Thickness Temperature Gradient Research Articles

Three-dimensional aero-thermo-elasticity analysis of functionally graded cylindrical shell panels

In the present paper, the aero-thermo-elastic behavior of a finite (three-dimensional) cylindrical curved panel geometry made from functionally graded material under high supersonic airflow is investigated. A generalized differential quadrature formulation is adopted while a steady-state through-the-thickness thermal field is also assumed. The geometry curvature and structural nonlinearity effects are included based on von Karman–Donnell strain–displacement relations. The nonlinear piston theory of third order is utilized in order to predict the unsteady aerodynamics loads induced from surrounding supersonic air stream. The functionally graded material is considered with temperature-dependent properties distributed in the thickness according to a power law function. Derived from the equilibrium equations, the aero-thermo-elastic governing equations are reduced to number of ordinary differential equations through using of the generalized differential quadrature method where the structure response is derived using fourth-order Runge–Kutta technique. The contribution of some parameters including flow Mach number, flow dynamic pressure, thickness temperature gradient, and functionally graded material volume fraction index on the flutter response as well as route-to-chaos behavior are reviewed. The calculated results are compared with those available in the literature wherever available and the accuracy and quality of the adopted generalized differential quadrature formulation in analyzing the aero-thermo-elastic behavior of three-dimensional functionally graded curved panels is shown. It reveals that using a three-dimensional approach, if any of Mach number and panel’s upper surface temperature is increased, the route-to-chaos behavior is reached through quasi-periodic motions.

Nonlinear dynamic response of eccentrically stiffened FGM plate using Reddy’s TSDT in thermal environment

ABSTRACTThe nonlinear dynamics of an eccentrically stiffened functionally graded material (ES-FGM) plates resting on the elastic Pasternak foundations subjected to mechanical and thermal loads is considered in this article. The plates are reinforced by outside stiffeners with temperature-dependent material properties in two cases: uniform temperature rise and through the thickness temperature gradient. Both stiffeners and plate are deformed under temperature. Using Reddy’s third-order shear deformation plate theory, stress function, Galerkin and fourth-order Runge–Kutta methods, the effects of material and geometrical properties, temperature-dependent material properties, elastic foundations, and stiffeners on the nonlinear dynamic response of the ES-FGM plate in thermal environments are studied and discussed. Some obtained results are validated by comparing with those in the literature.

Analysis of ultra-heavy plate rolling force based on thickness temperature gradient elements and experiment simulations

The thickness of the plate in temperature gradient rolling is first divided into 2 m elements, and m is an undetermined parameter which can be limited. Based on these thickness elements with different temperatures, the rolling force of this advanced process is first analyzed with slab method. Also the predictions of thickness ratio with different temperatures and reductions of each thickness elements are proposed in this paper. The results measured after rolling experiments are used to compare with these calculated by this model in order to verify its accuracy. In the experiment, a multi-metals riveting plate in the same temperature is designed to simulate a single metal one in gradient temperatures based on the thickness elements. Since the model is based on an analytical method which is strongly supported by the rolling theories, it can be applied in real gradient temperature rolling for ultra-heavy plate.

The effect of elevated temperatures on the bending behaviour of foam cored sandwich structures

The influence of elevated temperatures on the bending response of polymer foam cored sandwich structures is investigated. A new analytical model is proposed that enables the calculation of the stress/strain and deflection of sandwich beams subjected to load and elevated temperatures. The model is based on the classical sandwich beam theory, but the effect of a through thickness temperature gradient is accounted for by imposing different stiffnesses of the core for different temperatures. The sandwich beam specimen studied in the paper is loaded in a simply supported three-point bending configuration, where one of the face sheets is heated. The experimental approach utilises digital image correlation to obtain the point deflection of the specimen and more importantly to characterise the nonuniform deformation of the core. The results from the new analytical method agree well with corresponding experimental results for the beam deflection and core shear strain. It is found that the core shear stress remains uniform in the through thickness direction despite the temperature gradient and resulting stiffness gradient. Thereby the core shear yielding is initiated from the area with the highest temperature in the sandwich beam cross-section due to the reduction of core yield strength with increasing temperature.

