Uniform Thermal Loading Research Articles

Making chemical & biological protective gloves vapour permeable reduces thermoregulatory strain better than making armour, respirator or overboots permeable

Wearing chemical and biological (CB) protective equipment causes thermoregulatory strain by restricting evaporative cooling. We identified [1] that a moisture vapour impermeable (MVIP) body armour liner (BAL) imposed a greater thermal burden than MVIP CB gloves (G), overboots (O) or respirator (R). The previous study progressively and cumulatively removed these MVIP items across 5 conditions when wearing a CB protective suit. This study is a repeat, except that items were removed in isolation and replaced for subsequent conditions to maintain a more uniform thermal load across comparisons. The aims of this study were to quantify the thermal burden imposed by each MVIP item whilst maintaining a high thermal load between conditions to identify the potential benefits if future equipment was made moisture vapour permeable (MVP). A second aim was to determine whether the previous experimental design [1] influenced the thermal burden imposed by each MVIP item. We hypothesised that removal of a MVIP item would reduce heat strain in this order BAL>G>R>O.

Thermal and thermomechanical postbuckling of FGM sandwich plates resting on elastic foundations with tangential edge constraints and temperature dependent properties

This paper investigates nonlinear bending and postbuckling behavior of functionally graded sandwich plates resting on elastic foundations and subjected to uniform external pressure, thermal loading and uniaxial compression in thermal environment. The material properties of both face sheets and core layer are assumed to be temperature-dependent, and effective material properties of FGM layers are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Formulations are based on first order shear deformation theory taking von Karman nonlinearity, initial geometrical imperfection, Pasternak type elastic foundations and tangential edge constraints into consideration. Approximate solutions are assumed and Galerkin procedure is applied to derive nonlinear relations of load and deflection. In thermal postbuckling analysis, an iteration algorithm is adopted to obtain buckling temperatures and postbuckling curves. The effects of material, geometry and foundation stiffness parameters, face sheet thickness to total thickness ratio, imperfection and degree of tangential restraint of edges on the nonlinear bending and postbuckling behavior of FGM sandwich plates are analyzed and discussed in detail.

Analyzing Thermal Stability of Circular Plates Made of FGM Bimorphs Considering The First–Order Shear Deformation Theory

In the present study the exact solution of thermal buckling of circular plates made of Functionally Graded Materials (FGMs) bimorphs under uniform thermal loading with regard to the first-order shear deformation theory and nonlinear asymmetrical Von Karman assumptions was provided under clamped and simply supported conditions. Properties of the FGM compared to the middle surface of the asymmetrical plate and in term of the power law changes in line with thickness. In a way that the middle surface of the circular plate is pure metal and the margins are made of pure ceramic. Using the energy method, asymmetrical equation of equilibrium was extracted and the stability equations were used by the adjacent equilibrium method and adjacent to determine the critical buckling temperature and a closed-form solution finally was achieved. The impact of different factors including rate of thickness variations to the plate radius, volume fraction index, variation of materials percentage and the impact of the Poisson’s ratio on the critical temperature were assessed. The results were compared with the classical theory and the existing research.

Thermo-elastic analysis of functionally graded circular plates resting on a gradient hybrid foundation

In this paper an attempt is made to investigate the thermo-elastic behavior of functionally graded (FG) circular plates embedded on gradient hybrid foundation and subjected to non-uniform asymmetric mechanical and uniform thermal loads. The supporting medium is modeled as the Horvath–Colasanti type foundation with variable coefficients in the radial and circumferential directions. The thermal environment is assumed to be uniform over the bottom and top surfaces of the plate and varies along the thickness direction only. The governing state equations are extracted in terms of displacements and temperature based on 3D theory of thermo-elasticity, and assuming the material properties of the plate except the Poisson’s ratio vary continuously throughout the thickness direction according to an exponential function. These equations are solved using a semi-analytical method and some numerical results are displayed to clarify the effects of material heterogeneity indices, foundation stiffness coefficients, foundation gradient indices, loads ratio and temperature difference between the upper and lower surfaces of the plate on displacement and stress fields. The results are reported for the first time and the new results can be used as a benchmark for researchers to validate their numerical and analytical methods in the future.

