Estimation of thermal stress level in cylindrical samples at large heating rates

1969 ◽  
Vol 1 (2) ◽  
pp. 180-182 ◽  
Author(s):  
Yu. M. Shemegan ◽  
V. A. Terletskii
Keyword(s):  
Thermal Stress ◽  
Stress Level ◽  
Heating Rates ◽  
Cylindrical Samples ◽  
Large Heating

Growth Kinetics and Thermal Stress in AlN Bulk Crystal Growth

2002 ◽  
Author(s):  
Bei Wu ◽  
Ronghui Ma ◽  
Hui Zhang ◽  
Michael Dudley ◽  
Raoul Schlesser ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Crystal Growth ◽  
Temperature Distribution ◽  
Stress Level ◽  
Grown Crystal ◽  
Power Level ◽  
Chemical Species ◽  
Group Iii Nitrides ◽  
Minor Effect ◽  
Group Iii

Group III nitrides, such as GaN, AlN and InGaN, have attracted a lot of attention due to the development of blue-green and ultraviolet light emitting diodes (LEDs) and lasers. In this paper, an integrated model has developed based on the conservation of momentum, mass, chemical species and energy together with necessary boundary conditions that account for heterogeneous chemical reactions both at the source and seed surfaces. The simulation results have been compared with temperature measurements for different power levels and flow rates in a reactor specially designed for nitride crystal growth at NCSU. It is evident that the heat power level affects the entire temperature distribution greatly while the flow rate has minor effect on the temperature distribution. The results also show that the overall thermal stress level is higher than the critical resolved shear stress, which means thermal elastic stress can be a major source of dislocation density in the as-grown crystal. The stress level is strongly dependent on the temperature gradient in the as-grown crystal. Results are correlated well with defects showing in an X-ray topograph for the AlN wafer.

The Response of an Idealized Atmosphere to Localized Tropical Heating: Superrotation and the Breakdown of Linear Theory

2018 ◽  
Vol 75 (1) ◽  
pp. 3-20 ◽  
Author(s):  
Nicholas J. Lutsko
Keyword(s):  
Temperature Gradient ◽  
General Circulation ◽  
Circulation Model ◽  
Mean Flow ◽  
Heating Rates ◽  
Momentum Fluxes ◽  
The Mean ◽  
The Stability ◽  
The Waves ◽  
Large Heating

An equatorial heat source mimicking the strong diabatic heating above the west Pacific is added to an idealized, dry general circulation model. For small (<0.5 K day−1) heating rates the responses closely match the expectations from linear Matsuno–Gill theory, though the amplitudes of the responses increase sublinearly. This “linear” regime breaks down for larger heating rates and it is found that this is because the stability of the tropical atmosphere increases. At the same time, the equatorial winds increasingly superrotate. This superrotation is driven by stationary eddy momentum fluxes by the waves excited by the heating and is damped by the vertical advection of low-momentum air by the mean flow and, at large heating rates, by the divergence of momentum by transient eddies. These dynamics are explored in additional experiments in which the equator-to-pole temperature gradient is varied. Very strong superrotation is produced when a large heating rate is applied to a setup with a relatively weak equator-to-pole temperature gradient, though there is no evidence that this is a case of “runaway” superrotation.

scholarly journals Calculation of the Temperature Distribution in Cylindrical Samples of Alumina and Copper Produced by Spark Plasma Sintering

Ceramics ◽  
2021 ◽  
Vol 4 (3) ◽  
pp. 437-446
Author(s):  
Vyacheslav V. Krizhanovskiy ◽  
Vyacheslav I. Mali
Keyword(s):  
Electrical Conductivity ◽  
Temperature Distribution ◽  
Aluminum Oxide ◽  
Physicochemical Properties ◽  
Spark Plasma Sintering ◽  
Numerical Calculations ◽  
Heating Rates ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Cylindrical Samples

Numerical calculations were carried out to simulate, under conditions of close spark plasma sintering (SPS), the temperature distribution during the passage of current in dense cylindrical samples of two materials: aluminum oxide and copper located in graphite forms and clamped between cylindrical graphite punches. The investigated materials differ greatly in their electrical conductivity and other physicochemical properties. Calculations were carried out for various geometric parameters of the samples, as well as graphite molds and punches at varying heating rates from the passing current.

scholarly journals THERMAL SHOCK AND DYNAMIC THERMOELASTICITY

2016 ◽  
Vol 11 (1) ◽  
pp. 67-74
Author(s):  
A. Yu. Strigunova ◽  
E. M. Kartashov
Keyword(s):  
Thermal Stress ◽  
Thermal Shock ◽  
Boundary Surface ◽  
Thermal Reaction ◽  
The Body ◽  
Tensor Algebra ◽  
Inertial Effects ◽  
Dynamic Problems ◽  
Heating Rates ◽  
Cooling Mode

This paper considers the problem of thermal shock in the case of a massive body in different conditions of heating and cooling. The most dangerous mode of heating was identified. The influence of inertial effects on the value of emerging thermal stress was investigated. A new equation of compatibility of stress with the inertial effects, which generalizes the known Beltrami-Mitchell relation for quasi-static cases, was obtained by methods of the tensor algebra. The theory of thermal shock in solids was developed in terms of dynamic problems of thermoelasticity in different forms of heat stress: temperature heating; thermal heating; heating medium. Equations for the calculation the jumps in the front of thermoelastic waves were obtained. The most dangerous mode of thermal shock was identified. The effect of relaxation in thermal problems was described in the context of the investigation of thermal stress state of a massive body. It was shown that an increase in relaxation time, i.e. heating rates of the boundary surface of the body, causes a reduction of thermal stress maxima. Original results of the thermal reaction of a solid to cooling were obtained. It was shown that, in comparison with the heating mode, the cooling mode is more devastating, especially for nearsurface layers of solids. The role of the relaxation temperature in the cooling mode was identified. New functional structures were proposed as analytical solutions to the major dynamic problems of thermomechanics on the basis of the use of the Kar functions, which are relatively new.

