• Proceedings of the KWS Conference
• /
• 1997.10a
• /
• pp.77-80
• /
• 1997

Spot welding has been used in the sheet metal joining processes because of its high productivity and convenience. In this study, predicting methods of fatigue life of spot welded joint have been studied fatigue life of conch-peel spot welded joint was influenced by tail effect. Fatigue life was estimated by stress index parameter considering multiaxial stresses and tail effect. Fatigue tests were conducted with the coach-peel specimens using SPCC.

• Tribology and Lubricants
• /
• v.18 no.2
• /
• pp.160-166
• /
• 2002

In case of rough contact fatigue, the accurate calculation of surface tractions is essential to the prediction of crack initiation life. Accurate Surface tractions influencing shear stress amplitude can be obtained by contact analysis based on the morphology of contact surfaces. In this study, to simulate rough contact under sliding condition, gaussian rough surface generated numerically in the previous study was used and to calculate clack initiation life in the substrate, dislocation pileup theory was used.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2000.11a
• /
• pp.72-79
• /
• 2000

In case of rough contact fatigue, the accurate calculation of surface tractions is essential to the prediction of crack initiation life. Accurate Surface tractions influencing shear stress amplitude can be obtained by contact analysis based on tile morphology of contact surfaces. In this study, to simulate rough contact under sliding condition, gaussian rough surface generated numerically in the previous study was used and to calculate crack initiation life in the substrate, dislocation pileup theory was used.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.9
• /
• pp.1027-1032
• /
• 2012

Two types of very small multiplying gears and arrays have been developed for new dental hand-pieces, and the increased speed ratios, modules, number of teeth, gear diameters, and gear types were calculated based on the dynamics of the machinery. The contacting and bending strengths were evaluated for gear teeth with two design concepts using AGMA equations and finite element analyses, and the contacting stresses on teeth with and without DLC (diamond-like-carbon) coating layers were calculated. Fatigue and tension tests were performed to obtain an S-N curve, the Young's modulus, and the strength of the gear material, and these were utilized in the analyses. Slightly larger stresses were found for 2-axis-type gears than for other types of gears, and the S-N curves showed that a gear lifetime of 109 cycles was satisfied. The contacting stresses in gears coated with DLC were reduced by 30%. A new prototype model of a hand-piece with small gears was successfully fabricated and tested.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.11
• /
• pp.1453-1459
• /
• 2011

A roller pinion gear (RPG) system composed of either a pin or a roller and its conjugated cam gear can improve the gear endurance from that of a conventional gear system by reducing the sliding contact while increasing the rolling motion. In this paper, we first proposed the exact cam gear profile and the self-intersection condition obtained when the profile shift coefficient is introduced. Then, we investigated the Hertzian contact stresses and the load stress factors while the varying the shape design parameters to predict the gear surface fatigue life, which is strongly related to the gear noise and vibration at the contact patch. The results show that the pitting life can be extended significantly by increasing the profile shift coefficient.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.112-118
• /
• 2005

Ball bearings which were fitted between housing and shaft play an important role in rotating shaft system smoothly, Therefore bearing's running accuracy has significant influence on that of rotating machinery. Manufacturing accuracy of bearings as well as that of shaft and housing is main factor to affect bearing running accuracy In this paper, bearing's vibration and fatigue life considering raceway roundness of ball bearing before and after being fitted into housing are theoretically estimated. To perform analysis, a simple three degrees of freedom model was proposed and then these analysis was conducted utilizing the Newton-Raphson iterative method. The results show that vibration magnitude of ball bearing fitted into housing is considerably larger than before assembly, and bearing's theoretical L$_{10}$ fatigue life that ninety percent of the bearing population will endure decreased in about fifty percent.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.9
• /
• pp.1391-1398
• /
• 2004

Railway wheels and axles belong to the most critical components in railway vehicles. The service conditions of railway vehicles became more severe in recent years due to the increase of speed. Therefore, a more precise evaluation of wheelset life and safety has been requested. Wheel/rail contact fatigue and thermal cracks due to braking heat are two main mechanisms of the railway wheel failure. In this paper, an evaluation procedure for the contact fatigue life of railway wheel is proposed. One of the main sources of the contact zone failure is the residual stress. The residual stress on wheel is formed during the manufacturing process which includes a heat treatment, and then is changed by contact stress developed by wheel/rail contact and thermal stress induced by braking. Also, the cyclic stress history for fatigue analysis is determined by applying finite elements analysis for the moving contact load. The objective of this paper is to estimate fatigue life by considering residual stress due to heat treatment, braking and repeated contact load, respectively.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.8
• /
• pp.35-41
• /
• 2010

White Etching Layer(WEL) is a phenomenon that occurs on the surface of rail due to wheel/rail interactions such as excessive braking and acceleration. Rolling Contact Fatigue(RCF) cracks on the surface of rail have been found to be associated with WEL. In this study, we have investigated RCF damages of white etching layer using twin disc testing and fatigue analysis. These tests consist of wheel flat tests and rolling contact fatigue tests. WEL has been simulated by wheel flat test. It has been founded that the WEL with a bright featureless contrast is formed on the surface of specimen by etching. Rolling contact fatigue test was conducted by using flat specimens with the WEL generated by the wheel flat test. It has been observed that two types of cracks occur within the specimen. The contact fatigue test was simulated in 2D elastic-plastic FE simulations. Based on loading cycles obtained from the finite element analysis, the fatigue life analysis according to the thickness variation of WEL was carried out. The longest fatigue life was observed from the thickness of 20um.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.6
• /
• pp.613-620
• /
• 2012

Rails are subjected to damage from rolling contact fatigue, which leads to defects such as cracks. Rolling contact fatigue damages on the surface of rail such as head check, squats are one of growing problems. Another form of rail surface damage, known as "Ballast imprint" has become apparent. This form of damage is associated with ballast particles becoming trapped between the wheel and the surface of rail. These defects are still one of the key reasons for rail maintenance and replacement. In this study, we have investigated whether the ballast imprint is an initiator of head check type cracks and effect of defect size using Finite element analysis. The FE analysis were used to investigate stresses and strains in subsurface of defects according to variation of defect size. Based on loading cycles obtained from FE analysis, fatigue analysis for each point was carried out.

• Tribology and Lubricants
• /
• v.35 no.4
• /
• pp.237-243
• /
• 2019

Through this study, we investigate the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings. The fatigue life of untreated and UNSM-treated needle roller bearings is evaluated using a roller fatigue tester at various contact stress levels under oil-lubricated conditions. We can ascertain that the fatigue life of an UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with an untreated one, where the effectiveness of UNSM technology diminishes with increasing contact stress. The surface roughness and surface hardness of needle roller bearings before and after being treated by UNSM technology are compared and discussed to understand the role of UNSM technology in improving the fatigue life of needle roller bearings. In addition, a fractograph of the damaged bearings is observed using a scanning electron microscopy to shed light on the fracture mechanisms of bearings under different contact stress levels. We can therefore conclude that the application of UNSM technology to the needle roller bearings improves the fatigue life by reducing the friction coefficient and increasing the wear resistance; this may be attributed to a reduction in surface roughness from 0.5 to $0.149{\mu}m$ and an increase in surface hardness from 58 to 62 HRc.