Fatigue Reliability Evaluation Research Articles

Probability Analysis of Duration of Stochastic Process Exceeding Fixed Threshold and Its Application on Structural Cumulative Damage and Fatigue Reliability Evaluation

Probability Analysis of Duration of Stochastic Process Exceeding Fixed Threshold and Its Application on Structural Cumulative Damage and Fatigue Reliability Evaluation

Fatigue reliability evaluation for impellers with consideration of multi‐source uncertainties using a WOA‐XGBoost surrogate model

AbstractWhen using Monte Carlo simulation involving repeated finite element analysis (FEA) to perform fatigue reliability evaluation for an impeller, a variety of uncertainties should be considered to ensure the comprehensiveness of fatigue predictions. These uncertainties include the aleatory uncertainty from the geometric, material and load condition, and epistemic uncertainty from the parameters of the physics‐of‐failure (PoF) model to yield fatigue prediction. However, the latter uncertainty is often ignored in fatigue reliability analysis. And the reliability assessment will become computationally unaffordable and inefficient when there are many random variables involved, as an enormous amount of FEAs are demanded. To address this problem, a Whale Optimization Algorithm‐extreme gradient boosting (WOA‐XGBoost) surrogate model is developed, based on relatively few FEA results obtained using a Latin hypercube sampling (LHS). Its strengths lie in the interpretability of the design variables and effective determination of fine‐tuned hyperparameters. A case study on an impeller is conducted considering uncertainties from 11 input variables, where an efficient XGBoost model with an R2 greater than 0.93 on test set is established using 400 samples from practical FEAs. In addition, the importance analysis indicates that elasticity modulus and density play the greatest impact on the maximum strain, showing a combined importance of 82.3%. Furthermore, the reliability assessment results under fatigue parameter derived from the Median method tend to be more conservative compared to those obtained from the Seeger method.

Fatigue Reliability Assessment for Orthotropic Steel Decks: Considering Multicrack Coupling Effects

Multiple fatigue cracks are generally present in practical engineering due to the existence of welding; the size and number of cracks of orthotropic steel bridge decks are greatly uncertain. The component failure conditions caused by these cracks may have correlations. Currently, it is still a challenging issue to develop a physical model of multiple fatigue crack propagation in bridge decks and perform a fatigue reliability assessment, which is also the motivation that drives the innovation of this study. A fatigue reliability evaluation method is presented for orthotropic steel bridge decks, considering the coupling effect of multiple cracks and the randomness of vehicle loading. A numerical simulation method for multifatigue crack growth is developed by combining the ABAQUS and FRANC3D programs. The equivalent crack depth under different spacing and depths of collinear cracks is calculated by using numerical simulation and the multicrack equivalent characterization method. The critical damage accumulation function of multiple fatigue cracks is established using linear elastic fracture mechanics. Subsequently, the critical damage accumulation function of multiple fatigue cracks is established based on linear elastic fracture mechanics. In order to solve the time-consuming problem of traditional Monte Carlo method, the iHL-RF method and AK-MCS method are developed for fatigue reliability analysis. The results show that compared with the single-crack model, the fatigue reliability of orthotropic steel deck will be crucially reduced considering the coupling effect of double cracks. The MCS, iHL-RF and AK-MCS methods can effectively solve the fatigue reliability analysis problem. Compared with the MCS method, the reliability calculation time based on AK-MCS method is significantly reduced. The AK-MCS method-based method reduces the time for calculating the reliability of orthotropic steel decks by 50% compared with the iHL-RF method. The reliability analysis of orthotropic steel deck bridge based on AK-MCS method is proved to be efficient and accurate.

