Papers by Keyword: Fatigue Life Prediction

Abstract: This paper introduces a novel fatigue failure criterion that leverages the evolution of residual stresses under cyclic loading to more accurately predict fatigue life in advanced materials. Traditional fatigue models often overlook the dynamic nature of residual stresses, which can significantly influence crack initiation and propagation. The proposed criterion incorporates a combination of experimentation and mathematical modeling to capture the complex interplay between cyclic loading, material microstructure, and fatigue damage. The criterion's effectiveness is validated through a series of fatigue tests on representative materials, demonstrating its superior predictive capability compared to conventional methods. This research offers a new paradigm for fatigue analysis, enabling more reliable design and performance assessment of critical components in various engineering applications.

Abstract: Accurately modeling the fatigue life and strength of additively manufactured (AM) components ensures their reliability and performance in critical applications. However, this task is hindered by the complexities of AM processes, including material defects, anisotropy, residual stress, and surface roughness. This review explores how integrating surrogate modeling, transfer learning, and Bayesian inference can address these challenges and elevate predictive capabilities to new levels of accuracy and robustness. Surrogate modeling offers computationally efficient approximations of the intricate relationships between AM process parameters and fatigue behavior, enabling rapid exploration and optimization of design spaces. Transfer learning facilitates the adaptation of knowledge across different machines and process conditions, improving predictions even in low-data scenarios. Bayesian inference adds a layer of reliability by incorporating uncertainty quantification and prior knowledge into the modeling process. Together, these advanced methodologies present a transformative opportunity to improve the quality, efficiency, and robustness of fatigue life predictions for AM components, setting the stage for their broader adoption in high-performance applications

Abstract: Fatigue life prediction of a welded structure is a complex phenomenon due to the nature of fatigue and the welding process. Additionally, Finite Element Method (FEM) results are extremely sensitive to the size of elements. Therefore, it is difficult to adopt a method to estimate the fatigue life, especially for welded structures. Besides, mesh size independence is a critical issue to perform fatigue life prediction methods that eliminates the need for excessive element numbers in the mesh. This paper investigates the Master S-N Curve Approach (MCA) using the output parameters of the mesh insensitive Structural Stress Method (SSM). MCA based on SSM employs structural stresses recovered from nodal forces and nodal moments. To recover these inputs, FEM model should be established properly. Thus, boundary conditions and applied loads were prepared for the model according to the BS EN 13749:2021. The submodeling technique in ANSYS software was used to analyze the bogie structure. To justify the mesh independence for the model, different mesh sizes were tested. In a specific range for shell bodies, SSM was shown to provide sufficient mesh independence feature. Furthermore, MCA was compared with Hot Spot Stress Method and Nominal Stress Method based on their fatigue life estimations.

Abstract: Fatigue life of drill pipe is studied systematically based on reliability analysis. Calculation results show that bending and tensile stress in drill pipe body is significantly greater than that in the tool joint during drilling process. Drill pipe body’s fatigue strength is about 500MPa under the condition that the stress ratio is -1. The fatigue strength of tool joint is about 360MPa under the condition that the average tensile stress is 496MPa. The fatigue fracture position of drill pipe is concentrated on pipe body, and most fatigue cracks originate from pipe’s outer surface. Compared with material fatigue life, the fatigue life of whole drill pipe is significantly lower. Under the condition that the confidence level is 95% and deviation is 5%, drill pipe’s fatigue life distribution is normal distribution while the stress amplitude is 660MPa, 620MPa, 580MPa and 540MPa respectively. With the decreasing of stress amplitude, the peak of logarithmic fatigue life’ probability density distribution curve decreases gradually, and its dispersion increases gradually. Drill pipe’s fatigue life prediction equations whose reliability are 50%, 90%, 99% and 99.9% are calculated separately.

