Thermal Actions Research Articles

Influence of mechanical and thermal actions on domain structure and magnetostriction of iron-based soft magnetic alloys

Certain mechanical and thermal actions are considered as sources of stresses in ferromagnetic materials, which generate 90-degree magnetic domains, thus increasing saturation magnetostriction. It is established that the value of internal residual stresses in crystallites (grains) depends significantly on the difference between the thermal expansion coefficients of phases generated upon thermal processing of ferromagnetic materials and the surrounding matrix.

Thermal Kinetic Analysis of Tert-butyl Peroxybenzoate under Dynamic and Adiabatic Conditions

This study demonstrates the thermal actions of tert-butyl peroxybenzoate (TBPB) which is widely used in the plastic and rubber industries. The thermodynamic and kinetic analysis were performed on the basis of dynamic and adiabatic calorimetric applications which had been accepted as good assistants for investigating materials’ thermal decomposition. In essence, TBPB is reactive and exothermically unstable. Differential scanning calorimetry (DSC) and accelerating rate calorimeter (ARC) were employed to supply basic data and safety index. Experiments were taken under different scanning rates as well as various sample mass. The temperature and pressure curves of TBPB during decomposition were recorded. Based on the significant parameters calculated, self-accelerating decomposition temperature (SADT) of TBPB worked out was 50°C.

On thermal stress and fatigue life evaluation in work rolls of hot rolling mill

The paper proposes an approach for thermal stress evaluation and fatigue life assessment of work rolls in hot rolling mills. Temperature and thermal stress distributions are calculated with a simplified finite element approach, based on a plane model of work roll loaded on its boundary by rotating thermal actions for a typical hot rolling configuration. A transient of one hour is simulated and the calculated temperature field is next applied as thermal loading in elastic–plastic mechanical simulation, to get thermal stresses and elastic–plastic strains in work roll. Calculated cyclic stresses and strains are finally used to estimate work roll service life, based on Universal Slopes equation that is modified to account for the multiaxial stress state. A comparison of results by three multiaxial fatigue criteria is provided. The obtained results show that, according to such multiaxial criteria, stress multiaxiality would have a great effect on fatigue life, despite it is generally neglected in approaches usually adopted in literature.

Fe2O3/TiO2 Tube-like Nanostructures: Synthesis, Structural Transformation and the Enhanced Sensing Properties

The paper describes for the first time the successful synthesis of Fe(2)O(3)/TiO(2) tube-like nanostructures, in which TiO(2) shell is of quasi-single crystalline characteristic and its thickness can be controlled through adjusting the added amount of aqueous Ti(SO(4))(2) solution. The characterization of samples obtained at different stages using transmission electron microscope indicates that the outer TiO(2) shell is changed gradually from amorphous and polycrystalline phase into quasi-single crystal under thermal actions through the Ostwald ripening process, accompanying the corrosion of the central parts of Fe(2)O(3) nanorods, and the formation of small particles separating each other, leading to the special core/shell nanorods. Furthermore, Fe(2)O(3)/TiO(2) tube-like nanostructures can be transformed into Fe(2)TiO(5) nanostructures after they are thermally treated at higher temperatures. Those nanostructures exhibit enhanced ethanol sensing properties with respect to the monocomponent. Our results imply that not only hollow nanostructures, but also a novel type of nanostructures can be fabricated by the present method for nanodevices.

Structural and phase transformations in high-nitrogen austenitic steel 05Kh20AG10N3MF during thermal action

The structural and phase transformations in high-nitrogen austenitic steel 05Kh20AG10N3MF under various thermal actions are studied. The transformations are shown to occur only in the Fe-Cr diffusion couple, and they resemble the phase transformations in an Fe-20% Cr binary alloy. At 1200°C, hightemperature phase separation is detected; at 550°C or below, low-temperature separation is detected; and at 700 and 800°C, ordering with the formation of a Laves phase is observed. The ordering-low-temperature separation phase transition in the steel differs substantially from that occurring in Fe-Cr binary alloys.

