Time dependent and temperature dependent properties of the forward voltage characteristic of InGaN high power LEDs

An analytic study of planar beams and arches subjected to significant thermal cycling from ambient temperatures up to 800°C is presented. The study employs a recently unified nonlinear hereditary type of viscoelastoplastic constitutive law to characterize the time- and temperature-dependent properties of Hastelloy X, a typical aerospace alloy. The results demonstrate a strong interaction between the backstress variable of the constitutive law and the time-dependent stress distribution produced by the deformation. This interaction tends to control, in a highly nonlinear manner, the creep ratchetting response of the beam or arch. Moreover, temperature gradients in the thickness direction tend to exert an important influence during thermal cycling.

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On Transient Thermal Stresses in Viscoelastic Materials With Temperature-Dependent Properties

Journal of Applied Mechanics ◽

10.1115/1.3641651 ◽

1961 ◽

Vol 28 (2) ◽

pp. 193-207 ◽

Cited By ~ 180

Author(s):

Rokuro Muki ◽

Eli Sternberg

Keyword(s):

Thermal Stresses ◽

Constitutive Law ◽

Time Dependent ◽

Temperature Dependent ◽

Infinite Extent ◽

Temperature Dependent Properties ◽

Transient Thermal ◽

Temperature Time ◽

Symmetric Temperature ◽

Actual Test

This paper deals with the quasi-static analysis of transient thermal stresses in the linear theory of viscoelastic solids with temperature-dependent properties. The underlying constitutive law rests on the temperature-time equivalence hypothesis. Following an exposition of the theoretical framework exact solutions to two specific problems are deduced: The first concerns the thermal stresses in a slab of infinite extent, generated by a temperature field that depends arbitrarily on the thickness co-ordinate and time; the second application concerns the stresses produced in a sphere by an arbitrary time-dependent radially symmetric temperature distribution. The numerical illustrations of the results obtained include a quantitative study based on actual test data for a polymethyl methacrylate.

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The time-dependent temperature distribution in a cylindrical conductor with Joule heating and temperature-dependent properties

Journal of Physics D Applied Physics ◽

10.1088/0022-3727/19/6/013 ◽

1986 ◽

Vol 19 (6) ◽

pp. 975-989 ◽

Cited By ~ 9

Author(s):

V T Morgan ◽

N G Barton

Keyword(s):

Temperature Distribution ◽

Joule Heating ◽

Time Dependent ◽

Temperature Dependent ◽

Cylindrical Conductor ◽

Temperature Dependent Properties

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Temperature-Dependent Properties of Molten Li2BeF4 Salt Using Ab Initio Molecular Dynamics

ACS Omega ◽

10.1021/acsomega.1c02528 ◽

2021 ◽

Author(s):

Khagendra Baral ◽

Saro San ◽

Ridwan Sakidja ◽

Adrien Couet ◽

Kumar Sridharan ◽

...

Keyword(s):

Molecular Dynamics ◽

Ab Initio ◽

Ab Initio Molecular Dynamics ◽

Temperature Dependent ◽

Temperature Dependent Properties

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Green’s function for an elastic layer with temperature-dependent properties

Materials Science ◽

10.1007/s11003-013-9544-z ◽

2013 ◽

Vol 48 (5) ◽

pp. 607-613 ◽

Cited By ~ 3

Author(s):

S. J. Matysiak ◽

D. M. Perkowski

Keyword(s):

Green’S Function ◽

Green's Function ◽

Elastic Layer ◽

Temperature Dependent ◽

Temperature Dependent Properties

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Crystal structure and temperature-dependent properties of Na2H4Ga2GeO8 – a novel gallogermanate

Zeitschrift für Naturforschung B ◽

10.1515/znb-2020-0159 ◽

2020 ◽

Vol 75 (9-10) ◽

pp. 805-813

Author(s):

Irma Peschke ◽

Lars Robben ◽

Christof Köhler ◽

Thomas Frauenheim ◽

Josef-Christian Buhl ◽

...

Keyword(s):

Crystal Structure ◽

Decomposition Temperature ◽

Spectroscopic Techniques ◽

Charge Balance ◽

Temperature Dependent ◽

Raman Spectroscopic ◽

Debye Temperatures ◽

Diffraction Lattice ◽

Temperature Dependent Properties ◽

Balance Structure

AbstractSynthesis, crystal structure and temperature-dependent behavior of Na2H4Ga2GeO8 are reported. This novel gallogermanate crystallizes in space group I41/acd with room-temperature powder diffraction lattice parameters of a = 1298.05(1) pm and c = 870.66(1) pm. The structure consists of MO4 (M = Ga, Ge) tetrahedra in four-ring chains, which are connected by two different (left- and right-handed) helical chains of NaO6 octahedra. Protons coordinating the oxygen atoms of the GaO4 tetrahedra not linked to germanium atoms ensure the charge balance. Structure solution and refinement are based on single crystal X-ray diffraction measurements. Proton positions are estimated using a combined approach of DFT calculations and NMR, FTIR and Raman spectroscopic techniques. The thermal expansion was examined in the range between T = 20(2) K and the compound’s decomposition temperature at 568(5) K, in which no phase transition could be observed, and Debye temperatures of 266(11) and 1566(65) K were determined for the volume expansion.

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A new boundary element algorithm for modeling and simulation of nonlinear thermal stresses in micropolar FGA composites with temperature-dependent properties

Advanced Modeling and Simulation in Engineering Sciences ◽

10.1186/s40323-021-00193-6 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Mohamed Abdelsabour Fahmy

Keyword(s):

Modeling And Simulation ◽

Boundary Element ◽

Thermal Stresses ◽

Computation Time ◽

Functionally Graded ◽

Temperature Dependent ◽

Time Step ◽

Kirchhoff Transformation ◽

Nonlinear Temperature ◽

Temperature Dependent Properties

AbstractThe main aim of this article is to develop a new boundary element method (BEM) algorithm to model and simulate the nonlinear thermal stresses problems in micropolar functionally graded anisotropic (FGA) composites with temperature-dependent properties. Some inside points are chosen to treat the nonlinear terms and domain integrals. An integral formulation which is based on the use of Kirchhoff transformation is firstly used to simplify the transient heat conduction governing equation. Then, the residual nonlinear terms are carried out within the current formulation. The domain integrals can be effectively treated by applying the Cartesian transformation method (CTM). In the proposed BEM technique, the nonlinear temperature is computed on the boundary and some inside domain integral. Then, nonlinear displacement can be calculated at each time step. With the calculated temperature and displacement distributions, we can obtain the values of nonlinear thermal stresses. The efficiency of our proposed methodology has been improved by using the communication-avoiding versions of the Arnoldi (CA-Arnoldi) preconditioner for solving the resulting linear systems arising from the BEM to reduce the iterations number and computation time. The numerical outcomes establish the influence of temperature-dependent properties on the nonlinear temperature distribution, and investigate the effect of the functionally graded parameter on the nonlinear displacements and thermal stresses, through the micropolar FGA composites with temperature-dependent properties. These numerical outcomes also confirm the validity, precision and effectiveness of the proposed modeling and simulation methodology.

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