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Purpose The purpose of this study is to develop an analytical model that is capable of predicting the behavior of shear endplate beam-column assemblies when exposed to fire, taking into account the thermal creep effect. Design/methodology/approach An analytical model is developed and validated against finite element (FE) models previously validated against experimental tests in the literature. Major material and geometrical parameters are incorporated in the analysis to investigate their influence on the overall response of the shear endplate assembly in fire events. Findings The analytical model can predict the induced axial forces and deflections of the assembly. The results show that when creep effect is considered explicitly in the analysis, the beam undergoes excessive deformation. This deformation needs to be taken into account in the design. The results show the significance of thermal creep effect on the behavior of the shear endplate assembly as exposed to various fire scenarios. Research limitations/implications However, the user-defined constants of the creep equations cannot be applied to other connection types. These constants are limited to shear endplate connections having the material and geometrical parameters specified in this study. Originality/value The importance of the analytical model is that it provides a time-effective, simple and comprehensive technique that can be used as an alternative to the experimental tests and numerical methods. Also, it can be used to develop a design procedure that accounts for the transient thermal creep behavior of steel connections in real fire.

The study of fluid flow and heat transfer inside micromechanical systems is the focus of many researchers due to their importance in microchannels as small-scale devices. Reducing the size of chann...

Thermal creep effects on fluid flow and heat transfer in a microchannel gas flow at low velocities are studied numerically. The continuity and Navier–Stokes equations in vorticity–stream function form, coupled with the energy equation, are solved, considering the thermal creep effect due to the longitudinal temperature gradient along the channel wall in addition to the combined effects of viscous dissipation, pressure work, axial conduction, shear work, and nonequilibrium conditions at the gas–wall interface. The governing equations are also solved without thermal creep, and comparisons between the two solutions are presented to evaluate the thermal creep effect on the flow field in the slip flow regime at relatively low Reynolds numbers. The results presented show that the thermal creep effect on both velocity and temperature fields become more significant as the Reynolds number decreases. Thermal creep effect on the velocity field also extends a longer distance downstream the channel as the Reynolds number decreases, hence increasing the hydrodynamics entrance length. Thermal creep can cause high positive velocity gradients at the upper channel wall for gas heating and hence reverse the flow rotation in the fluid layers adjacent to the wall. Thermal creep also results in a higher gas temperature in the developing region and higher heat exchange between the fluid and the channel wall in the entrance region. Thermal creep effect on heat exchange between the gas and the channel wall becomes more significant as the Knudsen number decreases.

This study investigates the effect of thermal creep of steel on the behavior of shear tab beam-column connections due to fire temperatures. FE simulations are first developed under fast steady-state temperature conditions to study the behavior of the shear tab connections at different temperatures and validated against experimental data available in the literature. Parametric studies are performed to investigate the impact of major geometric parameters on the behavior of the shear tab connections during fire temperatures with and without creep effect. Then, creep effect is explicitly included in the FE models under steady-state temperature conditions to study the time-dependent deformations of shear tab connections when applied forces and temperatures are kept constant. Also, isochronous force-rotation curves are developed to better understand the time effect on the strength and rotational capacity. Results from the simulations and parametric studies show that the connection experiences additional rotation/displacement and a change in failure mode is observed when the effect of thermal creep is included in predicting the response of the shear tab connections. These results clearly indicate the importance of including creep in predicting the response of shear tab connections subjected to fire temperatures and its effect on the behavior.

The creep of concrete is significantly affected by ambient temperature and humidity. In design codes, the influence of ambient temperature and humidity on concrete creep is approximately considered by correction coefficient terms. However, this method is not suitable for creep analysis of specific structure under complex temperature and humidity environments. At present, the Microprestress-Solidification (MPS) theory is widely adopted to analyze the complex influence of temperature and humidity on concrete creep. However, the MPS theory still has some shortcomings (The MPS theory fails to reflect the size effect in drying creep. Besides, the humidity dependence of transient thermal creep cannot be correctly modeled.). On the basis of MPS theory, this paper makes some appropriate corrections and modifications: firstly, the evolution equation of micro-prestress S is reasonably updated by redefining the relationship between the long-term creep viscosity and micro-prestress S. Meanwhile, based on the thermodynamics, the influence of temperature and humidity variation on the evolution of micro-prestress S is reformulated and the transient thermal creep effect is modified to be humidity-dependent. In order to verify the improved MPS model, experiment data in literatures are adopted to make verifications. Results prove the correctness of the modifications and the practicability of the improved model.

