• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.3
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• pp.252-259
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• 1990

This paper present new scheme for a Side Wall Masked Isolation(SWAMI) technology which take all the advatages provided by conventional LOCOS process. A new SWAMI process incorporates a sloped sidewall by reactive ion etch and a layer of thin nitride around the side walls such that both intrinsic nitride stress and volume expansion induced stress are greatly reduced. As a fabricate results, a defect-free fully recessed zero bird's beak local oxidation process can be realized by the sloped wall anisotropic oxide isolation. No additional masking step is required. The leakage current of PN diodes of this process were reduced than PN diode of conventional LOCOS process. On the other hand, the edge junction part was larger than the flat juction part in the density of leakage current.

• Structural Engineering and Mechanics
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• v.70 no.5
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• pp.623-637
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• 2019

This paper analyzes the non-stationary vibration and super-harmonic resonances in nonlinear dynamic motion of viscoelastic nano-resonators. For this purpose, a new coupled size-dependent model is developed for a plate-shape nano-resonator made of nonlinear viscoelastic material based on modified coupled stress theory. The virtual work induced by viscous forces obtained in the framework of the Leaderman integral for the size-independent and size-dependent stress tensors. With incorporating the size-dependent potential energy, kinetic energy, and an external excitation force work based on Hamilton's principle, the viscous work equation is balanced. The resulting size-dependent viscoelastically coupled equations are solved using the expansion theory, Galerkin method and the fourth-order Runge-Kutta technique. The Hilbert-Huang transform is performed to examine the effects of the viscoelastic parameter and initial excitation values on the nanosystem free vibration. Furthermore, the secondary resonance due to the super-harmonic motions are examined in the form of frequency response, force response, Poincare map, phase portrait and fast Fourier transforms. The results show that the vibration of viscoelastic nanosystem is non-stationary at higher excitation values unlike the elastic ones. In addition, ignoring the small-size effects shifts the secondary resonance, significantly.

• Korean Journal of Materials Research
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• v.31 no.2
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• pp.97-100
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• 2021

We report the effect of Standard Clean-1 (SC-1) cleaning to remove residual Ti layers after silicidation to prevent Al diffusion into Si wafer for Ti Schottky barrier diodes (Ti-SBD). Regardless of SC-1 cleaning, the presence of oxygen atoms is confirmed by Auger electron spectroscopy (AES) depth profile analysis between Al and Ti-silicide layers. Al atoms at the interface of Ti-silicide and Si wafer are detected, when the SC-1 cleaning is not conducted after rapid thermal annealing. On the other hand, Al atoms are not found at the interface of Ti-SBD after executing SC-1 cleaning. Al diffusion into the interface between Ti-silicide and Si wafer may be caused by thermal stress at the Ti-silicide layer. The difference of the thermal expansion coefficients of Ti and Ti-silicide gives rise to thermal stress at the interface during the Al layer deposition and sintering processes. Although a longer sintering time is conducted for Ti-SBD, the Al atoms do not diffuse into the surface of the Si wafer. Therefore, the removal of the Ti layer by the SC-1 cleaning can prevent Al diffusion for Ti-SBD.

• Corrosion Science and Technology
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• v.21 no.1
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• pp.62-67
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• 2022

The objective of this study was to perform failure analysis of an inlet pipe located in a governor valve of a steam turbine in a district heating system. During the operation, the temperature of the governor valve was increased to as high as ~500 ℃, which induced thermal expansion of the inlet pipe along both axial and radial directions. While the inlet pipe did not have contact with the valve seat, the side plane of the upside was constrained by the casing part, which led the inlet pipe to experience stress field in the form of fatigue and creep. The primary crack was initiated at about 30 mm below the top where the complex stress field was anticipated. These results suggest that the main failure mechanism is a combination of thermal fatigue and creep during the operation supported by the observation of apparent beach marks on the fracture surface and pores near the cracks, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.3
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• pp.246-254
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• 2022

Localized heat can be generated using electrically conductive word-lines built into a 3D NAND flash memory string. The heat anneals the gate dielectric layer and improves the endurance and retention characteristics of memory cells. However, even though the electro-thermal annealing can improve the memory operation, studies to investigate material failures resulting from electro-thermal stress have not been reported yet. In this context, this paper investigated how applying electro-thermal annealing of 3D NAND affected mechanical stability. Hot-spots, which are expected to be mechanically damaged during the electro-thermal annealing, can be determined based on understanding material characteristics such as thermal expansion, thermal conductivity, and electrical conductivity. Finally, several guidelines for improving mechanical stability are provided in terms of bias configuration as well as alternative materials.

