Modeling of High Homologous Temperature Deformation Behavior Using the Viscoplasticity Theory Based on Overstress (VBO): Part II—Characteristics of the VBO Model

1997 ◽  
Vol 119 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Yukio Tachibana ◽  
Erhard Krempl
Keyword(s):  
Hold Time ◽  
Cyclic Strain ◽  
Tensile Tests ◽  
Temperature Deformation ◽  
Extreme Conditions ◽  
Alloy 800H ◽  
Homologous Temperature ◽  
High Homologous Temperature ◽  
Term Creep

Characteristics of the high homologous temperature VBO model under extreme conditions such as very fast and very slow tensile tests, long-term-creep and relaxation tests are investigated via numerical experiments and analysis. To this end, material constants of Alloy 800H determined from other tests in Part I were utilized for the prediction. Although no experiments are available for the extreme conditions, the predictions are plausible. For cyclic, strain controlled hold-time tests the predictions compare well with sparse experimental data. The results give confidence that VBO can be used to predict the long-term behavior at high homologous temperature once the constants have been determined from regular, short-term tests.

Modeling of High Homologous Temperature Deformation Behavior Using the Viscoplasticity Theory Based on Overstress (VBO): Part I— Creep and Tensile Behavior

1995 ◽  
Vol 117 (4) ◽  
pp. 456-461 ◽  
Author(s):  
Yukio Tachibana ◽  
Erhard Krempl
Keyword(s):  
Cyclic Hardening ◽  
Back Stress ◽  
Tensile Tests ◽  
Tensile Behavior ◽  
Temperature Deformation ◽  
State Variables ◽  
Homologous Temperature ◽  
Variable Theory ◽  
Alloy 800 ◽  
High Homologous Temperature

The viscoplasticity theory based on overstress (VBO) is a state variable theory without a yield surface and without loading/unloading conditions. It contains two tensor valued state variables, the equilibrium (back) stress and the kinematic stress that is a repository for work hardening (softening). The scalar valued isotropic or time (rate)-independent stress models cyclic hardening (softening). For application to high homologous temperature, the effects of diffusion which counteracts the hardening of inelastic deformation has to be accounted for. Recovery of state terms are introduced in the growth laws for the state variables. A high homologous temperature VBO model is introduced and applied to the creep and tensile tests of Alloy 800 H between 750°C and 1050°C. Primary, secondary and tertiary creep as well as tensile behavior were well reproduced. It is shown that the transition to fluid state can be modeled with VBO.

Modeling of High Homologous Temperature Deformation Behaviour Using the Viscoplasticity Theory Based on Overstress (VBO): Part III—A Simplified Model

1998 ◽  
Vol 120 (3) ◽  
pp. 193-196 ◽  
Author(s):  
Yukio Tachibana ◽  
Erhard Krempl
Keyword(s):  
Deformation Behaviour ◽  
Three Dimensional ◽  
Simplified Model ◽  
Temperature Deformation ◽  
Alloy 800H ◽  
Homologous Temperature ◽  
Static Recovery ◽  
Long Time Behaviour ◽  
Long Time ◽  
High Homologous Temperature

A simplified version of the Viscoplasticity Theory Based on Overstress (VBO) is applied to modeling of Alloy 800H at homologous temperatures between 0.6 and 0.8 The present formulation is simplified to the extent that omission of any constant would deprive the model to represent phenomena. Examples of such a phenomenon are tertiary creep and static recovery. The three-dimensional formulation of the simplified model for Alloy 8OOH at high homologous temperature needs a total of 10 constants. The parent theory from which the simplified model is derived has 18 constants that must be determined from experiments. The simplified theory has essentially the same modeling capability as the parent theory. There are differences in the predictions of the two versions for very long-time behaviour for which no test data are available. When material data are available for comparison the modeling of the regular and the simplified versions are very good and show roughly the same amount of deviation. The results suggest that the simplified version should be tried first when a given material has to be modeled.

scholarly journals Determination of Long-Term Creep Properties for 316H Steel Using Short-Term Tests on Pre-strained Material

2021 ◽  
Author(s):  
H. Zhou ◽  
A. Mehmanparast ◽  
K. Nikbin
Keyword(s):  
Mechanical Response ◽  
Tensile Tests ◽  
Primary Objective ◽  
Creep Rupture ◽  
Creep Ductility ◽  
Creep Properties ◽  
Material State ◽  
Term Creep

AbstractDetermination of long-term creep rupture properties for 316H steel is both costly and time-consuming and given the level of scatter in the data would need substantial number of tests to be performed. The primary objective of this study is to estimate the long-term creep properties of cross-weld (XW) and as-received (AR) 316H stainless steel by performing accelerated tests on pre-compressed (PC) material. In this work, uniaxial creep rupture tests have been performed on XW specimens and the results have been used to establish a correlation with accelerated test results on the PC material. Moreover, tensile tests have been performed on XW specimens at room temperature and 550 °C to examine the pre-conditioning effects on the mechanical response of the material. Similar power-law creep properties have been found for the creep strain rate and rupture time behaviour of the XW and PC specimens. It also has been found that the creep ductility data points obtained from XW and PC specimens fall upon the estimated trend for the AR material at 550 °C when the data are correlated with the applied stress normalised by 0.2% proof stress. The results show that the long-term creep properties of the XW and AR material can be estimated in much shorter time scales simply by performing tests on the PC material state.