The effect of temperature on the failure modes of polymer foam cored sandwich structures

The influence of elevated temperature on the stability of sandwich structures is investigated. A new analytical solution is proposed that enables the calculation of the critical wrinkling stress in sandwich beams subjected to load and elevated temperatures. The effect of a through thickness temperature gradient is accounted for by imposing different stiffnesses of the core for the different temperatures. The sandwich beam studied in the paper is loaded in a simply supported four-point bending configuration, where one of the face sheets is heated. The experimental approach utilises high-speed imaging where the strains are calculated from measured displacements obtained from digital image correlation (DIC). A shift of the failure mode from face sheet yielding to face sheet wrinkling is observed with increasing temperatures. The results from the new analytical method agree well with corresponding experimental results. Finite element analysis is also conducted, which shows excellent correspondence with the theory and the experimental data. The work clearly demonstrates that under certain conditions the load response of the sandwich beam can become nonlinear and unstable, and hence will fail well below face sheet yielding load because of the loss of stiffness of the core material.

Systematic Evaluation of the Advantages of Static Shoulder FSW for Joining Aluminium

Static Shoulder Friction Stir Welding (SS-FSW) is a modification to conventional FSW that was originally developed to improve the weldability of titanium alloys by reducing through thickness temperature gradients. Surprisingly, to date, there have been no published systematic studies comparing SS-FSW to FSW for aluminium welding. This may be because the high conductivity of aluminium means the heat input produced by the shoulder is thought to be beneficial. In the work presented when welding a high strength 7050 aluminium alloy, even in a relatively thin 6 mm plate, it is shown that SS-FSW has several advantages; including a reduction in the heat input, a massive improvement in surface quality, and a more uniform through thickness temperature distribution, which leads to narrower welds with a reduced heat affected zone width and more homogeneous through thickness properties. The reasons for these benefits are discussed.

Assessment of the Advantages of Static Shoulder FSW for Joining Aluminium Aerospace Alloys

Stationary (or Static) Shoulder Friction Stir Welding (SS-FSW) is a variant of FSW that was developed primarily to improve the weldability of titanium alloys by reducing the through thickness temperature gradient. Surprisingly, SS-FSW has been largely ignored by the Al welding community because it is widely supposed a rotating shoulder is an essential aspect of the process and that the higher conductivity means the surface heating effect of the shoulder is generally beneficial. In the work presented it is shown that SS-FSW has major advantages when welding high strength aluminium alloys; including a reduction in the heat input, a massive improvement in surface quality, and a narrower and more symmetric temperature distribution, which leads to narrower welds with a reduced heat affected zone width and lower distortion. The reasons for these benefits are discussed based on a systematic study aimed at directly comparing both processes.

Development Status of a SiC-Foam Based Flow Channel Insert for a U.S.-ITER DCLL TBM

The U.S.-ITER DCLL (Dual Coolant Liquid Lead) TBM (Test Blanket Module) uses a Flow Channel Insert (FCI), to test the feasibility of high temperature DCLL concepts for future power reactors. The FCI serves a dual function of electrical insulation, to mitigate MHD effects, and thermal insulation to keep steel-PbLi interface temperatures below allowable limits. As a non-structural component, the key performance requirements of the FCI structure are compatibility with PbLi, long-term radiation damage resistance, maintaining insulating properties over the lifetime, adequate insulation even in case of localized failures, and manufacturability. The main loads on the FCI are thermally induced due to through the thickness temperature gradients and due to non-uniform PbLi temperatures along the flow channel (∼1.6 m). A number of SiC-based materials are being developed for FCI applications, including SiC/SiC composites and porous SiC bonded between CVD SiC face sheets. Here, we report on an FCI design based on open-cell SiC-foam material. Thermo-mechanical analysis of this FCI concept indicate that a SiC-foam FCI structure is capable of withstanding anticipated primary and secondary stresses during operation in an ITER TBM environment. A complete 30 cm long prototypical segment of the FCI structure was designed and is being fabricated, demonstrating the SiC-foam based FCI structure to be very low-cost and viability candidate for an ITER TBM FCI structure.