• Structural Engineering and Mechanics
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• v.82 no.1
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• pp.17-30
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• 2022

The use of composite patches for the reduction of stresses at the level of the damaged zone in aeronautical structures has experienced rapid expansion given its advantages over conventional mechanical processes (riveting, bolting, etc.). Initially, The research axes in this field were aimed at choosing suitable mechanical properties for the composite and the adhesive, then to optimize the shape of the composite patch in order to ensure good load transfer and avoid having a debonding at the level of the edges essentially for the case of a repair by single side where the bending moment is present due to the non-symmetry of the structure. Our work falls within this context; the objective is to analyze by the finite element method the fracture behavior of a damaged plate repaired by composite patch. Stress reduction at the edge is accomplished by creating a variable angle chamfer on the composite patch. The effects of the crack length, the laminate sequence and the nature of the patch as well as the use of a hybrid patch were investigated. The results show clearly that a beveled patch reduces the stress concentrations in the damaged area and even at its edges. The hybrid patch also ensures good durability of the repair by optimizing its stacking sequence and the location of the different layers according to the fibers orientations.

• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.359-374
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• 2024

A high-fidelity numerical analysis methodology was proposed for evaluating the fuel rod cladding integrity of a Prototype Gen IV Sodium Fast Reactor (PGSFR) during normal operation and Design basis events (DBEs). The MARS-LMR code, system transient safety analysis code, was applied to analyze the DBEs. The results of the MARS-LMR code were used as boundary condition for a 3D computational fluid dynamics (CFD) analysis. The peak temperatures considering HCFs satisfied the cladding temperature limit. The temperature and pressure distributions were calculated by ANSYS CFX code, and applied to structural analysis. Structural analysis was performed using ANSYS Mechanical code. The seismic reactivity insertion SSE accident among DBEs had the highest peak cladding temperature and the maximum stress, as the value of 87 MPa. The fuel cladding had over 40 % safety margin, and the strain was below the strain limit. Deformation behavior was elucidated for providing relative coordinate data on each active fuel rod center. Bending deformation resulted in a flower shape, and bowing bundle did not interact with the duct of fuel assemblies. Fuel rod maximum expansion was generated with highest stress. Therefore, it was concluded that the fuel rod cladding of the PGSFR has sufficient structural safety margin during DBEs.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.4112-4119
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• 2023

This study employs the microshear test method to examine the local mechanical properties of narrow-gap welded joints, revealing the mechanical inhomogeneity by evaluating the microshear strength, stress-strain curves, and failure strain. On this basis, the influence of weld joints micromechanical inhomogeneity on the crack tip opening displacement (CTOD) fracture toughness is investigated. From the root weld layer to the cover weld layer, the fracture toughness at the center of the weld seam demonstrates an increasing trend, with the experimental and calculated CTOD values showing a good correspondence. The microproperties of the welded joints significantly impact the load-bearing capacity and fracture toughness. During the deformation process of the "low-matching" microregions, the plastic zone expansion is hindered by the surrounding microregion strength constraints, thus reducing the fracture toughness. In contrast, during the deformation of the "high-matching" microregions, the surrounding microregions absorb some of the loading energy, partially releasing the concentrated stress at the crack tip, which in turn increases the fracture toughness.

• Transactions of Materials Processing
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• v.33 no.5
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• pp.330-340
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• 2024

The martensitic Ni-Ti shape memory alloys(SMA) can achieve a two-way shape memory effect (TWSME) through thermomechanical training/cycling. In this study, the surface of Ni-Ti SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers using a selective laser meling (SLM) process to enhance TWSME. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 training cycles when the optimum number of five Ti layers was deposited. A larger HAZ and lower cooling rate pushed more Ti particles into the grains rather than the grain boundaries, providing more time for Ti to react with NiTi to form Ti-rich intergranular Ti2Ni(Ox) precipitates. This resulted in further hindering of dislocation movement within the grains and the generation of internal stress fields required for attaining a larger TWSME. With an increase in the number of Ti-deposited layers, there was no noticeable reduction in the one-way shape memory effect (OWSME) through the initial cycling. This was due to the high residual tensile stress caused by the lower thermal expansion of the Ti layer compared to the Ni-Ti sheet.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.274-282
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• 2020

This study examined the effect of job stress and mental health factors on the oral symptoms of caring service workers in Seoul. For the research method, a survey was conducted from July 24 to August 6, targeting 150 caring service workers. The survey items were job stress, mental health (physical symptoms, anxiety, and insomnia), and self-diagnosed oral symptoms. The results of the study were as follows. Job stress (p=0.001) had a significant effect on the oral symptoms. In addition, physical symptoms (p<0.001), anxiety symptoms (p<0.001), and insomnia symptoms (p<0.001) all had significant effects on the oral symptoms. Among the risk factors, physical symptoms had the greatest influence on oral symptoms. In addition, according to the correlation result of job stress, anxiety symptoms, insomnia symptoms, oral symptoms, as job stress increases, physical symptoms (p<0.001), anxiety symptoms (p<0.001), insomnia symptoms (p<0.001), oral symptoms (p<0.01) showed an increasing positive correlation and a statistically significant difference. Physical and psychological labor power is greatly exhausted by care service workers performing tasks that require physical and mental care for those who are being cared for. Therefore, there is a need for systematic expansion measures for the mental health of workers and the introduction of customized oral health education programs to improve oral health because improved health and oral health conditions can increase work performance.