In this work, a physics-based thermal creep model is developed based on the understanding of the microstructure in Fe-Cr alloys. This model is associated with a transition state theory-based framework that considers the distribution of internal stresses at sub-material point level. The thermally activated dislocation glide and climb mechanisms are coupled in the obstacle-bypass processes for both dislocation and precipitate-type barriers. A kinetic law is proposed to track the dislocation densities evolution in the subgrain interior and in the cell wall. The predicted results show that this model, embedded in the visco-plastic self-consistent framework, captures well the creep behaviors for primary and steady-state stages under various loading conditions. The roles of the mechanisms involved are also discussed.

We carried out two types of drop tower experiments to quantify gas and particle motion induced by temperature gradients inside a porous structure in a low pressure environment. In one setup 400 μm sized particles were traced inside heated channels at pressures of a few Pascal. Their motion is consistent with pure thermophoresis. In the second setup tracer particles were used to track the thermal creep gas flow through a porous dust bed. Here, the flow was traced outside of the dust bed and without thermophoretic motion. The results are consistent with a simple capillary model of the dust bed.

In a rarefied gas the temperature field and the gas motion are closely related, and the temperature field can cause, in a confined flow geometry, a steady flow without the help of external forces. This is due to the creep of the fluid along the walls induced by a wall temperature gradient, as a consequence of the molecular transfer of momentum to the wall. Experiments performed in microgravity conditions in two small cells, with mono- and bi-atomic carrier gases (Ar, N 2 ), and a thermal gradient between upper and bottom horizontal plates, allowed the measurement of the width of the thermal creep and the induced velocity of the gas near the vertical cell wall, due to thermal gradient. In addition, experiments demonstrated the existence of the thermal creep flow in the cells, even with Knudsen number as low as 10 −5 . The work evidences experimentally, and for the first time, the thermal creep flow in small cells, due to wall temperature gradient, with Knudsen number as low as 10 −5 . In view of these results, the no-slip boundary conditions of the Navier–Stokes law in the “continuum” regime can be inadequate in non-isothermal flow geometry and in microgravity conditions.

Modeling fuel behavior requires an accurate description of the cladding stress response for both operational and safety considerations. The transient creep response of Zirconium alloys is commonly modeled using a strain hardening rule which is known to hold in cases with monotonously increasing stresses. However, the strain hardening rule is experimentally known to fail in scenarios such as load drop or reversal. In this paper we derive a simple and easily implementable set of rules for primary creep based on experimental results which contradict the strain hardening rule. The primary creep predicted by these rules is compared with data from published thermal creep experiments and Halden in-pile creep experiment IFA-585. The model thus created is shown to perform well in describing both transient stress scenarios with monotonously increasing stress and scenarios involving load drops and reversals.

International audience; The objective of this research is to understand the behavior of concrete subjected to temperatures up to 180°C and to gas absolute pressures up to 5 bars applied during the two weeks envisioned in the “loss of coolant accident” (LOCA) scenario. Previous studies about delayed mechanical behavior of concrete have pointed out an increase of delayed strains with the temperature rise: the basic creep can be multiplied by a factor 10 at 80°C, and coupling between creep and heating can lead to damage and to transient thermal creep. These phenomena could be predominant if the LOCA induced conditions are maintained several days and more probably several weeks. So, a model able to predict the cracking and the gas leakages has to be developed. It has to consider these phenomena and their coupling with other possible causes of concrete damage previous to the LOCA. In fact, if the LOCA occurs on structure already damaged by early age cracking or endogenous chemical reactions, such as AAR or ettringite, the leakage risk could be increased. The paper will focus on some important aspects of these phenomena (creep rate dependency on temperature, scale effects at early age, damage induced by swelling reactions), and on their coupling in a finite element model.

