• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10a
• /
• pp.386-390
• /
• 2003

As a trial of application of hydrostatic pressure in micro fomring, burr-free punching has been conducted by means of hydro-mechanical procedure. Even though it is in beginning stage, result of the hydro-mechanical punching is promising. Hydrostatic pressure helps delay fracture initiation and makes it possible to get clean shearing surface. Without any burr on both side of sheet, smooth holes are archived as intended. To verify the significance of hydro-mechanical punching, conventional punching is performed under similar conditions and relatively larger portion of fracture surface is detected in the punching hole. Despite the quality of sidewall is not good enough, it might be possible to make the hole shaped upright, reduce the roll-over radius and minimize the fracture surface by optimizing process parameters.

• Maxillofacial Plastic and Reconstructive Surgery
• /
• v.21 no.3
• /
• pp.312-316
• /
• 1999

When the external force was applied to the orbit the most thin area might be displaced. These were usually orbital floor and/or medial wall of orbit. Among these cases some who showed the entrapment of the muscle between the fractured fragments needed the surgical treatment. We had operated 4 cases of the "blow-out" fracture via subciliary approach. The entrapped muscles were freed from fragments and the bony defect was restored with micro-titanium mesh. Mean follow-up periods was 15 months and there were no complication observed.

• Structural Engineering and Mechanics
• /
• v.18 no.5
• /
• pp.691-707
• /
• 2004

This paper presents the micro-mechanical modeling for predicting concrete behavior under compressive loading. The model is able to represent the heterogeneities in the microstructure up to three phases, i.e., aggregate particles, matrix and interfaces. The smeared crack concept based on non-linear fracture mechanics is implemented in order to formulate the constitutive relation for each component. The splitting tensile strength is considered as a fracture criterion for cracking in micro-level. The finite element method is employed to simulate the model based on plane stress condition by using quadratic triangular elements. The validation of the model is verified by comparing with the experimental results. The influence of tensile strength from both aggregate and matrix phases on the concrete compressive strength is demonstrated. In addition, a guideline on selecting appropriate tensile strength for each phase to obtain specified concrete compressive strength is also presented.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.04a
• /
• pp.237-240
• /
• 2004

High strain-rate deformation behavior of NiAl/Ni micro-laminated composites was characterized by split hopkins on pressure bar(SHPB). When the strain rate increased, the compressive stress of micro-laminated composites were increased a little. When the intermetallic volume fraction increased, the compressive stress of micro-laminated composites increased linearly irrespective of strain rate. Absorbed energy during the quasi-static and SHPB tests was calculated from the integrated area of stress-strain curve. Absorbed energy of micro-laminated composites deviated from the linearity in terms of the intermetallic volume fraction but merged to the value of intermetallic as the strain rate increased. This was due to high tendency of intermetallic layer for the localization of shear deformation at high strain rate. Microstructure showing adibatic shear band(ASB) confirmed that the shear strain calculated from the misalignment angle of each layer increased and ASB width decreased when the intermetallic volume fraction. Simulation test impacted by tungsten heavy alloy cylinder resulted that the absorbed energies multiplied by damaged volume of micro-laminated composites were decreased as the intermetallic volume fraction increased. Fracture mode were changed from delamination to single fracture when the intermetallic volume fraction and this results were good matched with previous results[l] obtained from the fracture tests.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.10a
• /
• pp.334-339
• /
• 2004

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 endmilling 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 state monitoring is also presented in the paper.