Application of Optimizing Multifactor Correction in Fatigue Life Prediction and Reliability Evaluation of Structural Components

Application of Optimizing Multifactor Correction in Fatigue Life Prediction and Reliability Evaluation of Structural Components

The high-throughput bridge to the rapid evaluation of fatigue reliability of structural engineering materials

A high-throughput strategy using miniature specimens to evaluate the ASTM-defined fatigue endurance limits of some engineering materials through a high-throughput symmetry bending cantilever beam fatigue testing system is proposed. Employing such a high-throughput testing method for examining some typical engineering materials, we reveal that the fatigue limits obtained by the traditional testing standard can be directly determined by the high-throughput method-obtained fatigue limit multiplied by a suitable conversion factor. Such a high-throughput method was validated theoretically by the proposed crack initiation model and experimentally by the F316 stainless steel specimens subjected to different aging treatments and Gamma-ray irradiation.

Discussion on Fatigue Reliability Evaluation Method of Welded Structure of Carbody Based on Digital Twin

Abstract Taking the key welds of the heavy-duty gondola carbody as the research object, first, the fatigue assessment of the carbody is carried out based on the quasi-static the main S–N curve method, and the quasi-static evaluation method is discussed; second, the typical welds are selected. Based on the full-size bench physical test and virtual test of railway freight carbody, the quasi-static method is discussed; finally, the line test is used to verify the results. The results show that: (1) among all the load conditions in the quasi-static analysis of railway freight cars, the damage of the core plate needs to be considered according to different parts of the carbody, and this condition is effective for the evaluation of the bearing area of the linear load transfer of the carbody for the welds with nonlinear load transfer such as floor, the stress response caused by core plate load has the problem of over-estimation of damage. (2) The lap weld of floor and beam is less damaged under heavy load, but the stress response is larger in empty state, which indicates that the vibration effect should be considered in the design. (3) The virtual test can make up for the problem of traditional quasi-static analysis. The combination of the two can better realize the fatigue reliability evaluation of carbody.

Research on fatigue reliability assessment of engine cylinder head based on neural network

Fatigue reliability (FR) evaluation is crucial for extending the service life and improving the reliability of automotive engines. This study proposed a general framework for assessing high cycle FR based on the back propagation neural network (BPNN). Using a diesel engine cylinder head (CH) as an example, the stochastic finite element analysis was implemented by considering the uncertainties of materials and loads. Subsequently, the stochastic finite element calculation process was replaced with the BPNN model to expedite fatigue life prediction. Ultimately, the reliability assessment of the CH was conducted, taking into account the influence of the load sequence. The research findings indicated that the reliable life t0.95 of the CH considering the load sequence was approximately 75 h, representing a 7.1% increase compared to the linear cumulative damage. During the service life of the CH, the failure probability sensitivity factor for the gas force load exceeded 0.9, offering an important reference for optimizing FR.

Fatigue reliability evaluation of reinforced concrete bridges under stochastic traffic loading based on truck weight limits

To investigate the fatigue reliability of reinforced concrete (RC) bridges under stochastic traffic loading and the effectiveness of limiting the truck load, this study presented an analysis method for evaluating the bridge fatigue reliability under the action of random traffic flows based on truck weight limits. Firstly, a simply RC T-beam bridge was selected as an example to illustrate the presented approach, and the traffic-induced stress spectrum of the tensile rebars in the critical girder of the bridge was obtained. Secondly, based on the collected traffic data from two specific areas, the corresponding random traffic flow was simulated respectively, and then calibrated using the weight limit referring to the current regulation and overload violation rates ( VR) to exclude overweight trucks. Finally, based on the S–N curve from Eurocode 3 and Miner’s cumulative damage model, the effects of violation rate, average daily truck traffic ( ADTT) and truck weight limit ( TWL) on the fatigue reliability index of the bridge were studied. The results show that heavy duty trucks will induce serious cumulative fatigue damage, and degrade the durability of RC bridges, while limiting the truck weight can obviously slow down the reduction of the fatigue reliability index. Both the ADTT and the VR can significantly affect the fatigue reliability of the bridge. More specifically, the bridge fatigue reliability index shows a clear downward trend with the increase in the ADTT and the VR. Furthermore, the performance to satisfy the target fatigue reliability of the bridge was compared between TWL for each type of trucks and unified TWL for all the trucks, and then the unified TWL for all the trucks are determined to ensure the target reliability index of the RC bridge after 100 years’ service life.

