Effect Of Thermal Loading Research Articles

In situ leading-edge-induced damages of melting and cracking W/Cu monoblocks as divertor target during long-term operations in EAST

The leading-edge-induced thermal loading effect due to assembly tolerance between neighboring castellated plasma-facing components is a critical issue in fusion devices. Actively cooled ITER-like W/Cu monoblocks were successfully installed for the upper divertor target in EAST which significantly increases the performance of the divertor power exhaust. The misalignment between neighboring monoblocks was formed inevitably during manufacturing and assembly processes, providing a possibility to demonstrate the leading-edge-induced thermal damage. Indeed, the leading-edge-induced melting phenomena of W/Cu monoblocks on upper divertor targets were observed using CCD a camera during plasma discharges with a large number of droplets ejected from the divertor target, which were also identified at the leading edges of W/Cu monoblocks. Not only that, but also many macro cracks with widths of ∼70 μm and depths of <5 mm along radial and toroidal directions were also found universally at the leading edges of W/Cu monoblocks by post-mortem inspection after plasma campaigns. Thermal–mechanical analysis by means of finite element simulation demonstrated that the maximum temperature could reach W melting point under the current projected heat load of ∼3 MW m−2 on flat top surface with large misalignment up to 3 mm at the leading edges. Meanwhile, the high temperature also induced high thermal stress and strain concentration at the center of leading edges, at which thermal fatigue cracking could be initially generated. Such type of cracks at leading edges on W/Cu monoblocks may be unavoidable due to long-term, pulsed fatigue effects. However, the influence of these cracks seems to be acceptable thanks to the limited propagated distance due to the self-castellation effect, which still needs long-term tracking. The in situ leading-edge-induced melting and cracking damage on W/Cu monoblocks of the EAST upper divertor target provides significant insight on understand the leading-edge-induced thermal effect in ITER and future fusion devices.

Long-term deformation analysis of prestressed concrete bridges under ambient thermal and vehicle loads

Few studies have focused on the combined effects of ambient thermal and vehicle loads on the long-term deformation of prestressed concrete bridges. Based on preliminary work, a method for establishing the equivalence of random ambient temperature loads is proposed here. With this method, the temperature distributions of bridges under random weather conditions can be obtained. Subsequently, a concrete creep model considering cyclic thermal and vehicle loads is established. Finally, an analysis method for establishing the long-term deformation of prestressed concrete bridges under ambient thermal and vehicle loads is proposed. This was applied to the example of a prestressed concrete bridge; the meteorological parameters around the bridge were collected, and the equivalent environmental thermal loads were obtained. It was found that higher temperatures made the coupled effect of thermal and vehicle loads more obvious, leading to faster deformation. The long-term deformation of a continuous beam was found to be related to the residual stress after sunshine. The long-term deformation can be affected by the temperature-distribution mode, but the random properties of weather have almost no notable effect. The temperature difference between the inner and outer surfaces of the web and the prestress loss are the main reasons for the cracking of the inner surface of the web.

Analysis of a hollow piezoelectric semiconductor composite cylinder under a thermal loading

Piezoelectric semiconductors (PSs) are the most promising building blocks for multifunctional electronic devices due to the polarization field resulting from piezoelectricity and pyroelectricity. In this article, we investigate the electromechanical coupling behaviors of a hollow PS composite (HPSC) cylinder under a uniform temperate change. The HPSC cylinder is consist of an outer thin PS layer and an inner elastic layer. Taking the interactions of thermoelasticity, piezoelectricity, and pyroelectricity into account, we develop one-dimensional equations for the HPSC cylinder with axisymmetric deformation, and present analytical solutions of the physical fields in the HPSC cylinder with perfect and imperfect interfaces for different boundary conditions. For the static equilibrium equation of the PS layer, the approximate relationship between the electric field and the average electric field is employed. The effects of geometrical parameters and imperfect interface, as well as the tuning effect of thermal loadings, on the multifield coupling responses and piezotronic effects of the HPSC cylinder are discussed in detail. The numerical results show that the physical fields are sensitive to the thermal loading, and the geometrical parameters, boundary conditions, and the interface bonding condition play an important role in the design of PS devices.

