• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.3
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• pp.267-272
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• 1999

Micro-defects in the undoped and MgO-doped $LiNbO_3$ single crystals, which were grown from a congruent melting composition (48.6 mol% $Li_2$O) by the CZ (Czochralski) method, were analyzed using microscopic techniques such as optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Effects of the dopant and g value (the fraction solidfied) on the domain structure and micro-defect were investigated to build a corelationship with a growth condition of crystal. It was observed that the micro-defect concentrated near the domain wall is caused by high stress. Especially, the micro-defect was observed to be biased toward a certain side of the domain wall.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.177-184
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• 2001

C3M(chemical mechanical micro machining) is applied for diminishing the size of burr and fabricating the massless patterning for aluminium wafer(thickness of 1${\mu}m$). It is difficult to perform the micro size machining with the radically increased shear stress. While the miniaturization and function-orientation of parts has been needed in the many field such as electronics, optics and medicine. etc., it is not enough to satisfy the industry needs in the machining technology. In this paper feasibility test of diminishing burr and fabricating maskless pattern was experimented and analyzed. In the experiment oxide layer was farmed on the aluminium with chemical reaction by ${HNO_3}$(10wt%), then the surface was grooved with tungsten carbide tool for the different condition such as the load and fred rate. The result was compared with the conventional machining to show the improvement of C3M with SEM for burr diminish and XPS for atomic existence, AFM for more precise image.

• Advances in nano research
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• v.8 no.1
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• pp.69-82
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• 2020

In this study, the free and forced vibration analysis of micro sandwich plate with porous core layer and magneto-electric face sheets based on modified couple stress theory and first order shear deformation theory under simply supported boundary conditions is illustrated. It is noted that the core layer is composed from balsa wood and also piezo magneto-electric facesheets are made of BiTiO₃-CoFe₂O₄. Using Hamilton's principle, the equations of motion for micro sandwich plate are obtained. Also, the Navier's method for simply support boundary condition is used to solve these equations. The effects of applied voltage, magnetic field, length to width ratio, thickness of porous to micro plate thickness ratio, type of porous, coefficient of porous on the frequency ratio are investigated. The numerical results indicate that with increasing of the porous coefficient, the non-dimensional frequency increases. Also, with an increase in the electric potential, the non-dimensional frequency decreases, while and with increasing of the magnetic potential is vice versa.

• Computers and Concrete
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• v.24 no.3
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• pp.185-192
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• 2019

In this paper, the buckling of micro sandwich hollow circular plate is investigated with the consideration of the porous core and piezoelectric layer reinforced by functionally graded (FG)carbon nano-tube. For modeling the displacement field of sandwich hollow circular plate, the high-order shear deformation theory (HSDT) of plate and modified couple stress theory (MCST) are used. The governing differential equations of the system can be derived using the principle of minimum potential energy and Maxwell's equation that for solving these equations, the Ritz method is employed. The results of this research indicate the influence of various parameters such as porous coefficients, small length scale parameter, distribution of carbon nano-tube in piezoelectric layers and temperature on critical buckling load. The purpose of this research is to show the effect of physical parameters on the critical buckling load of micro sandwich plate and then optimize these parameters to design structures with the best efficiency. The results of this research can be used for optimization of micro-structures and manufacturing different structure in aircraft and aerospace.

• Steel and Composite Structures
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• v.50 no.1
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• pp.63-75
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• 2024

In this paper, the modified couple stress theory (MCST) and first order shear deformation theory (FSDT) are employed to investigate the free vibration and bending analyses of a three-layered micro-shell sandwiched by piezoelectric layers subjected to an applied voltage and reinforced graphene nanoplatelets (GPLs) under external and internal pressure. The micro-shell is resting on an elastic foundation modeled as Pasternak model. The mixture's rule and Halpin-Tsai model are utilized to compute the effective mechanical properties. By applying Hamilton's principle, the motion equations and associated boundary conditions are derived. Static/ dynamic results are obtained using Navier's method. The results are validated with the previously published works. The numerical results are presented to study and discuss the influences of various parameters on the natural frequencies and deflection of the micro-shell, such as applied voltage, thickness of the piezoelectric layer to radius, length to radius ratio, volume fraction and various distribution pattern of the GPLs, thickness-to-length scale parameter, and foundation coefficients for the both external and internal pressure. The main novelty of this work is simultaneous effect of graphene nanoplatelets as reinforcement and piezoelectric layers on the bending and vibration characteristics of the sandwich micro shell.

