Fatigue life of steel notched elements including the complex stress state

A new computational methodology is proposed for fatigue life prediction of notched components subjected to variable amplitude multiaxial loading. In the proposed methodology, an estimation method of non‐proportionality factor (F) proposed by authors in the case of constant amplitude multiaxial loading is extended and applied to variable amplitude multiaxial loading by using Wang‐Brown's reversal counting approach. The pseudo stress correction method integrated with linear elastic finite element analysis is utilized to calculate the local elastic‐plastic stress and strain responses at the notch root. For whole local strain history, the plane with weight‐averaged maximum shear strain range is defined as the critical plane in this study. Based on the defined critical plane, a multiaxial fatigue damage model combined with Miner's linear cumulative damage law is used to predict fatigue life. The experimentally obtained fatigue data for 7050‐T7451 aluminium alloy notched shaft specimens under constant and variable amplitude multiaxial loadings are used to verify the proposed methodology and equivalent strain‐based methodology. The results show that the proposed methodology is superior to equivalent strain‐based methodology.

Section: Discussionmentioning

confidence: 99%

“…Δγ max 2 2 r in Equation 22 can be equal to the equivalent strain amplitude ε a ð Þ and the right term σ n, mean is equal to zero. In such cases, Shang-Wang multiaxial fatigue damage model (Equation 22) can be reduced to the traditional strain vs life relationship.…”

Section: Multiaxial Fatigue Damage Calculationmentioning

confidence: 99%

Multiaxial notch fatigue life prediction based on pseudo stress correction and finite element analysis under variable amplitude loading

Tao

Shang

Sun

et al. 2018

“…According to different functional requirements of engineering components, environmental concerns demand eco‐friendly material usage but at same time achieving costs reduction and requiring better balanced designs of structures and machines by introducing empirical or semi‐empirical safety factors . In order to meet the above‐mentioned design requirements, it is critical to achieve the accurate calculation of fatigue strength or lifetime, rather than using empirical methods or life divergence coefficients, which might greatly reduce the optional design space for engineering components . This is particularly important when considering the notch effect on the fatigue resistance of components, which varies considerably with notch geometric features .…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5] In order to meet the above-mentioned design requirements, it is critical to achieve the accurate calculation of fatigue strength or lifetime, rather than using empirical methods or life divergence coefficients, which might greatly reduce the optional design space for engineering components. [6][7][8][9] This is particularly important when considering the notch effect on the fatigue resistance of components, which varies considerably with notch geometric features. [10][11][12][13] Under external loads, geometric discontinuities unavoidably raise stress concentrations as well as complex stress-strain responses within the structure, in which the structural geometry suddenly changes (see Figure 1) and thus result in complex fatigue problems and induce surface fatigue cracks, even under conditions of inconspicuous plastic deformation.…”

Section: Introductionmentioning

confidence: 99%

Recent advances on notch effects in metal fatigue: A review

Liao

Zhu

Correia

et al. 2020

173

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.

“…4 Considering the complex state of stress, determination of fatigue characteristics is difficult. 4 Considering the complex state of stress, determination of fatigue characteristics is difficult.…”

mentioning

confidence: 99%

Determining fatigue life of bent and tensioned elements with a notch, with use of fictitious radius

Krzyżak

Robak

Łagoda

2014

The work presents verification of Neuber's fictitious radius method, used in fatigue life calculation of notched elements and welded joints. Stress values, calculated according with fictitious radius method, were compared with smooth specimens Basquin fatigue curves, and number of cycles was read. However, obtained calculated number of cycles of fatigue life does not correspond to experimental fatigue life, especially in a low cycle fatigue range. Hence, different equivalent microstructural length values were calculated for different loading levels. It was observed that equivalent microstructural length depends on loading level and type of loading. Finally, equivalent microstructural length was presented in a linear regression equation, as dependant on loading level and its relation to yield strength.