Thermo-hydro-mechanical behaviour of partially saturated fine-grained soils in the context of energy geostructures

The multi-physical phenomena, particularly water content and temperature variations, governing the behaviour of soils should be considered in the design and analysis of the energy geostructures. Soil temperature and water content variations impose a significant risk on the stability and serviceability of existing and future geostructures. Although potential failure modes, impacts at a system scale, and the response of saturated soils to thermal loads are previously discussed, interpretation of the thermo-hydro-mechanical behaviour of partially saturated soils in the context of energy geostructures is not thoroughly investigated. In this regard, this paper brings together the experimental data from several laboratory investigations to attain a comprehensive understanding of the partially saturated fine-grained soils response under thermo-hydro-mechanical loading, which plays a vital role in the analysis of the soil behaviour and energy geostructures in contact with them. In this paper, the effect of thermal loading in different matric suctions and hydraulic loading at different temperatures on soil preconsolidation stress, water content variation, thermal and hydraulic conductivities, and compression indexes are studied. Furthermore, soil thermal deformation is studied in detail for different overconsolidation ratios and matric suctions.

Profit based unit commitment problem solution using metaheuristic optimisation approach

Earlier power utilities had generated electrical power with the goal of minimising the costs and meeting both demand and reserves. Generation companies (GENCOs) schedule their generators under a new structure to maximise the profit. This paper provides a computational methodology based on monarch butterfly optimisation (MBO) to find a solution to the problem of profit-based unit commitment (PBUC), taking into account the power and reserve conditions. The proposed method allows GENCOs to determine how much power and reserve should be sold in the markets in order to achieve maximum profit. The binary variables of unit commitment problems are handled by modifying the continuous-time nature of the monarch butterfly algorithm. The computational approach maximises the profit but also handles the mixed constraints of the commitment problem. The effect of thermal turbine valve point loading is also taken into consideration. The computational technique has been used to solve two test systems in the absence and presence of steam turbine valve point loading effects. The results obtained are in agreement with the recent results available in the literature. Comparative analysis shows the effectiveness of the proposed MBO based solution methodology in terms of profit earned and execution time in relation to other techniques.

Fatigue damage evaluation of steel bridges considering thermal effect

With the change of external environmental factors, thermal loads are changing and causing fluctuating thermal stresses in critical fatigue details of steel bridges, which contribute to fatigue damage cumulation significantly. This paper proposed two fatigue evaluation methods considering the coupling effects of traffic load and thermal load: (1) Evaluation based on vehicular fatigue load model (VFLM) and thermal fatigue load model (TFLM). (2) Evaluation based on measurements of thermal load and traffic load. The analytical approach for obtaining the thermal fatigue load model was introduced, and the concept of the coupling stress model of ‘wave-surfer model’ was set up according to the mechanism of fatigue damage cumulation. Taking a steel box girder bridge as a case study, the collections of temperature data and traffic information were carried out. The two evaluation methods based on different load information were applied to two typical fatigue details, and the corresponding fatigue damage was calculated, which demonstrates that thermal effects should be taken into account for fatigue evaluation.

The Combining Effect of Inclination Angle, Aspect Ratio and Thermal Loading on the Dynamic Response of Clamped-Clamped Pipe Conveying Fluid

The investigation of the vibration of pipes containing flowing fluid is very essential to obtain an understanding of their dynamic behavior and prevent their catastrophic failure due to fatigue. Pipelines are subjected to environmental static and dynamic loading including self-weight, restoring, and Carioles forces. This research aims to investigate the vibrations of pipeline structures for examining their structural integrity under these conditions. A linear Euler-Bernoulli beam model is used to analyze the dynamic response of flexible, inclined, and fixed ends pipe conveying fluid made of polypropylene random-copolymer. Closed-form expression for dynamic response is presented by using combining of finite Fourier sine and Laplace transforms method. The influences of the inclination angle, thermal load, and aspect ratio (ratio of outside diameter to the length of pipe) on the dynamical behavior of the pipe–fluid system are studied. The obtained results attest to the importance of considering combining effects of the inclination angle, thermal load, and aspect ratio in analyzing and designing pipe conveying fluid. It is observed that the dynamic deflection can be significantly increased by increasing temperature, aspect ratio, and fluid velocity, while it reduced by increasing the inclination angle with the horizontal axis in the range of (0-90).

