Fatigue Reliability Of Structures Research Articles

Time-dependent reliability analysis for structures under multilevel loads based on fatigue damage theory

This paper proposes an efficient method to evaluate the time-dependent fatigue reliability of structures under complex multilevel loads using a finite set of fatigue test data obtained under single-level loading conditions. The method preserves the simplicity of linear damage accumulation theory while considering the interactions among multiple load levels and the influence of load sequence on reliability. Leveraging the linear damage rule, a cumulative damage probability model was established under single-level constant amplitude loading. This model incorporates a fatigue life degradation function to characterize the cumulative damage effect of load cycles and corrects the fatigue reliability curve under single-level constant amplitude loading. By employing the principle of fatigue damage equivalence, the method determines the damage equivalence at the load switching point using the damage curve method, enabling the conversion of equivalent reliability under multilevel loads. The proposed method was validated by combining the test data obtained under three working conditions, including two-level loads loading, load blocks loading, and changing loads loading. The results demonstrate that the proposed method can accurately and efficiently evaluate the time-dependent fatigue reliability under different types of multilevel loads, using only a limited set of fatigue life data under single constant amplitude loads.

Sensitivity analysis of aircraft structural fatigue reliability under mixed uncertainty

Fatigue is the main failure mode of the structure. The aircraft structure is subject to multi-level cyclic loading, which is prone to fatigue damage, reduces reliability, and affects flight safety. Various uncertainties are inevitably associated with the factors related to the fatigue performance of the structure. In particular, for the variables with insufficient information, their uncertainties are hard to describe by the probability density function. In this paper, these variables are treated as interval variables. The sensitivity analysis of the aircraft structure fatigue reliability model under mixed uncertainties is studied. On the basis of the definition of the distance between interval numbers, the interval distance indexes are proposed as a global sensitivity measure for a mixed random-interval model system. To reduce the computational cost, the method combining the space partition with unscented transformation (SP-UT) is used to calculate the proposed indexes. Lastly, the proposed indexes and method are applied to solve the aircraft structure fatigue problem. Compared with the traditional MCS method, the proposed method has proved to be more conducive and efficient.

Structural fatigue reliability analysis based on active learning Kriging model

The paper introduces the active learning Kriging (ALK) model into the structural fatigue reliability analysis. Firstly, the structural variable stress is obtained by experimental tests or finite element simulation (FES). On this basis, the cyclic stress corresponding to the fatigue life is analyzed based on the rain-flow counting method and the structural fatigue life is correspondingly computed using the Miner-Palmgren damage rule. Secondly, the uncertainties to affect the structural variable stress are considered and thus the prediction of structural fatigue lives can be obtained. Further, the structural fatigue reliability model is established, and its reliability is obtained by computing the probability that the predicted fatigue lives are greater than the allowable life. Finally, to balance the accuracy and efficiency for computing the structural fatigue reliability, a small number of boundary sample points for experiment or FES are produced and the corresponding fatigue lives are computed. Sequentially, the Kriging model is adopted to approximate the structural fatigue reliability model and it is adaptively updated by the active learning strategy. Several examples are also given to demonstrate the effectiveness of the proposed ALK-based structural fatigue reliability method.

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.

Analysis on statistical uncertainties of wave loads and structural fatigue reliability for a semi-submersible platform

The statistical uncertainties of wave loads have large proportions in the structural fatigue strength analysis of offshore platforms. To investigate the uncertainties of wave loads during predicting fatigue loads, the assessing methods and formulas are proposed involving the wave spectrum, sea wave height, wave loading transfer function, zero-crossing period, possibility of sea state occurrence and wave direction; meanwhile, the model test of the wave loads is carried out in a see-keeping basin for studying the uncertainty of the wave loading transfer function. The corrected formulas of the significant wave height and mean zero-crossing period are statistically regressed by calculating the sea states in the Northwest Pacific and South China Sea. Furthermore, the influence factors of the sea states of difference seasons are analysed, and the distribution law of the wave direction of the wave loads and fatigue life of a semi-submersible platform are investigated. Finally, the fatigue reliability index of typical structures for a semi-submersible platform is assessed on the basis of uncertainties of wave loads and the other uncertainties of structural factors.