This study examines how thermal creep affects the mixed convection in a long horizontal parallel-plate microchannel under a pressure drop and a temperature rise. The analytical solutions of the fully developed thermal-flow fields and the corresponding characteristics are derived based on the Maxwell boundary conditions with thermal creep and presented for the physical properties of air at the standard reference state. The calculated thermal-flow characteristics reveal that thermal creep has an appreciable effect on the velocity slip, flow rate, and heat transfer rate but a negligible effect on the flow drag. Such a creep effect could be further magnified by decreasing the pressure drop or increasing the Knudsen number.

This paper illustrates, by example, the incompleteness of the Navier–Stokes–Fourier (NSF) equations for the case of thermally compressible fluids, namely fluids possessing a nonzero coefficient of thermal expansion. The work is a follow-up to a recent publication that offered elementary arguments quantifying that incompleteness but did not provide an explicit physical example thereof. The present example was chosen strictly for the simplicity of the calculations required to bring it to fruition, rather than for its importance in applications. The example analyzes steady-state, one-dimensional (albeit nonunidirectional) heat conduction through a quiescent fluid bounded by concentric spheres maintained at different temperatures. This example is counterpart to the classic NSF case of steady-state, one-dimensional (but now unidirectional) heat conduction through a quiescent fluid bounded by flat plates maintained at different temperatures. The contrasting results obtained for the two cases illustrates effects arising from the proposed amendments to the traditional NSF equations. For the case of gases the amended results indicate the possibility of their differing significantly from classical results based on the NSF equations when the gas is rarefied. For liquids, however, physically realizable values of the relevant parameters governing the amended equations are such that no sensible deviations from classical NSF behavior are observed. The difference owes to the relative incompressibility of liquids compared with gases. The smallness of the effect for liquids is, however, noted to be atypical of the amended consequences arising in circumstances where the temperature varies along, rather than purely normal to solid surfaces, as in the present concentric-sphere example. In that case Maxwell thermal creep effects would create more profound effects than in the present example, whether for liquids or gases.

A thermal creep process is studied in quite wide rectangular micro channels, sufficiently wide so that it is possible to consider this configuration as two parallel plates. The inlet and outlet reservoirs are maintained at the same constant pressure. A constant temperature gradient exists along the walls of the channel joining the two tanks. Thus a gas flow is induced and thermally sustained until steady conditions are reached. A complete analytical solution is derived in slip regime, yielding all the flow parameters, for Knudsen numbers smaller than 0.25. The analytical results are in good agreement with the numerical “exact” solution of the continuum equation system. Furthermore our continuum approach data are compared to those deduced from approaches based on Boltzmann equation model treatments: these various methods lead generally to a satisfactory agreement between their respective mean parameters. Nevertheless significant differences appear on the transversal velocity profiles and are further discussed.

The Cercignani–Lampis scattering kernel of the gas–surface interaction is applied to numerical calculations of the Poiseuille flow and thermal creep through a long tube. The S model of the Boltzmann equation was numerically solved by the discrete velocity method. The calculations have been carried out in the wide ranges of the rarefaction parameter and of the accommodation coefficients. Comparing the present results with experimental data the values of the accommodation coefficients have been calculated.

An analytical variation of the discrete ordinates method is used to establish a concise and accurate solution to the plane Poiseuille and thermal creep problems based on the S-model kinetic equations. The results are of high accuracy and include the flow rates and the heat fluxes of both problems for a wide range of Knudsen numbers and various values of the accommodation coefficient at the boundaries.

