In the case of TV products, space constraints and design requirements make it advantageous to use a worm gear that has a small volume and a self-locking function. Single enveloping worm gear teeth are classified as ZA, ZN, ZK, ZI, and ZC according to international standards. However, combining worm shafts and worm wheels with different tooth profiles can significantly worsen meshing transmission errors and reduce the lifespan of the worm gear. Despite these challenges, due to processing limitations, ease of manufacturing, and cost reduction, combinations of worm shafts and worm wheels with different tooth profiles are still considered. In this study, we confirmed the meshing transmission error for a worm gear that combined a ZA tooth shape worm shaft with a ZI tooth shape worm wheel. Additionally, we examined the contact stress and fatigue life characteristics of the material combinations using finite element analysis (FEM).
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.
In highly mobile workplaces, wearable walking assistant robots can reduce muscle fatigue in the lower extremities of workers and increase energy efficiency. In this study, walking efficiency according to the development of an ultralight wearable hip-assist robot for industrial workers was verified. Five healthy adult males participated in this study. Their muscle fatigue and energy consumption were compared with and without the robot while walking on a flat treadmill and stairs. When walking on the treadmill while wearing the robot, muscle fatigue in the rectus femoris and gastrocnemius decreased by 90.2% and 37.7%, respectively. Oxygen uptake and energy expenditure per minute also decreased by 8.9% and 13.1%, respectively. When climbing stairs while wearing the robot, fatigue of the tibialis anterior, semitendinosus, and gastrocnemius muscles decreased by 18.2%, 33.3%, and 63.6%, respectively. Oxygen uptake and energy expenditure per minute also decreased by 3.6% and 3.7%, respectively. Although wearing a hip-assist robot could reduce muscle fatigue and use metabolic energy more efficiently, it is necessary to further increase the energy efficiency while climbing stairs. This study is intended to provide basic data to improve the performance of robots.
A Continuous Ship Unloader (CSU) is a facility in which multiple buckets rotate to excavate cargo from a ship to land. It is typically designed to have a lifespan of 20 years. However, fatigue damage is likely to occur before the end of its designated lifespan. This study aims to examine the possibility of extending the component"s lifespan by evaluating the remaining useful life of L-holder, a part of CSU, that has been in use for 20 years. Fatigue load history was predicted by measuring the strain with or without strain at the L-holder part requiring periodic replacement. Through tensile and fatigue tests, the remaining life was evaluated when cracks were not present. In addition, the remaining life in the presence of cracks was evaluated through destructive toughness test and fatigue crack propagation test. Life prediction results based on test cycles were obtained. The proposed guidelines are expected to be helpful for preventing CSU accidents.
The automotive electronic control unit outputs control signals using electrical signals of various input sensors installed in the vehicle to control the state of the engine, automatic transmission, and electric power steering (EPS). These units are installed inside the vehicle or engine room, and the temperature rises and falls by several tens of degrees due to the heat of the engine and the self-heating of the electronic control unit. Therefore, it was exposed to a thermal fatigue environment due to the difference in the coefficient of thermal expansion between the components, which caused frequent component damage. Solder cracks due to thermal fatigue in electronic control units are a key failure mode. However, because of its great heat capacity, the electronic control unit for automobiles took a long time to attain the desired temperature of high or low, and as a result, the 1,000-cycle test for thermal fatigue life verification required 3,167 hours (or 4.4 months). Therefore, in this study, the thermal shock cycle test time for the verification of the thermal fatigue life of electronic control units for automobiles was reduced by dividing it into two types.
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Design of Electric Propulsion System Considering Propulsion Performance of Vessels Keun-Seok Park, Min-Ho Park, Yeon-Seok Park, Ki-Chan Kim Journal of Electrical Engineering & Technology.2025; 20(5): 3367. CrossRef
A Study on the Statistical Life Prediction of Automotive Electronic Control Unit Considering High Temperature Degradation Taekyung Kim, Junghwan Lee Transaction of the Korean Society of Automotive Engineers.2025; 33(5): 385. CrossRef
Evaluation of local muscle fatigue has been conducted over past decades to investigate the process of fatigue accumulation and to reduce effect of fatigue in EMG field. The purpose of this study was to investigate fatigue in isotonic contractions, which can inflict the same fatigue on the subject during dynamic contractions. Local muscle fatigue was measured by changing the load level and exercise time in dumbbell curl comprising isotonic contractions through power spectrum changes. Five healthy males and five healthy females performed dumbbell curls with 1 kg load for two minutes, and on other days when no fatigue occurred due to the previous exercise, performed for one minute with a 2 kg load. The muscle fatigue was estimated by median frequency before and after fatigue, the decrease was greater than in the trial wherein a load of 2 ㎏ was applied for one minute than in the trial where a load of 1 kg was applied for two minutes for the females. The decrease in the median frequency is quantitative data indicated by the slowing of the motor unit actional potential (MUAP), suggesting exercise intensity is more sensitive to the slowing of the MUAP than the exercise duration.
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.