Fatigue life assessment method of bogie frame with time-domain extrapolation for dynamic stress based on extreme value theory

Structural fatigue reliability assessment is one of the research directions for railway vehicles' mechanical problems. Obtaining the representative stress spectrum is the basis of fatigue life assessment, and its adequacy and integrity will directly affect the accuracy of the assessment results. However, because of the limited conditions, many dynamic stress tests are completed in the short-term, which makes the fatigue evaluation results based on short-term test data challenging to reflect the structure's anti-fatigue status under the long-term service. Therefore, it is necessary to extrapolate the stress spectrum from small samples to large samples while retaining real data probability distribution characteristics. In this paper, a fatigue life assessment method with time-domain extrapolation for dynamic stress based on extreme value theory is proposed for the first time. Take a test point near the weld of the rotary arm positioning seat of a railway vehicle's bogie frame as a case study. Firstly, three time-series signals of dynamic stress of the test point in the initial, middle, and final stages of a whole wheel reprofile period are selected. The pre-processing and equal-weight linear superposition are carried out to them. Secondly, the tail probability distribution of the time-series signal after linear superposition is estimated by applying the POT Pareto distribution model, and its confidence level is 99%. Finally, the dynamic stress spectrum under the long-term service is obtained by several-multiple extrapolation of the superimposed time-series signals with the fitting probability distribution function, and the fatigue life of the test point based on the extrapolated dynamic stress spectrum is assessed. Compared with the commonly-used linear extrapolation method, the cumulative fatigue damage with the time-domain extrapolation method based on extreme value theory increased by 0.168%, and the safe operation mileage decreased by 2670 km. Therefore, indicate that using the fatigue analysis results under short-term load (i.e., linear extrapolation) to replace the fatigue analysis results under long-term load will cause the apparent error, which is indeed worthy of attention. And the fatigue life assessment method based on time-domain extrapolation is safer. Provide the method reference and theoretical support for fatigue life assessment under the long-term service.

Probabilistic modeling of uncertainties in fatigue reliability analysis of turbine bladed disks

Turbine bladed disks normally operate under complex loadings coupling with uncertainties originate from multiple sources, including material variability, load variation and geometrical uncertainty. The influence of these uncertainties on mechanical response of engineering components are critical for their fatigue assessment and reliability evaluation. In this work, a general framework for fatigue reliability analysis is developed by coupling the Latin hypercube sampling with FE analysis to describe the combined effects of multi-source uncertainties. Fatigue reliability analysis of a full-scale bladed disk under multi-source uncertainties was performed as well as sensitivity analysis for fatigue design. In order to describe the manufacturing errors or tolerances, random dimensions are inputted. Comparing the predicted fatigue lifetime distributions with/without geometrical uncertainty, it shows that geometrical uncertainty matters in structural fatigue reliability. Particularly, sensitivity analysis indicates that the geometrical uncertainty exerts more critical influences on the fatigue lifetime and reliability of the turbine bladed disk than others. The sensitivity factors of three typical dimensions emerges the influence of designed sizes and dimensional tolerances on the failure probability, which provides a reference for engineering design.

Fatigue damage and reliability assessment of subway train bogie frames under operating conditions

Fatigue cracks developed on subway train bogie frames before reaching the designed lifetime, which poses great challenges to operational safety. This article presents a structural fatigue reliability assessment method combining both the in-service measurement of dynamic stress and probabilistic approach for lifetime prediction. It was found that curved interval with rail corrugation can induce the elastic vibration and the modal stress on the frame, which caused the accelerated accumulation of the fatigue damage. The predicted failure mileage for the welding joint with 99% reliability was only 340,000 km, which agreed well with the real operation situation.

Probabilistic Modeling of Fatigue Damage in Orthotropic Steel Bridge Decks under Stochastic Traffic Loadings

Fatigue truck models with deterministic parameters were developed int a stochastic vehicle flow model. A response surface method was used to approximate the function between vehicle axle weight and equivalent fatigue stresses with few training data to solve the time-consuming problem of bridge finite element analysis under traffic flow loads. A probabilistic fatigue damage modeling method was presented and applied to the rib-to-deck details of steel box girder bridges. Finally, the fatigue damage model was applied to the reliability assessment of steel box girder bridges, and influences of traffic flow parameters on structural fatigue reliability were studied. Numerical results indicate that the higher occupancy rate of heavy vehicle flow in a slow lane than in a fast lane mainly explains the decrease in the fatigue reliability of corresponding rib-to-deck details. The increase in vehicle axle weight causes a rapid decrease in the fatigue reliability index of steel box girders. The fatigue reliability index of rib-to-deck detail in the slow lane decreases from 3.42 to 0.72 when the annual linear growth factor ranges from 0 to 1%. The stochastic fatigue vehicle flow model and the probabilistic model for fatigue damage exhibit considerable potential in the probability assessment of bridge fatigue damage.

Fatigue reliability study on T-welded component considering load shedding

In this paper, a coupled reliability method for structural fatigue evaluation considering load shedding is first proposed based on probabilistic fracture mechanics in which the uncertainties of the structural parameters are taken into account. Then, the method is applied to predict the fatigue reliability of the T-welded structure to the case of considering load shedding or not. The compared results show that by considering the load shedding, the structural fatigue reliability might be improved with less conservativeness. The influence rules of the load-shedding coefficient on the fatigue failure probability of the T-welded component are investigated, and some interesting results are obtained. That is, the influences of load-shedding coefficient on the fatigue failure probability can be divided into three regions, namely the high, medium and low fatigue failure areas. The last area is the most intriguing when we try to design a T-welded structure. The thickness of T-welded structure along the crack propagation direction is found to be one of the important design variables for the design of fatigue reliability, in which the low-fatigue failure zone is used as one of the reliability constraints. The basic design frame of T-welded structure is established to constrain the fatigue failure probability within the low-fatigue failure area.