The slip phenomena in gas mixtures are of fundamental significance in the specification of boundary conditions for flows in the slip regime. In a recent paper, new explicit results for the slip coefficients appropriate to binary gas mixtures were reported. The present work being reported extends the previous work to a higher level of accuracy by involving a higher order Chapman-Enskog expansion. In particular, new expressions for the slip coefficients are presented which are applicable for arbitrary models of the intermolecular interaction. Limiting expressions for the slip coefficients are given (for a simple gas) and the accuracy of the theory is discussed. Numerical calculations of the slip coefficients for different binary gas mixtures using the first and second order Chapman-Enskog approximations and the rigid sphere and Lennard-Jones (12-6) potential models have been carried out. The thermal creep and diffusion slip coefficients are found to be sensitive to the order of the approximation and to the potential model used. A comparison of the new higher order results with some of our previously obtained experimental data for the thermal transpiration effect has also been carried out and shows excellent agreement between the theory and the experiments which confirms the accuracy of the theory.

In this article, a discrete effect in the thermal Lattice BGK two-speed model is studied. These effects are due to the non-equilibrium state in the particle distribution function, and the non-equilibrium occurs near walls. The mechanism of the LBM counterpart of the thermal creep flow, which appears due to the temperature gradient of the boundary in rarefied gases, is clarified analytically and numerical calculations are performed for some cases. A technique for eliminating this effect is also shown.

Uniaxial compression tests with monosized and binary beryllium pebble beds were performed in a temperature range between ambient temperature and 480 °C and pressures up to 8 MPa. Empirical correlations for the moduli of deformation are given for the different bed types and first measurements for thermal creep are presented. Stress-strain relations depend sensitively on the initial state of the bed and with this on the filling procedure. This is of special importance for binary beds where it must be ensured that a homogeneous distribution of small pebbles in the bed is obtained. First results for triaxial compression tests for monosized and binary beds are reported. The internal friction of these beds is significantly larger than that of beds with particles with smooth surfaces.

A version of the discrete-ordinates method is used to solve, for the case of flow in a cylindrical tube, the classical Poiseuille and thermal-creep problems based on the Bhatnagar, Gross, and Krook model in the theory of rarefied-gas dynamics. In addition to the development of a discrete-ordinates solution that is valid for a wide range of the Knudsen number, the solution is evaluated numerically for selected cases to yield results, thought to be correct to many significant figures, for the slip velocities, the macroscopic velocity profiles, and the flow rates.

The problem of a spherically symmetric stress state in a spherical fuel element with a cavity at the center for collecting gaseous fission products is examined. A system of equations, which are exact within the framework of the physical model, is derived for this case, a numerical method for solving this system is proposed, and the evolution of the strain in the cladding is studied for characteristic cases. The results of numerical estimates of the temporal development of strain in the cladding are presented. 2 figures. 10 references.

It is well known that in a gas-filled duct or channel along which a temperature gradient is applied, a thermal creep flow is created. Here we show that a mass and momentum flux can also be induced in a gas confined between two parallel structured surfaces at different temperatures, i.e. \textit{orthogonal} to the temperature gradient. We use both analytical and numerical methods to compute the resulting fluxes. The momentum flux assumes its maximum value in the free-molecular flow regime, the (normalized) mass flux in the transition flow regime. The discovered phenomena could find applications in novel methods for energy-conversion and thermal pumping of gases., 6 pages, 5 figures, updated fig.5, updated text for the numerical method

The new method of solving thermal creep problems, accounting for cyclic variations of external force and thermal fields was put forward. Asymptotic expansions and period averagings were used to derive the systems of basic and auxiliary equations. The equation of state for cyclic thermal creep was proposed and validated. Numerical simulation of the creep of cylinders under cyclic temperature variations was carried out.

We present numerical simulations of a new system of micro-pump based on the thermal creep effect described by the kinetic theory of gases. This device is made of a simple smooth and curved channel with a periodic temperature distribution. Using the Boltzmann-BGK model as the governing equation for the gas flow, we develop a numerical method based on a deterministic finite volume scheme, implicit in time, with an implicit treatment of the boundary conditions. This method is comparatively less sensitive to the slow flow velocity than the usual Direct Simulation Monte Carlo method in case of long devices, and turns out to be accurate enough to compute macroscopic quantities like the pressure field in the channel. Our simulations show the ability of the device to produce a one-way flow that has a pumping effect. AMS subject classifications: 76P05, 82B40, 82D05, 82C80, 65M06

This paper deals with an initial-boundary value problem for the discrete Boltzmann equation confined between two moving walls at different temperature. A model suitable for the quantitative analysis of the initial boundary value problem and the relative existence theorem are given.