肉厚方向に温度分布を有するＮｉ基超合金製円筒試験片の熱疲労き裂進展挙動

This paper studies crack growth behaviors in thermal fatigue tests for Rene80 conventional cast and YH61 single crystal nickel base superalloys. A cylindrical specimen with 19.5mm outer diameter and 2mm thickness was used in the thermal fatigue tests. A rapid temperature gradient in cylinder thickness was realized by induction heating of the outer surface and water cooling of the inner surface. Thermal fatigue tests were conducted by changing the outer surface temperature from 303 to 1173K and temperature holdings of 10 and 60minits were inserted at 1173K. Temperature gradient in thickness was 650K. Crack growth behaviors were inspected with interrupting tests. Crack initiation sites coincided with the ‹100› direction on the outer surface whereas ‹110› direction on the inner surface. It was confirmed that crack initiation sites coincide with stress distribution obtained from a structural analysis considering the anisotropy of the single crystal. Cracks were arrested at the depth of approximately 1.0mm due to stress gradients in the specimen.

Pyroelectric and piezoelectric properties of thick PZT films produced by a new sol–gel route

The pyroelectric and piezoelectric properties of thick PZT films processed via a new sol–gel method are being investigated. The films were deposited on gold-coated alumina substrates. The pyroelectric properties are being evaluated using pyrodynamic measurements with either a laser or thermoelectric heat source. The pyroelectric coefficient is obtained from pyroelectric current measurements. The piezoelectric properties are being measured using a laser vibrometer-lock-in amplifier set-up. It is shown that the pyroelectric coefficient obtained with laser heating lies in the range of 108 μC/m 2 K, whereas heating from the rear of the specimen with the thermoelectric element lead to a value of in the range of 350 μC/m 2 K. These results are explained in terms through thickness temperature gradients. The piezoelectric displacement amplitude versus applied voltage shows a no-linear behaviour, which is explained in terms of materials chemistry. The maximum effective piezoelectric coefficient, d 33, is obtained as 340 pm/V, and is superior to the values known for ferroelectric thin films.

Mechanical and chemical consequences of through thickness thermal gradients in polyimide matrix composite materials

Abstract Composite material parts may be exposed during their service life to through thickness temperature gradients where the difference between the inner and outer faces may exceed 150 °C. The effect of these conditions on 4,4′-bismaleimidodiphenylmethane and diallylbisphenol-A based BMI resin reinforced with glass fabrics was investigated as a function of location through the laminate thickness. It was found that a gradient of chemical, physical and mechanical properties exists through the laminate thickness. A decrease of interlaminar shear strength and an increase of glass transition temperature follow high temperature exposure that causes resin chemistry changes. The material becomes less flexible and more sensitive to microcrack development as a result of these changes.

Criteria for Heated Band Width Based on Through-thickness Temperature Distribution. Numerical Study on Local PWHT of Butt Welded Pipe. Report 1.

The heated band width is the most important processing parameter for local postweld heat treatment of tubes and pipes.A correct heated band width must be chosen so that the allowable maximum temperature difference in the soak band is maintained and a sufficient degree of stress relaxation is achieved.In this paper, the effects of the geometrical and the thermal parameters in the postweld heat treatment are investigated using axisymmetric FEM.The most severe condition in which the heat input and insulation are only applied to the outside surface of the pipe has been studied in detail. The effect of the geometrical and the thermal parameters on the through thickness temperature gradients is investigated.Through this study, it is found that the required heated band width is mainly influenced by the wall thickness and the heat transfer coefficient on the internal surface.The computed results show that the Hi number is inadequate for practical use under general conditions.A more general Hi number is proposed as a linear function of the thickness. Further, based on the computed results, the authors propose criteria for the heated band width which includes the effect of the geometrical and the thermal parameters.