Statistical Analysis of Loader’s Drive Axle Housing Random Load Spectrum

Statistical analysis of load spectrum is an important part on structural fatigue life and reliability research, it is generally considered that axle’s load spectrum follows Weibull distribution. This paper tested ZL50 loader’s loading history of different working conditions , and obtained the corresponding load spectrum by rain-flow counting method, then analyzed three distributions’ (normal distribution, lognormal distribution, Weibull distribution) fitting degree of load spectrum and effect on the fatigue reliability. Results show that the highest fitting degree of distribution function should be used to fit load spectrum, which can reduce the error in structural fatigue reliability prediction.

A probabilistic model for the fatigue reliability of structures under random loadings with phase shift effects

A probabilistic model is proposed for the high-cycle fatigue reliability of structures subject to multiaxial Gaussian random loadings with non-zero means. It is based on the Sines’criterion combined with an oriented prismatic hull approach for its equivalent shear stress amplitude J 2 , a in order to account for possible phase shifts between stresses involves in these loadings. The extreme value distributions along the founded directions are efficiently assessed in the frequency domain, from which we formulate the distribution of J 2 , a . This allows assessing the fatigue reliability of 3D structures. The complete methodology is illustrated by a didactic example and on a realistic problem having a wide-band power spectral density field of stresses.

Research progress on structural fatigue reliability design and analysis methods of Chinese railway vehicles

state-of-art 评论在疲劳可靠性设计和中国铁路车辆的结构的分析方法上被给新进展。首先，结构服从于强调历史和这历史的复杂随机的疲劳应该被联合动态模拟和联机检查决定。第二，随机的疲劳体质属于内在的疲劳现象，一个概率的模型被开发很好与幸存概率和信心的二大小描述他们，类似的模型也为随机的压力生活关系被介绍并且适当地外推进长疲劳生命政体。第三，疲劳限制的概念应该在给定的疲劳生活作为疲劳力量被理解，一个所谓的本地 Basquin 模型方法为测量随机的力量被建议。Inaddition，绘画并且为不可分地描绘随机的疲劳力量的 Goodman 铁匠图的应用程序方法以十公里被建立。第四，一个基于 reliabilitystress 的方法与随机的组成的关系的考虑被构造。Thesenew 进展为铁路疲劳可靠性设计和分析形成一个新框架工作。

STRUCTURAL STRESS-BASED FATIGUE RELIABILITY ANALYSIS CONSIDERING THE RANDOM CYCLIC CONSTITUTIONS

A structural fatigue reliability analysis method is presented to consider random cyclic constitutions.A charac- terization for the random constitutions is established by using two probabilistic measurements of survival probability and confidence.The entire material constants in the constitutive equation are reasonably taken as dependent random variables. The probabilistic S-N relations covering from mid-short life regime to long life regime,representing structural fatigue strength,are also given on the two probabilistic measurements. Considering that the random constitutions derive random stresses of structures under cyclic loading and the probabilistic S-N relations introduce random strengths of structures anti-fatigued cycling,reliability assessment is then constructed by considering interference of the random cyclic stress and strength.The method can be applied to realize fatigue reliability life prediction and reliability assessment at arbitrary probability level.Availability of the present method has been indicated by the reliability life prediction and reliability assessment of RD2 type axle of Chinese railway freight cars.

Fatigue reliability of structures based on probability and possibility measures: Liu, T. S. and Huang, G. R. Comput. Struct. (3 Oct. 1992) 45 (2) 361–368

Fatigue reliability of structures based on probability and possibility measures: Liu, T. S. and Huang, G. R. Comput. Struct. (3 Oct. 1992) 45 (2) 361–368

Fatigue reliability of structures based on probability and possibility measures

The randomness of fatigue life prediction has been commonly recognized, but recently researchers have begun to recognize the fuzziness of fatigue failure descriptions resulting from the lack of distinct definitions and precise information. In this paper, both probability- and possibility-based reliabilities of components subjected to fatigue loading are investigated. In the probability-based reliability, the material properties and the amplitude of a loading history are assumed to be random. In the possibility-based method, the fuzzy linear regression method is employed to account for the fuzziness. This work employs S-functions to define fuzzy limit state functions. Failure probabilities are calculated in terms of probability distributions of fuzzy damage and fuzzy limit state functions. Both probability- and possibility-based reliabilities of a portal frame are examined. Accordingly, the reliability of systems in the presence of fuzziness is calculated and compared to the results obtained from the probability-based method.