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This paper presents a methodology for the development of two creep models for the welds and the steel base material that are capable of predicting the thermal creep behavior of transverse welded lap joints. This methodology is based on the experimental program of the thermal creep effect on transverse welded lap joints conducted previously as a part of this research. The experimental results are in the form of creep curves and they are used to develop a Norton–Bailey power law creep equation for the welded lap joints. Then, two creep models for the welds and steel base material are proposed by introducing temperature-dependent scaling factors to the Norton–Bailey power law creep equation of the welded lap joints. Finite element (FE) simulations are then developed in ABAQUS to predict the thermal creep behavior of the welded lap joint using the two proposed creep models for the welds and the steel base material. The two creep models are calibrated by changing the power law creep constants in order to predict the experimental creep curves with reasonable accuracy. Another series of FE simulations is conducted using Fields and Fields creep model for the steel base material instead of the proposed one for comparison purposes. The weld and structural steel creep models are intended to support the development of modeling the creep behavior of large-scale welded connections for structural-fire engineering application.

Traditional structural optimization is mainly based on the assumption that the materials are elastic, which cannot represent real stress fields in structures. In this study, the genetic algorithm, big bang-big crunch algorithm, and hybrid big bang-big crunch algorithm were employed to optimize the design factors of ship lock heads during concrete construction. The optimization goal was to determine the minimum volume of concrete. The factors considered included the hydration heat, the early-stage creep, and the transient deformation under external loads. In the finite element analysis, three types of boundary conditions were considered. The whole construction process was simulated, and the maximum tensile and compressive stresses, the stability, and the overturning of the lock head were examined. Based on the finite element analysis, to reduce the consumption of memory, a set of implicit recursive equations were used to calculate the thermal creep stress. Thirty-four design variables were distinguished for optimization. A case study on the optimization of a ship lock head was used to demonstrate the optimization process. The optimization results showed that the hybrid big bang-big crunch algorithm was more effective, and some conclusions were derived.

The creep behavior of Ni–Cr–W alloy at 950 °C has been investigated by a novel creep testing system which is capable of in-situ measurement of strain. Tubular specimens were pressurized with argon gas for effective stresses up to 32 MPa. Experimental results show that the thermal fatigue reduces the creep life of the tubular specimens and with the introduction of thermal cycling fatigue the primary stage disappears and the creep rate higher than the pure thermal creep (without thermal fatigue). Also the creep behavior of Ni–Cr–W alloy doesn't consist in the secondary stage. A new creep equation has been derived and implemented into finite element method. The results from the finite element analyses are in good agreement with the creep experiment.

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 experimental temperature is 613.15~763.15 K, and the strain rate is 0.01~10 s−1. The hot compression creep test of the 6082-T6 aluminum alloy sample is carried out by Gleeble-3500 hot compression simulation compressor, and its creep behavior is studied by scanning electron microscope. The results show that the DRX crystal has an irregular shape and that content of the Mg phase, Si phase, and Mn phase in the crystal are the main factors to change the color of DRX crystal. Temperature and strain rate are important factors affecting dynamic recrystallization. Reducing temperature and increasing strain rate will weaken dynamic recrystallization, and DRX critical condition and peak stress (strain) will increase. The constitutive equation of hot creep of 6082 aluminum alloy was established by introducing the work hardening rate-rheological stress curve, and the relationship between DRX critical condition, peak stress (strain) and parameter Z during creep was explored. Based on the Av rami equation, the prediction equation of the DRX volume fraction is established. With the increase of strain, DRX volume fraction is characterized by slow increase, then rapid increase and then slowly increase. In the hot -forming extrusion process of 6082 aluminum alloy, according to the volume fraction prediction equation, the DRX can be reduced, and the internal structure of the material can be optimized by changing the extrusion conditions and particle size.