A Monolithic Solution Procedure for a Thermal fluid-Structure Interaction System of Thermal Shock

This paper is concerned with the modelling of the interaction of thermal fluid flow with thermoelastic solid structure. Research is preformed on dynamic stress characteristic of thermal shock which is produced by the mechanical and thermal actions in thermal fluid-structure interaction system.The thermal viscous flow is modelled with velocity-pressure finite elements with the Boussinesq approximation. An arbitrary Lagrangian-Eulerian (ALE) strategy is employed for the motion of the fluid domain. An efficient data transfer strategy based on instrinsic coordinates and finite element interpolation of the interface variables is employed to guarantee kinematic consistency and equilibrium of the stresses and heat along the interface. The resulting strongly coupled set of non-linear equations for fluid,structure,heat and coupling conditions is formulated in a single equation system and solved by a monolithic solution procedure.

Experimental and numerical studies on the behaviour of concrete sandwich panels

ABSTRACT Precast concrete panels are often used for the façades of modern warehouses and commercial malls. During the last two decades, they have generally been made of two concrete layers with interposed thermal insulating polystyrene boards. Traditionally, perimeter concrete ribs allow the weight of the external concrete layer to be transferred to the internal thus causing unavoidable thermal bridges which reduce the energy performance of the building. In the sandwich cladding panel, the two concrete layers can be linked by low-conductivity shear connectors crossing through the insulation layer, thus ensuring the overall thermal efficiency of the building. In this paper, the results of a wide numerical study on the behaviour of concrete sandwich panels realized with glass fibre-composite pultruded connectors are presented, focusing on the stresses and deformations caused by dead load, thermal actions and shrinkage.

Thermal conditions and stress-strain state in the grain-matrix system of diamond tools

Numerical modeling of stationary and nonstationary fields of temperatures, strains and stresses in the diamond-matrix system is carried out. It is shown that the stress-strain state in the system greatly depends on thermal actions and the highest stress intensity in the system is in a transition layer between the grain and the matrix. We analyze the influence of physical properties of the matrix and transition layer, grain depth in the matrix, and the coefficient of heat transfer to environment on the temperature field and stress state in the system.

Study on Structures and Properties of CaSO<sub>4</sub> Whiskers/PVC Composites

Structures of CaSO4 whisker(A) and CaSO4 whisker(B) were characterized by IR and XRD, and the morphologies were observed by optical microscope. The results showed that the modified CaSO4 whisker(B) has perfect crystal structure, high crystallinity and less defects. Mechanical properties and static thermal stability time(190 °C) of two composites which were prepared by CaSO4 whisker(A) / PVC and CaSO4 whisker(B) / PVC were tested separately, and the degradation processes were analyzed by TG at 50 °C-400°C, N2 atmosphere, and the dispersing states of two whiskers in the composites were observed by means of optical microscope and SEM. The research results showed that the tensile strength and elongation at break increased over 3 MPa and 40% separately, and the static thermal stability time was over 90 min of CaSO4 whisker(B) / PVC, the initial degradation time was delayed comparing with CaCO3 / PVC composite. The consistency and interfacial configuration between whisker and PVC resin were perfect, and the toughness and thermal stability of the composite was improved after CaSO4 whisker was modified. The research results indicated that modified CaSO4 whisker has better toughness and thermal stability actions for PVC.

A micromechanical model to describe thermal fatigue and bowing of marble

Marble slabs are frequently used as façade panels to externally cover buildings. In some cases a bowing of such façade panels after a certain time of environmental exposure is experienced. The bowing is generally accompanied by a reduction of strength which increases with increasing degree of bowing. In the present paper, a theoretical model to calculate the progressive bowing and the thermal fatigue of marble slabs submitted to temperature cycles is presented. The model, developed within the framework of fracture mechanics, takes into account the mechanical microstructural characteristics of the marble as well as the actual cyclic temperature field in the material. The slabs are subjected to a thermal gradient along their thickness (due to different values of temperature between the outer and inner sides of the slab) as well as to thermal fluctuation on the two sides of the slab due to daily and seasonal temperature excursions. This thermal action causes a stress field which can locally determine microcracks due to decohesion of calcite grains. Stress intensification near the cracks occurs and leads to crack propagation in the slab. Such crack propagation under thermal actions is evaluated and the corresponding deflection (bowing) is calculated. Some examples are presented which show the strong influence of material microstructure on the degree of bowing.

