Fatigue Life Distribution Research Articles

Fatigue Life and Stress Analysis of a Single Cylinder Four Stroke Crankshaft

This paper focuses on the optimization of a crankshaft using ANSYS software in terms of weight and strength. The initial designs of the crankshaft, piston, and connecting rod were created using SolidWorks. The force generated by the gas during the combustion process was calculated to be 12017 N. Next, the SolidWorks assembled system was imported into ADAMS View software for simulation, which revealed a time-variant force of the crankpin of 14049 N. The calculated value was verified with results obtained from analytical calculations, showing a deviation of 0.23%. Finite element analysis was done for the crankshaft using ANSYS transient structural after applying loadings and boundary conditions. The optimization process aimed to minimize the crankshaft's weight while maintaining its strength and durability. The results of the ANSYS simulations showed a weight reduction of 2.5% from the original 2.983 kg to 2.907 kg, while maintaining the required strength and durability. The optimized crankshaft was compared to its original design in terms of fatigue life, weights, and stresses. The maximum von Mises stress was reduced by 16%, shear stress by 3.5%, and deformation by 3.5%, which were validated through analytical calculations. The crankshaft analysis resulted in a significant increase in fatigue life, calculated to be infinite under the given conditions. To conclude, the objective to optimize the crankshaft for performance and efficiency was achieved, demonstrating a 2.5% weight reduction and substantial improvements in fatigue life and stress distribution, proving the effectiveness of ANSYS software for the design optimization process.

Analytical method of incorporating failure probability to predict the fatigue life of ultra-high-performance concrete (UHPC)

This study predicted the fatigue life (N) of UHPC incorporated with different volume fractions (Vf = 0.0%, 0.5%, 1.0%, 1.5% and 2.0%) of steel fiber under flexural cyclic loading at various stress levels (S). The Weibull distribution, a two-parameter model, was utilized to estimate the distribution of fatigue life in UHPC. Subsequently, three methods were employed to calculate the parameters: the graphical method, the method of moments, and the method of maximum likelihood. The averaged values of these parameters were then obtained to enhance the accuracy of the estimation. The results are presented in the form of S-N diagrams, which depict the quantitative relationship between stress (S) and fatigue life (N). This relationship was determined using the Wohler equation, the modified Wohler equation, and the power equation. By employing these equations, the flexural fatigue strength of UHPC can be accurately predicted. Subsequently, the fatigue failure probability (Pf) was incorporated to enhance the reliability of the S-N quantitative relation. The fatigue testing results were presented in the form of S-N-Pf curves, which comprehensively reflect the relationship between stress, fatigue life, and failure probability. Furthermore, the mathematical relation of the S-N-Pf curves was derived to predict the fatigue life of UHPC with a given failure probability, providing a more comprehensive and accurate assessment of its fatigue behavior.

Probabilistic fatigue life prediction using multi-layer perceptron with maximum entropy algorithm

In the structural fatigue fields, such as aerospace, maritime, and civil engineering, the accurate construction of the Probability-Stress-Life (P-S-N) curve is crucial for preventing unexpected structural failures and is fundamental to the engineering design process. Conventional methods usually assume that the fatigue life distribution follows a normal or weibull distribution, which overlooks the differences of life distribution at different stress levels and introduces subjective errors. To address this issue, this paper proposes a new approach based a multi-layer perceptron model with maximum entropy algorithm (MPME) for probabilistic fatigue life prediction. During the derivation of life probability distribution function in this approach, the type not require any pre-assumption, thus effectively avoiding the introduction of subjective errors. Specifically, the dispersed information of fatigue life is quantified as various life distribution statistical features such as mean, variance, skewness, and kurtosis. Next, learn the continuous functional relationship between stress and these features using a multi-layer perceptron (MLP). Finally, the target probability distribution is derived using the maximum entropy algorithm, with the predicted distribution features obtained from the MLP serving as constraints for it. In addition, to ensure the consistency between the prediction of MLP and physical laws, we encode physical knowledge into the network loss to guide the updating of network parameters. Experimental results of two different material fatigue data demonstrate that, compared to traditional deterministic model-based methods and machine learning methods, the MPME in this paper can more accurately predict the probabilistic fatigue life.

