• Structural Engineering and Mechanics
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• v.50 no.4
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• pp.525-539
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• 2014

Bonded composite-patch repair has been widely used to restore or extend the service life of damaged structures due to its effectiveness as a mechanical repair technique. In this paper using extended finite element method (XFEM), three-dimensional crack models are developed to examine the fracture behavior of centrally cracked aluminum plates repaired with single and double sided composite patches. Stress intensity factor (SIF) at the crack tip is used as the fracture criterion. In this regard, the effects of the crack lengths, patch materials, orientation of plies, adhesive and patch thickness are examined to estimate the SIF of the repaired plate and the repair performance. The obtained results show that composite patches have significant effect on reduction of the SIF at the crack tip. It is also proved that using double symmetric repair, in comparison to single one, reduces considerably SIF at the crack tip. Hence, the residual strength can be improved significantly as well as fatigue life of the structure. Investigation of ply orientation effects shows SIF increase as the ply orientation is changed from $0^{\circ}$ (perpendicular to the advancing crack) to $90^{\circ}$ (parallel to the crack line). However, the effectiveness of the ply orientation depends on the loading direction and the crack direction.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.339-349
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• 2017

This paper is related to structural design evaluation of 19,000 TEU ultra large container ship, dealing with hydroelastic response, i.e. springing and whipping. It illustrates application of direct calculation tools and methodologies to both fatigue and ultimate strength assessment, simultaneously taking into account ship motions and her elastic deformations. Methodology for springing and whipping assessment within so called WhiSp notation is elaborated in details, and in order to evaluate innovative container ship design with increased loading capacity, a series of independent hydroelastic computations for container ship with mobile deckhouse and conventional one are performed with the same calculation setup. Fully coupled 3D FEM - 3D BEM model is applied, while the ultimate bending capacity of hull girder is determined by means of MARS software. Beside comparative analysis of representative quantities for considered ships, relative influence of hydroelasticity on ship response is addressed.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.439-449
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• 2002

This paper reviews our recent research works on the interconnection technologies in electronic packaging and assembly. At the aspect of advanced joining methods, laser-ultrasonic fluxless soldering technology was proposed. The characteristic of this technology is that the oxide film was removed through the vibration excitated by high frequency laser change in the molten solder droplet. Application researches of laser soldering technology on solder bumping of BGA packages were carried out. Furthermore, interfacial reaction between SnPb eutectic solder and Au/Ni/Cu pad during laser reflow was analyzed. At the aspect of soldered joints' reliability, the system for predicting and analyzing SMT solder joint shape and reliability(PSAR) has been designed. Optimization design method of soldered joints' structure was brought forward after the investigation of fatigue failure of RC chip devices and BGA packages under temperature cyclic conditions with FEM analysis and experimental study. At the aspect of solder alloy design, alloy design method based on quantum was proposed. The macroproperties such as melting point, wettability and strength were described by the electron parameters. In this way, a great deal of the experimental investigations was replaced, so as to realize the design and research of any kinds of solder alloys with low cost and high efficiency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.376-381
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• 2009

The increasing needs for higher cargo capacity in the container vessels' fleet has led to ship builder's demand for higher power output rating engine to meet the propulsion requirement, thus, leading to the development of super large two stroke low speed diesel engines. This large sized bore engines with more than 12 cylinders are capable of delivering power output up to more than 100,000 bhp at maximum continuous rating. The thrust variation force due to axial vibration occurring in propulsion shafting of these ships are transmitted to ship structure via thrust bearing. This force may vibrate the super structure of ship in the fore-aft direction and the fatigue strength of crank shaft can be decreased by additional bending stress increase in crank shaft pin and journal. In this paper, the axial vibration of propulsion shafting system on the 14RT-flex96C super large diesel engine with 14 cylinders is identified by theoretical analysis and vibration measurement.

