High-temperature fatigue: Example of creep lifetime prediction for grade 2 alloy 800 at 550°C (original) (raw)
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On Creep Fatigue interaction of components at elevated temperature
Journal of Pressure Vessel Technology, 2015
The accurate assessment of creep–fatigue interaction is an important issue for industrial components operating with large cyclic thermal and mechanical loads. An extensive review of different aspects of creep fatigue interaction is proposed in this paper. The introduction of a high temperature creep dwell within the loading cycle has relevant impact on the structural behavior. Different mechanisms can occur, including the cyclically enhanced creep, the creep enhanced plasticity and creep ratchetting due to the creep fatigue interaction. A series of crucial parameters for crack initiation assessment can be identified, such as the start of dwell stress, the creep strain, and the total strain range. A comparison between the ASME NH and R5 is proposed, and the principal differences in calculating the aforementioned parameters are outlined. The linear matching method (LMM) framework is also presented and reviewed, as a direct method capable of calculating these parameters and assessing a...
2018
This paper presents a novel direct method, within the Linear Matching Method (LMM) framework, for the direct evaluation of steady state cyclic behaviour of structures subjected to high temperature – creep fatigue conditions. The LMM was originally developed for the evaluation of shakedown and ratchet limits. The latest extension of the LMM makes it capable of predicting the steady state stress strain solutions of component subjected to cyclic thermal and mechanical loads with creep effects. The proposed iterative method directly calculates the creep stress and cyclically enhanced creep strain during the dwell period for the assessment of the creep damage, and also creep enhanced total strain range for the assessment of fatigue damage of each load cycle. To demonstrate the efficiency and applicability of the method to assess the creep fatigue damage, two types of weldments subjected to reverse bending moment at elevated temperature of 550C are simulated by the proposed method conside...
Materials Science and Engineering: A, 2010
The accumulation of creep-fatigue damage over time is the principal damage mechanism which will eventually lead to crack initiation in critical high temperature equipment. A model has been developed that assumes on a macroscopic level that the energy dissipated in the material may be taken as a measure of the creep damage induced in the material and hence the creep damage is directly proportional to absorbed internal energy density. The model developed is derived from considerations of mechanistic cavity growth and is based on rupture elongation to failure data using true strain. The predictions of the energy density exhaustion approach are compared with the results of creep-fatigue tests on low alloy ferritic steels. The predicted results of the energy density model are found to have good correlation with the measured creep-fatigue lives.
2013
This paper presents a novel direct method, within the Linear Matching Method (LMM) framework, for the direct evaluation of steady state cyclic behaviour of structures subjected to high temperature – creep fatigue conditions. The LMM was originally developed for the evaluation of shakedown and ratchet limits. The latest extension of the LMM makes it capable of predicting the steady state stress strain solutions of component subjected to cyclic thermal and mechanical loads with creep effects. The proposed iterative method directly calculates the creep stress and cyclically enhanced creep strain during the dwell period for the assessment of the creep damage, and also creep enhanced total strain range for the assessment of fatigue damage of each load cycle. To demonstrate the efficiency and applicability of the method to assess the creep fatigue damage, two types of weldments subjected to reverse bending moment at elevated temperature of 550C are simulated by the proposed method conside...
Creep and creep–fatigue crack growth
International Journal of Fracture, 2015
Creep and creep-fatigue considerations are important in predicting the remaining life and safe inspection intervals as part of maintenance programs for components operating in harsh, high temperature environments. Time-dependent deformation associated with creep alters the crack tip stress fields established as part of initial loading which must be addressed in any viable theory to account for creep in the vicinity of crack tips. This paper presents a critical assessment of the current state-of-the-art of time-dependent fracture mechanics (TDFM) concepts, test techniques, and applications and describes these important developments that have occurred over the past three decades. It is concluded that while big advances have been made in TDFM, the capabilities to address some significant problems still remain unresolved. These include (a) elevated temperature crack growth in creep-brittle materials used in gas turbines but now also finding increasing use in advanced power-plant components (b) in predicting crack growth in weldments that inherently have cracks or crack-like defects in regions with microstructural gradients (c) in development of a better fundamental understanding of creep-fatigue-environment interactions, and (d) in prognostics of high temperature
Creep-Fatigue Lifetime Assessment with Phenomenological and Constitutive Material Laws
Procedia Engineering, 2013
Variations in steam temperature due to start-up a thermomechanical stresses, which can lead to fatigu heated surface. With respect to component integrit mandatory. Lifetime assessment models have bee conducted. This paper presents a comparison and phenomenological approach, based on the generaliz account creep rupture damage at stress relaxation as as is an enhanced interaction method for the influenc viscoplastic constitutive material model of the type C of the types 1CrMoNiV (1Cr), 2CrMoNiWV (2Cr), The model allows the recalculation of the material be applicability and accuracy of the models is finally uniaxial and multiaxial experiments on notched speci
Creep-fatigue crack behavior has been investigated for a welded component with 316L stainless steel and Mod. 9Cr-1Mo steel through assessment and test. The evaluation of creep-fatigue crack initiation and propagation was carried out for 316L stainless steel according to the French RCC-MR A16 guide, and the evaluation of creep-fatigue crack initiation for a Mod.9Cr-1Mo steel specimen was carried out with an extended A16 method. A test for a structural specimen with a diameter of 500 mm, height of 440 mm, and thickness of 6.3 mm was performed to compare its results with that by an assessment according to the A16 guide. The specimen was subjected to creep-fatigue loads with 2 h of dwell time at 600°C and various primary loads. The creep-fatigue crack behaviors for the two materials were assessed, observed, and compared. The results showed that the A16 guide for the austenitic stainless steel was fairly conservative for the assessment of creep-fatigue crack initiation while it was reasonably conservative for creep-fatigue crack growth for the present specimen.
Interaction of high cycle fatigue with high temperature creep in two creep-resistant steels
Materials Science and Engineering: A, 1990
The interaction of high cycle fatigue with high temperature creep was studied in bainitic steel of the type 2.25Cr-1Mo (pressure vessel steel) at 600 °C and in austenitic steel of the type AISI 304 at 700 °C. The cyclic stress component strongly affects both the minimum creep rate and the time to fracture. For a constant maximum stress in the stress cycle, o,,~, the creep rate and the time to fracture depend on the stress ratio R = Omin/Oma x in a non-monotonous way. From the practical point of view it is important that even small vibrations superimposed on the static load increase the time to fracture substantially. The explanation of the effect of the cyclic stress component on the deformation processes is based on a composite model of dislocation structure.
Model for life prediction of fatigue–creep interaction
Microelectronics Reliability, 2008
This paper discusses the development of a procedure for computing creep and stress relaxation at the critical location in a through-hole structure. A high-speed methodology was developed for calculating cyclic creep and stress relaxation at critical locations of a pile on elastic foundation subjected to cyclic thermomechanical loading. This simplified analysis was exercised for two cases involving a pile on elastic foundation problem with different thermomechanical loading. The simplified analysis exhibited no computational problems and gave a stable solution for the full dwell times. Comparisons made with experimental results for these cases gave an excellent agreement at a much faster computing time. This simplified procedure is expected to be even much faster when an entire pile on elastic foundation assembly is analyzed.
Lifetime prediction in creep-fatigue environment
Materials Science-poland, 2008
The creep-fatigue interaction has been studied and innovative mathematical models are proposed to predict the operating life of aircraft components, specifically gas turbine blades subject to creep-fatigue at high temperatures. The historical evolution of the creep-fatigue lifetime prediction is given in order to place the present study in the context. A literature review of the life estimation under creep-fatigue environment is presented.