Effects of fixing point positions on thermal response of four point-supported glass façades

Different fixing forms of four point-supported glass façades are extensively used to satisfy the aesthetic requirement of modern buildings. While it may easily break and fall out when subjected to a fire, which could significantly affect compartment fire dynamics by creating a new opening for air to enter. In this work, sixteen cases with different fixing positions are designed to investigate the thermal response of four point-supported glass façades under both uniform and non-uniform thermal loadings. The Coulomb–Mohr criterion and stress intensity factors based mixed-mode criterion are employed to predict the crack initiation and growth, respectively. The glass stress distributions, breaking time and initiation and propagation of crack are presented, using three-dimensional finite element method. It is observed that all the cracks initiate at fixing points, which is attributed to the combination effect of constraining at supporting points and non-uniform temperature distribution. Fixing points changing in horizontal, vertical and diagonal directions has significant effects on glass breaking behavior. Moreover, thermal loading form also markedly affects the time of first crack initiations. The variation tendency of breaking time agrees well with our previous experimental study. It is intended that these results will provide some practical guidelines for fire safety engineers.

Axisymmetric thermo-magneto-electro-elastic field in a heterogeneous circular plate subjected to a uniform thermal load

This paper presents thermo-magneto-electro-elastic field in a heterogeneous circular plate subjected to thermal loadings uniformly distributed on the main boundaries. As a prior, the temperature distribution is determined by solving the heat conducting equation. Then, direct displacement method is employed to derive the coupling magneto-electro-elastic field analytically. Finally, numerical calculations are performed to validate the present analysis and to investigate the influence of the material heterogeneity, the multi-field coupling and the cylindrical conditions.

Energy release rates for a misfitted spherical inclusion under far-field mechanical and uniform thermal loads

A misfitted spherical inclusion embedded in an infinite matrix under far-field triaxial mechanical and uniform thermal loads is analyzed in three-dimensional linear elasticity. Closed-form expressions for each loading case have been obtained separately utilizing proper continuity and far-field loading conditions. The principle of superposition has been utilized to obtain the complete solution from these three individual solutions. The solutions are discussed in terms of stress distribution, magnitude and locations of stress concentrations. Closed-form expressions for energy release rates have been derived based on the stress and strain solutions by employing the path-independent integrals, J, L and M considering the inclusion as a defect. The measure of self-similar expansion energy release rate provided by the M-integral brings some interesting insight which can be applicable to many practical cases such as phase transformations in metals and nanoscale defects. The fundamental work presented here will help to better understand the behavior of materials with a misfitted inclusion subjected to various loading environments.

Three-Dimensional Thermo-Electro-Elastic Field in a Circular Plate of Functional Graded Materials with Transverse Isotropy

This article presents a set of axisymmetric solutions for a circular plate of functional graded materials with transverse isotropy subjected to uniform thermal loadings on the upper and lower surfaces. The temperature field in the plate is obtained as a prior, by integration. A direct displacement method is then employed to explicitly derive the thermo-electro-elastic field induced by the thermal loadings. Numerical calculations are carried out to validate the present results and to show the effect of material heterogeneity on the distributions of the coupled field. Some interesting phenomena have been observed.

Nonlinear thermal stability of geometrically imperfect shape memory alloy hybrid laminated composite plates

The instability of geometrically imperfect shape memory alloy (SMA) fibers reinforced with hybrid laminated composite (SMAHC) plates and subjected to a uniform thermal loading is analytically investigated. The material properties of the SMAHC plates are assumed to be functions of temperature. Nonlinear equations of the plates’ thermal stability are derived based on a higher order shear deformation theory incorporating von Karman geometrical nonlinearity via stationary potential energy. The structural recovery stress, which is generated by martensitic phase transformation of the prestrained SMA fibers, is calculated based on the one-dimensional thermodynamic constitutive model by Brinson. Adopting the Galerkin procedure, the governing nonlinear partial differential equations are converted into a set of nonlinear algebraic equations, in which systems of equations are solved by introducing an analytical approach. Closed-form formulations are presented to determine the load-deflection path and critical buckling temperature of the plate. Based on the developed closed-form solutions, ample numerical results are presented to provide an insight into the effects of the volume fraction, prestrain, location and orientation of the SMA fibers, composite plate geometry, geometrical imperfection and temperature dependence on the stability of the SMAHC plates. It is shown that a proper application of SMA fibers results in a considerable delay of the thermal bifurcation and controllable thermal post-buckling deflection of the SMAHC plate.