Confidence Intervals for Ratio of Percentiles of Birnbaum-Saunders Distributions and Its Application to PM2.5 in Northern Thailand

In the statistical literature, the Birnbaum-Saunders distribution has garnered considerable attention as an important fatigue life distribution for engineers. This distribution finds applications in medicine, engineering, and science. A percentile denotes a threshold below which a designated percentage of scores or data points are situated. In particular cases, percentiles are the preferred choice over mean and variance, especially when dealing with skewed data. This paper investigates confidence intervals for the ratio of percentiles of Birnbaum-Saunders distributions. It discusses the generalized fiducial confidence interval, Bayesian credible interval, and the highest posterior density intervals using a prior distribution with partial information and a proper prior with known hyperparameters. To compare the performance of these confidence intervals, the study employs coverage probability and average length measurements. Monte Carlo simulation via the R package is used to calculate the coverage probability and average length. The results indicate that the highest posterior density interval using a prior distribution with partial information outperforms the other confidence intervals. Finally, the paper presents the results of the simulation study and applies them in the field of environmental sciences.

The fatigue behavior of TC17 titanium alloy under different test environments: The effect of saltwater on fatigue failure characteristics and life estimation

The study of fatigue behavior in saltwater for TC17 titanium alloy has become a potential research issue in practical engineering and theoretical scientific research. In this study, it is found from the designed fatigue test that the corrosiveness of the test environment has a significant negative effect on the fatigue life of titanium alloy, and the distributions of fatigue life in 3.5%NaCl solution and 5%NaCl solution are similar. Typical surface failure characteristics and obvious corrosion traces are detected due to the coupling effect of corrosion and fatigue load. Then, electron back scatter diffraction (EBSD) is performed to figure out the change of micro grains from fine grains to coarse grains with the test environment changes from water to NaCl solution, and the strain concentration regions are detected at grain boundary and internal of coarse grains. Finally, the comparison of S-N curve with different models are carried out, Basquin model is proved to be suitable for the S-N curve estimation of TC17, and S-N models for different test environments are established. The micro test results provide a clear understanding of the corrosion fatigue failure behavior, and the newly established model considering the corrosiveness of test environment is novel and essential to the further fatigue study in theoretical research and engineering practice.

An AK‐MCS‐based probabilistic fatigue life prediction framework for turbine disc with a mean stress correction model

AbstractThe turbine disc plays a crucial role in aerospace engine, significantly influencing both their fatigue life and overall reliability. Due to the substantial uncertainties present, devising a method for the probabilistic analysis of turbine disc fatigue life becomes crucial. This paper introduces a novel framework that combines adaptive Kriging Monte Carlo simulation (AK‐MCS) with a mean stress correction model to evaluate fatigue life distribution effectively. AK‐MCS, stands out as an algorithm that constructs a Kriging model, effectively reducing the need for an extensive finite element analysis. Furthermore, a mean stress correction model is proposed for the Masson‐Coffin equation tailored for fatigue life prediction of GH4133 disc material. This model has been empirically validated to be effective. The presented framework for probabilistic fatigue life analysis not only holds considerable engineering value but also offers innovative approaches for tackling analogous challenges in the field.

Microstructure analysis and life prediction of DD6 superalloy under 760 °C combined high and low cycle fatigue conditions

The impact of high and low cycle combined loads on the fatigue performance of DD6 alloy was investigated in this work. Specifically, the combined high- and low-cycle fatigue response of DD6 alloy was examined at a temperature of 760 °C under different low cycle stress amplitudes (960, 1000, and 1040 MPa). The findings revealed that higher low cycle stress amplitudes result in shorter combined high and low cycle fatigue life and less dispersion in life. Correlations between the microstructural features (crystal plane distribution, fracture elevation difference, and the area proportion of crack propagation zone) and fatigue performance were accurately established, demonstrating a linear relationship between these microstructural features and the logarithm of fatigue life. The study also uncovered the evolution rule of microstructural features in high- and low-cycle combined fatigue. Furthermore, the fracture mechanism was analyzed and the distribution of high and low cycle combined fatigue life of DD6 alloy at 760 °C was statistically validated using the dual-parameter Weibull distribution theory. Building upon the crystal plasticity theory, a fatigue life prediction model was developed, and the combined cycle fatigue lifespan under various low cycle stress amplitudes was compared. The comparison between the predicted life and actual fatigue life indicated that the predicted lifespan falls in three times the scatter band.