Stochastic Propagation of Fatigue Cracks in Welded Joints of Steel Bridge Decks under Simulated Traffic Loading.

The fatigue cracking of orthotropic steel bridge decks (OSDs) is a difficult problem that hinders the development of steel structures. The most important reasons for the occurrence of fatigue cracking are steadily growing traffic loads and unavoidable truck overloading. Stochastic traffic loading leads to the random propagation behavior of fatigue cracks, which increases the difficulty of the fatigue life evaluations of OSDs. This study developed a computational framework for the fatigue crack propagation of OSDs under stochastic traffic loads based on traffic data and finite element methods. Stochastic traffic load models were established based on site-specific, weigh-in-motion measurements to simulate fatigue stress spectra of welded joints. The influence of the transverse loading positions of the wheel tracks on the stress intensity factor of the crack tip was investigated. The random propagation paths of the crack under stochastic traffic loads were evaluated. Both ascending and descending load spectra were considered in the traffic loading pattern. The numerical results indicated that the maximum value of KI was 568.18 (MPa·mm1/2) under the most critical transversal condition of the wheel load. However, the maximum value decreased by 66.4% under the condition of transversal moving by 450 mm. In addition, the propagation angle of the crack tip increased from 0.24° to 0.34°-an increase ratio of 42%. Under the three stochastic load spectra and the simulated wheel loading distributions, the crack propagation range was almost limited to within 10 mm. The migration effect was the most obvious under the descending load spectrum. The research results of this study can provide theoretical and technical support for the fatigue and fatigue reliability evaluation of existing steel bridge decks.

Fatigue reliability analysis of floating offshore wind turbines considering the uncertainty due to finite sampling of load conditions

The fatigue reliability-based design is critical for the structural safety of floating offshore wind turbines (FOWTs). In principle, infinite potential load conditions that the FOWT may experience should be considered in fatigue assessment, while in practice only limited number of load conditions are used, which inevitably induces uncertainty to fatigue estimation. However, to this uncertainty, little attention has been paid. In this study, the fatigue reliability of a FOWT is investigated with a focus on this uncertainty. The C-vine copula method is adopted to model concurrent wind and wave conditions, and the probability-based sampling method is employed to determine the load conditions used for fatigue analysis. This uncertainty is assessed quantitatively via bootstrap method based on numerous simulations. The Gaussian random variable can be used to describe the uncertainty, and the standard variation is proportional to the −0.5 power of the number of load conditions. The fatigue reliability evaluation model of FOWT is established considering this uncertainty, and sensitivity analysis is performed to assess the influence of different random variables. The results indicate that the effect of this uncertainty is comparable to some other uncertainties in certain cases, and should be paid attention to in practice.

Fatigue reliability assessment method for wind power gear system based on multidimensional finite element method

As a core strategic technology industry, the wind power plays an important role in protecting national energy reserves. The large gear component is one of the core foundation parts in wind turbines, and its quality indexes greatly affect the service performance of the wind turbine drive chain and even the wind turbine as a whole. This paper calculates the fatigue load history of the wind power large gear system under the coupling mechanism of elastic behavior based on a multidimensional finite element method, and obtains the probabilistic fatigue strength of gear teeth through the gear low circumference fatigue test and life distribution transformation method, and deeply explores the inherent characteristics of the wind power gear system in functional implementation and then establishes a system fatigue reliability evaluation model. Finally, a mapping path from the global structural elements of the wind power gearbox to the reliability indexes of the gear system is constructed with significant simulation and test cost advantages. It can provide structural optimization guidance in the development and design of large wind power gear systems, and significantly reduce the cost of achieving reliability indexes in the design iterations of such large high-end equipment. At the same time, it can provide cost-effective training data for intelligent optimization algorithms such as the deep reinforcement learning, which will eventually achieve multi-objective optimal stiffness matching for wind power gearboxes under reliability index constraints.

