The failure of gas turbines’ hot components due to fatigue significantly affects their efficient and stable operation. Conducting online damage assessment of components subjected to complex cyclic ...loads based on the working conditions of gas turbines can provide real-time reflection of component fatigue damage and achieve the purpose of predictive maintenance. In this study, we propose an online cycle counting method that considers temperature fluctuations during the cycle process. Our method is based on the four-point online rainflow counting method by coupling the counting variable with time, introducing the concept of the duration time for full cycles and half cycles, and incorporating a characteristic temperature that better represents the temperature information during the cycle process. With reference to the characteristic temperature, our proposed method comprehensively considers the form and parameters of subsequent life assessment models. This paper provides a detailed explanation of the proposed method and applies it to the fatigue damage assessment of turbine vanes in a micro gas turbine, thereby verifying its accuracy and applicability.
•An analysis framework for crosswind fatigue of wind-excited structures is presented.•The hardening non-Gaussian response character caused by nonlinear aerodynamic damping is considered.•A correction ...factor as a function of response kurtosis is introduced for analysis of non-Gaussian fatigue.•The accuracy of proposed framework is illustrated using simulated and full-scale response data.
This study addresses crosswind fatigue analysis of wind-excited flexible structures at the vicinity of vortex lock-in speed where the nonlinear aerodynamic damping effect is significant. The nonlinear aerodynamic damping is modeled as a polynomial function of time-varying displacement or velocity of vibration. The crosswind response is a narrow-band hardening non-Gaussian process with a reduced peak factor and having a distribution of vibration amplitude different from Rayleigh distribution. Analytical solutions of cycle number and fatigue damage are derived and their accuracy is validated through comparison with rainflow cycle counting method using simulated response time histories. A correction factor as a function of response kurtosis is also introduced that facilitates the calculation of non-Gaussian fatigue damage from the Gaussian fatigue prediction. The effectiveness and accuracy of the proposed framework are illustrated by crosswind responses of a squared tall building and a two-dimensional structural section model, and by full-scale vibration measurement data of a traffic-signal-support-structure. This study provides an improved estimation of crosswind fatigue of wind-excited flexible structures with a consideration of hardening non-Gaussian response character.
Based on the critical plane determined by the weight function method, two algorithms for multiaxial cycle counting method are proposed by modifying the rainflow and range cycle counting methods. The ...proposed two algorithms can be applied to multiaxial random loading, and be suitable to any critical plane-based fatigue life prediction models, since the counted cycles or reversals are represented by the start time and end time. The proposed two algorithms are used to predict multiaxial fatigue life by the experimental data of 7075-T651 aluminum alloy, En15R steel and 7050-T7451 aluminum alloy conducted under multiaxial random loading in both high-cycle and low-cycle fatigue region. The life prediction results are in good agreement with the experimental data.
In this work, the performance of the SSF criterion is evaluated under variable amplitude loading conditions. The main objective was to inspect the validity of the hypothesis in which the SSF damage ...map remains valid for any high strength steel. In order to achieve that, fatigue life correlation of the 1050QT steel and 304L stainless steel was analyzed under multiaxial loading conditions. The loading block considered in the study comprises 360 proportional loading cycles with different stress amplitude ratios and stress levels. Despite being made of proportional branches, this loading block is a non-proportional loading due to its principal directions variation. This feature allows the evaluation of combined loading effects under variable amplitude loading conditions, which makes this loading block suitable to mimic the loading effects usually found in the field. Results show very good agreements, which reinforces the aforementioned hypothesis
Multiaxial fatigue is a very important physical phenomenon to take into account in several mechanical components; its study is of utmost importance to avoid unexpected failure of equipment, vehicles ...or structures. Among several fatigue characterization tools, a correct definition of a damage parameter and a load cycle counting method under multiaxial loading conditions show to be crucial to estimate multiaxial fatigue life. In this paper, the SSF equivalent stress and the virtual cycle counting method are presented and discussed, regarding their physical foundations and their capability to characterize multiaxial fatigue damage under complex loading blocks. Moreover, it is presented their applicability to evaluate random fatigue damage.
In this work, the performance of the SSF criterion is evaluated under variable amplitude loading conditions. The main objective was to inspect the validity of the hypothesis in which the SSF damage ...map remains valid for any high strength steel. In order to achieve that, fatigue life correlation of the 1050QT steel and 304L stainless steel was analyzed under multiaxial loading conditions. The loading block considered in the study comprises 360 proportional loading cycles with different stress amplitude ratios and stress levels. Despite being made of proportional branches, this loading block is a non-proportional loading due to its principal directions variation. This feature allows the evaluation of combined loading effects under variable amplitude loading conditions, which makes this loading block suitable to mimic the loading effects usually found in the field. Results show very good agreements, which reinforces the aforementioned hypothesis
Multiaxial fatigue is a very important physical phenomenon to take into account in several mechanical components; its study is of utmost importance to avoid unexpected failure of equipment, vehicles ...or structures. Among several fatigue characterization tools, a correct definition of a damage parameter and a load cycle counting method under multiaxial loading conditions show to be crucial to estimate multiaxial fatigue life. In this paper, the SSF equivalent stress and the virtual cycle counting method are presented and discussed, regarding their physical foundations and their capability to characterize multiaxial fatigue damage under complex loading blocks. Moreover, it is presented their applicability to evaluate random fatigue damage.
The paper presents an overview through the development in the field of load spectra modelling published so far by the author et al. and replays to the criticism given by Nadarajah and Kotz Nadarajah ...S, Kotz S. On the recent papers by Nagode et al. Int J Fatigue 2007.
doi:10.1016/j.ijfatigue.2006.12.017
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For service life prediction and stochastic reconstruction of load histories, rainflow matrices have been recently predominately used to describe the scatter of loading. Typically, only limited data ...are available due to the costs of measurements. As a consequence of this, discrete rainflow matrices have to be modelled and extrapolated. So far non-parametric methods have most frequently been used to transform discrete matrices into smooth functions. In this paper, two appropriate parametric models: a mixture of joint Weibull–normal distributions and a mixture of multi-variate normals, as well as two algorithms for parameter estimation: the EM algorithm and the algorithm developed by Nagode and Fajdiga are thoroughly discussed and compared. Finally, a method to describe the scatter of rainflow matrices is presented.
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