Time-dependent analysis of cable trusses -Part II. Simulation-based reliability assessment

One of the possible alternatives of simulation-based time-dependent reliability assessment of pre-stressed biconcave and biconvex cable trusses, the Monte Carlo method, is applied in this paper. The influence of an excessive deflection of cable truss (caused by creep of cables and rheologic changes) on its time-dependent serviceability is investigated. Attention is given to the definition of the basic random variables and their statistical functions (basic, mutually dependent random variables such as the pre-stressing forces of the bottom and top cable, structural geometry, the Young's modulus of elasticity of the cables, and the independent variables, such as permanent load, wind, snow and thermal actions). Then, the determination of the response of the cable truss to the loading effects, and the definition of the limiting values considering serviceability of the structure are performed. The potential of the method, using direct Monte Carlo technique for simulation-based time-dependent reliability assessment as a powerful tool, is emphasized. Results obtained by the First order reliability method (FORM) are compared with those obtained by the Monte Carlo simulation technique.

Comparison of the dynamics of grid structures under thermal and radiation actions on amorphous Co-Ni-P alloys

The dynamics of the grid structures of Co-Ni-P alloys is investigated via transmission electron microscopy under thermal action and irradiation by γ quanta. Statistical processing of the electron-microscopic images of grid structures makes it possible to construct the empirical functions of size distribution of grid cells in the presence of different types of actions. Analysis of empirical distribution functions and their moments has been performed to study the statistics of distribution functions corresponding to different stages of structural relaxation during thermal and radiation actions and to classify structural relaxation processes. The presence of correlative interaction between structure components has been found in the initial state of an amorphous alloy; the type of correlation has been determined. The correlation behavior is analyzed under irradiation by γ quanta and thermal action. It has been revealed that grid cells exhibit different correlative interactions determined by the type of action.

Modelling of Climatic Thermal Actions in Hollow Concrete Box Cross-Sections

The temperature distribution in concrete structures varies as a result of fluctuations in solar radiation, air temperature, wind speed and long-wave radiation. Variations in temperature may cause longitudinal and transverse movements. If these movements are restrained, stresses and strains can be induced, which may contribute to cracking in the structure. To predict such thermal actions in a hollow concrete section, a finite element (FE) model was developed. Hourly resolution of climatic input data was used in the FE model to capture the daily temperature variations in the structure. The FE model was validated against temperature measurements performed in the hollow concrete arch of the New Svinesund Bridge located at the border between Sweden and Norway. To be able to use the developed model for future studies of other structures, an iterative method to consider the inside cavity air was also developed. The results of the simulations show that the model can capture the daily temperature variations. In addition, the proposed model shows acceptable agreement with the measurements from the bridge, and the calculated linear temperature differences for the bridge show good agreement with the design values in the Eurocode. The model is well suited for predicting temperature distributions and can be used for further studies of bridges, including those with box cross-sections, as well as for other concrete structures.

Correlation between the sudden and regular releases of coal-bed methane and the structures of the organic matter of natural coals

A correlation between the structure of the organic matter of coal and the ability of coal to release gases upon thermal and mechanical actions was considered. It was found that coal-bed methane released in different modes (regular and sudden) during coal-bed mining is of mechanochemical rather than sorption nature. Relationships were proposed to determine the natural methane content of coals and the sorption capacity of coals from a metamorphic series for methane using a structure-chemical parameter: the concentration of paramagnetic centers calculated from a broad line of the EPR signal. The use of spectroscopic techniques provides an opportunity to considerably simplify and make cheaper a very labor intensive technology for the determination of natural gas content. The regulations of methane safety in coal mines should be corrected based on the original concepts of the nature of coal-bed methane.

Numerical procedure for residual stresses prediction in friction stir welding

The prediction of residual stresses is a relevant and, under many points of view, still open issue for a proper welding process design. In the present paper a 3D FE model, with general validity for different joint configurations, was used to simulate the Friction Stir Welding (FSW) process of butt joints through a single block approach. The model is able to predict the residual stresses by considering thermal actions only, thanks to a new time efficient approach. A good agreement between calculated and experimentally measured data was found; the effectiveness of the presented numerical procedure was evaluated by comparing the calculation times of the proposed method with the ones of already known FE approaches.

