Yong-Joo Cho

Application of a conservation integral to an interface crack interacting with singularities

A mutual integral, which has the conservation property is applied to the problem of an interfacial crack. The stress intensity factors K1, K2, K3 and T-stress for the problem in an infinite medium are easily obtained by using the mutual integral without solving the boundary value problem. In doing so the auxiliary solutions are required and they are taken from the known asymptotic solutions. This method is amenable to numerical evaluation of the stress intensity factors and T-stress if the interfacial crack in a finite medium is considered.

The Fatigue Crack Initiation Life Prediction Based on Several High-Cycle Fatigue Criteria under Spherical Rolling Contact

In this study, the simulation of rolling contact fatigue is conducted under spherical contact. To predict a crack initiation life accurately, it is necessary to calculate contact stress and subsurface stresses accurately. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions and the subsurface stress field is obtained using rectangular patch, solutions. Based on these stress values, several multiaxial high-cycle fatigue criteria are used and the critical loads corresponding to fatigue limits are calculated. The criteria were classified into three categories, namely the critical plane approach, the stress invariant approach and the approach based on the mesoscopic scale. The simulation results show that the critical load is decreasing rapidly and the site of crack initiation also moves rapidly to the surface from the subsurface when the friction coefficient exceeds a specific value for all three fatigue criteria. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

The Subsurface Stress Field Caused by Both Normal Loading and Tangential Loading

The subsurface stress field caused by both normal loads and tangential loads has been evaluated using the rectangular patch solution. The effect of tangential loading on the subsurface stress field has been investigated in detail for both the cylinder-on-cylinder contact and a spur gear teeth contact. For the cylinder-on-cylinder contact, the subsurface stress fields are moved more to the direction of tangential loads and the positions where the maximum stress occur are getting closer to the surface with the increasing tangential loads. The subsurface stress fields of the gear teeth contact are expanded more widely to the direction of tangential loads with the increasing tangential loads. The friction coefficient of a gear teeth contact is low because they are operated in a lubricated condition, and therefore surface tractions in the EHL condition hardly affect on the subsurface stress field.

Development of a Multi-Tasking Machine Tool for Machining Large Scale Marine Engine Crankshafts and Its Design Technologies

A multi-tasking machine tool for large scale marine engine crankshafts has been developed together with design technologies for its special devices. Since work pieces, that is, crankshafts to be machined are big and heavy; weight of over 100 tons, length of 10 m long, and diameter of over 3.5 m, several special purpose core devices are necessarily developed such as PTD (Pin Turning Device) for machining eccentric pin parts, face place and steady rest for chucking and resting heavy work pieces. PTD is a unique special purpose device of open-and-close ring typed structure equipped with revolving ring spindle for machining eccentric pins apart from journal. In order to achieve high rigidity of the machine tool, structural design optimization using TMSA (Taguch Method based Sequential Algorithm) has been completed with FEM structural analysis, and a hydrostatic bearing system for the PTD has been developed with theoretical hydrostatic analysis.

Surface profile estimation by digital filtering for wear volume calculation

Abstract A new technique has been suggested for estimating the profile of an original unworn surface. Using digital filtering the profile signals from the profilometer are divided into two types: waviness—low frequency signals and roughness—high frequency signals. The original profile of a wear track was estimated by combining the waviness and the roughness taken from the surface before the wear test. The results of the study show that this technique results in an accurate estimate of the original profile.

A Study on the Change in the Film Thickness of Ball Bearing in Starved EHL

In this study, we perform a numerical analysis to predict the film thickness and lubrication regions for a thrust ball bearing under different operating conditions. Film thinning and replenishment affect the film thickness in starved lubrication. As the inlet meniscus position is brought to the edge...

Surface profile estimation using a profilometer and digital filtering

A new technique is suggested for estimating the profile of an original unworn surface using a profilometer and digital filtering. The profile signals from the digital profilometer are divided into two types: waviness-low frequency signals, and roughness-high frequency signals. The original profile of a wear track was estimated by combining the waviness and the roughness taken from the surface before the wear test. The results of the study show that this technique results in an accurate estimate of the original profile. Comparing the estimated profile of an original unworn surface with the profile of a measured worn surface can be utilized in the calculation of wear volume.