Comparison of the Isochronous Method and a Time-Explicit Model for Creep Analysis

2008 ◽  
Author(s):  
William Koves ◽  
Mingxin Zhao
Keyword(s):  
Elevated Temperature ◽  
Large Scale ◽  
Time Dependent ◽  
Creep Model ◽  
Full Time ◽  
Pure Bending ◽  
Stress Strain ◽  
Creep Analysis ◽  
Generalized Time ◽  
Strain Method

The design of components or structures at elevated temperature is complex. The use of rigorous time dependent material models may not be practical for many large scale industrial problems. The use of simplified methods permits the creep analysis of components that would be impractical by rigorous time dependent models. The Isochronous Stress-Strain method is an approach that has been used extensively for the creep evaluation of elevated temperature components. The method has been used for the analysis of problems containing both primary and secondary stresses. The method has also been used to evaluate creep buckling problems. Although the method has been accepted as an alternative to a full time dependent creep analysis, the limitations and accuracy of the method have not been investigated systematically and are not fully understood. This study compares the isochronous stress-strain method with a generalized time-explicit creep model for materials in high temperature applications. Analytical solutions are developed for three basic loading configurations, including uniaxial tension, pure bending, and torsion in either load or displacement controlled conditions. Deformations, stresses, and creep strains are compared between the two different methods.

On Simplified Inelastic Method Using Material's Isochronous Stress–Strain Data for Creep Analysis

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
William Koves ◽  
Mingxin Zhao
Keyword(s):  
Elevated Temperature ◽  
Large Scale ◽  
Complex Loading ◽  
Pressure Vessels ◽  
Time Dependent ◽  
Creep Model ◽  
Stress Strain ◽  
Creep Analysis ◽  
Simplified Method ◽  
Strain Method

Design of components or structures at elevated temperature is complex and the use of rigorous time dependent material models may not be practical for many large scale industrial problems. The use of simplified methods permits creep analysis of components that would be impractical by rigorous time dependent models. The isochronous stress–strain method is an approach that has been used extensively for the creep evaluation of elevated temperature components. In practice, the method has been used for the analysis of problems containing both primary and secondary stresses, such as, for pressure vessels with structural discontinuities or creep buckling problems. Although the simplified method has been widely accepted as an alternative to creep analysis, its limitations and accuracy of the method have not been investigated systematically and are not fully understood under complex loading conditions. This study examines the isochronous stress–strain method against a generalized time-explicit creep model. Analytical solutions are developed for three basic loading configurations, including uniaxial tension, pure bending, and torsion, in either load or displacement controlled conditions. Fundamental behaviors of the simplified method are examined and discussed.

Review and Development of Primary Load Elevated Temperature Design Rules

2014 ◽  
Author(s):  
David J. Dewees ◽  
Benjamin F. Hantz
Keyword(s):  
High Temperature ◽  
Strain Analysis ◽  
Creep Model ◽  
Stress Strain ◽  
Creep Analysis ◽  
Elevated Temperature Design ◽  
High Temperature Steam ◽  
Multiaxial Creep ◽  
Selection Of

A recent high temperature steam header case study is extended here to include alternate methods of review, including elastic stress and isochronous strain analysis and accompanying limits. The previous creep analysis was formulated to be exactly consistent with the allowable stress basis, such that alternate design analysis methods and criteria could be rigorously compared. In the current work, the selection of the appropriate limits for elastic results is investigated, as discussed in previous literature, which is motivated by stress redistribution characteristics of the primary (and secondary) loading in a typical header. Next, use of isochronous stress-strain curves generated from the same consistent (Omega) creep model are used for analysis and compared to candidate strain limits. The analyses show that both elastic and isochronous analysis have potential for effective creep design in the context of current high temperature design modernization activities. Finally, multiaxial creep behavior and its effect on detailed creep, elastic and isochronous stress-strain analyses and corresponding limits is also introduced.