Coupled Nonlinear Finite-Element Analysis of Soil–Steel Pipe Structure Interaction

Numerical simulation of staged-construction modeling of large-diameter steel pressure pipes is accompanied by several complexities. Finite-element (FE) analysis was performed to simulate the behavior of buried steel pipes during staged-construction installation. The model deflections during the staged-construction process were verified with four different experimental soil box test results. The FE model and its associated analysis algorithm considered large deformation using total Lagrangian formulation. The material and contact nonlinear algorithms were also included in the analysis for both soil and steel pipe materials. The contact between each soil layer and soil-to-pipe was carefully implemented. Uniform thermal loading was applied to simulate the stresses induced by compaction forces on the pipe and trench walls. Finally, the vertical and lateral load-deformation plots obtained from the FE analysis results were compared with the full-scale experimental test results during the staged construction process and after the application of surcharge load. The results of FE analysis are shown to accurately model and simulate the test results.

Nonlinear analysis of thermally and electrically actuated functionally graded material microbeam

In this paper, we provide a unified and self-consistent treatment of a functionally graded material (FGM) microbeam with varying thermal conductivity subjected to non-uniform or uniform temperature field. Specifically, it is our objective to determine the effect of the microscopic size of the beam,the electrostatic gap, the temperature field and material property on the pull-in voltage of the microbeam under different boundary conditions. The non-uniform temperature field is obtained by integrating the steady-state heat conduction equation. The governing equations account for the microbeam size by introducing an internal material length-scale parameter that is based on the modified couple stress theory. Furthermore, it takes into account Casimir and van der Waals forces, and the associated electrostatic force with the first-order fringing field effects. The resulting nonlinear differential equations were converted to a coupled system of algebraic equations using the differential quadrature method. The outcome of our work shows the dramatic effect and dependence of the pull-in voltage of the FGM microbeam upon the temperature field, its gradient for a given boundary condition. Specifically, both uniform and non-uniform thermal loading can actuate the FGM microbeam even without an applied voltage. Our work also reveals that the non-uniform temperature field is more effective than the uniform temperature field in actuating a FGM cantilever-type microbeam. For the clamped-clamped case, care must be taken to account for the effective use of thermal loading in the design of microbeams. It is also observed that uniform thermal loading will lead to a reduction in the pull-in voltage of a FGM microbeam for all the three boundary conditions considered.

Optimized multi-floor throughflow micro heat exchangers

Multi-floor networks of straight-through counterflow liquid cooled microchannels have been investigated by performing conjugate heat transfer in a silicon substrate of size 15 × 15 × 1 mm. Two-floor and three-floor cooling configurations were analyzed with different numbers of microchannels on each floor, different diameters of the channels, and different clustering among the floors. Direction of microchannels on each floor changes by 90° from the previous floor. Direction of flow in each microchannel is opposite of the flow direction in its neighbor channels. Conjugate heat transfer analysis was performed by developing a software package which uses quasi-1D thermo-fluid analysis and a fully 3D steady heat conduction analysis. These two solvers are coupled through their common boundaries representing surfaces of the cooling microchannels. Using quasi-1D solver significantly decreases overall computing time and its results are in good agreement with 3D Navier–Stokes equations solver for these types of application. Multi-objective optimization with modeFRONTIER software was performed using response surface approximations and genetic algorithm. Maximizing total amount of heat removed, minimizing coolant pressure drop, minimizing maximum temperature on the hot surface, and minimizing non-uniformity of temperature on the hot surface were four simultaneous objectives of the optimization. Maximum number of cooling microchannels on each floor, diameter ranges of the microchannels on each floor, and vertical clustering range of the floors were the specified constraints. Pareto-optimal solutions demonstrate that thermal loads of 800 W cm−2 can be effectively managed with such multi-floor microchannel cooling networks. Two-floor microchannel configuration was also simulated with 1000 W cm−2 uniform thermal load and shown to be feasible.