Analysis of the Coupling Effect of Thermal and Traffic Loads on Cement Concrete Pavement with Voids Repaired with Polymer Grout

Under the repeated action of traffic and thermal loads, a cement concrete pavement slab may partially lose contact with its base course, and voids may develop underneath the slab. Such distress will greatly impact the pavement performance. To fill the voids and restore the base support to the slab, the technology of polymer grouting has been increasingly adopted in recent years due to its advantages of quick application and high efficiency. There is, however, a lack of research on the mechanistic responses and performance of such a repaired rigid pavement under coupled influences of thermal and traffic loads. Existing literature has mainly focused on normal cement concrete pavement structures (i.e., without polymer grouted voids). This study intends to fill the research gap by investigating the time-domain characteristics of thermal stress response of a cement concrete pavement with underlying voids filled with polymer grout, along with design traffic loads. The finite element method was adopted with a 3-dimensional nonlinear temperature field within the pavement. A program module was developed in the Abaqus FEA software environment for temperature effect analysis. It was found that under the coupling action of thermal and traffic loads, thermal stress had a greater influence on the critical slab stress at the slab corner than those at other slab locations. Through the comparative analysis before and after polymer grouting repair, the critical tensile stress at the slab corner under the vehicle and thermal loads can be effectively reduced. The polymer performance is stable after three years.

A layer-wise formulation for transient response of composite sandwich panel in the exposure of thermal shock loading by considering novel linear and torsional elastic foundation

In order to present practical ways to decline the adverse effects of thermal shock loading from the perspective of improving structural design, authors of this study put their main focus on the analysis of transient coupled poro-thermo-elastic behavior of the sandwich cylindrical panel under multi-directional initially stresses with functionally graded carbon nanotube reinforced (FG-CNTRC) face-layers and polymeric core resting on novel elastic foundation. With the aid of compatibility conditions, the sandwich structure with three layers are modeled. To guarantee the accuracy of the calculations, authors define the governing equations of the system within the context of the exact three-dimensional form of elasticity theory. Additionally, the Navier approach is employed as the analytical solution to find the response of the simply-supported structure in the content of shear stresses and transverse deflection. Dubner and Abate method is utilized to inverse the Laplace transform in order to determine the time history of the system. Convergence of the stress and deflections of the system with respect to passing time is examined and verified. The parametric study reveals that utilizing each of the CNT scattering patterns through the radial direction of the face-layers is useful for protecting specific proportion of the thickness against the applied thermal shock. Moreover, by tracking the effect of increasing the damper coefficient of the surrounding foundation on the different components of the stress, it is revealed that increasing this factor leads to increase of the transverse shear stress and decrease of the normal shear stress.

Estimation of crack growth on rails under the combined influence of thermo-mechanical loading due to the sliding of wheel

Development and growth of surface and subsurface cracks on rail profile is one of the major reasons for deterioration of rails near the halting zones. Rail tracks are subjected to combination of thermal loads during the sliding motion of the wheel while braking and structural load due to the weight of the vehicle. In this paper, an FEA model is been developed to study and analyze the effect of coupled thermo-mechanical load during braking on contact stress and contact area at the rail-wheel interface. Both elastic and elasto-plastic FEA models are used and compared with analytical Hertzian approach to accurately predict rail-wheel contact parameters. A synthetic loading spectrum is proposed to simulate the combination of thermal and thermo-mechanical loading cycles on the rail during braking of vehicle. The loading cycle is used to predict the growth of previously present flaws using Modified Paris Law and Generalized Frost-Dugdale approach. It has been found that elasto-plastic FEA is inclined to predict lesser contact stresses than the elastic FEA or Hertzian model. Furthermore, shape of the contact patch for elasto-plastic FEA is observed to be unsymmetrical in the rolling direction unlike the elliptical contact area in elastic FEA approach. Macro scale initial cracks having length more than 2 mm are also realized to grow faster than their smaller counterparts under the combined effect of thermal and mechanical loads.

Numerical analysis of mechanical damage on concrete under high temperatures

Abstract Concrete is a widespread material all over the world. Due to this material’s heterogeneity and structural complexity, predicting the behavior of concrete structures under extreme environmental conditions is a very challenging task. High temperatures lead to microstructural changes which affect the macrostructural performance. In this context, computational tools that allow the simulation of structures may assist the analysis, by reproducing varied situations of thermal and mechanical loading and boundary conditions. In order to contribute to this scenario, this study proposes a numerical methodology to simulate the thermomechanical behavior of concrete under temperature gradients, through inverse analyses and a user subroutine implemented in Abaqus software. Thermal loading effects were considered as loading data for a damage model. Experimental data available in the literature was adopted for adjustment and validation purposes. The preliminary results presented herein encourage further improvements so as to allow realistic simulations of such an important aspect of concrete’s behavior.

