In this study, the effect of flow rate ratio (R) and total flow rate (Q) on the surface temperature of thermal barrier coatings (TBC) was investigated using a newly developed small-scale methane-oxygen burner rig. Subsequently, the failure mode of electron beam physical vapor deposition (EB-PVD) TBC was examined, and the relationship between surface temperature and coating life was established. The surface temperature of the TBC was found to be strongly dependent on both the flow rate ratio and the total flow rate. Specifically, surface temperature exhibited a proportional relationship with total flow rate, while it showed an inverse relationship with flow rate ratio. The failure mode of the EB-PVD TBC involved a gradual increase in delamination from the rim to the center of the coin-shaped specimen, and this failure mode was found to be independent of surface temperature. Additionally, it was determined that the surface temperature of EB-PVD TBC has a perfectly inverse linear relationship with coating life. This finding implies that the derived linear regression line from the burner rig test can be directly used to predict coating life for any untested surface .temperature.
Rolling bearing fatigue life is an essential criterion in industrial equipment design and manufacturing and requires precise maintenance and replacement predictions. ISO/TS 281:2007 and 16281:2008 are commonly used for angular contact ball bearing (ACBB) fatigue life calculations, but they do not account for the characteristics of individual bearing elements under combined loading conditions. This study proposes an enhanced formula for calculating fatigue life modification factors that considers individual element-specific contact loads and resulting film thickness variations. The proposed fatigue life formula provides longer life predictions than the conventional method of determining modification factors based solely on maximum contact loads. This difference is particularly noticeable in low-speed and/or heavy-loading applications. Analysis conducted using the proposed fatigue life formula on various factors affecting fatigue life revealed that fluid kinetic viscosity coefficients, temperature-associated density changes, and changes in radial loads and rotational speeds could significantly impact the fatigue life of ACBBs. The proposed fatigue life formula is expected to increase the accuracy of ACBB fatigue life predictions.
The main shaft of a mechanical press inevitably includes significant stress concentrations that can trigger severe mechanical damage and finally lead to failure under repetitive use. In this study, an efficient procedure to quantitatively evaluate the fatigue life of the shaft system including the main shaft and its support bearings, based on the macroscopic failure analysis of the main shaft broken during actual use, was investigated. For this purpose, the bearing support was modeled as an elastic foundation, and the elastic foundation stiffness value was varied to determine the optimal value that best simulates the failure behavior, especially with respect to the failure location and failure sequence, of an actual shaft. While the finite element mesh size was kept the same, only the effect of elastic foundation stiffness was investigated. The optimum value for the main shaft investigated in this study was approximately 60 N/mm³, and the fatigue life of the shaft was evaluated based on the conventional maximum principal stress theory. Based on this, two modified designs to enhance the fatigue life of the existing shaft are proposed.
This paper presents the characteristics of tapered roller bearings (TRBs) taking into consideration the effects of tapered roller angle error which may occur during manufacturing. To this end, a TRB model including tapered roller angle errors was developed. The effects of tapered roller angle error on the contact load distribution, bearing stiffness and fatigue life were investigated with respect to changes in the tapered roller angle error. A statistical analysis of the fatigue life of TRBs was also provided with respect to tapered roller angle error. Simulation results show that the tapered roller angle error changes the load distribution of the rollers and causes angular misalignment in TRBs, and subsequently, influences the bearing stiffness and fatigue life. The statistical analysis shows that the Weibull distribution is an acceptable method to represent the statistical fatigue life for the practical range of tapered roller angle errors.
This paper presents the effects of bearing locations on the mechanical characteristics of a multi-stepped spindle system related to bearing fatigue life, natural frequency, and static stiffness. The multi-stepped spindle is supported by a pair of tapered roller bearings (TRBs) and subjected to radial loading. To solve the equilibrium equation of the spindle system which is inherently statically-indeterminate, this study adopts an integrated shaft-bearing model, where the spindle is modelled by the finite shaft elements and the supporting TRBs are modelled by the five degrees-of-freedom TRB model developed by the authors. An iterative computational method is used to estimate the spindle deflection coupled with bearing deflections, and afterwards the bearing stiffness and internal contact loads of rolling elements are computed. The bearing fatigue life based on the ISO standard and the first natural frequency of the spindle system are evaluated with the spindle-bearing model. The influences of bearing locations on the static stiffness and natural frequency of the spindle, and the fatigue life of TRBs are rigorously investigated. The numerical results show the noticeable effects of bearing locations on the spindle system characteristics. The presented results provide a comprehensive assessment to aid for design optimization of spindle-TRB system.