The Master Sinter Curve and Its Application to Binder Jetting Additive Manufacturing

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Evan Wheat ◽  
Gitanjali Shanbhag ◽  
Mihaela Vlasea
Keyword(s):  
Additive Manufacturing ◽  
Sintered Density ◽  
Prediction Errors ◽  
Heating Rates ◽  
Density Prediction ◽  
Axis Parallel ◽  
Apparent Activation Energies ◽  
Printing Direction ◽  
Binder Jetting ◽  
Cylindrical Samples

Abstract The master sinter curve (MSC) is an empirical model used to predict the density of a part after being sintered. The model is typically applied to components that undergo isotropic shrinkage. Parts manufactured using binder jetting additive manufacturing (BJAM) are known to have nonuniform powder systems and high levels of anisotropy. This work explores the application of the master sinter curve to components made by BJAM. Cylindrical samples were manufactured with the long axis parallel (vertical), perpendicular (horizontal), and 45 deg to the printing direction. A bimodal blend of titanium powder (0–45  µm and 106–150 µm) was used to make samples with consistent green densities (ranging from 47.2% to 52.3%) between the different orientations. Samples were then sintered at heating rates of 1, 3, and 5 °C/min to a maximum of 1400 °C. After sintering, the samples showed significant variation between the different orientations, with vertical samples on average 7.6 ± 2.98% and 4.7 ± 1.20% denser than the horizontal and the 45 deg samples, respectively. The calculated apparent activation energies for sintering were within the same range for all orientations, 200–260 kJ/mol for vertical and 45 deg, and 140–260 kJ/mol for horizontal samples. Validation sinter runs showed that the density prediction errors of the master sinter curves were between 0.9% and 4.3%. This work shows that the master sinter curve can be applied to predict the sintered density of components manufactured by binder jetting additive manufacturing.

Assembly Bonded at the Ends: Could Thinner and Longer Legs Result in a Lower Thermal Stress in a Thermoelectric Module Design?

2012 ◽  
Vol 79 (6) ◽  
Author(s):  
E. Suhir ◽  
A. Shakouri
Keyword(s):  
Thermal Stress ◽  
Stress Level ◽  
Thermoelectric Module ◽  
Interfacial Strength ◽  
Interfacial Stress ◽  
Electrical Performance ◽  
Shearing Stress ◽  
Interfacial Shearing Stress ◽  
Numerical Example ◽  
Module Design

An analytical (mathematical) thermal stress model has been developed for an electronic assembly comprised of identical components bonded at their end portions and subjected to different temperatures. The model is used to assess the effect of the size (dimension in the x-direction) and compliance of the bonded regions (legs) on the maximum interfacial shearing stress that is supposedly responsible for the mechanical robustness of the assembly. The numerical example is carried out for a simplified two-legged Bismuth-Telluride-Alloy (BTA)-based thermoelectric module (TEM) design. It has been determined that thinner (dimension in the horizontal, x-direction) and longer (dimension in the vertical, y-direction) bonds (legs) could result in a considerable relief in the interfacial stress. In the numerical example carried out for a 10 mm long (dimension in the x-direction) TEM assembly with two peripheral 1 mm thick (dimension in the x-direction) legs, the predicted maximum interfacial shearing stress is only about 40% of the maximum stress in the corresponding homogeneously bonded assembly, when the bond occupies the entire interface between the assembly components. It has been determined also that if thick-and-short legs are employed, the maximum interfacial shearing stress might not be very much different from the stress in a homogeneously bonded assembly, so that there is no need, as far as physical design and robustness of the assembly is concerned, to use a homogeneous bond or a multileg system. The application of such a system might be needed, however, for the satisfactory functional (thermo-electrical) performance of the device. In any event, it is imperative that sufficient bonding strength is assured in the assembly. If very thin legs are considered for lower stresses, the minimum acceptable size (real estate) of the interfaces (in the horizontal plane) should be experimentally determined (say, by shear-off testing) so that this strength is not compromised. On the other hand, owing to a lower stress level in an assembly with thin-and-long legs, assurance of its interfacial strength is less of a challenge than for an assembly with a homogeneous bond or with stiff thick-and-short legs. The obtained results could be used particularly for considering, based on the suggested predictive model, an alternative to the existing TEM designs, which are characterized by multiple big (thick-and-long) legs. In our novel design, fewer small (thin-and-short) legs could be employed, so that the size and thickness of the TEM is reduced for the acceptable stress level.

Thermal imaging combined with predictive machine learning based model for the development of thermal stress level classifiers

2020 ◽  
Vol 241 ◽  
pp. 104244
Author(s):  
Verônica Madeira Pacheco ◽  
Rafael Vieira de Sousa ◽  
Alex Vinicius da Silva Rodrigues ◽  
Edson José de Souza Sardinha ◽  
Luciane Silva Martello
Keyword(s):  
Machine Learning ◽  
Thermal Stress ◽  
Stress Level ◽  
Thermal Imaging
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