A mechanical model is developed to predict the time-independent (fast) and time-dependent (due to thermal creep) force-rotation characteristics of shear tab connections subjected to fire. The time-independent behavior of the connection is modeled using a group of springs that can predict the rotational stiffness and the strength of the connection when subjected to fire temperatures. A modified Burgers model is incorporated in the mechanical model to include the thermal creep effect. The modified Burgers model is composed of linear springs and viscous dashpots that can predict the time-dependent behavior of the shear tab connection before and after beam-column contact, and bolt bearing. The proposed model shows excellent agreement when compared with experimental results and finite element (FE) simulations. Furthermore, isochronous curves are developed to study explicitly the effect of different parameters, on the strength and rotational capacity of shear tab connections. The proposed model can be considered an important step toward the inclusion of thermal creep in fire design of shear tab connections.

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...

Correct assessment of the steel connection performance under fire requires including the time-dependent response of steel material in the structural analysis. Failure to do so might impose critical threats on the stability and integrity of steel structures. To this aim, the objective of this study is to investigate the effect of thermal creep on the behavior of shear endplate beam-column connections subjected to transient-state fire temperatures. First, finite element models of shear endplate assemblies are developed using ABAQUS and validated against experimental work available in the literature. Parametric studies are then carried out to study the effect of key geometrical, thermal, and material parameters on the overall response of the frame assembly in fire while explicitly including creep. This includes heating and cooling rates, initial cooling temperature, column size and height, load ratio, plate thickness, and steel grade. The results show that including thermal creep causes a reduction in the induced compressive forces and an increase in the mid-span beam deflection, for about six times higher in some cases, thus earlier development of beam catenary action. It is also concluded that lower heating and cooling rates result in larger beam tying forces on the shear end plate connections, which can reach values around ten times larger than when creep is neglected. This study shows that the current practice of neglecting creep in fire analyses, especially in slow heating, may underestimate the forces that are exerted on the shear endplate connections during fire and thus leads to unsafe structural design.

In recent years Super-alloys have gained popularity in all sectors due to its potentiality to withstand the High Temperature about 1800˚F(980˚C)without deformation. Whereas the high temperature applications of super-alloys are extensively improved in the components of aircraft, automotive, petroleum equipments and nuclear plant. Super-alloys have enormous characteristics of excellent mechanical strength, resistance to corrosion, resistance to thermal creep deformation and good surface stability. Machining of High temperature super alloys is extremely difficult in conventional machining due to its high hardness and tool wear rate. WEDM(Wire Electrical Discharge machining) is a specialized thermal machining technique. They are capable of accurately machining the components irrespective of their hardness and complex shapes. Moreover, many researchers work in the process of WEDM and there is a need of more Research contributions in High Temperature alloys. This paper reviews the machining of super-alloys in high temperature applications, Material Removal rate, Surface roughness, Summary of literature and indicating the future research works.

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.

Knowledge of elevated-temperature mechanical properties of structural steel is essential for accurate evaluation of structural behavior in a fire. As a result, various test procedures have ...

In this paper, the effect of temperature and out-of-plane dynamic moments on ratcheting behavior of pressurized elbows have been investigated. The combined hardening model (Chaboche kinematic hardening model with isotropic hardening rule) is used for the plastic analysis of materials. Piping elbow specimens had temperatures of 50, 100, 150 and 200 °C. By using of many tension–compression-stabilized tests of specimens under symmetric strain-controlled, constant parameters for materials are obtained. The results obtained by the FE method of specimens show that the deformations occurred mainly because of creep at high temperature and ratcheting strain by out-of-plane moments. Also, ratcheting rate increases by increasing moment bending and temperatures. Initial, strain accumulation rate is low, and it increases with the increasing temperatures, which express softening phenomenon due to thermal creep. The strain accumulation is highest along the hoop direction at flanks, similar to results from experimental data without considering temperature effects. The results show that the increase in ratcheting due to high temperature may lead to incontrollable damages to pipework structures. Of course, the prediction of strain accumulation is improved in the presence of isotropic hardening rule.

Creep is a common phenomenon for soft clays. The paper focuses on investigating the influence of temperature on the time-dependent stress-strain evolution. For this purpose, the temperature-dependent creep behavior for the soft clay has been investigated based on experimental observations. A thermally related equation is proposed to bridge the thermal creep coefficient with temperature. By incorporating the equation to a selected one-dimensional (1D) elastic viscoplastic (EVP) model, a thermal creep-based EVP model was developed which takes into account the influence of temperature on creep. Simulations of oedometer tests on reconstituted clay are made through coupled consolidation analysis. The bonding effect of the soil structure on compressive behavior for intact clay is studied. By incorporating the influence of the soil structure, the thermal creep EVP model is extended for intact clay. Experimental predictions for thermal creep oedometer tests are simulated at different temperatures and compared to that obtained from reconstituted clay. The results show that the influence of temperature on the creep behavior for intact clay is significant, and the model, this paper proposed, can successfully reproduce the thermal creep behavior of the soft clay under the 1D loading condition.

