Design and Analysis

Isochronous Stress–Strain Method With General State of Stress and Variable Loading Conditions for Creep Evaluation

[+] Author and Article Information
Mingxin Zhao

 UOP LLC, A Honeywell Company, Des Plaines, IL 60017mingxin.zhao@uop.com

William Koves

 Pi Engineering Software Inc., Hoffman Estates, IL 60195wjk77@sbcglobal.net

J. Pressure Vessel Technol 134(5), 051205 (Sep 10, 2012) (6 pages) doi:10.1115/1.4007038 History: Received October 20, 2011; Revised June 12, 2012; Published September 10, 2012; Online September 10, 2012

The isochronous stress–strain method for creep evaluation in pressure vessels is a very effective and efficient alternative analysis method to the rigorous time dependent numerical approach. However, the isochronous data are generated from uni-axial load-controlled constant stress state. Its constraints or limitations have not been systematically studied for general or three-dimensional state of stress and variable loading conditions. In reality, pressure components are subjected to complex and combined loading conditions that may vary during operation, resulting in general state of stress and nonconstant loads. In this study, the accuracy of the isochronous stress–strain method for general state of stress and the concept and application of differential isochronous stress–strain data for slowly time-varying loads are brought up and investigated, wherever the time-varying loads can be approximated by piecewise constant step functions. By introducing the differential curve, the isochronous method is expanded into certain nonconstant loading conditions.

Copyright © 2012 by by ASME
Topics: Creep , Stress
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Figure 5

Ratios of creep strain and overstress

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Figure 4

Load history curves for x or y component stress

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Figure 3

Conventional and differential isochronous stress–strain curves

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Figure 2

A cube subjected to uniform surface stresses in x and y directions

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Figure 1

Creep strain and overstress condition for simplified inelastic method

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Figure 6

Finite element model of a straight pipe

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Figure 7

History curves for three loading components



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