• 한국정보디스플레이학회:학술대회논문집
• /
• 2008.10a
• /
• pp.1455-1458
• /
• 2008

Amorphous silicon (a-Si:H) thin-film transistors (TFTs) are fabricated on flexible organic polymer foil substrates. As-fabricated performance, electrical bias-stability at elevated temperatures, electrical response under mechanical flexing, and prolonged mechanical stability of the TFTs are studied. TFTs made on plastic at ultra low process temperatures of $150^{\circ}C$ show initial electrical performance like TFTs made on glass but large gate-bias stress instability. An abnormal saturation of the instability against operation temperature is observed.

• Journal of the Korean Society for Precision Engineering
• /
• v.12 no.3
• /
• pp.32-41
• /
• 1995

In the analysis of metal forming processes by the finite element method, there are many numerical instabilities such as element locking, hourglass mode and shear locking. These instabilities may have a bad effect upon accuracy and convergence. The present work is concerned with improvement of stability and efficiency in two-dimensional rigid-plastic finite element method using various type of elemenmts and numerical intergration schemes. As metal forming examples, upsetting and backward extrusion are taken for comparison among the methods: various element types and numerical integration schemes. Comparison is made in terms of stability and efficiency in element behavior and computational efficiency and a new scheme of adaptive directional reduced integration is introduced. As a result, the finite element computation has been stabilized from the viewpoint of computational time, convergency, and numerical instability.

• Journal of the Korean Society of Safety
• /
• v.18 no.4
• /
• pp.16-22
• /
• 2003

Generally the rupture of steam generator tubes proceeds from significant plastic deformation before failure. In this study, the burst pressures of damaged steam generator tubes were calculated from the plastic instability analysis with the finite element method. Two wear types, flat and circumferential types were considered. An equation for the burst pressure was proposed by using the strength reduction factor and the Svensson equation. The analysis results were compared with the experiment data from published references and they showed a good agreement with the experiment data.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.5
• /
• pp.928-937
• /
• 1989

Applicability of $T_{\delta}$ proposed by Shin et al as an instability parameter for ductile material is investigated, Both general fracture test and instability fracture test are performed using compact tension specimens of structural alloy steel(SCM4), The values of ( $T_{\delta}$)$_{app}$(applied tearing modules) estimated from the real load vs. crack growth curve measured from experiments are compared with those estimated from the limit load vs. crack growth curve. The results are:(1) the $T_{\delta}$ parameter may be used as a crack instability parameter:(2) the use of ( $T_{\delta}$)$_{app}$ estimated from the load-crack growth curve, proposed in this study is reasonably justified.ified.d.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.03a
• /
• pp.18-21
• /
• 1999

The wrinkling of thin sheet metal induced by compressive instability is one of major defects in sheet metal forming processes. compressive instability is influence by many factors such as mechanical properties of the sheet material geometry of the sheet contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show swide variations even for small deviations of the factors. in this work the bifurcation theory is introduced for the finite elemental analysis of the instability behavior of a thin sheet with initially sound geometry and property. All the above-mentioned factors are conveniently considered by the finite element method. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. Wrinkling initiation and growth in the deep drawing process are analyzed.

• Transactions of Materials Processing
• /
• v.12 no.3
• /
• pp.184-193
• /
• 2003

• Structural Engineering and Mechanics
• /
• v.14 no.4
• /
• pp.455-472
• /
• 2002

The paper involves the study on the elastic and elasto-plastic stress wave propagation in the 1-D and 2-D solid media. The Smooth Particle Hydrodynamics equations governing the elastic and elasto-plastic large deformation dynamic response of solid structures are presented. The proposed additional stress points are introduced in the formulation to mitigate the tensile instability inherent in the SPH approach. Both incremental rate approach and leap-frog algorithm for time integration are introduced and the new solution algorithm is developed and implemented. Two examples on stress wave propagation in aluminium bar and 2-D elasto-plastic steel plate are included. Results from the proposed SPH approach are compared with available analytical values and finite element solutions. The comparison illustrates that the stress wave propagation problems can be effectively solved by the proposed SPH method. The study shows that the SPH simulation is a reliable and robust tool and can be used with confidence to treat transient dynamics such as linear and non-linear transient stress wave propagation problems.

• Archives of Plastic Surgery
• /
• v.41 no.1
• /
• pp.29-34
• /
• 2014

The septal extension graft is a very useful method of controlling nasal lengthening and tip projection, rotation, and shape by fixing a graft to the septum, which leads to a strong supporting structure. Enhancing graft stability is important for better long-term outcomes and minimizing complications or relapse, and even more efficient application of these methods is needed for East Asians who lack enough cartilage to be harvested in addition to possessing a weak cartilage framework. In this paper, the methods for overcoming the drawbacks of the septal extension graft, such as instability, a fixed tip, and insufficiency of cartilage, are presented, and the applications of each method for greater satisfaction with surgical outcomes are also discussed.

• Journal of the Korean Society of Safety
• /
• v.12 no.3
• /
• pp.52-59
• /
• 1997

Hill's anisotropy theory and isotropy theory under the deformed profile assumed two separate cases(that is circular and ellipitical) are applied to predict the plastic deformation characteristics of bulge, the strain and polar height under instability condition, using thin square diaphragms of stainless steel, mild steel, brass, copper and aluminum. In this study it was found that the pressure-polar height curves, and the polar height-the polar radius of curvature curve, under anisotropy theory and isotropy theory, assuming a circle profile, agree well with the experimental results, and the equivalent strains of the instability condition under anisotropy theory are better good agreement with the experimental results than those of the instability condition under isotropy theory. Beside, FLCo(plane Strain Intercept) obtained by Bethlehem FLC method and standard FLC method (modified) agree well with the experimental result.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.9
• /
• pp.2223-2233
• /
• 1993

An engineering method is suggested to calculate the applied load versus crack extension in the elastic-plastic fracture. The condition for an increment of crack extension is set by a critical increment of crack-up opening displacement(CTOD). The ratio of the CTOD increment to the incremental crack extention is a critical crack-tip opening angle(CTOA), assumed to be constant for a material of a given thickness. The Dugdale model of crack-tip deformation in an infinite plate is applied to the method, and a complete solution for crack extension and crack instability is obtained. For finite-size specimens of arbitrary geometry in general yielding, an approximate generalization of the Dugdale model is suggested so that the approximation approaches the small-scale yielding solution in a low applied load and the finite-element solution in a large applied load. Maximum load is calculated so that an applied load attains either a limit load on an unbroken ligament or a peak load during crack extension. The proposed method was applied to three-point bend specimens of a carbon steel SM45C in various sizes. Reasonable agreements are found between calculated maximum loads and experimental failure loads. Therefore, the method can be a viable alternative to the J-R curve approach in the elastic-plastic fracture analysis.