• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.301-306
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• 1999

Application of bonded dissimilar materials in various industries are increasing. When these materials are used in structures, it needs to investigate strength evaluation applying fracture mechanics. Al/Epoxy bonded dissimilar materials with an interface crack and an interface crack emanating from an edge semicircular hole were prepared for the static tests so that experiment of fracture toughness were carried out. Stress intensity factors of interface cracks in bonded dissimilar materials were computed with boundary element method(BEM) and the fracture criteria of mixed mode crack were analyzed. From the results, the fracture criteria and the method of strength evaluation by the fracture toughness in Al/ Epoxy bonded dissimilar materials were proposed.

• Journal of Powder Materials
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• v.26 no.6
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• pp.508-514
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• 2019

In the development of advanced ceramic tools, material improvements and design freedom are critical in improving tool performance. However, in the die press molding method, many factors limit tool design and make it difficult to develop innovative advanced tools. Ceramic 3D printing facilitates the production of prototype samples for advanced tool development and the creation of complex tooling products. Furthermore, it is possible to respond to mass production requirements by reflecting the needs of the tool industry, which can be characterized by small quantities of various products. However, many problems remain in ensuring the reliability of ceramic tools for industrial use. In this study, alumina inserts, a representative ceramic tool, was manufactured using the digital light process (DLP), a 3D printing method. Alumina inserts prepared by 3D printing are pressurelessly sintered under the same conditions as coupon-type specimens prepared by press molding. After sintering, a hot isostatic pressing (HIP) treatment is performed to investigate the effects of relative density and microstructure changes on hardness and fracture toughness. Alumina inserts prepared by 3D printing show lower relative densities than coupon specimens prepared by powder molding but indicate similar hardness and higher fracture toughness values.

• Transactions of Materials Processing
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• v.3 no.2
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• pp.147-155
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• 1994

The service life of tools in metal forming technology is to a large extent limited by wear and fatigue fracture of the active elements. This presents a basic request for tool cost minimization and reduction of extensive machine down time, caused by premature tool failure. Currents developments are dominated by steps to reduce the causes of tool failure. A main problem of forming technology remains the insufficient reliability of tools due to a large and incalculable life time fluctuation. Only a systematic investigation of the failure mechanisms and operational loading of tools can lead to future improvements in tool layout, that is optimization of tool usage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.1944-1949
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• 2001

Four SiC-Si$_3$N$_4$ceramic cutting tools with different composition have been fabricated by hot-pressing. Correlations among the annealing time, the corresponding microstructure and the mechanical properties of resulting ceramics have been investigated. The fracture toughness and the grain size of both SiC and Si$_3$N$_4$in SiC-Si$_3$N$_4$composites increased with the annealing time. 1\`he hardness of SiC-Si$_3$N$_4$composites was relatively independent of the grain size and the sintered density. These ceramic cutting tools were tested under various cutting conditions and compared with the commercial Si$_3$N$_4$ceramic cutting tools. The experimental results were compared in terms of tool life and cutting force. The performance of SiC-Si$_3$N$_4$ceramic cutting tool shows the possibility to be a new ceramic tool.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.1 s.178
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• pp.64-71
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• 2006

Ultraprecision machining and MEMS technology have been taken more and more important position in machining of microparts. Micro endmilling is one of the prominent technology that has wide spectrum of application field ranging from macro parts to micro products. Also, the method of micro-grooving using micro endmill is used widely owing to many merit, but has problems of precision and quality of products due to tool wear and tool fracture. This investigation deals with state monitoring using acoustic emission(AE) signal in the micro-grooving. Characteristic evaluation of AE raw signal, AE hit and frequency analysis for condition monitoring is presented. Also, the feature extraction of AE signal directly related to machining process is executed. Then, the distinctive micro endmill state according to the each tool condition is classified by the fuzzy C-means algorithm.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.192-194
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• 2005

