• Journal of Ocean Engineering and Technology
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• v.17 no.2
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• pp.47-53
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• 2003

The development of new materials with light weight and high strength has become vital to the machinery, aircraft and auto industries. However, there are a lot of problems with developing such materials that require such expensive tools, as well as a great deal of time and effort. Therefore, the improvement of fatigue life through, the adoption of residual stress, is the main focus. The compressive residual stress was imposed on the surface according to each shot velocity(1800, 2200, 2600, 3000rpm) based on Shot-peening, which is the method of improving fatigue life and strength. By using the methose mentioned above, we arrived at the following conclusions; 1. The fatigue crack growth rate(da/dN) of the Shot-peened material was lower than that of the Un-peened material. In stage I, $\Delta$K$_{th}$, the threshold stress intensity factor, of the shot-peen processed material is high in critical parts, unlike the Un-peened material. Also m, fatigue crack growth exponent and number of cycle of the Shot-peened material was higher than of the Un-peened material. That is concluded from effect of da/dN. 2. Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. Compressive residual stress of the surface on the Shot-peen processed operate resistance force of fatigue crack propagation.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.93-98
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• 1999

Generally, the - life of die is limited by fatigue fracture or dimensional inaccuracy originated from wear. In this paper, to predict the fatigue life of the dissimilar materials die, the stress and stxain histories of die can be predicted by the analysis of elasto-plastic finite element neth hod and the elastic analysis of die during the process analysis of workpiece. Using heat shrink fit analysis, initial stress of the k r t die is computed. Also, the stress-life curve of die material can be obtained through experiment. With the above two facts, we propose the analysis method of predicting fatigue life in die. In the proposed model, tlz analysis of elastic-plastic finite element method for material is carried out by using ABAQUS. Surface force resulted from the contacting border of the die and workpiece is tmnsformed into the nodal force of die to implement elastic analysis. Besides, the proposed analysis model of die is applied to the one material and the dissimilar materials extrusion die.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.104-111
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• 2006

The non-linear properties of rubber material which are described as strain energy function are important parameter to design and evaluate of rubber spring. These are determined by material tests which are uni-axial tension and bi-axial tension. The computer simulation using the nonlinear element analysis program executed to predict and evaluate the load capacity and stiffness for chevron spring. In order to investigate the heat-aging effects on the rubber material properties, the acceleration test were carried out. Compression set results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the compression set test, several useful life prediction for rubber material were proposed.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.119-125
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• 2002

In Kwangjin industrial company, mill is operating for the foundry sand production at the rate of 25t/hr from quartzite. Foundry sands fall into four distinct categories: silica sand, lake sand, bank sand, and natural molding sand. Silica sand is a general term used to describe crushed, washed, graded, dried, and cooled clay-free sands. This study was conducted for the investigation of the foundry sand productivity and the life span of the hammer according to the material quality. The life time of hammer from several manufacturer were compared in order to find out the grinding efficiency of the various hammer material. In the result of tests, the life time of high-Mn hammer was 10.5 hours while that of high-Cr was 19.5 hours. The life time in case of typical worn shape hammers was about 12 hours and the average time of a blowhole hammer was about 6.5 hours.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.199-205
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• 2002

This paper presents a numerical technique to analyze wear life of automotive disk brake pad, where FFT-FEM method is adopted to determine the transient temperature distribution of the disk surface. A specimen ova frictional material is tested on a small scale brake dynamometer to find the dependency of the wear rate on temperature change, from which and the temperature analysis results, given the wear test mode, wear behavior of the pad material fur the vehicle can be predicted. Numerical examples show the predicted wear life of the vehicle coincides with the manufacture's recommended time interval for replacing the pads.

• Journal of the Korean Society of Safety
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• v.21 no.4 s.76
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• pp.13-18
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• 2006

In spite of frequent defect in industrial boilers, life assessment or diagnostic method for them has not been actively studied. In this research, SS400 carbon steel used in industrial boilers is simulated with artificial aging heat treatment. To do qualitative life assessment, differences in micro-structures and hardness of SS400 by the degradation time are studied. In addition, variation in material properties by aging was observed with the tensile test at room temperature and $179^{\circ}C$ and changes in ductile to brittle transition temperature was observed with the charpy impact test performed at several test temperature.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.3
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• pp.167-173
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• 1998

In order to estimate the life time of epoxy composites used for modeling material of transformer, the AC breakdown experiments of it were experimented and then the AC breakdown data were also simulated by Weibull distribution equation in this study. The life time of H100F65 specimen was the shortest and it of SH100F65 specimen was the longest, and as the AC voltage was applied to specimen for 50[min], the breakdown probability of each specimen was 31.2[%], 17.00[%], 84.36[%] and 12.35[%], respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.10
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• pp.1770-1775
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• 2010

An acceleration life test for rubber gasket of pole transformer was performed. The Arrhenius method was applied as an accelerated degradation test. The failure mode was considered as an elongation, and the failure mechanism is counted as a heat. It is found that both the current material(NBR: Nitrile Butadiene Rubber) and recommended alternative material(HNBR: Hydrogenated Nitrile Butadiene Rubber) have the same Weibull distribution as a life characteristic. For life expectation 95% reliability level of characteristic life is used at using temperature. The test results for NBR and HNBR are 7.7 years and 28.0 years on $50^{\circ}C$ of using temperature, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.903-907
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• 1996

Under two level block loading, the carbornitrizing specimen can be expected to show different behavior from other uniform material because the properties of surface layer and inner material are different from each other. In this research, the modified Marco-Starkey cumulative theory, which considers load interaction effect, can predict the life of SCM415 carbornitrizing and original notched and smooth specimen, In the low-high test of carbornitrizing specimen which has long life, however, we may additionally consider the increase of life by means of the stress hardening of inner original material.

• Journal of the Korean Society for Railway
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• v.8 no.6 s.31
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• pp.525-532
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• 2005

Fatigue life of catenary wires in various environments is reduced when stress is concentrated on some points, which are often found in corroded areas by surrounding pollutants. Therefore, the fatigue test were performed in order to investigate the effect of the surface corrosion on the destructive behavior in service environment and accelerated corrosion environment as well as th examine the corrosive property and mechanism of the catenary wires. In the fatigue test of the messenger stranded wire, the corrosion degraded materials showed 35~50% of fatigue life at a same stress amplitude compared to original material. Because the catenary wires have variable load by the interaction of periodic contacts with pantographs the maximum stresses of trolley wire and messenger wire calculated by simulation at the messenger wire during operation was estimated thought the corrosion behavior interpretation of variable stress and fatigue test.