Field Temperature Rise Research Articles

The Coupled Thermal-Structural Resonance Reliability Sensitivity Analysis of Gear-Rotor System with Random Parameters

The resonance of the gear-rotor system will produce a large number of responses that do not exceed the threshold value, resulting in structural fatigue failure and transmission failure, affecting its life and reliability. It is particularly critical to consider the temperature rise under high-speed and heavy-load conditions. Therefore, the research will take the main drive gear-rotor system of a certain type of aeroengine accessory gearbox as the research object, consider the influence of the temperature field on the natural frequency of the gear-rotor system, and take the difference between the natural frequency of the gear-rotor system and the excitation frequency (gear meshing frequency) as the performance function. The PC-Kriging and adaptive design of experimental strategies are applied to the thermal-structural coupling parametric model to analyze the resonance reliability and sensitivity of the gear-rotor system. For complex mechanical mechanisms, the method has better accuracy than other surrogate models and greatly saves the time of finite element simulation in reliability analysis. The results show that the natural frequency of a gear rotor decreases with an increase in temperature, and the natural frequency of different orders varies with the change in temperature. The influence of the sensitivity of different random parameters on the resonance reliability of the gear-rotor system is obtained. Reliability research on resonance failure of high-speed and heavy-load aviation gear-rotor systems considering random parameters under a temperature rise field has important practical engineering application value and scientific research significance.

Static and buckling characteristics of the porous ring reinforced by graphene nanofillers

The present work focuses on the static and buckling characteristics of the confined functionally graded porous (FGP) ring consolidated by graphene nanofillers (GNF). The ring is under a temperature rise field when a point load is applied on the crown position. The Halpin-Tsai micromechanics theory is used to evaluate the distribution of Young’s modulus, and the Gaussian random field theory is used to evaluate the distribution of the porosity and mass density, respectively. The influence of the thermal field on the buckling load is quantized by applying the energy function and nonlinear thin-walled shell theory. The analytical buckling load is examined numerically, and good agreement is obtained. Furthermore, the present analytical and numerical results are verified effectively by other closed-form predictions when the FGP-GNF ring reduces to a homogeneous ring. Finally, comprehensive parametric study is taken by analyzing the effect of parameters on the buckling load. These parameters include the temperature rise, porosity coefficient, weight fraction, geometric parameters of GNF, friction coefficient and Young’s modulus of the medium.

Structural failure performance of the confined liner with a non-uniformly annular gap subjected to a point load under a thermal rise field

The present investigation focuses on the failure performance of the confined liner with a non-uniform annular gap. The liner is subjected to a radial point load under a temperature rise field. An admissible displacement function is assumed to establish the nonlinear equilibrium equations. The principle of minimum potential energy is employed to obtain the analytical expressions of the critical buckling load (failure load) for the elastic liner encased in the rigid medium. It is found that the temperature rise field has a substantial increase in the critical buckling load. Subsequently, the buckling and post-buckling load-displacement equilibrium paths are plotted by the analytical solutions, and such equilibrium paths can also be traced by developing a two-dimensional (2D) finite element model (FEM). The maximum load (buckling load) obtained from the numerical results show excellent agreement with that from the proposed analytical solutions, and other closed-form expressions. Furthermore, the liners with inelastic material properties and geometric nonlinearities are considered numerically, and the critical buckling load shows its sensitivity to the initial gap, the initial out-of-roundness imperfection, and Young's modulus of the medium. Finally, the effect of friction is examined and plays a small role in the critical buckling load.

Thermoreflectance Temperature Mapping of Ga2O3 Schottky Barrier Diodes

There is increasing adoption of SiC and GaN for various high-power applications, including in the areas of transportation, electricity production and distribution, control of industrial machinery, and military systems. These applications are expanding the market for wide bandgap materials beyond the existing important uses in chargers for smartphones, laptops, and television sets. The primary attraction of wide bandgap semiconductors is their ability to deliver higher power density and better efficiency as compared to equivalent devices made with silicon. Wide bandgap materials, such as SiC, GaN, and Ga2O3 can also withstand much higher temperatures, thus reducing the need for costly cooling systems. A major drawback of Ga2O3 as compared to other candidate semiconductors is its low thermal conductivity. This apparent limitation could potentially be mitigated by transferring devices to other substrates as has already been demonstrated for GaN, and/or by using heat spreaders and even top-side heat extraction. At present, the electrical performance of Ga2O3 rectifiers is limited by the presence of defects and by lower than desired breakdown voltage initiated in the depletion region near the electrode corners. In the more established SiC and GaN rectifier technologies, these shortcomings are mitigated by the use of edge termination methods whose effect is to smooth out the electric field distribution around the rectifying contact periphery. Such methods have included field plates and ion-implanted high-resistivity layers. But the recent success in producing Ga2O3 bulk wafers as well as doped epitaxial layers grown on these wafers are promising developments for power device applications of Ga2O3, especially vertical geometry rectifiers. So, if continued efforts can be successful in minimizing the on-state resistance Ron while increasing the breakdown voltage, Ga2O3-based devices can extend power switching to voltages above those possible with SiC and GaN. The thermal behavior of such devices is not only an important gage of electrical performance, but can also serve as an early indicator of the onset of failure, both spatially and temporally. Therefore, in this work, we set out to report on the thermal performance of edge-terminated, vertical geometry, Schottky diode devices. By using thermoreflectance-based thermography, we were able to map the temperature distribution on the surface of a diode with deep submicron resolutions. We also pulse activated the diodes with various prescribed periods and duty cycles, and tracked their thermal response by capturing the surface temperature fields at different times within each activation period. In doing so, we were able to resolve the thermal rise and decay of the active diodes. The attached figure shows an example of the temperature map obtained on the surface of a 100-µm Ga2O3 Schottky diode. The device under test is shown on the left side of the image while on the right side, the temperature rise field is shown just before the device is turned off. The line plot on the bottom left side shows the average temperature in the center of the device at different time points within the 5-second period that the shown device was pulsed at. Figure 1