In the constructions of multilayer cylindrical shells in heat-and-power engineering the materials, exhibiting rheological properties, such as concrete, polymers or fiber glass are widely used. In this connection, the study of temperature stresses in polymers, the analysis of the influence of various factors on the processes course under consideration, is of great importance. The paper presents an analytical solution of the thermal creep problem in polymers using the Kelvin-Voigt model for a rigidly clamped rod for various cases of temperature loading. The analysis of these solutions is also made on the example of a specific material for certain laws with changing temperature loads.

Steel connections play a crucial role in maintaining the integrity and stability of steel building frames especially when exposed to fire temperatures. The behavior of flush endplate connections in fire is shown to be governed by tension bolt failure as bolts lose their strength and stiffness more rapidly at higher temperatures. As a result, the ability to predict the development of stresses in tension bolts of flush endplate connections at different stages of fire is of special importance. One of the factors influencing bolt stresses in fire is the thermal creep or time-dependent inelastic response of steel to elevated temperatures. Therefore, time- and temperature-dependent behavior of tension bolts of flush endplate connections in fire is the focus of this study. Stress-time histories in tension bolts are obtained by explicit consideration of thermal creep of steel in FE models of flush endplate connections at elevated temperatures. To better understand the effect of thermal creep on tension bolt behavior, the correlation between time-dependent rotational deformation of flush endplate connections and bolt stresses is also investigated. Further, the isochronous representation is utilized to study the rotational deformation and the tension bolt stresses under various applied moments ranging from 50% to 95% of the moment capacity and fire temperatures ranging from 450°C to 600°C with 25°C increment. Through such representation, it is indicated that the connection behavior is not only dependent on bolt strength degradation and applied moment, but also affected by the time duration of applied moments and temperatures. Also, with the inclusion of thermal creep of steel, the connection experiences higher rotation and excessive endplate deformation with stress relaxation leading to top tension bolt failure at earlier stages of fire. More specifically, for time exposure greater than or equal to 60 min, the failure temperature of the connection decreases from 600°C to around 550°C. Therefore, neglecting thermal creep of structural steel may result in an unsafe prediction of the overall response of flush endplate connections in fire.

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 dependence of dimensional changes occurring in the structural parts made of E-635 zirconium alloy on the metallurgical and operational factors as a result of thermal creep, radiation growth, and radiation creep was studied. Tests close to operating conditions showed high resistance to radiation growth and thermal and radiation creep of the structural parts of VVER-1000 fuel assemblies made of E-635 zirconium alloy. Parts with greater resistance to creep without irradiation also possess high resistance to creep in the presence of irradiation. However, in-reactor creep can be almost 10 times greater than creep with no irradiation.

12C18Cr10NiТi and 0.08C16Cr11Ni3Мo austenitic steels serve as structural materials for fuel assembly covers in the BN-350 fast reactor, as well as for the covers of transport packagings for transportation and storage of spent nuclear fuel (SNF). To predict failure of these elements, it is of paramount importance to know their mechanical properties at elevated temperatures after in-pile irradiation. We performed tensile and creep tests at room temperature (RT), 350 °C and 450 °C of irradiated samples cut from the higher half of fuel duct pipes of the BN-350 reactor. A non-monotonic temperature dependence of tensile strength, yield stress, and relative elongation was shown. Microstructural investigation revealed the origin of this dependence lies in the different distribution of carbides and is also associated with the formation of α'-phase.