Fatigue reliability evaluation of heavy-haul locomotive car body underframe based on measured strain and virtual strain

Fatigue reliability evaluation of heavy-haul locomotive car body underframe was conducted based on measured strain and virtual strain.The coupler load was calibrated by combining bench test and linear fitting. Acceleration responses and dynamic strains of key positions were measured. The load–strain transfer coefficients of the car body were obtained by finite element analysis (FEA). The virtual strain was calculated by combining the obtained coefficients with the measured coupler load history and acceleration history. The frequency spectrum of the measured strain and the virtual strain was compared. The fatigue damage and fatigue life of measured strain and virtual strain under reliabilities of 95% and 97.7% were compared.

A multi-state Semi-Markov model for nuclear power plants piping systems subject to fatigue damage and random shocks under dynamic environments

Fatigue degradation is a vital damage mechanism for piping systems in nuclear power plants (NPPs). The accurate fatigue reliability evaluation of piping systems is significant for assessing the safety and reliability of an NPP. In this work, we presented a multi-state model for the fatigue degradation process of piping systems in NPPs, which accounts for the effects of random shocks and dynamic environments. The fatigue degradation of the piping was described by a Semi-Markov process, which allows accounting for generic distributions of the holding times of the system states. The arrival of the shocks was assumed to be governed by a Poisson process. The dynamic environment in which the piping is located was assumed to be governed by a Markov process. The analytical solution of the time-dependent state probability of the piping was derived. We developed a Monte Carlo (MC) algorithm for the simulation of the stochastic process describing the integrated stochastic evolution of the dynamic environment, system degradation and random shocks, which was applied to verify the correctness of the proposed model. The effectiveness of the proposed model was demonstrated by applying the model to numerical illustrations.

Structural fatigue reliability evaluation based on probability analysis of the number of zero-crossings of stochastic response process

Structural fatigue failure is closely related to the number of stress cycles. Therefore, the number of the intersections between stochastic response process and zero-boundary is a key problem in structural fatigue reliability analysis. In this paper, the relationship between the number of the multiple intersections and the fatigue cumulative damage index is derived according to the Miner rule-based high cycle fatigue random cumulative damage index. Then, use random walk to approximately simulate Wiener process, and get the first intersection probability between Wiener process and the zero-boundary. Next, further utilize the renewal process to solve the distribution law of the number of intersections between the Wiener process and the zero-boundary in a period of time. Finally, based on the fatigue failure criterion considering the randomness of the failure threshold, the calculation formula the structural fatigue reliability is derived. As a practical example, the fatigue reliabilities of the key part of Metro Bogie under different operation periods are analyzed using the proposed method.

Fatigue Reliability Prediction Method of Large Aviation Planetary System Based on Hierarchical Finite Element

The reliability of planetary equipment determines the economic affordability and service safety, to a large extent, for a helicopter transmission system. However, with the continuous improvement of the progressiveness and large-scale degree of new aviation planetary equipment, the contradiction between reliability design indexes and R&D economy is also gradually highlighted. This paper takes the large aviation planetary system as a research object, aims to accurately evaluate the system reliability level formed in design processes, and deeply excavates the inherent characteristics of the planetary system in functional realization and builds a system fatigue reliability evaluation model accordingly. An advanced hierarchical finite element technology is used to calculate dangerous tooth load histories under the influence of system global elastic behavior, and the tooth probability fatigue strength is obtained through the gear low-cycle fatigue test and life distribution transformation method, so as to provide economic load and strength input variables, respectively, for the reliability model. This prediction method can provide targeted structural optimization guidance in the development and design of the large aviation planetary system and significantly reduce the cost of reliability index realization for this kind of large-scale, high-end equipment in design iteration processes.