Abstract: The capability of the strip yield (SY) model to predict crack growth in structural steel is investigated. To this end the SY model implementation developed by the present authors is applied to simulate crack growth observed in S355J2 steel specimens under constant amplitude and simple variable amplitude loading. A particular attention is given to the calibration of the model using the constraint factors and examining whether tuning the model, based on constant amplitude loading, allows the adequate predictions for variable amplitude loading.

Abstract: Fibre reinforced polymer composites have been widely used in automotive industries due to its high tensile strength, lightweight and potential resistance towards environmental conditions. This paper presents a study on the fatigue life prediction of fibre-reinforced polymer (FRP) and the application of FRP composite in manufacturing engineering industries. Four designs of I-beam with different thickness and fillet were studied. The analyses of fatigue life of the designs were done using ANSYS software. Results from the analysis showed that the combination of glass/polyester and the design of I-beam with a fillet of 10mm and thickness of 20mm was the best combination in terms of its good fatigue life, factor of safety and stronger top surface.

Abstract: A damage accumulation model is presented for fatigue life prediction of metallic structures. Based on the energy theory and material fatigue test data, the plastic strain threshold for damage initiation was modified for HCF and LCF respectively. The damage evolution parameters were determined according to the fatigue test results of standard specimens. A damage mechanics-finite element full-couple method was adopted to simulate the process of fatigue damage evolution, incorporating elastic modulus reduction due to fatigue damage. Comparisons are made with the fatigue tests of 2A12-T4 open-hole plates and good agreement was obtained.

Abstract: This work aims to predict fatigue life of hybrid integrated circuit (HIC) hermetical metal sealing structure mounted on PCB under random vibration loading. The prediction method consists of following steps. Firstly, finite-element model was developed to obtain model parameters (including natural frequencies and mode shapes) and power spectral density (PSD) of the critical part of sealing structure by ANSYS workbench. Secondly, modal test and random vibration test were conducted to verify the results of simulation. Thirdly, the Von Mises stress PSD was transformed into time-history data through inverse Fourier transform with Matlab program after calculating from the FEA results. The rainflow-counting algorithm was employed to evaluate cumulative damages of the critical part. The material’s S-N curve, Palmgren-Miner’s damage accumulation rule and rainflow-counting algorithm were used to predict fatigue life. A specially designed fixture and board with heat sink were used in the experiment to verify the first five mode shapes and response spectrum of the six critical points with hammer excitation. The calculation result of in this study is 70.3 hours which could be a reference for structural design of hybrid integrated circuit hermetical metal sealing under vibration conditions.

Abstract: Fatigue cracking reported in a lighting pole on an elevated bridge structure near Wellington raised the question of how to better design for and predict the fatigue life of lighting poles subject to wind induced fatigue. There have been concerns as to the reliability and currency of the methods commonly used in New Zealand. The paper therefore reviews current international design methods and describes the development of an improved fatigue design method for lighting poles in New Zealand. The new method uses fracture mechanics based crack growth formulations in conjunction with a modified J.D. Holmes Method for wind response analysis of the pole to varying wind speeds. Cumulative crack growth is calculated iteratively rather than using an S-N curve based Palmegran-Miner summation. Wind spectra used in the method are developed from long term meteorological records at representative locations. Software has been prepared to enable quick assessment of the expected fatigue life of lighting poles, and associated gear openings and holding down bolts The method and software has been calibrated with reference to full scale laboratory fatigue proof testing of representative base stubs and natural wind response testing of a 12 m high lighting pole.

Abstract: An experimental study was conducted to evaluate notch effects on fatigue behavior of a neat polymer (PP impact co-polymer) and a composite made of 30 wt% short glass fibers in polybutylene terephthalate (PBT). A plate-type specimen geometry with a central circular hole was used. The experiments were conducted at room temperature in uniaxial tension-tension (R = 0.1) and tension-compression (R = -1) loading conditions. Some analytical methods including Neubers rule and the method of critical distances were used in addition to FEA to predict fatigue life of notched specimens. Neubers rule commonly used for metallic materials proved to be an accurate method for predicting the notched fatigue life of the thermoplastics considered.