Statistical reinterpretation of the long term creep behaviour of the Ismetpasa segment of North Anatolian Fault, Turkey

2021 ◽  
pp. 228947
Author(s):  
Gokhan Gurbuz ◽  
Caglar Bayik ◽  
Saygin Abdikan ◽  
Kurtulus Sedar Gormus ◽  
Senol Hakan Kutoglu
Keyword(s):  
Creep Behaviour ◽  
North Anatolian Fault ◽  
Term Creep

scholarly journals Influence of the Environment on the Reliability of Security Magnetic Contacts

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 401
Author(s):  
Martin Boros ◽  
Andrej Velas ◽  
Viktor Soltes ◽  
Jacek Dworzecki
Keyword(s):  
Global Warming ◽  
Extreme Conditions ◽  
Alarm System ◽  
Test Device ◽  
Reaction Distance ◽  
Ambient Temperatures ◽  
Thermal Chamber

Magnetic contacts are one of the basic components of an alarm system, providing access to buildings, especially windows and doors. From long-term reliability tests, it can be concluded that magnetic contacts show sufficient reliability. Due to global warming, we can measure high as well as low ambient temperatures in the vicinity of magnetic contacts, which can directly affect their reliability. As part of partial tests, research into the reliability of magnetic contacts, we created a test device with which their reaction distance was examined under extreme conditions simulated in a thermal chamber. The results of the practical tests have yielded surprising results.

scholarly journals Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 84
Author(s):  
Pramod Koshy ◽  
Naomi Ho ◽  
Vicki Zhong ◽  
Luisa Schreck ◽  
Sandor Alex Koszo ◽  
...  
Keyword(s):  
High Temperature ◽  
Fly Ash ◽  
Mineral Resources ◽  
Nucleating Agent ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Stable Phase ◽  
Power Stations ◽  
Firing Shrinkage

Fly ash is an aluminosilicate and the major by-product from coal combustion in power stations; its increasing volumes are major economic and environmental concerns, particularly since it is one of the largest mineral resources based on current estimates. Mullite (3Al2O3·2SiO2) is the only stable phase in the Al2O3-SiO2 system and is used in numerous applications owing to its high-temperature chemical and mechanical stabilities. Hence, fly ash offers a potential economical resource for mullite fabrication, which is confirmed by a review of the current literature. This review details the methodologies to utilise fly ash with different additives to fabricate what are described as porous interconnected mullite skeletons or dense mullite bodies of approximately stoichiometric compositions. However, studies of pure fly ash examined only high-Al2O3 forms and none of these works reported long-term, high-temperature, firing shrinkage data for these mullite bodies. In the present work, high-SiO2 fly ashes were used to fabricate percolated mullite, which is demonstrated by the absence of firing shrinkage upon long-term high-temperature soaking. The major glass component of the fly ash provides viscosities suitably high for shape retention but low enough for ionic diffusion and the minor mullite component provides the nucleating agent to grow mullite needles into a direct-bonded, single-crystal, continuous, needle network that prevents high-temperature deformation and isolates the residual glass in the triple points. These attributes confer outstanding long-term dimensional stability at temperatures exceeding 1500 °C, which is unprecedented for mullite-based compositions.

scholarly journals Study of the Ultraviolet Effect and Thermal Analysis on Polypropylene Nonwoven Geotextile

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1080
Author(s):  
Clever Aparecido Valentin ◽  
Marcelo Kobelnik ◽  
Yara Barbosa Franco ◽  
Fernando Luiz Lavoie ◽  
Jefferson Lins da Silva ◽  
...  
Keyword(s):  
Uv Light ◽  
Polymeric Materials ◽  
Tensile Tests ◽  
Thermomechanical Analysis ◽  
Material Stiffness ◽  
Before And After ◽  
Electron Microscopy Analysis ◽  
Physical Tests ◽  
Nonwoven Geotextile

The use of polymeric materials such as geosynthetics in infrastructure works has been increasing over the last decades, as they bring down costs and provide long-term benefits. However, the aging of polymers raises the question of its long-term durability and for this reason researchers have been studying a sort of techniques to search for the required renewal time. This paper examined a commercial polypropylene (PP) nonwoven geotextile before and after 500 h and 1000 h exposure to ultraviolet (UV) light by performing laboratory accelerated ultraviolet-aging tests. The state of the polymeric material after UV exposure was studied through a wide set of tests, including mechanical and physical tests and thermoanalytical tests and scanning electron microscopy analysis. The calorimetric evaluations (DSC) showed distinct behaviors in sample melting points, attributed to the UV radiation effect on the aged samples. Furthermore, after exposure, the samples presented low thermal stability in the thermomechanical analysis (TMA), with a continuing decrease in their thicknesses. The tensile tests showed an increase in material stiffness after exposition. This study demonstrates that UV aging has effects on the properties of the polypropylene polymer.

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