A systematical weight function modified critical distance method to estimate the creep-fatigue life of geometrically different structures

Self Cite

In the present study, both the as-received and the 600-h-serviced turbine blades were tested under the creep-fatigue loading. The results showed that the service-exposed blades exhibited a longer creep-fatigue life than the asreceived ones due to the refinement of grain size and the increasing of hardness during the service process. Micro structural characterization revealed that there was no directional coarsening or rafting of γ 0 precipitate after 600 h of service. Moreover, the as-received blades exhibited initial cyclic hardening followed by saturation and softening, whereas the 600-h-serviced blades only exhibited continuous softening until fracture. A conservative service life prediction approach was proposed considering the experienced mission profile. This service life estimation method provides a new way to assess the durability of turbine blade.

Section: Methodsmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

normalΔ ε_{t} / 2 = \frac{normalΔ ε_{t_{italicma}}}{2 X_{eff}} \int_{x_{italicsta}}^{x_{italicend}} σ_{n} ((), x) ω {(x, χ (x))}_{fatigue} normald x = ε_{f}^{'} {(2 N_{f} {((), \frac{1 ‐ R}{2})}^{1 / 2 b})}^{c} + \frac{σ_{f}^{'}}{E} {(2 N_{f} {((), \frac{1 ‐ R}{2})}^{1 / 2 b})}^{b}

({, \begin{array}{c} \lg t = b_{0} + b_{1} T + b_{2} normalx + b_{3} x^{2} + b_{4} x^{3} \\ normalx = \lg ((), \frac{σ_{italicma}}{X_{italiceff}} \int_{x_{italicsta}}^{x_{italicend}} σ_{n} ((), x) ((), 1 ‐ θ ((), x ‐ x_{sta}) (||, χ ((), x))) normald x) \end{array})

where Δ ε t ,

normalΔ ε_{t_{italicmax}}

Section: Introductionmentioning

confidence: 99%

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Experimental investigation on creep‐fatigue behaviours of as‐received and service‐exposed turbine blades: Mechanism and life evaluation

Shi

Yang

et al. 2020

Self Cite

“…The structures of an aero-engine were usually subjected to the random thermal-mechanical fatigue loadings. In the previous studies of the authors, 57,58 the maximum stress of a turbine blade was calculated as 630MPa at the maximum speed in flight. The accelerated fatigue tests on the as-received and service-exposed full-scale turbine blades were performed at a limited amount of critical area overstress and overtemperature, with the nominal load ratio of 0.1.…”

Section: Test Matrixmentioning

confidence: 99%

Residual fatigue life prediction based on a novel damage accumulation model considering loading history

Shi

et al. 2020

Self Cite

The influence of prior low‐cycle fatigue (LCF) on the residual fatigue life was investigated experimentally. A Ni‐based alloy was cyclically loaded under stress‐controlled low‐high (LH) block loading. In the first loading step, low‐amplitude loading was performed with the stress amplitude of 283.5MPa at 710°C. Different cycles of preloading were performed, varying from 100 to 10 000. Subsequently, high‐amplitude fatigue loading was carried out with the stress amplitude of 315MPa at 800°C. Experimental results show that the previous loading was beneficial to the residual fatigue life when the consumed life fraction is below 0.2 and detrimental when the consumed life fraction is larger than 0.2. A novel nonlinear fatigue damage accumulation model was proposed to estimate the residual LCF life under LH loading path considering the effects of load sequence and preloading cycles. The proposed model provided a better life prediction than some existing models, such as Kwofie‐Rahbar model, Miner' rule, Peng model, and Ye‐Wang model. Lastly, this model was further validated using various materials under LH and high‐low block loadings.

“…This is particularly important when considering the notch effect on the fatigue resistance of components, which varies considerably with notch geometric features . 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 ) and thus result in complex fatigue problems and induce surface fatigue cracks, even under conditions of inconspicuous plastic deformation . According to this, the complete understanding of notch effect is pivotal to ensure safety and durability of engineering components.…”

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.