Applications of Isochronous Data in Creep Analysis

2007 ◽  
Author(s):  
Mingxin Zhao ◽  
William Koves
Keyword(s):  
Effective Means ◽  
Computing Time ◽  
Time Dependent ◽  
Implicit Time ◽  
Stress Strain ◽  
Simplified Approach ◽  
Material Data ◽  
Inelastic Analysis ◽  
Creep Analysis ◽  
Embedded Method

This paper evaluates the use of isochronous stress-strain material data for the creep analysis of metals in high temperature applications. Performing an inelastic analysis using isochronous stress-strain data is a simplified approach for computing time dependent behavior using an implicit time embedded method. This method has been widely used as an effective means to evaluate the creep behavior of complex components without performing a detailed time dependent creep analysis. In order to examine the effectiveness and limitations of this method, isochronous stress-strain material data was numerically constructed from a time dependent creep law at various temperatures, sustained stress levels, and time durations. Component stresses and strains are compared from results obtained by running both the isochronous time embedded inelastic and time dependent creep analyses for some example problems. The effectiveness and limitations of this method under different loading conditions, such as primary and secondary stresses, are demonstrated and explained. It is recognized that this method was not intended to apply to thermal stress problem, and the thermal problem was studied to understand constraint effects.

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

scholarly journals Residual stress-strain relationship for the biochar-based mortar after exposure to elevated temperature

2021 ◽  
pp. e00540
Author(s):  
Satheeskumar Navaratnam ◽  
Hendrik Wijaya ◽  
Pathmanathan Rajeev ◽  
Priyan Mendis ◽  
Kate Nguyen
Keyword(s):  
Residual Stress ◽  
Elevated Temperature ◽  
Stress Strain ◽  
Strain Relationship

In Situ Tests on Creep Behavior of Rock Mass with Joint or Shearing Zone in Foundation of Large-Scale Hydroelectric Projects

2004 ◽  
Vol 261-263 ◽  
pp. 1097-1102 ◽  
Author(s):  
Jian Liu ◽  
Xia Ting Feng ◽  
Xiu Li Ding ◽  
Huo Ming Zhou
Keyword(s):  
Rock Mass ◽  
Creep Behavior ◽  
Large Scale ◽  
Time Dependent ◽  
Three Gorges Project ◽  
Three Gorges ◽  
The Three Gorges ◽  
The Three Gorges Project

The time-dependent behavior of rock mass, which is generally governed by joints and shearing zones, is of great significance for engineering design and prediction of long-term deformation and stability. In situ creep test is a more effective method than laboratory test in characterizing the creep behavior of rock mass with joint or shearing zone due to the complexity of field conditions. A series of in situ creep tests on granite with joint at the shiplock area of the Three-Gorges Project and basalt with shearing zone at the right abutment of the Xiluodu Project were performed in this study. Based on the test results, the stress-displacement-time responses of the joints and basalt are analyzed, and their time-dependent constitutive model and model coefficients are given, which is crucial for the design to prevent the creep deformations of rock masses from causing the failure of the operation of the shiplock gate at the Three-Gorges Project and long-term stability of the Xiluodu arc dam.

The Effects of Part-Time Work on Women's Occupational Mobility in Britain: Evidence from the 1958 Birth Cohort Study

2012 ◽  
Vol 222 ◽  
pp. R20-R37 ◽  
Author(s):  
Shirley Dex ◽  
Erzsébet Bukodi
Keyword(s):  
Cohort Study ◽  
Large Scale ◽  
Occupational Mobility ◽  
Birth Cohort Study ◽  
Full Time ◽  
Downward Mobility ◽  
Time Work ◽  
Part Time ◽  
Nationally Representative ◽  
Part Time Work

The effects of working part time on job downgrading and upgrading are examined over the life course of British women born in 1958. We use longitudinal data with complete work histories from a large-scale nationally representative cohort study. Occupations were ranked by their hourly average earnings. Analyses show a strong link between full-time/part-time transitions and downward and upward occupational mobility over the course of up to thirty years of employment. Probabilities of occupational mobility were affected by women's personal traits, occupational characteristics and demand-side factors. Downward mobility on moving from full-time to part-time work was more likely for women at the top levels of the occupational hierarchy working in male-dominated or mixed occupations and less likely in higher occupations with more part-time jobs available.

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