A thermal creep process is studied in a wide rectangular micro channel considered as two infinite parallel plates. The inlet and outlet reservoirs are kept at the same constant pressure. A constant temperature gradient exists along the walls of the channel joining the two tanks. Thus a gas flow is induced and thermally sustained until steady conditions are reached. A complete steady analytical solution is derived in slip regime for Knudsen numbers smaller than 0.25. The analytical results are in good agreement with the numerical “exact” solution of the continuum equations system. Furthermore our continuum approach results are compared to those deduced from the approaches based on the Boltzmann equation model treatments: these various methods lead generally to a satisfactory agreement between their respective mean parameters. Nevertheless significant differences appear on the transversal velocity profiles in the close vicinity of the wall.Copyright © 2007 by ASME

Inelastic strain of the first wall in steady operation mode is estimated numerically up to 5years. It includes swelling, radiation creep in addition to thermal creep. Structural integrity of the first wall is estimated on the basis of ASME Code Case N-47. First wall may have lifetime more than 5years only if neutron radiation is less than 3M W/m2.

Thermal creep flow of rarefied gases in enclosures has been investigated numerically by employing Navier-Stokes (NS) and augmented Burnett equations as mathematical models. An explicit multistage time stepping scheme has been exploited to solve cell centred finite volume representations of the governing equations. We have investigated the momentum diffusion mechanism by comparing computed stress components of both models at each order and we conclude that the flow can be assumed, like a purely shear driven flow, diffusion dominated motion because of the linearly varying first order shear. The analyses show that the creep velocity could not be ignored in the continuum limit. We furthermore observed that as Kn number increases, the maximum creep velocity resulting from the Burnett model decreases in contrast to NS equations.

Thermal creep flow of a gas around a spherical particle of an arbitrary thermal conductivity suspended near a plate is analyzed, neglecting shear velocity slip. The thermal force acting on the particle at an arbitrary distance from the plate is given as a function of ratio of the thermal conductivity of the particle to that of the gas. Effects of the collector plate on the drift velocity of a precipitating particle are clarified.

A variational method based upon the linearized Boltzmann equation is employed to evaluate field-dependent thermal creep. The result compares reasonably well with recent experimental observations for CO.

The problem of gas slip at a plane wall is solved on the basis of a linearized kinetic equation with a model collisional term (the S-model, which provides the correct value of the Prandtl number). Expressions are obtained for the Poiseuille slip and thermal creep which contain integrals of the scattering kernel over the velocity half-space. These expressions are made concrete for three particular cases corresponding to well-known models of the scattering kernel.

Using a method which averages the system of moment equations over the channel section, the authors have obtained expressions for Poiseuille flow and thermal creep flow in a capillary at intermediate Knudsen numbers (Kn⩽0.25).

Synopsis In a previous paper it was shown that four strain components can be identified when concrete, stored in an environment with a varying temperature, is subjected to a sustained load. They are: (a) elastic strain; (b) delayed elastic strain; (c) transitional thermal creep; (d) flow. Each component is, in some sense, related to temperature, and the first part of this paper is devoted to the development of explicit functions for each of the components in terms of temperature and time. In particular, it is shown that all the time-dependent strains can be generated from a single curve in which flow is plotted against weighted maturity. The expressions are used in the second part of the paper to predict the strains in mortar tubes under torsional loading, when subjected to severe regimes of temperature change. The predictions show reasonable agreement with experimental results, and a simplified method of prediction, for use in practice, is also demonstrated.

In this paper, we present the results of analysis of data provided by SANDVIK Steel Research Center for the high temperature properties of HT-9. We develop design equations for use in inelastic structural mechanics applications, for the most important thermal creep parameters. Empirical correlations for creep rupture time and the complete description of elongation vs. time are presented. A phenomenological description of steady-state creep is also developed. It is found that dislocation creep can explain the measured data.

