• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.23 no.2
• /
• pp.127-132
• /
• 2014

Micro/nano-injection molding is one of the main processing techniques for polymer micro-fabrication. Most of the difficulties encountered in polymer micro-molding are caused by the demolding, rather than the filling of molds. Therefore, studying the demolding process is vitally important for manufacturing polymer replicas. The most important parameters are the thermal stress, friction and adhesion forces, and mechanical strength of the resist. In this research, we determinedthe effects of the processing conditions on the ejection force for cases involving two common thermoplastic polymers. The results showed that the processing conditions noticeably influenced the ejection force.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.427-432
• /
• 2003

An analytical method to predict the flexural behavior of composite girder is presented in which the early-age properties of concrete are specified including maturing of elastic modulus, creep and shrinkage. The time dependent constitutive relation accounting for the early-age concrete properties is derived in an incremental format by expanding the total form of stress-strain relation by the first order Taylor series with respect to the reference time. The sectional analysis calculates the axial and curvature strains based on the force and moment equilibriums. The deflection curve of the box girder approximated by the quadratic polynomial function is calculated by applying to the proper boundary conditions in the consecutive segments. Numerical applications are made for the 3-span double composite steel box girders which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The one dimensional finite element analysis results are compared with those of the three dimensional finite element analysis and the analytical method based on the sectional analysis. Close agreement is observed among the three methods.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.463-468
• /
• 2003

A finite element formulation to predict the flexural behavior of composite girder is presented in which the early-age properties of concrete are specified including maturing of elastic modulus, creep and shrinkage. The time dependent constitutive relation accounting for the early-age concrete properties is derived in an incremental format by expanding the total form of stress-strain relation by the first order Taylor series with respect to the reference time. The total potential energy of the flexural composite member is minimized to derive the time dependent finite element equilibrium equation. Numerical applications are made for the 3-span double composite steel box girders which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The numerical analysis with considering the variation of concrete elastic modulus are performed to investigate the effect of it on the early-age behavior of composite structures. The one dimensional finite element analysis results are compared with the analytical method based on the sectional analysis. Close agreement is observed among the two methods.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2006.11a
• /
• pp.197-200
• /
• 2006

The portion of thin plate is expected to increases as to the development of design and fabrication technology. The weld-induced deformation is more serious in thin plates than in thick plates because heat affect zone of thin plates is wider than that of thick plates, and in addition internal and external constraints much more influence upon weld-induced deformation of thin plates. This paper deals with the application of the mechanical tensioning method to fillet weld of thin plates to reduce the weld-induced deformation. For this, fillet welding test have been carried out for several thin plate specimens with varying plate thickness and magnitude of tensile load. From the present study, it has been found that the tenssoning method is effective on reduction of weld-induced deformation.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.1295-1300
• /
• 2008

During the manufacturing and the service life of Au-Al wire bonded electronic packages, the ball bonds experience elevated temperatures and hence accelerated thermal diffusion reactions that promote the transformation of the Au-Al phases and the IMC growth. In this paper, the IC under high temperature storage (HTS) tests at $175^{\circ}C,\;200^{\circ}C$, and $250^{\circ}C$ are meticulously investigated. Thermal exposure resulted in the IMC growth, Kirkendall void and the crack of the Au-Al phases. The crack propagation occurs resulting in the failure of the Au-Al ball bonds. As the IC was exposed at the high temperature, decreased in the lifetime.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.06a
• /
• pp.135-147
• /
• 1997

The production of light metal parts using aluminum is mainly performed by die casting and squeeze casting, which directly fabricate the required shape from the liquid state. However, die casting is subject to defects such as shrinkage porosity and air trapped when molten metal enters the cavity, whilst squeeze casting also has defects due to turbulent flow in the die cavity. Both diecasting and sqeeze casting have inhomogeneous mechanical property in terms of dendritic structure during solidification. Active research has been carried out on semi-solid processing, rather than on conventional process methods such as die casting, which involve various problems. Therefore in this paper, to introduce the fundamental technology for d e design, in die casting and forging process with semi-solid materials, relationship between stress and strain of semi-solid materials, and for producing parts die design has been proposed as parameters of globulization of the microstructure and gate shape. The prevention of various defects to produce sound parts are also introduced.

• Textile Coloration and Finishing
• /
• v.18 no.2 s.87
• /
• pp.31-38
• /
• 2006

Silk fabrics are very popular and widely used because of their elegant appearance. However, silk fabrics generally have easy wrinkle, and do not stretch and deform permanently after machine washing. Then the stretched properties of silk fabrics are important for the application of industrial textile materials such as formal and sports wear. Thus, this research surveys the covering, weaving and degumming conditions for stretched silk fabrics. As a result, yarn breaking stress was reduced with increasing spindle speed, and the yarn twists were optimized under the covering condition of polyurethane/silk with PVA pretreatment. In addition, the shrinkage of the silk fabrics treated with star degumming process was reduced by continuous NaOH degumming process. The fabrics showed the fabric physical properties with optimum stretched properties and evenness surfaces.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.7 no.1
• /
• pp.131-138
• /
• 2003

This paper presents an analytical prediction of the prestress losses of prestressed concrete bridges. In this study a numerical procedure and computer program is developed to analyze the behavior of prestressed concrete bridges considering the time-dependent properties of material. It accounts for the aging, creep and shrinkage of concrete and the stress relaxation of prestressed steel. The structural model uses two dimensional plane frame elements with three nodal degree of freedom and is analyzed based on the finite element method. Member cross section can consist of concrete, reinforcement and prestressing steel. Two different set of equations for the prediction of time-dependent material properties of concrete are presented, which are ACI, CEB-FIP. The proposed numerical method for the prestress losses of prestressed concrete bridges is verified by comparison with reliable experimental results.

• Journal of the Society of Naval Architects of Korea
• /
• v.44 no.6
• /
• pp.590-597
• /
• 2007

The portion of thin plate is expected to increases as to the development of design and fabrication technology. The weld-induced deformation is more serious in thin plates than in thick plates because heat affect zone of thin plates is wider than that of thick plates, and in addition internal and external constraints much more influence upon weld-induced deformation of thin plates. This paper is aimed at applying the mechanical tensioning method to fillet weld of thin plates to reduce the weld-induced deformation. For this purpose, fillet welding tests have been carried out for several thin plate specimens with varying plate thickness and magnitude of tensile load. From the present study, it has been found that the tensioning method is effective on reduction of weld-induced deformation.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.10a
• /
• pp.417-424
• /
• 2001

It is very important to know the magnitude of the restraint moment which is appeared at the inner-support of the continuous PSC girder. The Age-adjusted Effective Modulus Method(AEMM) is used to get the magnitude of the restraint moment for the purpose of the time-dependent analysis of the concrete. The important factors for computing the restraint moment, the creep coefficient and the shrinkage strain are computed by comparing Korean specification with AC1209. The restrain moment is created by the individual continuity load. The main purpose of this paper is ensuring the safety of structure by acquiring the time-dependent stress acting on the concrete because the process of construction is getting difficult due to the advance of technology. The negative moment at the inner-support is decreased about 55% by introducing the process of making the continuous bridge relatively early.