• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.429-436
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• 2004

For the in-situ health monitoring of critical members in civil infra-structures, ultrasonic guided Lamb waves-based non-destructive evaluation (NDE) is very suitable. However, a chief drawback of the Lamb wave techniques is that multiple modes exist at all frequencies and the modes are generally dispersive, which means that the received signals may be very complicated. To overcome these complications, selective transmitting and receiving of a single A/sub 0/ mode within a frequency range can be adopted. Furthermore, a wavelet technique can be utilized to decompose the Lamb wave response into wavelet coefficients as a tool for signal processing. The changes in the Lamb waves interacting with damages in the steel plates are successfully characterized by this wavelet technique, through the amplitude change of the wavelet coefficients. In this paper, the feasibility of detecting a line crack on the surface of a steel plate and loosened bolts in a joint steel specimen using the Lamb waves and the wavelet technique is investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.495-501
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• 2001

In this paper, a new technique which models the joints characteristics through reduction of DOFs of structures with joints using component mode synthesis (CMS) method is proposed. Bolt joints are modeled by mass-spring systems. Also generalized mass and stiffness matrices for this models are introduced. Because bolt joints have influence on eigenvalues of structures, exact eigenvalues from modal test are used. The results show that the behaviors of structures with bolt joints depend to a large extent on the translational DOFs and not on rotational DOFs of mass and stiffness matrices of bolts. Furthermore it is confirmed that lumped mass-spring systems as models of bolt joints are effective models considering the facts that joint characteristics converged to constant values in some iterations and eignevalues from proposed method are in good agreement with ones from modal test.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.4 s.97
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• pp.122-128
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• 1999

Bolted joint assembly for nuclear power plants consists of various components : cover plate, retainer plate, manway flange, gasket and stud bolts/nuts. To guarantee the soundness of the joint, it is important to prevent leakage through the gasket and reduce the stress concentration factor at the thread root. In this paper, Submodeling technique for the finite element method is proposed to accurately compute three dimensional contact stresses which govern the sealing performance and the maximum contact stresses at the threads root. For verification of global solutions used as boundary conditions of submodel solution, the stresses on the cover plate and the manway flange are measured by strain gages when internal pressure is applied to the bolted joint assembly. The numerical results are compared with the experimental results.

• Advanced Composite Materials
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• v.17 no.4
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• pp.343-358
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• 2008

This present study provides the structural design and analysis of main wing, horizontal tail and control surface of a small scale WIG (Wing-in-Ground Effect) craft which has been developed as a future high speed maritime transportation system of Korea. Weight saving as well as structural stability could be achieved by using the skin.spar.foam sandwich and carbon/epoxy composite material. Through sequential design modifications and numerical structural analysis using commercial FEM code PATRAN/NASTRAN, the final design structural features to meet the final design goal such as the system target weight, structural safety and stability were obtained. In addition, joint structures such as insert bolts for joining the wing with the fuselage and lugs for joining the control surface to the wing were designed by considering easy assembling as well as more than 20 years service life.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.3
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• pp.165-171
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• 2003

In a structure, many components are fastened together using bolts, nuts and rivets through drilled holes. Not only do these fastened joints enable easy assembly and dismantling, they are also able to transfer as well as to distribute loads applied onto the structures. The major drawback of such connections, however, is that the fatigue life of the components is reduced by the presence of the hole since the stress concentration around the hole is increased. In addition, the hole drilling process itself may introduce defects or roughness at the surfaces of the hole that may cause further decrease in fatigue performance of the components. For applications where fatigue loadings are important, one way to compensate the decrease in fatigue life of the components is by introduction of beneficial compressive residual stress around the hole using cold working. The material used for this research were A12024-T351 and A17050-T7451 using the primary member of aircraft. We present, In this paper, the characteristics of coldworking by evaluation of the hole expansion ratio, residual stress distribution, and fatigue properties.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1067-1072
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• 2001

In this study, the vibration diagnosis program for onboard machinery has been developed. The developed program includes signal monitoring module, system diagnosis module, and system modification module. The signal monitoring module is to monitor the vibration signal in time and frequency domains. And the system diagnosis module, which is developed by using Neural Network with error back propagation algorithm, can detect the abnormal symptom indicating the malfunction of the machinery onboard ships. The investigations of the developed system are presented through the experiment using Rotor Kit. Abnormal vibration signals are created by adding additional weight, manually misaligning the shaft, and loosening the bolts.