Material distribution optimization of functionally graded arch subjected to external pressure under temperature rise field

This paper investigates the material spatial redistribution optimization of the conventional functionally graded material (CFGM) arch. An inverted functionally graded material (IFGM) arch is developed to promote the critical buckling pressure of the heated arch without variation of the volume portion of the material constituents of the CFGM arch. Based on the classical thin-walled arch theories and admissible displacement functions, the total potential energy function of the IFGM arch is obtained. By variation of this energy function, the non-linear bifurcation equilibrium equations are established, and the analytical prediction of the critical buckling pressure is obtained for the IFGM arch. Subsequently, a two-dimensional (2D) finite element model (FEM) is established to trace the pressure-displacement equilibrium paths to obtain the maximum pressure (critical buckling pressure). The numerical results show very close agreement with the present analytical solutions. Furthermore, the IFGM arch shows a substantial increase of the critical buckling pressure compared with the CFGM arch. In addition, the critical buckling pressure of the heated homogeneous arch is compared with the available other closed-form expressions. Finally, to further understand the stability of the pressurized IFGM arch under temperature rise field, parametric studies are performed to examine the effects of the various involved parameters, such as the volume fraction exponent and temperature rise on the bending moment, the hoop force, the hoop strain and stress, the radial and hoop displacement through the arch span.

Size dependent thermal buckling and postbuckling of functionally graded circular microplates based on modified couple stress theory

ABSTRACTIn this article, size-dependent thermal buckling and postbuckling behavior of a functionally graded circular microplate under uniform temperature rise field and clamped boundary conditions is investigated. Material properties are assumed to gradually vary through the thickness according to a simple power law. Equilibrium equations and associated boundary conditions are derived using variational method and based on modified couple stress theory, classical plate theory and von Kármán geometric nonlinearity. The differential quadrature method is used to discretize the governing equations. This technique is accompanied by an iterative method to determine the thermal postbuckling behavior of microplate. Finally, effects of length scale parameter, power law index and ratio of thickness to radius on the thermal buckling and postbuckling behavior of FG circular microplate are investigated.

Thermal Post-Buckling of Functionally Graded Material Circular Plates Subjected to Transverse Point-Space Constraints

Axisymmetrical thermal post-buckling of functionally graded material (FGM) circular plates with immovably clamped boundary and a transversely central point-space constraint was studied. The material properties of the plate were assumed to vary as power law functions in the thickness direction and the temperature rise field to change only in the thickness direction. Based on von Karman's non-linear plate theory, governing equations in terms of the displacements of the middle plane were established. Temperature rise field was obtained by solving the one-dimensional heat conduction equation associated with specified boundary conditions at the top and bottom surface of the plate. By using the shooting method, thermal post-buckling deformation of the FGM circular plate was obtained before and after the plate contacting the point-space constraint. The changes in the characteristics of the deformation and the internal forces of FGM plates were discussed. The effects of gradients of material properties and non-uniform temperature rise parameters on the thermal post-buckling behaviors of FGM circular plates were also examined.

A constitutive model for the dynamic and high‐pressure behaviour of a propellant‐like material: Part II: Model development and applications

AbstractThis paper presents the second part of a work that aims at developing a mechanical model for the behaviour of propellant‐like materials under high confining pressure and strain rate. The model is to be employed to determine the temperature rise due to mechanical dissipation during a dynamic penetration event. Using the kinematical and thermodynamic background derived in the first part, a viscoelastic–viscoplastic–compaction model is put forward and identified. Viscoelasticity and compaction refer to the elastomeric nature of the material, while viscoplasticity, including implicit damage through dilatancy, reflects its granular nature. Some numerical exercises are performed, in view of determining the major model forces and weaknesses, and of assessing the numerical algorithm robustness. A penetration event is preliminarily simulated, and a temperature rise field predicted. Necessary model improvements are finally discussed, together with several ways of research for a longer term approach. Copyright © 2001 John Wiley & Sons, Ltd.