Cyclic deformation and damage mechanisms of 9%Cr steel under hybrid stress-strain controlled creep fatigue interaction loadings

Creep-fatigue interaction and its effect on damage of components in service have been a major concern to analysts. To deal with this problem, several criteria have been proposed and used, such as: cycle-time fraction summation rule, strain limit, fracture maps where damage mechanisms are based on crack initiation or propagation, and ductility exhaustion. These concepts are reviewed in this paper so that one can interpret the damage mechanisms caused by creep and by fatigue. If a long period of dwell-time at elevated temperature is imposed on a component under strain conditions, stress relaxation occurs. Relaxation data can be used, for example, in austenitic steels, in predicting creep stages; however, interpretation of data obtained from such tests could be misleading in assessing damage. An example is given for life prediction on the basis of two selected criteria: the fraction rule and ductility exhaustion.

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Study on the Stress-Strain Redistribution Caused by Inelastic Deformation in Perforated Plate

Volume 9: Rudy Scavuzzo Student Paper Symposium and Competition ◽

10.1115/pvp2012-78431 ◽

2012 ◽

Author(s):

Sho Ikeda ◽

Masakazu Sato ◽

Naoto Kasahara

Keyword(s):

Design Method ◽

Perforated Plate ◽

Chemical Plants ◽

Inelastic Behavior ◽

Stress Strain ◽

Elastic Plastic ◽

Pipe Model ◽

Elastic Core ◽

Creep Fatigue ◽

Breeder Reactors

Fast Breeder Reactors and chemical plants that is operated at elevated temperature must be designed considering creep deformation in addition to elastic-plastic deformation. Especially at structural discontinuities, strain concentration induced by stress-strain redistribution reduces creep-fatigue strength. For this reason, a design method is needed for appropriately evaluating inelastic behavior at a structural discontinuity. As one of simplified methods with elastic analysis, a rational method with Stress Redistribution Locus (SRL) has been studied during recent years. Previous studies have shown that SRL does not depend on constitutive equations or on the magnitude of loading. And through the elastic-plastic-creep analysis of a one-dimensional pipe model, it was revealed that there was a relation between stress-strain redistribution and the size of elastic core. The purpose of this study is to clarify the mechanism of stress-strain redistribution in complex structures like actual components. Multi-dimensional stress-strain distribution and multiaxial stress occur in those structures. For considering those effects, inelastic analyses on perforated plate were performed and the relation between the region of elastic cores and SRL was examined. Then, it was revealed that SRL could be divided into two parts. One half is affected by the region of elastic core and the other half depends on the loading type. Furthermore, this paper proposes the new SRL method based on the mechanism and validates the method.

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