• Steel and Composite Structures
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• v.44 no.1
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• pp.1-15
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• 2022

The weld quality has always been an important factor affecting the development of exposed CFT column-base joint. In this paper, a new type of exposed RCFST column-base joint is proposed, in which the high strength steel bars (USD 685) are set through the column and reinforced concrete foundation without any base plate and anchor bolts. Three specimens, the varying axial force ratio (0, 0.25 and 0.5), were tested under cyclic loadings. In addition, the bending moment capacity, energy dissipation capacity and deformation capacity of column-base joints were clarified. The experimental results indicated that the axial force ratio increases the stiffness and the bending moment and improves the energy dissipation capacity of column-base joints. This is because a large axial force can limit the slip between steel tubular and infilled concrete effectively. The specimens show stable hysteresis behavior.

• Journal of Korean Association for Spatial Structures
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• v.23 no.2
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• pp.45-52
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• 2023

Modular construction is an economical and efficient construction that reduces time and costs by manufacturing units in factories and constructing them on site. Currently, the demand for modular construction is increasing not only abroad but also domestically. As the demand for modular construction increases, a lot of development and research on connections between modular units are being conducted. Connections between modular units should be quick and simple to assemble when assembling units on site, and should be in a form that allows each unit to be connected regardless of direction. In addition, it must be able to exert sufficient strength against external loads. In this study, a connection between modular units using connecting steel plates and bolts was proposed, and the nonlinear behavior of the connection to external lateral force was analyzed through finite element analysis, and resistance performance was evaluated.

• Fashion & Textile Research Journal
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• v.21 no.6
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• pp.708-716
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• 2019

This study explored Jeju natural resources with healing function and tried mixed dyeing of Ecklonia cava and onion shell to improve dyeing. The results showed that silk dyed with a mixture of Ecklonia cava powder and onion shells rather than Jeju's individually dyed silk had better color power to develop fashion products. In addition, all friction lightning bolts, dry cleaning and sweat mining levels were excellent as well as excellent UV protection rates. The three baenaet jeogori worn during a birth anniversary and four rest suits that infants and children can wear comfortably maintained the dyeing and functioning of Ecklonia cava and onion shell mixture that was proven through abnormal experiments. For the three baenaet jeogori and two rest suits, the company has developed a fashion product recognized for high value-added merchandise using a variegation dyeing method made in a handmade style for expressing a person's natural sensibility through dyeing fabrics. Based on the results of the above research, it is expected that various fashion product developments will be possible by dyeing a mixture of functional and colorful extracts of the drug and colorful dye.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.6
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• pp.57-62
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• 2015

A large variety of pipe flanges are required in the marine and construction industry. Pipe flanges are usually welded or screwed to the pipe end and are connected with bolts. This approach is very simple and has been widely used for a long time; however, it results in high development costs and low productivity, and the products made through this approach usually have safety problems in the welding area. In this research, a new approach for forming pipe flanges based on cold forging and the floating die concept is presented. This innovative approach increases the effectiveness of the material usage and saves time and costs compared with the conventional welding method. To ensure the dimensional accuracy of the final product, finite element analysis (FEA) was carried out to simulate the process of cold forging, and orthogonal experiment methods were used to investigate the influence of four manufacturing factors (stroke of distance, pin die angle, forming of pipe diameter, and speed of the die) and predict the best combination of them. The manufacturing factors were obtained through numerical and experimental studies, which show that the approach is very useful and effective for the forming of pipe flanges and could be widely used in the future.