The effects of transient creep strain of concrete on post-tensioned concrete slabs in fire were investigated by means of numerical modelling. Employing the commercial package Abaqus, three-dimensional non-linear finite-element (FE) models were established. The thermal creep strain of prestressing steel tendons was explicitly incorporated into the FE models. Three concrete constitutive models were considered – a basic model without considering transient creep strain, a transient model explicitly considering transient creep strain and the Eurocode 2 (EC2) model, implicitly considering transient creep strain taken from BS EN 1992-1-2. Through comparing the numerical results with those obtained from available tests in the literature, excellent agreement was achieved. Based on this, the basic model was verified at ambient temperature and both the EC2 model and the transient model were also verified in test fire scenarios. A main conclusion from this study is that transient creep strain should be considered either explicitly or implicitly in numerical modelling for its positive contribution to the fire resistance of slabs.

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical constitutive models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. To improve upon this approach, a microstructurally-based zirconium alloy mechanical deformation analysis capability is being developed within the United States Department of Energy Consortium for Advanced Simulation of Light Water Reactors (CASL). Specifically, the viscoplastic self-consistent (VPSC) polycrystal plasticity modeling approach, developed by Lebensohn and Tom [1], has been coupled with the BISON engineering scale fuel performance code to represent the mechanistic material processes controlling the deformation behavior of light water reactor (LWR) cladding. A critical component of VPSC is the representation of the crystallographic nature ( defect and dislocation movement) and orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. A future goal is for VPSC to obtain information on reaction rate kinetics from atomistic calculations to inform the defect and dislocation behavior models described in VPSC. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON and provides initial results utilizing the coupled functionality. (C) 2016 Elsevier Inc. All rights reserved.

The literature on the thermal creep of steels with nominal yield strengths greater than 700MPa is scarce. Conventionally, mathematical models simulating the thermal creep of steel are developed based on steady-state tests. Transient-state testing, however, replicates structural fire conditions more realistically, and consequently, yields more reliable results for the fire design of structures. Hence, in response to the existing knowledge gap, the thermal creep of Grade 1200 ultra-high strength steel (UHSS) is examined and modeled in this study using the transient-state testing approach. First, by performing transient-state tests at a 10°C/min heating rate, the stress-strain diagrams of the UHSS at elevated temperatures are obtained, in which thermal creep has been implicitly included. Thermal expansion, elastic modulus, and yield strength of the material are derived at temperatures up to 750°C and compared with the predictions given by three world-leading design codes of practice. Due to the distinct microstructure and chemical composition of the UHSS, a significant disparity is observed between the results obtained for the UHSS and specifications provided by the design codes for mild steel. Then, based on transient-state tests at the heating rates of 5 and 20°C/min, an analytical thermal creep model is developed for the UHSS. Exclusively tailored to the transient-state conditions such as real fires, the proposed creep model is capable of simulating tertiary creep, and hence, ideal for structural fire design applications. The model is validated against the experimental data obtained for the heating rate of 10°C/min, where the model predictions are found to be in very good agreement with experimental results. By the explicit inclusion of thermal creep using the creep model, it is then shown that under 5 and 20°C/min heating rates, the yield strength of the UHSS can experience a difference as great as 30% at fire temperatures; hence, the necessity of the explicit modeling of thermal creep for the safe and accurate fire design of UHSS components is concluded.

This paper aims to investigate the mechanical properties and thermal creep of Q355 cold-formed steel (CFS) through tests. The yield strength, ultimate strength, and elastic modulus of the steel at elevated temperatures were obtained through steady tensile tests. The thermal creep tests were conducted in the temperature range of 450 °C to 750 °C under four different stress ratios, and creep strain versus time curves were obtained. To assess the difference of creep behaviour between CFS and virgin steel, the test results were compared with that of the Q355 virgin steel sheet available in the literature. It was found that CFS was more susceptible to the thermal creep, and its creep strain rate was at least twice that of the virgin steel at the same condition. The test results were fitted into a creep model and incorporated into a numerical simulation to reproduce fire tests of the CFS columns conducted in transient-state temperature with different heating rates. The simulation results demonstrated that the models with considering of creep provided better predictions on fire behaviour of the column than those without accounting creep, and the creep could significantly reduce the fire-resistance of CFS columns.

