• Journal of Korea Foundry Society
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• v.10 no.1
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• pp.31-42
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• 1990

The full mould casting process in one of the newly developed techniques which has many advantages. Unbonded sand mould has been prepared for the major mould and $CO^2$ gas mould has been used occasionally for comparison. Patterns were built up with expanded polystyrene and coated with three different materials. Silica, graphite and zircon were used for the coating layer. The effects on fluidity and temperature loss of molten metals were investigated. The molten metals were Al-5% Si alloy, Cu-30% Zn alloy and gray iron of approximately 4.0% of carbon equivalent. Experimental variables were runner section area, superheat, sprue height, coating materials, coating thickness and apparent density of EPS pattern. The effects of coating materials on fluidity and temperature loss of the molten metals during transient pouring are summarized as follows : As runner section area, superheat and sprue height increased, fluidity increased. Temperature loss decreased as runner section area and sprue height increased. However, reversed effects were observed in the case of superheat increment. The coating materials decreased the fluidity of each alloy in the order of silica, graphite and zircon. Zircon brought to the highest temperature loss among the coating materials used. The fluidity increased in the order gray iron, Cu-30% Zn and Al-5% Si alloy while temperature loss in the reverse order. Especially in case of reduced pressure process, the fluidity was increased apparently. Al-5% Si alloy showed the lowest temperature loss among the alloys. The increment of the apparent density of EPS pattern resulted in the fluidity decrease and temperature loss increase. The relation between fluidity and temperature loss of each alloy can be expressed by the following equation within the coating thickness limit of 0.5-1.5㎜. F^*={\frac{a}{T^*-b}}-c$ where, $F^*$ : fluidity in the Full mould, $T^*$ : temperature loss in the mould. a : parameter for full mould. b, c : constants.

• Journal of Ocean Engineering and Technology
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• v.2 no.1
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• pp.135-149
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• 1988

Friction welding has been shown to have significant economic and technical advantages. However, one of the major concerns in using friction welding is the reliability of the weld quality. No reliable nondestructive test method is available at present for detecting weld quality, particularly in a production environment. Friction welds are formed by the mechanisms of diffusion as well as mechanical interlocking. The severe plastic flow at the interface by forge action of the process brings the subsurfaces so close together that detection of any unbonded area becomes very difficult. This paper presents an attempt to determine the friction weld strength quantitatively using the ultrasonic pulse-echo method. Instead of detecting flaws or cracks at the interface, the new approach calculates the coefficient of reflection based on measured amplitudes of the echoes. It has been finally confirmed that this coefficient could provide the quantitative relationship to the weld quality such as tensile strength, torsional strength, impact value, hardness, etc. So a new nondestructive analysis system of friction weld strength of dissimilar metals using an ultrasonic technique could be well developed.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.603-610
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• 2006

The external unbonded strengthening offers advantages in speed and simplicity of installation over other strengthening techniques. Unlike externally bonded steel plate or carbon fiber sheet, surface preparation of the concrete for installation of high-tension bar is not required and installation is not affected by environmental conditions. Anchoring pin or anchoring plate are installed at the end of beam to connect the high-tension bar to concrete beam. The deviator are used in order that supplementary external bars would follow the curvature of the tested beam. A set often laboratory tests on reinforced concrete beam strengthened using the technique are reported. The main test parameters are the section area of strengthening bar, the depth of deviator and the number of deviators. The paper provides a general description of structural behavior of beams strengthened using the technique. The test result of strengthened beam are compared with those from a reference specimen. It is shown that the reinforcing technique can provide greater strength enhancements to unstrengthened beam and that the provision of deviator enhances efficiency. The ultimate moment of specimen with two deviators was higher than that of specimens with one deviator. It is also shown that the external bars enhance strength of beams in shear.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.361-370
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• 2017

Through the use of finite element analysis and acoustic emission techniques we have evaluated the interfacial failure of a carbon fiber reinforced polymer (CFRP) repair patch on a notched aluminum substrate. The repair of cracks is a very common and widely used practice in the aeronautics field to extend the life of cracked sheet metal panels. The process consists of adhesively bonding a patch that encompasses the notched site to provide additional strength, thereby increasing life and avoiding costly replacements. The mechanical strength of the bonded joint relies mainly on the bonding of the adhesive to the plate and patch stiffness. Stress concentrations at crack tips promote disbonding of the composite patch from the substrate, consequently reducing the bonded area, which makes this a critical aspect of repair effectiveness. In this paper we examine patch disbonding by calculating the influence of notch tip stress on disbond area and verify computational results with acoustic emission (AE) measurements obtained from specimens subjected to uniaxial tension. The FE results showed that disbonding first occurs between the patch and the substrate close to free edge of the patch followed by failure around the tip of the notch, both highest stress regions. Experimental results revealed that cement adhesion at the aluminum interface was the limiting factor in patch performance. The patch did not appear to strengthen the aluminum substrate when measured by stress-strain due to early stage disbonding. Analysis of the AE signals provided insight to the disbond locations and progression at the metal-adhesive interface. Crack growth from the notch in the aluminum was not observed until the stress reached a critical level, an instant before final fracture, which was unaffected by the patch due to early stage disbonding. The FE model was further utilized to study the effects of patch fiber orientation and increased adhesive strength. The model revealed that the effectiveness of patch repairs is strongly dependent upon the combined interactions of adhesive bond strength and fiber orientation.