Effect of plastic strain under roller bending on fatigue properties ofextruded 6063 T66 aluminium alloy profile

The tensile plastic strain of material sampled from profiled areas under roller bending and pre-strained material was analyzed. The experimental data of high-cycle fatigue were approximated by a probabilistic Weibull cumulative distribution (P−S−N curve). The fatigue life prediction model was implemented for numerical simulations of roller bending in the LS-Dyna solver and experimental data. The cyclic behaviour of the material shows a decrease in the fatigue life distribution with increasing static failure levels. The fractographic analysis of the fracture surface shows an increased level of intergranular cracking for the tensile pre-strain as a result of the dislocation accumulation in the neighbourhood of grain boundaries. The estimation results of the proposed model show good correlation of probabilistic scatter bands (error below 10%).

DYNAMIC LOADING EFFECTS ON CAR SUSPENSION COMPONENTS DURING ROAD DRIVING

Suspension system plays a vital role in providing a pleasure and safe driving experience. Because of that, studying the behaviour of suspension system during road driving is crucial. This paper describes the work carried out to investigate the dynamic loading effects on suspension components during rough road driving and analyse based on safety factor and fatigue life. A multibody simulation using SolidWorks software is conducted. Von Mises stress, strain, and displacement distribution plots are generated to visualize stress and deformation patterns. Fatigue life distribution plots indicate infinite fatigue life strength for the majority of components. Kinematic and compliance test examines roll centre, vertical movement of the wheel centre, toe angle and camber angle. This comprehensive analysis contributes to suspension system design and optimization, improving vehicle safety and durability.

To etch or not to etch, Part III: On the hydrophobic-rich content and fatigue strength of universal adhesives after long-term ageing

ObjectivesTo examine whether dentin-etching extension and/or the hydrophobic-rich content of hybrid layers would affect fatigue strengths of a mild universal adhesive after long-term aging. MethodsTwin-bonded resin-dentin interfaces were produced by etching sound midcoronal dentin beams with 32 % ortho-phosphoric acid for 15 s (OPA15s), 3 s (OPA3s) or 10 % meta-phosphoric acid for 15 s (MPA15s). Samples were bonded with a mild universal adhesive with or without additional coating using a solvent-free bisGMA-based bonding resin. Self-etch application served as control. Composite buildups were made with a nanofilled composite. Bar-shaped twin-bonded interfaces (0.9 × 0.9 × 12 mm) were aged for two years in artificial saliva at 37 ℃ and tested under 4-point flexure at quasi-static (n = 16) and cyclic loads (n = 35) until failure. The stress-life fatigue behavior was evaluated using the staircase method at 4 Hz. Crack initiation and fracture patterns were evaluated by SEM. Cyclic-loaded data was analyzed by Kruskal-Wallis on Ranks (α = 0.05). ResultsSignificantly higher fatigue life distributions and higher endurance limits were observed for less aggressive etch-and-rinse protocols (OPA3s and MPA15s) after long-term ageing. Hydrophobic-rich coating produced 20–32 % higher endurance limits, prevented micrometer-sized porosities at bonded interfaces, reduced etching-associated variability and lowered crack formation.SignificanceLong-term hydrolysis produces detrimental effects on the fatigue strength of resin-dentin interfaces. The bond-promotion effect of less aggressive etch-and-rinse protocols and the creation of hybrid layers with higher hydrophobic-rich content are critical to extend the durability of mild universal adhesives. Therefore, current oversimplification trends in adhesive dentistry may limit resin-dentin bonding performance.

A physics-guided modelling method of artificial neural network for multiaxial fatigue life prediction under irregular loading.

To improve the generalization of the artificial neural network (ANN) model on the prediction of multiaxial irregular cases, a physics-guided modelling method is proposed with inspiration from the Basquin-Coffin-Manson equation. The method suggested using two neurons in the last hidden layer of the ANN model and constraining the sign of weight and bias value. In this way, the prior physical knowledge of fatigue life distribution is introduced into the ANN model, which resulted in a satisfactory performance on the life prediction of multiaxial loading cases and better extrapolation ability. Furthermore, the physics-guided ANN model can also provide satisfactory prediction on irregular cases with the training of only regular cases. Compared with the conventional model, the average relative error and root mean squared error (RMSE) of prediction decreased by 33.29% and 44.29%, respectively. It greatly broadens the application scenarios of neural networks on multiaxial fatigue life prediction. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 1)'.