• Journal of Korean Medicine Rehabilitation
• /
• v.30 no.3
• /
• pp.23-44
• /
• 2020

Objectives The purpose of this study is to evaluate the healing effect of Hyeolbuchugeo-tang (HC) in rats with rib fracture. Methods Rats were randomly divided into 5 groups (naive, control, positive control, HC-L and HC-H). All groups except naive group were subjected to bone fracture of rib. Naive group received no treatment at all. Control group was fed with phosphate buffered saline. Positive control group was orally medicated with tramadol. Experimental group was orally medicated with HC extract (50 mg/kg for low concentration [HC-L], 100 mg/kg for high concentration [HC-H]). X-ray and micro-computed tomography (micro-CT) were conducted to assess the effect of HC. We analysed the level of 2) transforming growth factor-β1 (TGF-β1), Ki67, alkaline phosphatase (ALP), receptor activator of nuclear factor kappa-β, runt-related transcription factor 2 (Runx2) and tartrate resistant acid phosphatase (TRAP) on 7 and 14 days after fracture. ALP, alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, creatinine was measured for safety assessment. Results X-ray and micro-CT, showed HC enhance bone repair process. Callus formation was increased in experimental group at 7 days after fracture, but decreased at 14 days after fracture. 7 days after fracture, the level of TGF-β1 in experimental group was decreased. The level of Ki67, Runx2 in HC-H, TRAP in HC-L was increased. 14 days after fracture, the level of Ki67 in HC-L and HC-H was decreased. The level of ALP, Runx2, BUN in HC-L, TRAP in HC-L and HC-H was increased. Conclusions Taken together the results, HC promoted healing of bone fracture. In conclusion, HC has a potential to promote healing of bone fracture.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2005.05a
• /
• pp.162-167
• /
• 2005

Recently, the advanced industries using micro parts are rapidly growing. Micro endmilling is one of the prominent technology that has wide spectrum of application field ranging from macro to micro parts. Also, the method of micro-grooving using micro endmilling is used widely owing to many merit, but has problems of precision and quality of products due to tool wear and tool fracture. This study deals with condition monitoring using acoustic emission(AE) signal in the micro-grooving. First, 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 using the fuzzy C-means algorithm, which is one of the methods to recognize data patterns. These result is effective monitoring method of micro endmill state by the AE sensing techniques which can be expected to be applicable to micro machining processes in the future.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.10a
• /
• pp.332-335
• /
• 1997

With the advance of precision technique, the optical system is more precise and complex and the machining method of optical element which is composed of micro-grooves is developed. Especially, the method of micro-grooving using diamond tool is used widely owing to many merit, but has problems of damage of surface roughness due to tool wear and tool fracture. This paper deals with state monitoring using AE RMS in the micro-grooving. The change of AE RMS is very small with increment of cutting velocity and depth of cut. In spite of constance magnitude of principal force in machining using diamond tool of tool wear and tool fracture, AE RMS is highly fluctuated. Because changing of cutting state has relevance to surface roughness profile, surface toughness profile is expected using AE RMS.

• Transactions of Materials Processing
• /
• v.11 no.7
• /
• pp.575-580
• /
• 2002

To evaluate elastic and micro-failure properties of MEMS materials, the electro-statically operated test devices were designed and fabricated by micro machining technology. The test structures consist or comb drives for loading and suspending beams in testing. From the analysis of beam displacement based on elastic beam theory, elastic modulus and yield strength of Al film were measured. And, by introducing the micro notch and cyclic loading, the micro-failure was Induced and the micro-fracture toughness of Si film was evaluated. Moreover, the cycles to failure were estimated from the degradation of resonant frequency. Finally, the effects of notch on micro failure were discussed.

• Journal of Powder Materials
• /
• v.9 no.3
• /
• pp.148-152
• /
• 2002

The microstructures and indentation fracture of pressureless-sintered $DyNbO_4$ crystalline were investigated as a basic study for the application of weak phase of fibrous monolithic composites. They were comprised with many lamella twins as well as micro-cracks at the grain boundaries. The hardness at room temperature was remarkably low value(575 Hv) due to the low relative density and existence of microcracks at grain boundaries. The main fracture mode was a typical intergranular fracture, and showed remarkable micro-cracking effect. The heavy plastic deformation was observed around the site of indentation. In addition, the $DyNbO_4$ was expected to apply as a weak phase in the fibrous monolithic composites because of the low hardness and easily plastic deformation that could be led the preferable pulled-out and microcracking toughening under the failure.