Experimental and numerical studies on the behaviour of concrete sandwich panels

ABSTRACT Precast concrete panels are often used for the façades of modern warehouses and commercial malls. During the last two decades, they have generally been made of two concrete layers with interposed thermal insulating polystyrene boards. Traditionally, perimeter concrete ribs allow the weight of the external concrete layer to be transferred to the internal thus causing unavoidable thermal bridges which reduce the energy performance of the building. In the sandwich cladding panel, the two concrete layers can be linked by low-conductivity shear connectors crossing through the insulation layer, thus ensuring the overall thermal efficiency of the building. In this paper, the results of a wide numerical study on the behaviour of concrete sandwich panels realized with glass fibre-composite pultruded connectors are presented, focusing on the stresses and deformations caused by dead load, thermal actions and shrinkage.

Thermal effective action for1+1dimensional massive QED

In continuation of our earlier proposal for evaluating thermal effective actions, we determine the exact fermion propagator in 1+1 dimensional massive QED. This propagator is used to derive the finite temperature effective action of the theory which generates systematically all the one loop Feynman amplitudes calculated in thermal perturbation theory. Various aspects of the effective action including its imaginary part are discussed.

Mechanical Behavior of Structural Concrete Made with Recycled Aggregates from Tunnel Excavation

The results of an experimental study concerning the behavior of concretes made with recycled aggregates under repeated mechanical and thermal actions are presented. A comparison with the performances achieved by similar concretes made with traditional aggregates in the same working conditions eventually made it possible to estimate the actual quality and durability of the recycled concretes examined and identify possible limitations in their use. The laboratory protocol here adopted is suggested as a practical experimental procedure to test hardened concretes and pre-qualify their performances with respect to compressive actions and thermal solicitations.

Distress Investigation and Retrofit of a Pyramid-Shaped RC Building for Thermal and Seismic Effects

Seasonal variation of ambient temperature is rarely a cause of concern in structural design of normal buildings, but it has been found to cause recurring distress in a pyramid-shaped reinforced concrete (RC) building located in the foothills of the Himalayas. Abnormal stresses developed because of thermal movement of a large inclined roof exposed to direct sun and anchored to short columns at corners. Integral connection of a long corridor with the building compounds the effect of thermal movement of the building and corridor in opposite directions. A conventional linear analysis cannot correctly predict the observed distress. However, nonlinear analysis predicts the distress in close agreement with the observations. The building is situated in an area of high seismicity, and the inclined roof has a peculiar effect on the seismic response of the building, resulting in soft story phenomenon. Alternative retrofit schemes to safeguard the building against thermal and seismic actions are evaluated. It is observed that some of the retrofit strategies that are suitable for temperature effects may not be suitable for earthquake action.

On the unification of thermal perception and adaptive actions

Occupants exercise adaptive actions in response to discomforting environmental stimuli in an attempt to restore their comfort. These responses to adaptive actions are either ignored (conventional PMV models) or handled in an aggregated way (adaptive thermal comfort models). Furthermore the availability of adaptive actions and their effectiveness tends to be particular to a given building and climatic context. A good model should predict the probability with which available adaptive actions will be exercised and the feedback to occupants’ perceived comfort from these specific actions. In this paper we introduce a new modelling framework which does just that. Informed by results from detailed monitoring campaigns we first present a model to predict the probability distribution of thermal sensation in non air-conditioned buildings and a new method for deducing comfort zones in such buildings. We then introduce a methodology for combining recent advances in the prediction of occupants’ adaptive actions with the comfort feedback from these actions. We demonstrate how thermal sensation probability distribution may be deduced accounting for exercised adaptive actions and develop a comprehensive model for predicting comfort temperature which explicitly accounts for probable adaptive actions and their thermal feedback. We go on to describe how this modelling framework, which may be readily applied for thermal comfort prediction in specific building and climatic contexts, significantly deepens our understanding of adaptive thermal comfort mechanisms. Finally, we also describe ways of handling individuals’ diversity within this new framework as well as how it may be applied to evaluate visual and olfactory comfort.