Fatigue life prediction of stay cables under vehicle load considering corrosion variability

The combined effect of environmental corrosion and fatigue loads can accelerate the failure of stay cables. To ensure the safe operation of stay cables, this paper proposed a method for evaluating the fatigue life of stay cables, considering the variability of steel wire corrosion within the cable. Firstly, the relationship between the mean value and the standard deviation of uniform corrosion depth was established based on the experimental data of the corroded steel wires under the artificial accelerated corrosion environment. Then, the model of cable time-vary corrosion under the actual service environment was substituted, and the distributions of the weight loss rate of steel wires were obtained. Subsequently, a method for calculating the fatigue life of stay cables considering the corrosion variability of steel wires in the cable was proposed based on the parallel system theory and the Miner linear cumulative damage criterion. Finally, the North Channel Bridge (NCB) of Hangzhou Bay Bridge was used as an example, and the fatigue life distribution of stay cable under the combined action of corrosion and vehicle load was predicted. The results indicate that considering the corrosion variation of steel wires in the cable leads to a reduction in the fatigue life of stay cables, and neglecting this variability in fatigue life prediction methods is unsafe and non-conservative.

A selection criterion of small load truncation level based on the principle of same distribution of fatigue life

AbstractA new criterion of selecting the small load truncation level for simplification of fatigue test spectrum was developed, which is based on the principle that the truncated spectrum has the same fatigue life distribution as the original spectrum. Considering the influence of uncertainties of material fatigue performance and load spectrum on the fatigue life distribution, the relation between the distribution difference and the small load truncation level was established. According to the designed tolerance value of distribution difference, the appropriate small load truncation level could be determined accordingly. The selection criterion was verified by the fatigue tests of LC4CS aluminum alloy smooth sheet specimens. The results show that good simplification effect of spectrum can be achieved based on the criterion.

Random vibration-based virtual fatigue test for large-scale welded structures using frequency-domain structural stress method and its application to traction transformers

PurposeThis paper aims to present an engineering computational method for fatigue life evaluation of welded structures on large-scale equipment under random vibration load.Design/methodology/approachBased on a case study of the traction transformers, virtual fatigue test (VFT) was proposed via numerical simulation approach. Static analysis was conducted to identify the risky zone and then dynamic response of the risky welds under random vibration load was calculated based on frequency-domain structural stress method (FDSSM) theory, life distribution and associated survivability at various locations of the structure were obtained. Structural modification was finally performed according to the evaluation results. Moreover, experimental test was carried out and compared with the virtual test result.FindingsBy applying the virtual test, fatigue life of the complex welded structures on large-scale equipment can be accurately and efficiently obtained considering dynamic effect under random vibration load. Meanwhile, risky welds can be directly determined and targeted modification scheme can be accordingly concluded. Validity of the VFT result was proved by comparing with the experimental test.Originality/valueThe proposed method can help obtain equivalent structural stress and fatigue life distribution of the welded structure at any position with various survivability and make quantitative evaluation on the life-extending effect of the structural modification. This method shows significant cost and efficiency advantages over experimental test during design stage of the large-scale structures in numerous manufacturing industries.

A probabilistic constant amplitude life diagram modeling method for composite materials considering spatial mapping relation

AbstractConventional constant amplitude life diagrams (CLDs) model cannot reasonably describe mean stress effect and stochastic uncertainty present in the fatigue failure process of composite materials. To address this problem, taking the spatial mapping relationship between probabilistic S‐N curves and probabilistic CLD model as an entry point, a probabilistic CLD modeling method is proposed under the assumption of linear equations and the assumption of equiprobable quantile point between static strength distributions and fatigue life distributions. The p‐S‐N curve is established using fatigue test data from different load zones divided by different stress ratios.Subsequently, the p‐CLD model is derived through the spatial mapping relationship of the p‐S‐N curve. The method is validated by fatigue test data of glass fiber/polyester resin composites. The results indicate that the proposed method can offer an accurate description of the probabilistic behavior of composite materials.