The input shaft of gearbox usually bears a cyclic variation of torque, which may lead to the risk of experiencing a fatigue fracture. To evaluate the fatigue life accurately and identify the weak parts, the ANSYS is used to simulate the torsional fatigue of the input shaft for the gearbox, and the fatigue life of the weak part is obtained, which is then tested and verified by the torsional fatigue testing in the MTS torsional fatigue test rig. The test results show that the maximum difference is 14% between the calculated life and the testing results, indicating that the simulation value can reflect the actual fatigue life accurately. Notably, the cracks appear in the large oil holes, and its life is mainly concentrated in the crack initiation stage, accounting for 99.2% of the total life. The analysis results show that the fatigue life of the software simulation has the guiding significance for the life evaluation. The fatigue life of the shaft can be quickly calculated by the simulation to reduce the number of fatigue tests and achieve cost-effectiveness.
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%.
Process and die design of cold forging for the asymmetric part, engine mount adapter has been studied. Forging of the asymmetric part frequently causes die failure because of the high forging load and local stress concentration of the die. Thus, performing process design of cold forging to minimize forging load is required. Preform for the engine mount adapter was chosen based on the forging load and filling rate of forgings by the finite element analysis. In the die design, number of stress rings, interface radius, and relative interference were investigated in several cases with maximum principle stress by the finite element method. The shape of the die was determined by comparing the load changing the radius of the flange area. Also, the life of the designed die was calculated using the Goodman theory by cyclic fatigue loading. As a result, it was confirmed that the calculation life and results of the test were identical. In this study, it is verified that stress concentration and fatigue life should be considered simultaneously in the design of cold forging die for the asymmetric part.
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Analyzing Cold Heading of Self-Piercing Rivet Using FEM Sangchul Lee, Jaeho Hyun, Seung-Woo Hong, Kwon Hee Won, Heesoo Park, Soongkeun Hyun, Sang-Yeol Kim Journal of the Korean Society of Manufacturing Technology Engineers.2022; 31(1): 19. CrossRef
Mold-design Verification of Ball Housing Insert Die in Non Processing Type Multi-stage Cold Forging Won-Seok Hwang, Jong-Won Choi, Eu-Enn Jung, Myungchang Kang Journal of the Korean Society of Manufacturing Process Engineers.2021; 20(12): 8. CrossRef
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If fatigue failure occurs during aircraft operation, it can cause catastrophic injuries. So, it is necessary to study fatigue failure at the design stage. Frequency domain fatigue analysis is used to predict fatigue failure. During frequency domain fatigue analysis, results can be calibrated by PSD analysis. In this study, fatigue failure is predicted by the Dirlik method, Lalanne method and Steinberg method. Regarding results, life determined by the Dirlik method, Lalanne method and Steinberg method were 8.737, 8.314, and 7.901 times the standard life, respectively. The Steinberg method is the most conservative but the difference with other methods was approximately 10%. In the cycle histogram, the Dirlik method had more counts than the Lalanne method in lower stress range. However, it does not affect the life of material used in this study. However, if material has a lower fatigue limit or stronger PSD data is used, life difference will occur.
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Analysis of Acoustic Load Fatigue Life of Skin of POD for Aircraft considering Aspect Ratio Wonwoong Lee, Jaemyung Cho, Jongin Bae, Hoonhyuk Park Journal of the Korea Institute of Military Science and Technology.2025; 28(2): 126. CrossRef
A Study of Vibration Analysis of 100 MPa Class Fitting Thread for Mobile Hydrogen Charging Station JUNYEONG KWON, SEUNGJUN OH, JUNGHWAN YOON, JEONGJU CHOI Transactions of the Korean Hydrogen and New Energy Society.2024; 35(1): 83. CrossRef
Very high cycle fatigue on gas metal arc butt-welded AA6061-T6 plates Iksu Kim, Moon G. Lee, Martin Byung-Guk Jun, Jungho Cho, Yongho Jeon Journal of Mechanical Science and Technology.2023; 37(12): 6649. CrossRef
Vibration-Based Fatigue Analysis of Octet-Truss Lattice Infill Blades for Utilization in Turbine Rotors Sajjad Hussain, Wan Aizon W. Ghopa, S. S. K. Singh, Abdul Hadi Azman, Shahrum Abdullah, Zambri Harun, Hawa Hishamuddin Materials.2022; 15(14): 4888. CrossRef
Experimental Verification of Dirlik Fatigue Evaluation in Frequency Domain Using Beam Structure under Random Vibration Eunho Lee, Siyoung Kwak Transaction of the Korean Society of Automotive Engineers.2021; 29(2): 157. CrossRef
Gas turbine blades are important parts of a power plant, and thus, it is necessary to be able to predict the low-cycle fatigue life of the blades. In this study, a low-cycle fatigue test of In738LC, which is used primarily in gas turbine blade manufacture, was performed at various high temperatures (750oC, 800oC, and 850oC). From the test results, the stressstrain curve and the stress-strain hysteresis loop were obtained. It was established that In738LC has no strain hardening or softening. The life prediction equations for low-cycle fatigue were derived using the Coffin-Manson equation and the energy model. In conclusion, one equation for predicting the life low-cycle fatigue was obtained using the energy level with temperature as the varying factor.
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