Probabilistic fatigue life prediction of an aero-engine turbine shaft

PurposeAero-engine components endure combined high and low cycle fatigue (CCF) loading during service, which has attracted more research attention in recent years. This study aims to construct a new framework for the prediction of probabilistic fatigue life and reliability evaluation of an aero-engine turbine shaft under CCF loading if considering the material uncertainty.Design/methodology/approachTo study the CCF failure of the aero-engine turbine shaft, a CCF test is carried out. An improved damage accumulation model is first introduced to predict the CCF life and present high prediction accuracy in the CCF loading situation based on the test. Then, the probabilistic fatigue life of the turbine shaft is predicted based on the finite element analysis and Monte Carlo analysis, where the material uncertainty is taken into account. At last, the reliability evaluation of the turbine shaft is conducted by stress-strength interference models based on an improved damage accumulation model.FindingsThe results indicate that predictions agree well with the tested data. The improved damage accumulation model can accurately predict the CCF life because of interaction damage between low cycle fatigue loading and high cycle fatigue loading. As a result, a framework is available for accurate probabilistic fatigue life prediction and reliability evaluation.Practical implicationsThe proposed framework and the presented testing in this study show high efficiency on probabilistic CCF fatigue life prediction and can provide technical support for fatigue optimization of the turbine shaft.Originality/valueThe novelty of this work is that CCF loading and material uncertainty are considered in probabilistic fatigue life prediction.

Probabilistic fatigue life prediction model of natural rubber components based on the expanded sample data

A novel method for determine the probabilistic distribution model of natural rubber (NR) fatigue life is proposed. Uniaxial tension fatigue tests are carried out on dumbbell-shaped cylindrical specimens. According to the fatigue test data, a support vector machine (SVM) model is established, in which the empirical reliability and the rubber fatigue life are considered as input and output variables, respectively. The SVM model is used to expand the NR fatigue life data. The analysis of the expanded data demonstrates that the NR fatigue life follows a lognormal distribution. Accordingly, the fatigue reliability evaluation of NR components is carried out.

Polymer gear contact fatigue reliability evaluation with small data set based on machine learning

AbstractPolymer gears have shown potential in power transmission by their comprehensive mechanical properties. One of the significant concerns with expanding their applications is the deficiency of reliability evaluation methods considering small data set circumstances. This work conducts a fair number of polyoxymethylene (POM) gear durability tests with adjustable loading and lubrication conditions via a gear durability test rig. A novel machine learning-based reliability model is developed to evaluate contact fatigue reliability for the POM gears with such a data set. Results reveal that the model predicts reasonable POM gear contact fatigue curves of reliability–stress–number of cycles with 2.0% relative error and 18.8% reduction of test specimens compared with the large sample data case. In contrast to grease lubrication, the oil-lubricated POM gear contact fatigue strength improves by 10.4% from 52.1 to 57.6 MPa.

Structural Static/Fatigue/Damage Tolerance Comprehensive Design Optimization of Composite Laminate

This paper develops a structural static/fatigue/damage tolerance comprehensive design method for composite laminated structures under mechanical–thermal coupling environments. The developed design method can finely quantify the additional stress and deformation caused by the mechanical–thermal coupling effect. In addition, a new damage evolution-based fatigue reliability evaluation method is proposed, and the structural fatigue behavior can be described and predicted. The different failure modes of composite material and their correlations are considered during the damage evolution analysis. The structural possible accidental damage can also be taken into account by applying the global preset damage in design stage. Thus, the static requirement, fatigue requirement, and damage tolerance requirement can all be considered simultaneously during the design process. The structural comprehensive design of composite laminate is conducted by virtue of the two-level optimization method. A case of a notched composite laminate is employed to verify the proposed method. In addition, a case of a civil aircraft wing structure is used to explain the feasibility of the developed method in dealing with structural design problems in engineering.

Fatigue Reliability Evaluation of Aged Railway Steel Bridges Based on Probabilistic Fracture Mechanics

Fatigue Reliability Evaluation of Aged Railway Steel Bridges Based on Probabilistic Fracture Mechanics