Nonlinear dynamic analysis of FG/SMA/FG sandwich cylindrical shells using HSDT and semi ANS functions

Nonlinear dynamic analysis of FG/SMA/FG sandwich shells on elastic foundations subjected to the thermomechanical loading is performed in this paper for the first time. The sandwich shells are made of a shape memory alloy (SMA) fiber-reinforced composite and functionally graded (FG) face sheets. Material properties of FGM shells are assumed to be temperature dependent and graded in the thickness direction according to the power-law distribution in terms of the volume fractions of the constituents. The modified Brinson phenomenological model is employed to determine the constitutive characteristics of SMA fibers. The governing equations are established using the higher-order shear deformation theory (HSDT) enriched by semi assumed natural strain (ANS) functions. The nonlinear equations of motion are solved by the Airy’s stress function, the Galerkin method and the fourth-order Runge–Kutta method. In numerical results, the effects of material properties, geometrical parameters, elastic foundations, imperfections and thermal loads on the nonlinear dynamic analysis of FG/SMA/FG hybrid shells are investigated.

Nonlinear buckling and postbuckling of spiral stiffened FG-GPLRC cylindrical shells subjected to torsional loads

The nonlinear buckling behavior of functionally graded graphene platelet reinforced composite (FG-GPLRC) cylindrical shells reinforced by ring, stringer and/or spiral FG-GPLRC stiffeners under torsional loads is studied by an analytical approach. The governing equations are based on the Donnell shell theory with geometrical nonlinearity of von Kármán-Donnell-type, combining the improvability of Lekhnitskii’s smeared stiffeners technique for spiral FG-GPLRC stiffeners. The effects of mechanical and thermal loads are considered in this paper. The number of spiral stiffeners, stiffener angle, and graphene volume fraction, are numerically investigated. A very large effect of spiral FG-GPLRC stiffeners on the nonlinear buckling behavior of shells in comparison with orthogonal FG-GPLRC stiffeners is approved in numerical results.

Nonlinear buckling and postbuckling of spiral stiffened FG-GPLRC cylindrical shells subjected to torsional loads

The nonlinear buckling behavior of functionally graded graphene platelet reinforced composite (FG-GPLRC) cylindrical shells reinforced by ring, stringer and/or spiral FG-GPLRC stiffeners under torsional loads is studied by an analytical approach. The governing equations are based on the Donnell shell theory with geometrical nonlinearity of von Kármán-Donnell-type, combining the improvability of Lekhnitskii’s smeared stiffeners technique for spiral FG-GPLRC stiffeners. The effects of mechanical and thermal loads are considered in this paper. The number of spiral stiffeners, stiffener angle, and graphene volume fraction, are numerically investigated. A very large effect of spiral FG-GPLRC stiffeners on the nonlinear buckling behavior of shells in comparison with orthogonal FG-GPLRC stiffeners is approved in numerical results.

Nonlinear buckling and postbuckling of spiral stiffened FG-GPLRC cylindrical shells subjected to torsional loads

The nonlinear buckling behavior of functionally graded graphene platelet reinforced composite (FG-GPLRC) cylindrical shells reinforced by ring, stringer and/or spiral FG-GPLRC stiffeners under torsional loads is studied by an analytical approach. The governing equations are based on the Donnell shell theory with geometrical nonlinearity of von Kármán-Donnell-type, combining the improvability of Lekhnitskii’s smeared stiffeners technique for spiral FG-GPLRC stiffeners. The effects of mechanical and thermal loads are considered in this paper. The number of spiral stiffeners, stiffener angle, and graphene volume fraction, are numerically investigated. A very large effect of spiral FG-GPLRC stiffeners on the nonlinear buckling behavior of shells in comparison with orthogonal FG-GPLRC stiffeners is approved in numerical results.

René 41 & waspaloy based comparative study for high pressure turbine blades used in turboshaft engines

This study aims to present the comparison between 2 different nickel-based superalloy materials, rené 41 and waspaloy through their application in designing a high-pressure (HP) turbine blade for a turboshaft engine. NACA 4-digit airfoil profile has been used to create the airfoil for the HP turbine blade. MATLAB software is used to create a graphical user interface for the selection of various parameters used to define the airfoil profile including the NACA airfoil number, angle of attack, number of grid points, grid type, trailing edge type, chord length, and the plot style. For this study, NACA 9618 airfoil is used to model a single HP turbine blade. Numerical flow analysis using vortex panel method (VPM) is carried out on the airfoil to obtain the flow characteristics. Further, several types of failure methodologies occurring in the turbine blades and standard industrial methods used to reduce failure cycles are discussed. Comparisons are carried out showing precipitation-hardened rené 41 exhibiting relatively larger Von-Mises stress values in comparison with age-hardened waspaloy at elevated temperature for thermo-mechanical loading in the blade structure. Steady-state simulation at 39,000 rpm yields maximum temperature values of 1056 °C and 1220 °C for rené 41 and waspaloy respectively, also yielding relatively close values for critical displacement at the shroud section of the blade. Analysis models are proposed to determine the effect of mechanical and thermal loads on the high-pressure turbine blade design.