Safety Identifying of Integral Abutment Bridges under Seismic and Thermal Loads

Integral abutment bridges (IABs) have many advantages over conventional bridges in terms of strength and maintenance cost. Due to the integrity of these structures uniform thermal and seismic loads are known important ones on the structure performance. Although all bridge design codes consider temperature and earthquake loads separately in their load combinations for conventional bridges, the thermal load is an “always on” load and, during the occurrence of an earthquake, these two important loads act on bridge simultaneously. Evaluating the safety level of IABs under combination of these loads becomes important. In this paper, the safety of IABs—designed by AASHTO LRFD bridge design code—under combination of thermal and seismic loads is studied. To fulfill this aim, first the target reliability indexes under seismic load have been calculated. Then, these analyses for the same bridge under combination of thermal and seismic loads have been repeated and the obtained reliability indexes are compared with target indexes. It is shown that, for an IAB designed by AASHTO LRFD, the indexes have been reduced under combined effects. So, the target level of safety during its design life is not provided and the code's load combination should be changed.

Nonlinear axisymmetric thermomechanical response of piezo-FGM shallow spherical shells

Thermomechanical instability of shallow spherical shells made of functionally graded material (FGM) and surface-bonded piezoelectric actuators is studied in this paper. The governing equations are based on the classical shell theory of shells and the Sanders nonlinear kinematics equations. It is assumed that the property of the FGMs varies continuously through the thickness of the shell according to a power law distribution of the volume fraction of the constituent materials. The constituent materials of the functionally graded shell are assumed to be mixture of ceramic and metal. The analytical solutions are obtained for uniform external pressure, thermal loading, and constant applied actuator voltage.

Nonlinear finite element analysis of laminated composite spherical shell vibration under uniform thermal loading

In this article, nonlinear free vibration behavior of laminated composite shallow shell under uniform temperature load is investigated. The mid-plane kinematics of the laminated shell is evaluated based on higher order shear deformation theory to count the out of plane shear stresses and strains accurately. The nonlinearity in geometry is taken in Green-Lagrange sense due to the thermal load. In addition to that, all the nonlinear higher order terms are taken in the mathematical model to capture the original flexure of laminated panel. A nonlinear finite element model is proposed to discretise the developed model and the governing equations are derived using Hamilton’s principle. The sets of governing equations are solved using a direct iterative method. In order to validate the model, the results are compared with the available published literature and the limitations of the existing models have been discussed. Finally, some numerical experimentation has been done using the developed nonlinear model for different parameters (thickness ratio, curvature ratio, modular ratio, support condition, lamination scheme, amplitude ratio and thermal expansion coefficient) and their effects on the responses are discussed in detail.

Pareto optimum design of laminated composite truncated circular conical shells

This paper deals with multiobjective optimization of symmetrically laminated composite truncated circular conical shells subjected to external uniform pressure load and thermal load. The design objective is the maximization of the weighted sum of the critical buckling load and fundamental frequency. The design variable is the fibre orientations in the layers. The performance index is formulated as the weighted sum of individual objectives in order to obtain optimal solutions of the design problem. The first-order shear deformation theory (FSDT) is used in the mathematical formulation of laminated truncated conical shells. Finally, the effect of different weighting factors, length-to-radius ratio, semi-cone angle and boundary conditions on the optimal design is investigated and the results are compared.