• Corrosion Science and Technology
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• v.3 no.3
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• pp.112-117
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• 2004

This work investigated the material properties of Ni-P-B alloy electrodeposits obtained from a Ni sulfamate bath as a function of the contents of the P and B sources($H_3PO_3$ and dimethyl amine borane complex(DMAB), respectively) with/without additives. Chemical composition, residual stress, microstructure and micro hardness were investigated using ICP(inductively coupled plasma) mass spectrometer, flexible strip, XRD, TEM and micro Vickers hardness tester, respectively. From the results of the compositional analysis, it was observed that P and B are incorporated competitively during the electrodeposition and the sulfur from the additive is codeposited into the electrodeposit. The measured residual stress value increased in the order of Ni, Ni-P, Ni-B and Ni-P-B electrodeposits indicating that boron affects the residual tensile stress greater than phosphorus. As the contents of the alloying element sources of P and B increased, crystallinity and the grain size of the electrodeposit decreased. The effect of boron on crystallinity and grain size was also relatively larger than the phosphorus. It can be explained that the boron with a smaller atomic radius contributes to the increase of residual stress in the tensile direction and the larger restraining force against the grain growth more significantly than the phosphorus with a larger atomic radius. Introduction of an additive into the bath retarded crystallization and grain growth, which may be attributed to the change of the grain growth kinetics induced by the additive adsorbed on the substrate and electrodeposit surfaces during electrodeposition.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.770-776
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• 2003

#140 mesh and #600 mesh wheels were adopted to grind (111) and (100) oriented single crystalline silicon wafer and the grinding induced change of the surface integrity was investigated. For this purpose, microroughness, residual stress and phase transformation were analyzed for the ground surface. Microroughness was analyzed using AFM (Atomic Force Microscope) and crystal structure was analyzed using micro-Raman spectroscopy. The residual stress and phase transformation were also analyzed after thermal annealing in the air. As a result, microroughness of (111) wafer was larger than that of (100) wafer after grinding. It was observed using Raman spectrum that the silicon was transformed from diamond cubic Si-I to Si-III(body centered tetragonal) or Si-XII(rhombohedral). Residual stress relaxation was also shown in cavities which were produced after grinding. The thermal annealing was effective for the recovery of the silicon phase to the original phase and the residual stress relaxation.

• Ocean and Polar Research
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• v.43 no.3
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• pp.141-148
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• 2021

Microplastic contamination in waterbodies is a growing source of concern for researchers and other stakeholders. We investigated oxidative stress and toxicity in goldfish (Carassius auratus) in response to exposure to 1-㎛ diameter micro-polystyrene (MP) at concentrations of 0, 10, 100, and 1000 beads/mL (MP 0, MP 10, MP 100, and MP 1000 groups) for 7 d (at day 0, 1, 3, 5, and 7). We analyzed the survival rates; superoxide dismutase (SOD) and catalase (CAT) mRNA expression levels in the liver; SOD and CAT activity in the plasma; caspase-3 mRNA expression in the liver; and the levels of hydrogen peroxide (H₂O₂) in plasma. Terminal transferase dUTP nick end labeling (TUNEL) assays were also conducted to determine apoptosis levels in the liver. All fish in the MP 1000 group died by day 7 and the MP 100 group had a lower survival rate than the MP 10 and MP 0 groups. The mRNA expression as well as SOD, CAT, and caspase-3 activity levels were increased significantly with increases in MP concentration and exposure time. Finally, according to the TUNEL assay, more apoptosis was observed in the MP 1000 group at day 5 than in other groups. In summary, MP concentrations above 100 beads/mL caused death and oxidative stress to goldfish. We conclude that MP can cause oxidative stress and apoptosis in goldfish, which leads to death.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.333-346
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• 2002

The continuous indentation techniques are one of the most effective methods to nondestructively estimate mechanical properties. There are many applications in various dimensions of materials from macro-scale, through micro-scale, even to nano-scale range. The macro-range technology of kgf-load level is now focused on the evaluation of tensile properties and residual stress of bulk materials, for example, used in conventional load-bearing structures and in-use pipelines. The technology and the apparatus were successfully developed by a domestic research group. The micro-range technology of gf-load level can be applied to investigate some property-gradient materials such as weldment. Because it has better spatial resolution than the macro-range technology. The nano-range technology (called nanoindentation technique) of mgf-load level is basically used to evaluate hardness and modulus of micro- and nano-materials. Moreover, many researches are going on to measure tensile properties and residual stress. The nanoindentation technology is easy to be applied to the various fields, such as semiconductor devices, multiphase materials, and biomaterials, though other methods are too difficult to be applied due to dimensional or environmental limitations. On the basis of these accomplishments, the international and the domestic standards are being established.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.4 s.235
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• pp.526-533
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• 2005

Reliability problem in inkjet printhead, one of MEMS devices, is also very important. To eject an ink drop, the temperature of heater must be high so that ink contacting with surface reaches above $280^{o}C$ on the instant. Its heater is embedded in the thin multi-layer in which several materials are deposited. MEMS processes are the main sources of residual stresses development. Residual stress is one of the factors reducing the reliability of MEMS devices. We measured residual stresses of single layers that consist of multilayer. FE analysis is performed using design of experiment(DOE). Transient analysis for heat transfer is performed to get a temperature distribution. And then static analysis is performed with the temperature distribution obtained by heat transfer analysis and the measured residual stresses to get a stress distribution in the structure. Although the residual stress is bigger than thermal stress, thermal stress is more influential on fatigue life.