• Corrosion Science and Technology
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• v.8 no.1
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• pp.27-39
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• 2009

Non metallic composite materials, for example, GECM(graphite epoxy composite material) show high specific strength because of low density. These kinds of non metallic composite materials improved the structural effectiveness and operation economics. However, if these materials contacted several metals, corrosion can be arisen since non metallic composite materials have electrical conductivity. This paper dealt with galvanic corrosion between graphite epoxy composite material and several metals. Base on the electrochemical galvanic corrosion test between GECM and metals, corrosion current of carbon steel and aluminium increased with time but corrosion current of stainless steels and titanium decreased and galvanic potential increased. This behavior shows the galvanic corrosion depends upon the presence of passive film. Also, galvanic effect of GECM coupled with ferrous alloys and non-ferrous alloys was lower than that of 100% graphite, which is attributed to lower exposed area of graphite fiber in the GECM than apparent area of the GECM specimen used for the calculation of galvanic current in this work.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.68-68
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• 2009

Recently, resistance spot welding using Inverter DC is applied to improve the weldability of high strength steel for the auto-body fabrication. In this study, inverter DC spot welding machine, which is developed in the domestic, was evaluated weldability of the galvanized and cold rolled dual-phase steel(tensile strength : 590MPa). The welding conditions (welding time, current and force) were decided by tensile-shear test, and welding strength and nugget size were analyzed by statistical analysis methods which involved dynamic resistance and indentation. The results of the statistical analysis was utilized for real-time estimation of the invisible nugget size and tensile strength. Moreover, it can be achieved without the conventional destructive testing of welds.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.1
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• pp.82-90
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• 2003

Nowadays, many components used in machinery industry is required lightness and high strength. The shot-peening method is used in order to improve the fatigue life of spring steel(JIS G SUP-9) which is used in suspension of automobile. The compressive residual is induced in this shot-peening process. This paper investigated the effect of the residual compressive stress on the fatigue crack growth characteristics. Main results are summarized as follows. 1. The fatigue crack growth rate on stage II is conspicuous with the level of compressive residual stress and is dependent on Paris equation. 2. Although the maximum compressive residual stress is deeply and widely formed from surface, it does not improve the fatigue life comparing when maximum compressive residual stress is formed in surface. 3. The threshold stress intensity factor range is increased with increasing compressive residual stress. 4. In fracture surface of fatigue crack growth it is investigated that compressive residual stress remarkably retards fatigue crack growth.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.4
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• pp.426-435
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• 2005

The lightness of components required in automobile and machinery industries is requiring high strength of components. Therefore this requirement is accomplished as the process of shot-peening method that the compressive residual stress is made on the metal surface as one of various improvement methods. Special research is, therefore, needed about compressive residual stress on the metal surface in the process of shot-peening method. Therefore, in this paper the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in environmental condition(temperature) and mechanical condition(shot velocity, stress ratio) was investigated with considering fracture mechanics. By using the methods mentioned above, the following conclusions have been drawn. (1) The fatigue crack growth rate(da/dN) of the shot-peened material was lower than that of the un-peened one. In high temperature range. fatigue crack growth rate decreased with increasing temperature range, while fatigue crack growth rate increased by decreasing temperature in low temperature. (2) Fatigue life shows more improvement in the shot-peened material than in the un-peened material. And compressive residual stress of surface on the shot-peen processed operate resistance force of fatigue crack propagation.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.222-229
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• 2017

High manganese steel exhibits excellent mechanical properties with respect to strength and durability at low temperatures. Recently, high manganese steel has been considered as an alternative to existing materials, such as nickel steel and SUS304L for application as tank material for Liquefied Natural Gas (LNG) cargo containment systems. In the present study, tensile tests were performed at room and cryogenic temperatures in order to investigate the mechanical properties and non-linear tensile behavior of high manganese steel. In addition, elasto-plastic damage model was applied using the finite element analysis software ABAQUS via a user defined material subroutine (UMAT) to describe the material behavior. Finally, the results of the finite element simulations using the UMAT were compared to those of the tensile tests in order to validate the proposed UMAT. It has been demonstrated that the UMAT can effectively describe the non-linear tensile behavior of high manganese steel.