Experimental investigations of the film cooling effectiveness of a micro-tangential-jet scheme on a gas turbine vane

This paper presents experimental investigations of the film cooling effectiveness of a Micro-Tangential-Jet (MTJ) Film cooling scheme on a gas turbine vane using transient Thermochromic Liquid Crystal (TLC) technique. The MTJ scheme is a micro-shaped scheme designed so that the secondary jet is supplied tangentially to the vane surface. The scheme combines the benefits of micro jets and tangential injection. The film cooling performance of one row of holes on both pressure and suction sides were investigated at a blowing ratio ranging from 0.5 to 1.5 on the pressure side and 0.25 to 0.625 on the suction side. The average density ratio during the investigations was 0.93, and the Reynolds Number was 1.4E+5, based on the free stream velocity and the main duct hydraulic diameter. The pitch to diameter ratio of the cooling holes is 5 on the pressure side and 6.5 on the suction side. The turbulence intensity during all investigations was 8.5%. Minor changes in the Mach number distribution around the airfoil surface were observed due to the presence of the MTJ scheme, compared with the case with no MTJ scheme. The investigations showed great film cooling performance for the MTJ scheme, high effectiveness values and excellent lateral jet spreading. The performance of tangential injection over actual airfoil surfaces was found close, qualitatively, to that observed over flat plate. A 2-D coolant film was observed in the results, which is a characteristic of the continuous slot schemes only. The presence of this 2-D film layer helps minimize the rate of mixing between the main and the secondary streams. This film help establish uniform thermal loads on the surface. Furthermore, it was noticed that the rate of effectiveness decay on the suction side was lower than that of the pressure side while the lateral jet spreading on the pressure side was better than on suction side. The main disadvantage of the MTJ scheme is the increased pressure drop across the scheme, compared to traditional shaped schemes.

Multiobjective optimum design of laminated composite annular sector plates

This paper deals with multiobjective optimization of symmetrically laminated composite angle-ply annular sector plates subjected to axial uniform pressure load and thermal load. The design objective is the maximization of the weighted sum of the critical buckling load and fundamental frequency. The design variable is the fibre orientations in the layers. The performance index is formulated as the weighted sum of individual objectives in order to obtain the optimum solutions of the design problem. The first-order shear deformation theory is used for the mathematical formulation. Finally, the effects of different weighting factors, annularity, sector angle and boundary conditions on the optimal design are investigated and the results are compared.

Post-buckling analysis of a simply supported compound beams made of two symmetrically distributed materials under uniform thermal loading

Thermal post buckling analysis of axi symmetric compound stepped beams, made of two different materials with axially immovable ends, for simply supported conditions, and was studied numerically. The analysis was performed by using the energy principle. The compound beam is made of two different materials, with the end segments of equal lengths of the same material with a higher, and the central segment of a different length of another material with lower coefficients of linear thermal expansion. Similarly, the Young’s modulus of the material of the middle segment is higher than that of the symmetrically placed end segments. The buckling and post buckling strength of stepped compound beam is predicted by examining the influence of inertia, length and deflection ratios. As mentioned in the title of the present work, importance is given for predicting the non dimensional post buckling parameters for the two different material combinations such as steel-aluminum, titanium-aluminum and copper-aluminum as these combinations of materials finds a major applications in the fields of aerospace, electronic, power generation and automobile industry where high strength and low weight are desirable. For post buckling analysis, the accuracy and efficiency of the present method for a isotropic uniform beam with simply supported and fixed-fixed boundary conditions, have shown a good agreement with that of obtained by finite element method.

Static Behavior of FG-CNT Polymer Nano Composite Plate under Elevated Non-uniform Temperature Fields

In this paper, static behavior of functionally graded carbon nanotube reinforced polymer composite plate under non uniform elevated temperature fields has been investigated using finite element method. The effective material properties of the composite plate are obtained using the extended rule of mixture along with carbon nanotube efficiency parameters (to include size-dependent material properties). Parameter studies are carried out to analyze influence of boundary conditions of the plate, type of functional grading of the carbon nanotube and type of non uniform thermal loading on static behavior of the functionally graded carbon nanotube reinforced composite plate. It is found that static behavior of the composite plate has been significantly influenced by nature of temperature field and nature of functional grading of carbon nanotubes. Static bending deflection of the plate increases with volume fraction of the carbon nanotube except for unsymmetrical distribution of carbon nanotube.