The requested thermal efficiency for new buildings leads to use new materials. In recent years, many researchers have conducted studies on the phase change materials (PCM) concrete composite. Fire safety in buildings has become an important requirement and building materials should have good fire behaviour in order to be used in certain applications. However, there are not many studies on the fire behaviour of PCM concrete. Therefore, the main goal of this study is to develop a numerical multiscale approach to simulate the thermo-mechanical behaviour at high temperatures of concrete containing microencapsulated PCM. An investigation was also conducted on the effect of the thermo-mechanical properties of shell materials used to encapsulate the PCM. PCM have been taken into account explicitly in modelling by considering their size distribution in a representative elementary volume. The effective thermo-mechanical parameters of the cement paste and the concrete have been calculated by a numerical homogenization method. Coupled thermal and mechanical loads have then been applied to the concrete with 10% and 15% of PCM at high temperatures. The use of melamine formaldehyde, with a Young’s modulus of 4.5 GPa, and a particular curve of thermal expansion coefficient instead of polymethyl methacrylate (PMMA) as shell material, showed a better thermo-mechanical behaviour at high temperatures. The thermal deformation and the damage of the resultant PCM concrete were found to be acceptable for building use.

Currently the HCPB blanket concept is one of the four breeding blankets concepts under development for the European DEMO. This work reports on the results of an investigation of the thermal and structural performances of a new design of this blanket, proposed in 2015 by the KIT HCPB Team aimed at establishing a baseline design of the HCPB breeding blanket following the updated EU DEMO plant specifications. The thermal analyses have been reported in another paper, while the structural analyses are presented and discussed in this paper. A 3D slice model of the DEMO HCPB blanket has been set up to run thermo-mechanical analyses of the blanket under steady state and DEMO transient pulsed conditions. The analyses for the blanket have been assessed with respect to the structural design criteria and standards (mainly RCC-MR, completed by SDC-IC). The results identify some problematic regions in the design, concentrated in the connection regions of the cooling plates with the blanket back supporting structure. For monotonic damage modes, the blanket structure shows a global satisfying behavior in immediate plastic collapse and plastic instability damage modes, and thermal creep damage mode. While it fails to fulfill the criteria to prevent immediate plastic flow localization damage mode in some regions. Counter-actions to improve the design have been proposed and will be implemented in future design revisions. Considering the cyclic loadings, the FW shows a satisfying behavior against ratcheting and fatigue damage modes during plasma ramp-up and ramp-down phases.

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.

Generally, in the event of a fire, steel structures exhibit different characteristics in terms of mechanical property degradation, which is significantly affected by the manufacturing of the steel. Therefore, the mechanical properties of cold-drawn AISI 1018 steel (CDS 1018) at elevated temperatures under steady- and transient-state conditions were investigated. The thermal expansion of CDS 1018 is relatively less than the thermal expansion predicted using Eurocode and ASCE standards at temperatures ranging from 25 to 650 °C. Dynamic strain ageing (DSA) improves the mechanical strength of CDS 1018 at steady-state temperatures ranging from 400 to 500 °C. Under transient-state conditions, the mechanical strength of CDS 1018 is better than those of high-strength steel (HSS) and ultrahigh-strength steel (UHSS) grades in the temperature range of 500–600 °C. Application of the cold-drawing process to AISI 1018 steel provides thermal creep resistance at temperatures up to 600 °C. The current design standards from the Eurocode, ASCE and AISC cannot be adapted for the fire-resistant design of structural mild steel delivered by cold-drawing conditions. Therefore, the present experimental data series obtained from steady- and transient-state methods are applicable to predict the mechanical degradation of CDS 1018 for engineering applications in fire-safety design.

We numerically examine thermal effects on the skyrmion Hall angle for driven skyrmions interacting with quenched disorder. We identify a creep regime in which motion occurs via intermittent jumps between pinned and flowing states. Here the skyrmion Hall angle is zero since the skyrmions have time to relax into equilibrium positions in the pinning sites, eliminating the side-jump motion induced by the Magnus force. At higher drives we find a crossover to a viscous flow regime where the skyrmion Hall angle is finite and increases with increasing drive or temperature. Our results are in agreement with recent experiments which also show a regime of finite skyrmion velocity with zero skyrmion Hall angle crossing over to a viscous flow regime with a skyrmion Hall angle that increases with drive., Comment: 5 pages, 5 postscript figures

A systematic series of temperature-controlled oedometer tests on intact and remolded samples of sensitive clay from two depths has been performed. The focus is on studying the temperature e...

