Multi-axial creep-fatigue life prediction considering history-dependent damage evolution: A new numerical procedure and experimental validation

Considering the flexible operation conditions, the creep‐fatigue performance of P92 steel plays a crucial role in manufacturing structural components of ultra‐supercritical fossil power plants at 620°C–630°C. The creep‐fatigue interaction tests of P92 steel were conducted at 630°C in air with different duration periods, where the duration periods were simultaneously added on the peak tensile strain and valley compressive strain. The addition of hold time resulted in a rapid decrease of fatigue life, where the reduction amplitude increasing with the hold time. There was more than five times reduction as the hold time increased to 300 s. Moreover, the stress relaxation behavior during hold time exhibited a saturation behavior at long dwell time, where the limited relaxed stress gradually approached to the creep threshold stress. Furthermore, a modified strain energy density exhaustion model involving creep threshold stress was proposed and provided more accurate predictions in comparison with the conventional model, reducing the conservatism.

Section: Introductionmentioning

confidence: 99%

Analysis on stress‐strain behavior and life prediction of P92 steel under creep‐fatigue interaction conditions

Zhao

Han

et al. 2020

“…(7) On the basis of the comprehensive review on notch effects in metal fatigue, some prospective aspects deserve further investigations summarized as below: (a) study the mechanism of notch fatigue failure from the macroscopic and microcosmic perspectives in combination with experiments, realize the modelling and evaluation of the overall damage of the notch, and characterize the contribution of different material blocks inside the effective damage region to the overall fatigue failure; (b) quick analytical calculation of local stress and strain in the notched region and its combination with methods for notch fatigue analysis to achieve convenient and efficient fatigue strength evaluation, as recent analyses based on FEA are generally inefficient; (c) establish a general analytical framework suitable for diversiform notch geometries and load types, further incorporating the influences of multiple factors such as multiaxial fatigue, creep, and size effect on fatigue strength of the interest; (d) build a database of notched fatigue test results, summing up the applicability of each method under different loading conditions or geometry cases, which facilitates communication and innovation among different methods. In particular, the coupling analysis of notch and size effects is the premise of achieving the extrapolation of fatigue strength of large‐scale components/structures using experimental data of small‐scale specimens collected in laboratory.…”

Section: Discussionmentioning

confidence: 99%

Recent advances on notch effects in metal fatigue: A review

Liao

Zhu

Correia

et al. 2020

150

Notch features including holes, fillets, shoulders, and grooves commonly exist in engineering components. When subjected to external loads, these geometrical discontinuities generally act as stress raisers and thus present significant influences on the component strength and life, which are more remarkable under complex loading paths. Accordingly, numerous theories and approaches have been developed to address notch effects in metal fatigue as well as damage modelling and life predictions, which aim to provide theoretical support for structural optimal design and integrity evaluation. However, most of them are self‐styled or focus on specific objects, which limits their engineering applicability. This review recalls recent developments and achievements in notch fatigue modelling and analysis of metals. In particular, four commonly used methods for fatigue evaluation of metallic notched components/structures are summarized and elaborated, namely, nominal stress approaches, local stress‐strain approaches, and critical distance theories and weighting control parameters‐based approaches, which intend to provide a reference for further research on notch fatigue analysis and promote the integration and/or development among different approaches for practice.

“…However, much attention was paid on the relationship between FSED and SEDR at a fixed temperature in the previous studies, where the CSED is a constant parameter. 20,22,51 Herein, a unified damage model considering various temperatures was developed to describe the temperature-dependent creep-free stage as follows:…”

Section: Creep-fatigue Life Prediction Modelmentioning

confidence: 99%

Establishment of unified creep–fatigue life prediction under various temperatures and investigation of failure physical mechanism for Type 304 stainless steel

Wang

et al. 2022

Investigations into creep-fatigue life and the corresponding failure physical mechanism are crucial for guaranteeing the structural integrity of components.In this work, a series of strain-controlled fatigue and creep-fatigue tests were performed at different temperatures. Then, the EBSD-TEM combinative analysis was performed to reveal the microstructure evolution. The creep failure parameter dependence derived from standard creep experimental data and their importance in further creep-fatigue employment were discussed. Resultsshow that strain energy density has better relevance than ductility in connecting with creep failure. The temperature-dependent critical strain energy density and an equivalent failure strain energy density, considering geometric effect, were incorporated with the current energy-based model, which enables creep-fatigue life scatter within a factor of 1.5. Moreover, multi-slip activations and severe slip interactions under creep-fatigue conditions were responsible for the ultimately lifetime reductions based on microstructure observations.