Creep Analysis of Beams and Arches Based on a Hereditary Visco-Elastic-Plastic Constitutive Law

1990 ◽  
Vol 112 (2) ◽  
pp. 210-217 ◽  
Author(s):  
J. M. Stubstad ◽  
G. J. Simitses
Keyword(s):  
Thermal Cycling ◽  
Temperature Gradients ◽  
Constitutive Law ◽  
Time Dependent ◽  
Temperature Dependent ◽  
Hastelloy X ◽  
Ambient Temperatures ◽  
Creep Analysis ◽  
Highly Nonlinear ◽  
Temperature Dependent Properties

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.

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

1961 ◽  
Vol 28 (2) ◽  
pp. 193-207 ◽  
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.

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

AIP Advances ◽  
2017 ◽  
Vol 7 (3) ◽  
pp. 035206
Author(s):  
P. L. Fulmek ◽  
P. Haumer ◽  
F. P. Wenzl ◽  
W. Nemitz ◽  
J. Nicolics
Keyword(s):  
High Power ◽  
Voltage Characteristic ◽  
Time Dependent ◽  
Temperature Dependent ◽  
Forward Voltage ◽  
Temperature Dependent Properties

scholarly journals Dynamics of Rising Bubbles in a Quiescent Slag Bath with Varying Thermo-Physical Properties

2020 ◽  
Vol 51 (6) ◽  
pp. 2843-2861
Author(s):  
D. Obiso ◽  
D. H. Schwitalla ◽  
I. Korobeinikov ◽  
B. Meyer ◽  
M. Reuter ◽  
...  
Keyword(s):  
Physical Properties ◽  
Bubble Dynamics ◽  
Fluid Dynamic ◽  
Temperature Gradients ◽  
Slag Bath ◽  
Bubble Motion ◽  
Temperature Dependent ◽  
Slag Properties ◽  
Temperature Dependent Properties ◽  
Thermo Physical Properties

AbstractThe motion of bubbles in a liquid slag bath with temperature gradients is investigated by means of 3D fluid dynamic computations. The goal of the work is to describe the dynamics of the rising bubbles, taking into account the temperature dependency of the thermo-physical properties of the slag. Attention is paid to the modeling approach used for the slag properties and how this affects the simulation of the bubble motion. In particular, the usage of constant values is compared to the usage of temperature-dependent data, taken from models available in the literature and from in-house experimental measurements. Although the present study focuses on temperature gradients, the consideration of varying thermo-physical properties is greatly relevant for the fluid dynamic modeling of reactive slag baths, since the same effect is given by heterogeneous species and solid fraction distributions. CFD is applied to evaluate the bubble dynamics in terms of the rising path, terminal bubble shape, and velocity, the gas–liquid interface area, and the appearance of break-up phenomena. It is shown that the presence of a thermal gradient strongly acts on the gas–liquid interaction when the temperature-dependent properties are considered. Furthermore, the use of literature models and experimental data produces different results, demonstrating the importance of correctly modeling the slag’s thermo-physical properties.

Reliability Analysis in Flip Chip Package under Thermal Cycling

2004 ◽  
Vol 261-263 ◽  
pp. 489-494 ◽  
Author(s):  
Meng Kao Yeh ◽  
C.Y. Tsai
Keyword(s):  
Thermal Cycling ◽  
Flip Chip ◽  
Thermal Stresses ◽  
Temperature Dependent ◽  
Linear Elastic ◽  
Cte Mismatch ◽  
Sensitive Characteristics ◽  
Moisture Sensitive ◽  
Temperature Dependent Properties ◽  
Package Reliability

The material properties of underfill and substrate in flip chip package have temperature-dependent and moisture-sensitive characteristics. During the solder reflow process, the CTE mismatch in the package causes thermal stresses, which may reduce the reliability of the flip chip package. The package reliability can be improved by varying the die thickness, the fillet angle and the thickness of the underfill and by changing the underfill material. In this paper, the temperature- dependent properties of the underfill were established first. The flip chip reliability was then analyzed by finite element code ANSYS. Both underfill A and underfill B were used in the analysis. The results show that better reliability of the flip chip package was obtained for underfill A, for larger fillet angle of the underfill, for thinner die in the package, and for larger Young's modulus of underfill with linear elastic assumption. Also a hygrothermal preconditioning before thermal cycling reduces the reliability of the flip chip package.

scholarly journals Time-Dependent Reliability Analysis of Reinforced Concrete Beams Subjected to Uniform and Pitting Corrosion and Brittle Fracture

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1820
Author(s):  
Mohamed El Amine Ben Seghier ◽  
Behrooz Keshtegar ◽  
Hussam Mahmoud
Keyword(s):  
Reinforced Concrete ◽  
Brittle Fracture ◽  
Reliability Analysis ◽  
Pitting Corrosion ◽  
Structural Reliability ◽  
Time Dependent ◽  
State Function ◽  
Rc Beams ◽  
Highly Nonlinear ◽  
Reliability Method

Reinforced concrete (RC) beams are basic elements used in the construction of various structures and infrastructural systems. When exposed to harsh environmental conditions, the integrity of RC beams could be compromised as a result of various deterioration mechanisms. One of the most common deterioration mechanisms is the formation of different types of corrosion in the steel reinforcements of the beams, which could impact the overall reliability of the beam. Existing classical reliability analysis methods have shown unstable results when used for the assessment of highly nonlinear problems, such as corroded RC beams. To that end, the main purpose of this paper is to explore the use of a structural reliability method for the multi-state assessment of corroded RC beams. To do so, an improved reliability method, namely the three-term conjugate map (TCM) based on the first order reliability method (FORM), is used. The application of the TCM method to identify the multi-state failure of RC beams is validated against various well-known structural reliability-based FORM formulations. The limit state function (LSF) for corroded RC beams is formulated in accordance with two corrosion types, namely uniform and pitting corrosion, and with consideration of brittle fracture due to the pit-to-crack transition probability. The time-dependent reliability analyses conducted in this study are also used to assess the influence of various parameters on the resulting failure probability of the corroded beams. The results show that the nominal bar diameter, corrosion initiation rate, and the external loads have an important influence on the safety of these structures. In addition, the proposed method is shown to outperform other reliability-based FORM formulations in predicting the level of reliability in RC beams.

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

ACS Omega ◽  
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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