Three-dimensional fatigue crack growth based method for fatigue reliability of metallic materials

Fatigue is one of the greatest threats to structural integrity. It is sensitive to the uncertainties of material quality, manufacturing quality and service load, making fatigue reliability analysis important and challenging. Here, a reliability analysis method considering these uncertainties is proposed. Firstly, the distribution of equivalent initial crack sizes in the material was obtained from the S-N data by back-extrapolation based on three-dimensional (3D) fatigue crack growth prediction. Then, the sample set for reliability analysis was obtained by randomly combining the applied stresses and crack sizes under the assumption that the crack sizes and applied stresses are independent. Further, the fatigue life of every sample is predicted with the 3D crack growth method, and the cumulative distribution of fatigue life was obtained to analyze the reliability. Based on the obtained initial crack distribution with stress ratio R ≥ 0, the predicted P-S-N diagrams of different stress ratios and stress concentrations were in accordance with the experimental data, indicating that the obtained initial crack size distribution has a certain universality. Finally, the influence of sampling numbers on the reliability analysis is analyzed with five types of commonly used metallic alloys. It is shown that the cumulative distribution of fatigue lives could be obtained with a less sampling number. Compared with Monte Carlo and importance sampling methods, this method can reduce the number of samples effectively and achieve the reliable probability of different fatigue life intervals.

Effect of graphene nanoplatelets on fatigue performance of Glass Fiber Reinforced Composite materials based on recycled polyethylene terephthalate

Utilization of recycled polyethylene terephthalate (PET) based resins for manufacturing composites is an environment friendly and cost effective solution. This study attempts to explore the influence of graphene nanoplatelets (GPnP) addition on the fatigue performance of glass fiber reinforced composites based on recycled PET in terms of S–N Data, area of hysteresis loops during fatigue loading, fatigue life distributions, self generated temperature during fatigue loading and stiffness degradation. Incorporation of GPnP in rPET-UPR based composites brings their fatigue performance at par with virgin polyester resin based composites. Statistical analysis of fatigue life data using two parameter Weibull distribution established that GPnP addition has only marginal effect in increasing dispersion in fatigue lives.

Low-cycle tensile fatigue performance of a wire rope strand with an internal flaw in varied position and direction

Taking into account the effects of mean stress, elastic-plasticity and nonlinear contact, the finite element model of the tensile fatigue performance of an internal flawed wire rope strand is built by using the local stress strain method in the present study. A mesh model of the strand with a high-precision feature is established through a block-based method and refinement in the flaw region. The strand with a flaw is investigated to explore its fatigue life distribution, and the effects of the flaw’s position and direction on the strand’s fatigue and bearing performances are analyzed. The numerical results demonstrate that the low-cycle fatigue life zone occurs at the interwire contact region of the intact wire rope strand, while is located at the flaw region of the wire rope strand with an internally flawed wire. The minimum fatigue life of the wire rope strand decreases due to the occurrence of the internal flaw. Moreover, as the internal flaw’s direction angle decreases, the strand’s minimum fatigue life is reduced, and the internal flaw with the major axis perpendicular to the strand axis is the most dangerous. The internal flaw in the outer wire has a more severe influence on the fatigue property of the wire rope strand than a core wire flaw with the same dimension and direction. The wire rope strand is more prone to stress yielding due to the internal flaw, and the effect is getting more significant as the internal flaw’s direction angle decreases.

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.

Probability Modeling of Exchange Rate Fluctuation in Nigeria

The Naira's value has continued fluctuating in comparison with other currencies due to its depreciation. Because of this fluctuation, returns are difficult to forecast. The core objective of this study is to find a unified probability distribution for modelling the exchange rate in Nigeria and this will contribute immensely to the existing body of knowledge. The continuous nonnegative exchange rate data from 1970 to 2021 was used for this research paper. Previous studies have demonstrated different probability distributions from others in the real sense. Therefore, the selection of appropriate probability distributions is of great importance. This study adopted ten continuous probability distributions. The graph of the probability density function and Chi-square goodness of fit statistics show that the probability distributions fit the exchange rate data. Meanwhile, the log-likelihood value and the AIC show that Fatigue Life (3P) distribution is best done compared with fitted probability models. Therefore, the Fatigue Life (3P) is Nigeria's unified probability distribution for the modelling exchange rate.