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Thermo-mechanical and isothermal fatigue behavior of austenitic stainless steel AISI 316L
Škorík, Viktor ; Šulák, Ivo ; Obrtlík, Karel ; Polák, Jaroslav
Many structural components of nuclear power plant systems are made of austenitic stainless steels. These structures undergo degradation by thermo-mechanical fatigue (TMF) caused by simultaneous cyclic straining and temperature cycling, particularly during start-up, shut-down and transient operations. The present work reports the cyclic deformation behavior and fatigue damage of austenitic stainless steel AISI 316L during TMF and isothermal fatigue (IF) testing in air. Total strain controlled in-phase TMF loading in the temperature range 200 - 600 °C and isothermal fatigue (IF) at 600 °C were performed. Hardening/softening curves, cyclic stress-strain response and fatigue life diagrams were obtained both for TMF and IF tests. Fatigue damage was documented using surface relief and fracture surface observations. Mean stress evolution and fatigue degradation data are employed to discuss the fatigue behavior of 316L steel both in TMF and IF regimes.
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Fatigue properties of Eurofer steel developed for fusion application
Kuběna, Ivo ; Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
In this study fatigue properties of Eurofer 97 steel in room temperatures were measured. Fatigue parameters of the cyclic stress - strain curve and fatigue life curves (Coffin-Manson curve and derived Wöhler curve) were evaluated. Major attention was given to the measurement of kinetics of fatigue crack growth by two different methods. The initiation sites of fatigue cracks and short crack growth were observed and measured on cylindrical specimens with shallow notch. These cracks had a length from 20 micrometers to 1 mm. Kinetics of growth of long cracks with the length 15-30 mm was measured on CT specimens. It was found that results obtained by the both methods are in a good agreement if the J-integral is used. It was possible to determine the threshold values of J-integral and stress intensity factor and to calculate the Paris law parameters.
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Influence of spectral properties of combined random loading on fatigue life
Svoboda, Jaroslav ; Balda, Miroslav
The contribution deals with an influence of power spectral densities of random loading processes on fatigue lives of structures. Experimental results of uniaxial loading are presented. A philosophy of multiaxial tests, which will be carried out in the new grant project, is also discussed. It is expected that a new numerical method for prediction of fatigue lives of structures loaded by random processes with known spectral densities will be developed.
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An influence of normal static prestress on fatigue life construction by torsional random loading
Fröhlich, Vladislav ; Balda, Miroslav ; Svoboda, Jaroslav
Definition influence static prestress on fatigue life for case that uniaxial harmonic loading is in literature enough noted and isn't problem influence those components to the calculation of life constructional whole include. Complicated is it in the event of multiaxial loading of different character and especially in cases, when has this loading random character. In the workplace CDM in Pilsen we are already on basis results for Skoda Power Inc . implementation few experiments on piped figure with opening, loading combination normal and torsional load, during which time one of the applied load was election constant and second are harmonic with zero mean value dynamically impact. Along competitive examinations we watcht place of rice cracks.
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Fatigue strength and life of real structures under combined random loading
Svoboda, Jaroslav ; Balda, Miroslav ; Fröhlich, Vladislav
A rather often kind of combined stress is a case, when one of its components acts statically. The contribution deals with some rsults of research works,the goal of which has been to reveal an influence of the static component on a resulting fatigue life, and to find a way of its including into fatigue strength evalutions. A procedure for finding a critical stress for an estimating of a structure save life is presented. Unfortunately, the fatigue life calculation is more complicated and needs some experiments, which will yield additional informstion on a material behaviour under required stress combination and levels.
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