• Proceedings of the KWS Conference
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• 2002.10a
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• pp.720-725
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• 2002

In recent years, techniques for micro-assembly with high repeatability under a scanning electron microscope (SEM) are required to construct highly functional micro-devices. Adhesion phenomenon is more significant for smaller objects, becanse adhesional force is proportional to size of the objects while gravitational force is proportional to the third power of it. It is also known that adhesional force between micro-objects exposed to Electron Beam irradiation of SEM increases with the elapsed time. Therefore, mechanical manipulation techniques using a needle-shaped tool by adhesional force are often adopted in basic researches where micro-objects are studied. These techniques, however, have not yet achieved the desired repeatability because many of these could not have been supported theoretically. Some techniques even need the process of trial-and-error. Thus, in this paper, mechanical and adhesional micro-manipulation are analyzed theoretically by introducing new physical factors, such as adhesional force and rolling-resistance, into the kinematic system consisting of a sphere, a needle-shaped tool, and a substrate. Through this analysis, they are revealed that how the micro-sphere behavior depends on the given conditions, and that it is possible to cause the fracture of the desired contact interfaces selectively by controlling the force direction in which the tool-tip loads to the sphere. Based on the acquired knowledge, a mode diagram, which indicates the micro-sphere behavior for the given conditions, is designed. By refening to this mode diagram, the practical technique of the pick and place manipulation of a micro-sphere under an SEM by the selective interface fracture is proposed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.617-618
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• 2009

• Journal of the Korean Society for Precision Engineering
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• v.24 no.3 s.192
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• pp.91-99
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• 2007

Fractures of galvannealed coating layer during actual press forming in automotive applications were observed by scanning electron microscopy in order to understand fracture mechanism. Fracture behaviors of galvannealed coating layer in extra deep drawing quality steels and high strength steels have been studied by performing the tests describing the representative plastic deformation in sheet metal forming such as uni-axial tensile test, compression test, bi-axial test and plane strain test. Growth and direction of cracks were deeply related to the plastic deformation modes and history. The material properties of galvannealed coating layer were investigated by nano-indentation test equipped with Berkovich diamond indentor for the specimens. Hardness and elastic modulus of the coating layer were higher than bared steels and that was the reason for crack of coating layer. Flat friction test and drawbead friction test were performed to observe the effect of the surface morphology on the frictional characteristics. The micro-plasto hydrodynamic lubrication were appeared and played an important role in reducing the coefficient of friction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.224-231
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• 1984

Having found by means of a tension-shear test an optimal spot welding condition under which the maximum weld strength is to be brought forth, this study made an examination of behavior of fracture concerned with behavior of stress distribution, observed around the nugget periphery of the specimens prepared under the optimal conditions, with one point spot welded mild steel sheets. The resultant findings are as follows: (1)There remarkably exists an optimal spot welding condition to indicate the maximum weld strength, and fracture of the specimens spot welded under that condition occurs outside the nugget boundary. (2)An experiment on the basis of a photoelastic model reveals that the maximum stress is distributed along the center line of the steel plate width but occurs on the region corresponding to heat affected zone of spot welds. (3)Heat affected zone of spot welds consists of coarse grains with considerably low micro Vickers hardness value and of fine grains of high micro Vickers hardness value, and in this unbalanced structure weak region are represented in coarse grain region, where fracture is initiated and continues its propagation.

• Journal of Technologic Dentistry
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• v.41 no.3
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• pp.195-201
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• 2019

