Der Einfluß von Temperatur, Dehnungsgeschwindigkeit und Haltezeit auf das Zeitfestigkeitsverhalten von Stählen

Wellinger, Karl; Sautter, Sieghart

doi:10.1002/srin.197304496

Cited by 3 publications

(1 citation statement)

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“…However, the results published for more complex cycle shapes, and those including compressive dwell periods 26,27,31,34,36,42 are at variance with each other. The results of the present work suggest that introducing a dwell period at the maximum tensile strain in the cycle (laboratory and type 1 cycles) reduces the cyclic endurance more than introdu~ing a similar dwell period at zero strain (type 2 cycle).…”

Section: Discussioncontrasting

confidence: 61%

High-strain high-temperature fatigue properties of a 0·5Cr–Mo–V steam turbine casing steel

Batte¹,

Murphy²,

Stringer³

1978

Metals Technology

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The high-strain high-temperature fatigue behaviour of a cast 0·5 Cr-M 0-V steel for steam turbine casings has been evaluated extensively in tests lasting several years. The results define the influence of strain range, dwell period, fatigue-cycle shape, and test temperature on the cyclic endurance. The effect of these parameters on the peak stress and on the stress-relaxation behaviour is also described. A comprehensive review of the data available for Cr-Mo and Cr-Mo-V casing steels suggests that they all have similar resistance to high-strain high-temperature fatigue cracking. An accurate description of the data, facilitating interpolation and extrapolation, is given by ihe relationship established between dwell period and cyclic endurance. However, comparative evaluation of creep-fatigue damage accumulation models together with metal/ographic examination of test specimens indicates that the life-fraction rule provides the best method of predicting the behaviour of steam turbine components in service.MT/531Strain-controlled tests have, therefore, been used to obtain materials data. Much of the information was obtained from mechanical reverse-bend machines 14 since tests with an endurance of five years or more were required' and it is not practical to operate more sophisticated machines continuously over such long periods. However, axial pushpull tests, not continued to specimen failure, were used to provide the cyclic stress-strain data not obtainable from reverse-bend tests. The specimens, of designs used previously,15 were tested at 773, 798, or 823K, covering the most common inlet temperatures of high-temperature steam turbines. Testing was'in air, at a cyclic frequency of O·02Hz (reverse-bend) or 0·01 Hz (push-pull). Tests in steam have a slightly longer endurance than tests in air but the difference in endurance between tests at 0·01 Hz and 0·02Hz is negligible.l 5 -17 Dwell periods of up to 16h were introduced at either the maximum tensile strain (laboratory and type 1 cycles, Fig. I) or at the middle of the strain range (type 2 cycle, Fig. 1), these cycles representing the range of cycles which may occur in a component in service. 6 However, most of the data were generated using the laboratory cycle and these data have, therefore, been used in illustrating the present paper.Composition, wt-% During service, large steam turbine components experience cycles of thermal strain as a result of the temperature gradients which occur on heating and cooling during start-up and shut-down or load changes. These thermal transients are most severe at the surfaces exposed to hightemperature steam and, particularly in the region of stressconcentrating features, may result in cyclic plastic deformation. Furthermore, components operating in the creep range suffer creep damage during the on-load period.Prevention of crack formation under these combined creep-fatigue conditions is an important consideration in steam turbine practice 1 -n since inadequate allowance, in either design or operation, can lead to cracking in serv...

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Section: Discussioncontrasting

confidence: 61%

High-strain high-temperature fatigue properties of a 0·5Cr–Mo–V steam turbine casing steel

Batte¹,

Murphy²,

Stringer³

1978

Metals Technology

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Chapter 16-Fatigue and Fatigue Crack Growth

Klueh¹,

Harries²

2001

High-Chromium Ferritic and Martensitic Steels for Nuclear Applications

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High-temperature components in a steam power plant are subject during service to fatigue straining due to thermal cycling or a combination of thermal and mechanical deformation in which the strain cycle includes a hold period. The first wall in a D-T tokamak fusion system will also undergo thermomechanical fatigue (TMF) as a result of the mechanical and electromagnetic loadings and the cyclic strains induced by the temperature changes during the plasma burn and off-burn periods [1,2]. Two approaches may be adopted for estimating the lifetimes of the component materials under combined thermal and mechanical cycling. The first involves the formulation of failure relationships directly from TMF tests; however, the acquisition of TMF data on materials by testing with simultaneously varying temperature and strain is experimentally difficult, time consuming, and expensive, and the procedures have not yet been standardized. Consequently, most of the relevant materials data has been generated by the second approach of isothermal continuous cycling fatigue and creep-fatigue (hold time) testing. However, the service lives extend over many years, and it is not practical to reproduce the conditions in laboratory tests. It has therefore been necessary to develop models of the behavior to enable the long-term service lives of components exposed to TMF to be predicted from the results of the shorter-term laboratory tests.

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Critique of Predictive Methods for Treatment of Time-Dependent Metal Fatigue at High Temperatures

2009

Fatigue and Durability of Metals at High Temperatures

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This chapter provides a detailed review of creep-fatigue analysis techniques, including the 10% rule, strain-range partitioning, several variants of the frequency-modified life equation, damage assessment based on tensile hysteresis energy, the OCTF (oxidation, creep, and thermomechanical fatigue) damage model, and numerous methods that make use of creep-rupture, crack-growth, and void-growth data. It also discusses the use of continuum damage mechanics and includes examples demonstrating the accuracy of each method as well as the procedures involved.

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Der Einfluß von Temperatur, Dehnungsgeschwindigkeit und Haltezeit auf das Zeitfestigkeitsverhalten von Stählen

Cited by 3 publications

References 1 publication

High-strain high-temperature fatigue properties of a 0·5Cr–Mo–V steam turbine casing steel

High-strain high-temperature fatigue properties of a 0·5Cr–Mo–V steam turbine casing steel

Chapter 16-Fatigue and Fatigue Crack Growth

Critique of Predictive Methods for Treatment of Time-Dependent Metal Fatigue at High Temperatures

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