This paper summarizes results of a comprehensive computational study on the time-dependent or creep behavior of flush endplate beam-column connections subjected to elevated temperatures due...

The behaviour of prestressing steel tendons under fire and post-fire conditions is investigated numerically employing the ABAQUS package and its user-defined material subroutine UMAT which allows comprehensive constitutive relationships to be implemented. Based on an existing thermal creep model, a new set of parameters are proposed and calibrated against available test results in the literature. The proposed numerical model is versatile in predicting thermal creep, isothermal response and transient thermal relaxation of prestressing steel tendons. Moreover, parametric studies are conducted to investigate the effects of heating rate, heated length ratio, initial stress and various boundary conditions on the thermal relaxation of prestressing steel tendons. Besides, transient state analyses are carried out with constant heating rate and initial stress to investigate the rupture properties of prestressing steel tendons.

A composite material obtained via the diffusion welding of a multilayer sandwich of foils of highentropy (HE) FeCoNiMnCr alloy and foils of Al–Si alloy is studied. After pressure welding, diffusion layers of Me(Al, Si), Me2(Al, Si) and Me3(Al, Si) intermetallic compounds are generated instead of AlSi alloy. During welding, the external foils of HE alloy can also carbonize with the generation of carbide deposits based on chromium as the most carbide-forming element. Mechanical bend tests are performed in the range of 750–950°C, showing that the limit of proportionality of the obtained composite material up to 950°C remains steady in the range of ~665 ± 120 MPa, with a maximum strain of 920 ± 155 MPa. The results from prolonged thermal creep tests are presented. In terms of its high temperature properties, the resulting material can be compared to state-of-the-art alloys based on the Ti–Al family that have operating temperatures of up to 750–800°C. This level can be raised even higher, to 900–950°C.

It is known that the Boltzmann equation has close relation to the classical systems in fluid dynamics. However, it provides more information on the microscopic level so that some phenomena, like the thermal creep flow, can not be modeled by the classical systems of fluid dynamics, such as the Euler equations. The author gives an example to show this phenomenon rigorously in a special setting. This paper is completely based on the author’s recent work, jointly with Wang and Yang.

Microstructure plays an important role in strengthening of metallic materials. Various microstructures can be developed in titanium aluminide (TiAl) alloys, which can enable different combinations of properties for various extreme environments in advanced nuclear systems. In the present paper the mechanisms for microstructural strengthening and the effects of various microstructural features on thermal creep and radiation damage resistance of TiAl alloys are reviewed and compared. On the basis of the results, the evidence-based optimum microstructure for the best combination of thermal creep and radiation damage resistance of TiAl alloys is proposed. The heat treatment processes for manufacturing the optimal microstructure are also discussed.

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.

This paper describes the development and application of an efficient hybrid continuum-molecular approach for simulating non-isothermal, low-speed, internal rarefied gas flows, and its application to flows in Knudsen compressors. The method is an extension of the hybrid continuum-molecular approach presented by Patronis et al. (2013) [J. Comp. Phys., 255, pp. 558–571], which is based on the framework originally proposed by Borg et al. (2013) [J. Comp. Phys., 233, pp. 400–413] for the simulation of micro/nano flows of high aspect ratio. The extensions are: 1) the ability to simulate non-isothermal flows; 2) the ability to simulate low-speed flows by implementing a molecular description of the gas provided by the low-variance deviational simulation Monte Carlo (LVDSMC) method; and 3) the application to three-dimensional geometries. For the purposes of validation, the multiscale method is applied to rarefied gas flow through a periodic converging-diverging channel (driven by an external acceleration). For this flow problem it is computationally feasible to obtain a solution by the direct simulation Monte Carlo (DSMC) method for comparison: very close agreement is observed.\ud \ud The efficiency of the multiscale method, allows the investigation of alternative Knudsen-compressor channel configurations to be undertaken. We characterise the effectiveness of the single-stage Knudsen-compressor channel by the pressure drop that can be achieved between two connected reservoirs, for a given temperature difference. Our multiscale simulations indicate that the efficiency is surprisingly robust to modifications in streamwise variations of both temperature and cross-sectional geometry.