Joint strength of spot friction welded 5J32 Al alloy were investigated according to the tool shape and the tool penetration depth. General spot friction stir welding tool consists of a shoulder having bigger diameter and a threaded pin projected from the shoulder, which resulted in the generation of large up-lifting of upper plate around the weld nugget because of the deeper penetration and the severe stirring effect of threaded pin. Two kinds of welding tools without the threaded pin were used to avoid the distortion and improve the joint strength. One was a simple cylindrical shape and the other was cylindrical shape with small projection. Therefore, the process was named as spot friction welding comparing to spot friction stir welding because spot friction welding don't use a stirring effect. Using the cylindrical shape tool with small projection, the up-lifting of upper plate were avoided and joint strength were superior to that of the joint using simple cylindrical shape tool. At the 0.5mm of too penetration depth using cylindrical tool with small projection, nugget pull fracture mode can be observed and shear fracture mode were dominant at the rest conditions.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.1
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• pp.96-101
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• 2000

Ceramic, PCD and CBN tools are available for the difficult-to-cut-materials such as hardened carbon tool steel, stainless steel, Inconel 718 and etc.. Ceramic toolsare likely to be chipped and abruptly broken before the appearance of normal wear in turning. Ther2efore ceramic tools are suitable for continuous cut in turning not for intermittent in milling. In this study, TiN/TiCN multi-layer coated ceramic tools were found to restrain the chipping, breaking and early fracture and to increase the critical cutting speed owing to TiN/TiCN multi-layer coating in Arc Ion Plating of PVD method.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.310-315
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• 2000

In this paper, the problems of the external fixator that have developed for a distal radius fracture so far are analyzed, and accordingly, the characterizations, which must have a prototype, are arranged. C-Arm is used. This instrument makes it possible for the real play of the internal body by x-ray permeability. From this data, it is possible to induce important design factors. Finally, a basic mechanism, which has to be applied, is decided, and the Solid Edge program, which used a 3-D design tool, completes then total instrument design.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.331-338
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• 2005

The grain structure, dislocation density and second phase particles in various regions including the stir zone(SZ), thermo-mechanically affected zone(TMAZ), and heat affected zone(HAZ) of a friction stir weld 6.35mm thick aluminum 7075-T651 alloy were investigated and compared with the base metal. The microstruectures of nugget zone were compared according to tool rotation speeds and tool transition speeds. The hardness profiles of nugget zone were increased, while decreasing rotation speed and increasing welding speed. The optimal microstructure was gained at the low rotation speed 800rpm and th high welding speed 124mm/min. The nugget microstructures of fracture surface, transgranular dimple and quasicleavage type were showed different fracture type with the HAZ, shear fracture type.

• Asian Spine Journal
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• v.12 no.6
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• pp.992-997
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• 2018

Study Design: Feasibility study. Purpose: To evaluate the feasibility of using serum pentosidine level as a potential marker for osteoporotic vertebral compression fracture (OVCF). Overview of Literature: A review of previous studies suggests a negative correlation between serum pentosidine concentration and bone strength. However, it is unclear whether serum pentosidine level might be a potential marker of OVCF in Koreans. Methods: Forty patients who underwent bone mineral density examination were included in this study, and their serum pentosidine levels were prospectively analyzed. Serum pentosidine level was evaluated using enzyme-linked immunosorbent assay. Among all the patients, 11 with OVCF were assigned to the vertebral fracture group and 29 who did not have vertebral fracture were included in the non-fracture group. In addition, we used the Fracture Risk Assessment (FRAX) tool Korean version for assessing the 10-year probability of fracture. Results: There was a statistically significant difference in the mean serum pentosidine level (p=0.04) of the vertebral fracture group (110.8 ng/mL) and the non-fracture group (64.3 ng/mL). Logistic regression analyses showed that serum pentosidine was significantly associated with OVCF. The vertebral fracture group had significantly higher 10-year probability of major osteoporotic fracture as per FRAX than the non-fracture group. There was a positive correlation between pentosidine level and FRAX results (r=0.35, p=0.02). Conclusions: These results suggest that increased serum pentosidine level could be a potential marker for OVCF.