The stress redistribution brought about by differential thermal creep in non-uniformly heated concrete structures is considered. Theory is presented which permits stresses to be evaluated in both the transient creep phase and in the limiting steady-state condition, from direct procedures, when temperatures are either time-invariant or vary cyclically in time. Illustrative numerical examples are presented and these reflect the dominant behaviour of flexurally restrained sections as occur in the walls of concrete oil containment structures. They are used also, to highlight some of the influential parameters on the stresses, e.g. magnitude of temperature crossfall through wall, ratio of maximum to minimum temperatures, and the nature of the cyclic variations of temperature with time. It is concluded that creep, coupled with non-uniform temperature, causes significant time-dependent variations of the stresses to occur. The theory presented forms a useful means of making stress predictions for specified states of temperature and helps to assess the probability of possible cracking in sections which might otherwise be assumed to be ‘safe’ from a conventional elastic calculation. The analyses relate to prestressed sections where cracking does not dominate, and to stress levels in the ‘working’ range for which creep is linearly related to stress.

Creep processes, due to irradiation and thermal fields, have generally been assumed to relax stresses resulting from the loading of structural components. However, in order to determine failure modes and mechanisms, a global inelastic structural analysis is required. We have recently developed the STAIRE computer code to meet this need. This code is based on a modified beam theory for the self-consistent determination of stresses and deflections in beams of circular cross-section. The work is applied to the lifetime analysis of the M irror A dvanced R eactor S tudy (MARS) blanket modules. The objective of the present paper is to assess the global (3-dimensional) impact of both irradiation and thermal creep strains on the stresses resulting from thermal and swelling strains.

The simplified theory put forward in an earlier paper (***)‡ is extended and generalized to cover the case of the thermal creep buckling of prismatic two-member components such as reactor fuel elements, all phases of creep and elastic strains being considered. The tangent modulus approach is used and small deflections are assumed; it is shown that even with these assumptions a solution in closed form can be obtained only in the case of a single rod. Approximate methods of solution are then discussed, in which primary and secondary creep phases only are considered, but with certain simplifying assumptions. Throughout most of the analysis a modified form of Andrade's creep equation is used, namely ε = α t1/3+β t+γ t3, where α, β, and γ are functions of stress and temperature, ε and t are creep strain and time. Typical curves are presented, based on data for an aluminium alloy, illustrating the contribution to buckling deflection likely to be expected from primary creep, for the single rod.

This paper presents a theory of the thermomagnetic torque which is applicable at pressures so high that Knudsen effects can be neglected. Kinetic theory techniques are used to derive momentum and energy boundary conditions appropriate to transport in the presence of a magnetic field. It is found that thermal creep generated by the field‐induced annular flow of heat contributes substantially to the torque. Calculations based upon a combination of the kinetic theory of Levi, McCourt, and Beenakker and Senftleben—Beenakker experimental data are found to be in reasonable agreement with measurements of torque.

The effect of differential thermal creep of concrete is discussed in relation to the time-dependent stresses in a thick cylindrical prestressed concrete vessel subjected to a sustained radial temperature distribution and internal pressure. Two methods of analysis, capable of estimating these stresses are described and the solution to a worked example is included. It is concluded that slow heating of a vessel is desirable, if stresses are to be kept within reasonable limits, and that the long-term effect of creep is to give rise to undesirable reversals of stress on cooling. Using the rate of creep strain laws to calculate stress changes during the initial heating period and the steady-state stress theory for a long-term solution, it is possible to carry out a ‘safe’ design for a vessel structure without performing a complete historical analysis.

Various problems of non-linear collective transport through disordered media are discussed, using sliding charge density waves as a paradigm. These systems all exhibit features of nonlinear dynamics, statistical mechanics and critical phenomena.

The effect of velocity dependence of collision frequency on the flow profile in thermal creep sip problem is studied. A simple variable collision frequency model is used, and it is found that the flow profile is quite sensitive to the velocity dependence of the collision frequency.