This study aims to investigate the fatigue life of T-Type fillet welded joints for excavators subjected to bending loads, and also to verify the predicted fatigue life of the welded part using the effective notch stress method. Moreover, this study aims to determine an optimal toe angle of the T-Type fillet welded structure. In this context, the fatigue lives of T-Type fillet welded specimens (SM490A) were measured and the effective notch stress method for predicting the fatigue life of the T-Type fillet welded structure was verified by comparing with the FAT-225 curve of IIW (International Institute of Welding) as was suggested for the current types of welded structures. Considering simultaneously the scattering factor of the welded structure, the stress condition at the toe part higher than the root part, and the stress minimization condition of the toe part, the optimum toe angle at the T-Type fillet welding was identified at 30°. Likewise, the maximum stress (310.5 MPa) when the toe angle was 30° was about 14% less than the maximum stress (354.0 MPa) at 45°, and the fatigue life was improved by about 30%.
In general, it is noted that the time domain technique becomes difficult to predict with the use of the accurate fatigue life, due to the lack of dynamic information of the structure. When the multi-axial stress is generated by the random vibration excitation in the mechanical structure, the fatigue analysis should have performed in the frequency domain as based on the multi-axial PSDs due to the problems presented above. Notably, Premont proposed a method to calculate the equivalent stress using PSDs in the frequency domain. In calculating the equivalent stress PSD, the phase difference between the multi-axial stress components was not considered at that time. This study propose a frequency domain fatigue analysis technique which can calculate the equivalent stress from the multi-axial PSD, as it works considering the phase difference that can appear in the real vibration excited structure. To verify this method, the conventional time-domain method as similar to a multi-axial rainflow method, is compared with the proposed frequency domain method in a simple simulation model. The multi-axial PSD and finally the von Mises stress model is reviewed, according to whether the phase difference between the multi-axial stress components is considered or not is analyzed.
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A method for editing multi-axis load spectrums based on S-transform dual-threshold theory Yongjie Lin, Zhishun Yang, Lingyun Yao Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering.2025;[Epub] CrossRef
This paper presents an analysis of the stiffness and fatigue life of double-row angular contact ball bearings (D-ACBBs). To this end, a comprehensive quasi-static model was developed for D-ACBBs subjected to five degree-of-freedom (DOFs) loading and displacement. The model was verified by a commercial computational program. A rigorous numerical investigation was performed, based on the developed model regarding the effects of external load, rotational speed, axial clearance, bearing arrangement, and angular misalignment on the stiffness and fatigue life of the D-ACBB. The D-ACBB was subjected to negative axial clearance and yielded improved performance in terms of fatigue life and stiffness. The effect of angular misalignment on the bearing fatigue life was found to be significantly dependent on the amount of axial clearance. The moment stiffness of the D-ACBB in a back-to-back arrangement was higher than the face-to-face arrangement owing to the increased effective load center distance, whereas the radial stiffness and fatigue life were almost unchanged for back-to-back and face-to-face arrangements.
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Enhanced Fatigue Life Estimation Formula for Angular Contact Ball Bearings Subjected to Combined Loading Jin Hyeok Sa, Gilbert Rivera, Chan-Sik Kang, Seong Wook Hong Journal of the Korean Society for Precision Engineering.2024; 41(3): 231. CrossRef
Combined analysis of stiffness and fatigue life of deep groove ball bearings under interference fits, preloads and tilting moments Yi Jiang, Tianyu Zhu, Song Deng Journal of Mechanical Science and Technology.2023; 37(2): 539. CrossRef
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The stiffness characteristics analysis of the duplex angular contact ball bearings based on a comprehensive multi-degree-of-freedom mathematical model Tengfei Xu, Lihua Yang, Wei Wu, Yaoyu Han, Endian Xu, Kai Wang Applied Mathematical Modelling.2022; 106: 601. CrossRef
Characteristics of Duplex Angular Contact Ball Bearing with Combined External Loads and Angular Misalignment Tengfei Xu, Lihua Yang, Kai Wang Applied Sciences.2020; 10(17): 5756. CrossRef
Modeling of Crossed Roller Bearings Considering Roller Roundness Deformation Van-Canh Tong, Eui-Wook Jung, Seong-Wook Hong Journal of Tribology.2020;[Epub] CrossRef
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In this paper, a study on the effectiveness of micro-peening was accomplished for improvement of fatigue characteristics for reduction gear of manned and unmanned aircraft. The Almen saturation curve was obtained by various peening injection pressure supplied from a commercial air jet peening machine. The effective micro-peening process condition was adopted as five bar. The four points rotary bending fatigue test was conducted by using test specimen made of AISI alloy that was carburized based on AMS standard in this work. From the fatigue test result, the fracture life of specimen peened by nozzle pressure with five bar and six bar was higher than the un-peened specimen by approximately 323 percent and 146 percent respectively. However, the fracture life of specimen peened by the nozzle pressure with six bar was lower by approximately 221 percent than the peened specimen by five bar. For this reason, the peening nozzle pressure with five bar was decided as the optimum micro-peening condition. Effectiveness of micro-peening was validated and this micropeening technique will be used for real manned and unmanned aircraft gear parts or other durability mechanical parts.
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