Purpose: This study was investigated the effect of multilayer zirconia block type and sintering method on fracture strength, micro structure and color of zirconia copings. Methods: Three kinds of multi-layered zirconia blocks were used to identify the effects of the kinds of multi-layered zirconia blocks and sintering methods on fracture strength and color reproducibility of zirconia copings. 60 Zirconia copings were fabricated and fracture strength, micro structure and color reproducibility were compared and evaluated. Results: In all the blocks, the CS group, which refers to the general sintering method had higher fracture strength of zirconia copings than the MS group that refers to the microwave sintering method(MCS/MMS; 2,107.5N/1,930.4N, DCS/DMS; 917.0N/879.1N, UCS/UMS; 2,256.9/2,050.7N). In relation to CIE $L^*$, $a^*$, $b^*$ values of zirconia copings depending on the kinds of multi-layered zirconia blocks and sintering methods, the MS group using the microwave sintering method had lower brightness and chroma than the CS group using the general sintering method. Conclusion: In all the blocks, the CS group(general sintering) had higher fracture strength of zirconia copings than the MS group(microwave sintering). In relation to CIE $L^*$, $a^*$, $b^*$ values of zirconia copings depending on the kinds of multilayered zirconia blocks and sintering methods, the MS group using the microwave sintering method had lower brightness and chroma than the CS group using the general sintering method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.163-168
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• 2006

In a micro-unit of electronic-machine, vibration can be excited by a small impact, and this vibration acts as a fatigue load. To measure the vibration effect on the micro unit, a micro dynamic tester is needed to test a micro specimen. In this paper, it has confirmed a movement of the PZT(piezo actuator) to use a sine signal. And, it has confirmed a fracture of specimens by using a tension-tension input signal in PZT. A metal-material property in the micro scale has been tested to compare with the macro scale. A fatigue test has been conducted by using PZT actuator to give a bending-tension effect.

• Journal of Power System Engineering
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• v.21 no.3
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• pp.37-44
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• 2017

In this study, failure analysis of the angular pin for molding machines to aluminum component molding was carried out. SM45C steel was used for the angular pin, it was surface hardened by the induction surface hardening heat treatment. The cross section of damaged angular pin was observed, and micro Vickers hardness value from the fractured part was measured. Brittle fracture was occurred from the fracture surface of angular pin, therefore, impact toughness value was evaluated by V-notch Charpy impact test. It was confirmed that the impact absorption energy was high when was tempered at a high temperature for a long time, and the toughness was slightly increased. Also, 2-parameter Weibull statistical analysis was investigated in order to evaluate the reliability of the measured micro Vickers hardness values and absorbed energy. The micro Vickers hardness and absorbed energy well followed a two-parameter Weibull probability distribution, respectively. The reverse design against angular pin was proposed as possible by using test results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.631-638
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• 1995

In this study, mechanical characteristics test of Functionally Gradient Materia (FGM) was performed by means of Modified Small Punch (MSP) Test with FGM; NiCrAlY-8YSZ and PSZ-Ni. To determine fracture mechanic factor, it was carried out MSP test that has possibility with small specimen (10*10*0.5 mm$^{t}$ ) and AE test to analyze micro fracture mechanism. As a result, fracture behavior became varied from brittle fracture to ductile as the content of Ni(or NiCrAlY) composition was increased and fracture energy was increased too. AE characteristics demonstrated that AE technique can detect the onset of fracture processes and AE energy was suddenly increased in the vicinity of maximum load. Since Young's modulus, fracture stress and fracture toughness was determined by MSP test, it can be known that the composition of NiCrAly 75%/8YSZ25% has the best mechanical property and furthermore this result is supported with fracture surface observation.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.3
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• pp.133-140
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• 2014

Cleavage fracture behaviors were investigated in Ni-Mo-Cr steels with mixed microstructure of lower bainite and martensite. As the size of carbide decreased, the cleavage fracture strength increased, which was independent of the sizes of grain and packet. The measured cleavage fracture strengths were in good agreement with cleavage fracture strengths calculated by Petch model rather than by modified Griffith model in micro-structures with fine carbides, the size of which were small below a few hundred nanometer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2431-2435
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• 1996

In order to determine the effects of hydrostatic pressure on the mechanical behavior of graphite fiber reinforced composites, the modulus, fracture stress(maximum stress), and fracture strain of graphite/epoxy composites have been determined as a function of pressure. Composite specimens used in this study were 90-deg unidirectional and had a 60% fiber volume fraction. Compressive tests under five different pressure levels were conducted. The result showed the modulus measured from as initial slope of stress-strain curve increased bilinearly with pressure with a break at 200 MPa. It was also found that fracture stress and fracture strain increased in a linear fashion with pressure.