Predicting the impact of formation protocols on battery lifetime immediately after manufacturing

Predicting the impact of formation protocols on battery lifetime immediately after manufacturing

Morphological and structural damage investigation of nanostructured molybdenum fuzzy surface after pulsed plasma bombardment

Steady high-flux helium (He) plasma with energy ranging from 50 eV to 90 eV is used to fabricate a fiber-form nanostructure called fuzz on a polycrystalline molybdenum (Mo) surface. Enhanced hydrogen (H) pulsed plasma in a wide power density range of 12 MW/m2–35 MW/m2 is subsequently used to bombard the fuzzy Mo, thereby simulating the damage of edge localized mode (ELM) to fuzz. The comparisons of surface morphologies, crystalline structures, and optical reflectivity between the original Mo and the Mo treated with various He+ energy and transient power densities are performed. With the increase of He ion energy, the Mo nano-fuzz evolved density is enlarged due to the decrease of filament diameter and optical reflectivity. The fuzz-enhanced He release should be the consequence of crystalline growth and the lattice shrinkage inside the Mo-irradiated layers (∼ 200 nm). The fuzz induced by lower energy experiences more severe melting damage and dust release under the condition of the identical transient H plasma-bombardment. The H and He are less likely to be trapped due to aggravated melting evidenced by the enhanced crystalline size and distinct lattice shrinkage. As the transient power density rises, the thermal effect is enhanced, thereby causing the fuzz melting loss to aggravate and finally to completely disappear when the power density exceeds 21 MW/m2. Irreversible grain expansion results in huge tensile stress, leading to the observable brittle cracking. The effects of transient thermal load and He ion energy play a crucial role in etching Mo fuzz during ELM transient events.

Effect of temperature variation on the plate-end debonding of FRP-strengthened beams: A theoretical study

Steel/concrete structures strengthened with externally bonded FRP plates may be subjected to significant temperature variations during their service time. Such temperature variation (i.e., thermal loading) may significantly influence the debonding mechanism in FRP-strengthened structures due to the thermal incompatibility between the FRP plate and the substrate as well as the temperature-induced bond degradation at the FRP-to-steel/concrete interface. However, limited information is available on the effect of temperature variation on the debonding failure in FRP-strengthened beams. This paper presents a new and closed-form solution to investigate the plate-end debonding failure of the FRP-strengthened beam subjected to combined thermal and mechanical (i.e., flexural) loading. A bilinear bond-slip model is used to describe the bond behavior of the FRP-to-substrate interface. The analytical solution is validated through comparisons with finite element analysis results regarding the distributions of the interfacial shear stresses, the interfacial slips and the axial stresses of the FRP plate. Given that a constant bond-slip relationship is adopted, it is observed that an increase in service temperature will lead to an increased interfacial slip at the plate end and consequently a reduced plate-end debonding load, and vice versa. Further parametric studies have indicated that the thermal loading effects become more significant when shorter and stiffer FRP plates are applied for strengthening.

Mullins Effect and Crack Growth in Natural Rubber Vulcanizates during Heat Aging and Cyclic Loading

The effect of thermal aging and cyclic loading on mechanical properties and development of cracks in natural rubber vulcanizates was studied. After aging at 70oC and 110oC vulcanizates were subjected to cyclic loading. At a certain number of loading cycles, the samples were conducted in a tension test. At the aging condition of 70oC, the static tensile properties of material stay almost unchanged even after 88 aged hours and 8000 loading cycles. On the contrary, the dynamic fatigue resistance of vulcanizates decreases with increasing aging time. These results are attributed to the post-curing and the development of microcracks that might be caused by Mullins effect: in the case of static loading, the strain-induced crystallization may prevent cracks growth, but in the case of cyclic loading the strain-induced crystallization does not occur, so cracks develop without hindrance. However, at 110oC both static properties and dynamic fatigue resistance of material reduced dramatically because at high temperature the heat degradation exceeds both post-curing and strain-induced crystallization. Crack formation and propagation were examined by a digital optical microscope in the progress of cyclic loading. Results showed that natural rubber vulcanizate filled with carbon black has the best crack growth resistance (CGR) while the addition of modified and unmodified silica reduces CGR of materials. Moreover, the vulcanizate with unmodified silica has the lowest CGR.