• Journal of Advanced Engineering and Technology
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• v.11 no.4
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• pp.279-285
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• 2018

A shear connection between the steel beam and concrete slab determines the stability of composite beams. An extensive numerical study to evaluate the resistance of the shear connection in a solid slab at high temperature was conducted. Three-dimensional thermo-mechanical finite element models were developed using a dynamic explicit method and concrete damaged plasticity model. Temperature-dependent plasticity parameters of the concrete model were proposed, and the accuracy of the developed model was obtained against experimental data. This investigation has revealed that a stud shearing failure occurs regardless of temperatures, and its shearing location changes in accordance with a rise in temperature. A new strength reduction formula has been presented to estimate the resistance of the shear connection at high temperatures.

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.2049-2056
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• 2014

A simple method for exfoliating pristine graphite to yield mono-, bi-, and multi-layers of graphene sheets as a highly concentrated (5.25 mg/mL) and yielded solution in an organic solvent was developed. Pre-thermal treatment of pristine graphite at $900^{\circ}C$ in a sealed stainless steel bath under high pressures, followed by sonication in 1-methyl-2-pyrrolidinone solvent at elevated temperatures, produced a homogeneous, well-dispersed, and non-oxidized graphene solution with a low defect density. The electrical conductivities of the graphene sheets were very high, up to 848 S/cm. These graphene sheets were used to fabricate graphene-polyimide nanocomposites, which displayed a higher electrical conductivity (1.37 S/m) with an improved tensile strength (95 MPa). The synthesized graphene sheets and nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy.

• Steel and Composite Structures
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• v.23 no.2
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• pp.161-172
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• 2017

A new composite tube connection method called the pre-tightened teeth connection technique is proposed to improve the composite tube connection efficiency. This paper first introduces the manufacturing process of the proposed technique. It then outlines how the mechanical properties of this technology were tested using four test groups. The factors that influence the load-bearing capacity and damage model of the connection were analyzed, and finally, the transfer load mechanism was investigated. The following conclusions can be obtained from the research results. (1) The new technique improves the compressive connection efficiency by a maximum of 79%, with the efficiency exceeding that of adhesive connections of the same thickness. (2) Changing the depth of teeth results in two types of damage: local compressive damage and shear damage. The bearing capacity can be improved by increasing the depth, length, and number of teeth as well as the pre-tightening force. (3) The capacity of the technique to transfer high loads is a result of both the relatively high interlaminar shear strength of the pultruded composite and the interlaminar shear strength increase provided by the pre-tightening force. The proposed technique shows favorable mechanical properties, and therefore, it can be extensively applied in the engineering field.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.4
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• pp.385-393
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• 2007

The strength evaluation of the most weakest junction part is required for the safety design of all structures. Most of all. in order to enhance the reliability and safety of the welding part. whose use is the highest, it is very important to establish the efficient structure manufacturing technology by studying and investigating the evaluation of fatigue strength in various environments. This study analyzed the relations of da/dN, and th according to the welding methods of SMAW, FCAW, and SAW. In the stage II. the value of stress intensity factor range was the highest in SMAW welding method of stress ration R=0.1, and appeared under the sequence of FCAW and SAW and as the completion section of stress intensity factor was low, threshold stress intensity factor was lowly formed in da/dN - The fatigue life of each welding method is sensitively worked in high stress ratio. judging from the fact that the width of life reduction increases in the high stress ratio zone compared to the width of life reduction in the low stress ratio zone. In the fatigue limit of welding methods before corrosion. the welding of SMAW and FCAW shows the same fatigue limit compared to Base metal, and SAW holds the lowest fatigue limit value.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.9-12
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• 2008

PSC-I girder is widely used in designing bridge. Currently partial advanced country have constructed bridge with high strength concrete, while in-country rather less concrete strength(40MPa) has been used to build bridge girder. So, this paper presents characteristics and behavior of member casted by high strength concrete to apply practically. For this aim, 4 girders were fabricated to investigate performance and structural behavior. Prior to test, structural analysis was performed with common program. Steel gages and concrete gage were filled up to measure longitudinal and vertical strain of reinforcement and concrete. Linear Variable Differential Transducer and concrete surface gage were also set to measure deflection and strain of concrete. Load-deflection relation and crack mode were analyzed at transfer and test and compared with the structural analysis