The stability behaviour of steel structures in fire is strongly affected by the decreasing stiffness during heating, the nonlinear elevated temperature stress-strain response and thermal creep effects. The paper gives an overview of studies on the fire behaviour of steel structures. A major focus of the paper is to summarize recent studies on the material, cross-sectional, member and global structure level performed in Switzerland in recent years. The results of the studies indicate that the use of force-based analytical models using uniform temperature-dependent effective yield strengths, as used for ambient temperature designs, are less suitable for fire design and distinct nonlinear material behaviour then deformation-based models which have been proposed for different stability phenomena. These models seem to accurately predict the fire behaviour of steel structures on all structural levels. Das Stabilitatsverhalten von Stahltragwerken im Brandfall wird entscheidend von der abnehmenden Steifigkeit wahrend der Erwarmung, dem nichtlinearen Spannungs-Dehnungsverhalten von Baustahl bei erhohten Temperaturen sowie den Hochtemperaturkriecheffekten beeinflusst. Die Veroffentlichung gibt einen Uberblick uber Untersuchungen zum Brandverhalten von Stahlkonstruktionen und fasst dabei insbesondere die Ergebnisse neuerer in der Schweiz durchgefuhrter Studien auf Material-, Querschnitts-, Bauteil- und Tragwerksebene zusammen. Die Ergebnisse zeigen, dass verformungsgrosenorientierte analytische Modelle das Brandverhalten von Stahlkonstruktionen zutreffend beschreiben konnen und fur ausgepragt nichtlineares Materialverhalten besser geeignet sind als konventionelle schnittgrosenorientierte Tragmodelle.

The thermal creep is one of the major factors causing the buckle of steel columns in the fire events. But, few related studies have been reported to evaluate the factors affecting the thermal creep of steel column experimentally or numerically. In this study a series of Fire-resistant steel columns with three different slenderness ratios under a sustained load are tested under a uniform temperature up to six hours in order to evaluate the creep upon three selected factors, temperature, applied load, and column slenderness. Based on experimental results, a proposed creep strain rate model is established as the function of a single parameter of the load ratio of temperature LR(T) to determine the buckling time of steel column due to creep. Furthermore it is found that the creep can be neglected when LR(T) is smaller than 0.77.

The performance of ЧС68-ИД steel pipe in reactors may be judged indirectly from its high long-term strength and low axial thermal creep in high-temperature tests. The operational characteristics of pipe in fuel assemblies are determined by their structural-phase state, which depends on the chemical composition and thermal treatment of the material. Pile performance depends on the heat treatment of the pipe and subsequent cold deformation.

In this study, we employed pressurized creep tubes to investigate the biaxial thermal creep behavior of Inconel 617 (alloy 617) and Haynes 230 (alloy 230). Both alloys are considered to be the primary candidate structural materials for very high-temperature reactors (VHTRs) due to their exceptional high-temperature mechanical properties. The current creep experiments were conducted at 900 °C for the effective stress range of 15–35 MPa. For both alloys, complete creep strain development with primary, secondary, and tertiary regimes was observed in all the studied conditions. Tertiary creep was found to be dominant over the entire creep lives of both alloys. With increasing applied creep stress, the fraction of the secondary creep regime decreases. The nucleation, diffusion, and coarsening of creep voids and carbides on grain boundaries were found to be the main reasons for the limited secondary regime and were also found to be the major causes of creep fracture. The creep curves computed using the adjusted creep equation of the form ε=Aσcosh−1(1+rt)+Pσntm agree well with the experimental results for both alloys at the temperatures of 850–950 °C.

In this study, the performance of a rarefied gas transport system which works by thermal induced flow was studied experimentally. The driving force of the pump system presented in this study is thermal creep flow around the edge of a small circular plate. The thermal induced flow is generated by irradiating the plates, which are colored black on one side and white on the other. The system was constructed by arranging a series of such plates in a glass pipe which was connected to two vessels and irradiated with an infrared lamp. It was observed that the ratio of pressures in the two vessels was about 96% when the temperature difference between the black and white surfaces of the plates was about 40 °C.