site-Specific Extreme Load Estimation of a Long-Span Cable-Stayed Bridge

To provide benefit for design, rating, evaluation and management of signature bridges, site-specific extreme wind speeds, structural temperatures, and traffic load effects of a long-span cable-stayed bridge were estimated using relatively long-term structural health monitoring (SHM) data and compared with respective design values in this paper. The generalized Pareto distribution was adopted and briefly introduced to predict the extreme values in consideration of its advantage in making full use of limited measurement data available. The configuration and characteristics of the 3rd Nanjing Yangtze River Bridge and its SHM system were then presented. The extreme wind speed at the deck level and the four extreme temperatures of the bridge were estimated and compared with the corresponding design values. After a brief introduction to the simulation of traffic load effects, five extreme traffic load effects were finally estimated and compared with the design ones. The comparative results showed that the site-specific extreme wind speed, uniform girder temperature change, and five traffic load effects are all lower than the respective design values. The site-specific extreme vertical and transverse girder temperature differences and the site-specific extreme tower temperature difference were, however, larger than the respective design values.

Buckling treatment of piezoelectric functionally graded graphene platelets micro plates

Micro-electro-mechanical systems (MEMS) are widely employed in sensors, biomedical devices, optic sectors, and micro-accelerometers. New reinforcement materials such as carbon nanotubes as well as graphene platelets provide stiffer structures with controllable mechanical specifications by changing the graphene platelet features. This paper deals with buckling analyses of functionally graded graphene platelets micro plates with two piezoelectric layers subjected to external applied voltage. Governing equations are based on Kirchhoff plate theory assumptions beside the modified couple stress theory to incorporate the micro scale influences. A uniform temperature change and external electric field are regarded along the micro plate thickness. Moreover, an external in-plane mechanical load is uniformly distributed along the micro plate edges. The Hamilton's principle is employed to extract the governing equations. The material properties of each composite layer reinforced with graphene platelets of the considered micro plate are evaluated by the Halpin–Tsai micromechanical model. The governing equations are solved by the Navier's approach for the case of simply-supported boundary condition. The effects of the external applied voltage, the material length scale parameter, the thickness of the piezoelectric layers, the side, the length and the weight fraction of the graphene platelets as well as the graphene platelets distribution pattern on the critical buckling temperature change and on the critical buckling in-plane load are investigated. The outcomes illustrate the reduction of the thermal buckling strength independent of the graphene platelets distribution pattern while meanwhile the mechanical buckling strength is promoted. Furthermore, a negative voltage, -50 Volt, strengthens the micro plate stability against the thermal buckling occurrence about 9% while a positive voltage, 50 Volt, decreases the critical buckling load about 9% independent of the graphene platelet distribution pattern.

A comprehensively overall track-bridge interaction study on multi-span simply supported beam bridges with longitudinal continuous ballastless slab track

Track-bridge interaction has become an essential part in the design of bridges and rails in terms of modern railways. As a unique ballastless slab track, the longitudinal continuous slab track (LCST) or referred to as the China railway track system Type-II (CRTS II) slab track, demonstrates a complex force mechanism. Therefore, a comprehensive track-bridge interaction study between multi-span simply supported beam bridges and the LCST is presented in this work. In specific, we have developed an integrated finite element model to investigate the overall interaction effects of the LCST-bridge system subjected to the actions of temperature changes, traffic loads, and braking forces. In that place, the deformation patterns of the track and bridge, and the distributions of longitudinal forces and the interfacial shear stress are studied. Our results show that the additional rail stress has been reduced under various loads and the rail's deformation has become much smoother after the transition of the two continuous structural layers of the LCST. However, the influence of the temperature difference of bridges is significant and cannot be ignored as this action can bend the bridge like the traffic load. The uniform temperature change causes the tensile stress of the concrete track structure and further induce cracks in them. Additionally, the influences of the friction coefficient of the sliding layer and the interfacial bond characteristics on the LCST's performance are discussed. The systematic study presented in this work may have some potential impacts on the understanding of the overall mechanical behavior of the LCSTbridge system.

Wave propagation analysis of porous functionally graded curved beams in the thermal environment

In the present paper, wave propagation behavior of porous temperature-dependent functionally graded curved beams within the thermal environment is analyzed for the first time. A recently-developed method is utilized which considers the reciprocal effect of mass density and Young's modulus in order to explore the influence of porosity. Three different types of temperature variation (uniform temperature change (UTC), linear temperature change (LTC), sinusoidal temperature change (STC)) are employed to study the effect of various thermal loads. Euler-Bernoulli beam theory, also known as classic beam theory is implemented in order to derive kinetic and kinematic relations, and then Hamilton's principle is used to obtain governing equations of porous functionally graded curved beams. The obtained governing equations are analytically solved. Eventually, the influences of various parameters such as wave number, porosity coefficient, various types of temperature change and power index are covered and indicated in a set of illustrations.