• Journal of the Korean Institute of Gas
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• v.6 no.4 s.18
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• pp.17-22
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• 2002

LNG demand has been rapidly increasing in Korea for a variety of reasons including stable supply, non-polluting, and high combustion efficiency characteristics. One of the most important structural core element of the LNG storage tank is the membrane, consisting of stainless steel. The membrane to be applied inside of LNG storage tank is provided with corrugations to absorb thermal contraction and expansion caused by LNG temperature. Experimental studies are presented to investigate the deformation and strength of the membrane which is designed by Kogas. All experiments are conducted on the basis of RPIS, and we found the results is fully satisfied with the RPIS.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.3
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• pp.269-277
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• 2015

Compressed natural gas (CNG) composite vessels for vehicles have been generally made of 34CrMo4 for a inner liner part and E-glass/epoxy for a composite layer part. But, there is a problem of material loss of CNG composite vessels used in vehicles due to the design of excessive thickness of the liner. And, light weight of the CNG composite vessel is required for improving fuel efficiency. In this study, optimal design for CNG composite pressure vessel was performed by using basalt fiber, which is the environment-friendly material having a good mechanical strength. The optimal thickness of each part (inner liner and composite layer) was determined by theoretical analysis and FEA for satisfying structural safety and lightweight of the vessel. Also, for improving fatigue life, optimal autofrettage pressure was derived from FEA results.

• Carbon letters
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• v.9 no.4
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• pp.324-339
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• 2008

The principal aims of the review paper are (1) to establish broad overview information, both qualitative and quantitative, relating to the world market for polyacrylonitrile (PAN) or pitch-based carbon fibers; and (2) to generate an effective analysis and break down of consumption by process route and eventual end-use. The review paper also designed specifically to provide subscribers with an accurate, independent, and realistic assessment of the current status and future perspective of the market for carbon fibers in the world. The world market for carbon fibers continues to grow rapidly, fuelled by new industrial end uses, such as sport and leisure goods, aerospace, automotive applications, civil engineering and infrastructure repair, and immerging applications in energy generation. Demands for properties of carbon fibers used in those applications include many things such as strength, toughness, fatigue property, corrosion resistance, heat resistance, etc., and these become to be higher level. On the other hand, demands for manufacturing technologies of carbon fibers become to be difficult with these demands for properties, and these are wide variety such as high efficiencies, high qualities, many functions, labor saving, and low cost. In this review paper, thus, the recent carbon fibers corresponded to these needs, and its latest manufacturing technologies as well as market prospects are described.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.2
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• pp.151-156
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• 2017

Shot peening is widely used to improve the fatigue life and strength of various mechanical parts and an accurate method is important for the prediction of the compressive residual stress caused by this process. A finite element (FE) model with an elliptical multi-shot is suggested for random-angled impacts. Solutions for compressive residual stress using this model and a normal random vertical-impact one with a spherical multi-shot are obtained and compared. The elliptical multi-shot experimental solution is closer to an X-ray diffraction (XRD) than the spherical one. The FE model's peening coverage also almost reaches the experimental one. The effectiveness of the model based on an elliptical shot ball is confirmed by these results and it can be used instead of previous FE models to evaluate the compressive residual stress produced on the surface of metal by shot peening in various industries.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.623-631
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• 2003

It is considered that the application of advanced composite materials to the prostheses for the disables is important to improve their bio-mechanical performance. Particularly, energy storing foot prosthesis is mostly important to restore gait ability of the disables with low-extremity amputation since it could provide propulsion at terminal stance enhancing the disables ability to walk long distance even run and jump. Therefore, the energy storing spring of Prosthetic foot keel under cyclic bending moment use mainly of high strength glass fiber reinforced plastic. The main objective of this study was to evaluate the stacking sequence effect using the delamination growth rate(dA$_{D}$/dN) of energy storing spring in glass fiber reinforced plastic under cyclic bending moment. The test results indicated that the shape of delamination zone depends on stacking sequence in GFRP laminates. Delamination area(A$_{D}$) turns out that variable types with the contour increased non-linearly toward the damage zones.nes.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.12
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• pp.110-116
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• 2009

Thick-walled cylinders, such as a cannon or nuclear reactor, are autofrettaged to induce advantageous residual stresses into pressure vessels and to increase operating pressure and the fatigue lifetimes. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. However, the Bauschinger effect reduces the compressive residual stresses as a result of prior tensile plastic strain, and decreases the beneficial autofrettage effect. The purpose of the present paper is to predict the accurate residual stress of SNCM8 high strength steel using the Kendall model which was adopted by ASME Code. The uniaxial Bauschinger effect test was performed to decide BEF, then this constant was used in calculation. There were some differences between theoretical solution and modified solution.