• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.9
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• pp.2792-2799
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• 1996

It was shown in the previous study that the numerically derived elastic work factor for CLS specimen was independent of fiber direction for a unidirectional case. Also, it was proposed the elastic work factor could be used to determine energy release rate from a single test record. In the present study, elastic work factor was derived from a simple beam theory to investigate its dependence on material property and geometric condition. Also, the elastic work factor of CLS specimen was applied experimentally to determine critical energy release rate in order to prove its validity determining critical energy release rate from a single specimen. For this purpose, critical energy release rate determined using the elastic work factor was compared with that determined by the compliance method. The results showed that while elastic work factor is affected by $t_2/t_1$ and $L_2/L_1$ it is independent of fiber angle for a unidirectional case. It was also found that critical energy release rates determined by both methods are comparable each other, thus elastic work factor approach can be used to determine energy release rate from a single test specimen.

• Journal of Engineering Education Research
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• v.20 no.1
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• pp.63-68
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• 2017

This research is as a case study of innovative engineering education system through idea factory of korea maritime and ocean university and deals with development of temperature-humidity control device (THCD) for fiber storage on composites in viewpoint of problem solving method. Fiber reinforced plastic (FRP) includes many variables on the composite manufacturing process. Above all, the interfacial adhesion between the fiber and the matrix acts as an important thing that decided mechanical property of the FRP, and also it is profoundly linked to external temperature and relative humidity. High void fraction leads to a result in interlaminar fracture. Therefore, in this research, to establish correlation between fiber reinforcement and fiber storage conditions of temperature and relative humidity we developed a THCD for fiber reinforcement. To evaluate performance of the THCD, glass fiber reinforced plastic (GFRP) is made under the extreme conditions each temperature $34^{\circ}C$, relative humidity 98 % and it can be said that there are the change of mechanical properties according to fiber storage conditions. As a result, the THCD showed sufficient possible application for understanding and applied research of composites field in material engineering. Also, we could check that the necessity of introduction of innovative system such as idea factory existed.

• Transactions of Materials Processing
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• v.8 no.3
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• pp.233-233
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• 1999

To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62χ)Nb-18Si-l00Mo-l0Ti-χW (χ=0, 5, 10 and 15 mol.%) in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)/sub 5/Si₃, silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti(/sub 5/Si₃, silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.65-74
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• 2001

A study on the corrosion behavior in case of As-welded and PWHT temperature 55$0^{\circ}C$ of welding part of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential measurement of weld metal(WM), base metal(BM) and heat affected zone(HAZ), both Al anode generating current and Al anode weight loss quantity under sacrificial anode cathodic protection conditions. And also we carried out slow strain rate test(SSRT) in order to research both limiting cathodic polarization potential for hydrogen embrittlement and optimum cathodic protection potential as well as mechanical properties by post-weld heat treatment(PWHT) effect. Hardness of HAZ was the highest among three parts(WM, BM and HAZ) and the highest galvanic corrosion susceptibility was HAZ. And the optimum cathodic polarization potential showing the best mechanical properties by SSRT method was from -770mV to -875mV(SCE). In analysis of SEM fractography, applied cathodic potential from -770mV to -875mV(SCE) it appeared dimple pattern with ductile fracture while it showed transgranular pattern (Q. C : quasicleavage) under -900mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement was under -900mV(SCE).

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.110-116
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• 2002

At elevated temperature, very complex precipitations occur in STS316. To investigate the effect of the precipitation on mechanical properties in SIS316, tensile tests and fatigue crack growth tests were carried out at $650^{\circ}C$ using artificially degraded materials. The material degradation was simulated by aging for up to 20000 hrs. at $750^{\circ}C$, which is equal to 179000hrs (about 20yrs) of service life at $650^{\circ}C$, after conducting solution treatment for 20 min. at $11300^{\circ}C$. The result of the hardness test and the tensile test showed that both properties are closely related to the mean free distance of carbides. Also, from the results of fracture tests at $650^{\circ}C$, ${\triangle}K_{th}$, after values were found to decrease as aging time and microstructure, as the volume fraction of $\sigma$ phase increased.

• Journal of Powder Materials
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• v.8 no.3
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• pp.157-162
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• 2001

An optimum route to fabricate the ferrous alloy dispersed $Al_2O_3$ nanocomposites such as $Al_2O_3$/Fe-Ni and $Al_2O_3$/Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of $Al_2O_3$ and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded $Al_2O_3$, forming nanocomposite powder. The sintered $Al_2O_3$/Fe-Ni composite showed the formation of Fe$Al_2O_4$ phase, while the reaction phases were not observed in $Al_2O_3$/Fe-Co composite. Hot-pressed $Al_2O_3$/Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

• Korean Journal of Materials Research
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• v.17 no.4
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• pp.192-197
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• 2007

The effects of immersion time in the liquid nitrogen on the behavior of aluminum alloys used for the hydrogen storage tank of auto-mobile at cryogenic temperature were investigated. With increasing immersion time in the liquid nitrogen, the elongation of AI 5083 alloy at cryogenic temperature decreased because of non-uniform fracture of precipitates on the grain boundary, and the serration also occurred because of discontinuous slip due to rapid decreasing of the specific heat. The mechanical properties of AI 6061 alloy at cryogenic temperature were characterized by uniformed yield strength, tensile strength and elongation regardless of the immersion time in the liquid nitrogen. These mechanical properties of aluminum alloys at cryogenic temperature were interpreted by the strength of grain boundary and the slip deformation behavior.

• Transactions of Materials Processing
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• v.11 no.8
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• pp.668-675
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• 2002

The circles deform into various shape during deformation, the major and minor axes of which indicate the direction of the major and minor principal strains. Likewise, the measured dimensions are used to determine the major and minor principal strain magnitudes. This circular grid technique of measuring strains can be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, of incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

• Transactions of Materials Processing
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• v.12 no.6
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• pp.588-596
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• 2003

The relationships between evolution of microstructure and mechanical properties of porous Al-3Si-2Mg-2Cu alloy after the foaming and various heat treating were investigated. The foamed alloy having various densities were manufactured by powder compact foaming and heat treated. Then compression test was performed with deformation rate of 0.5/s. The ultimate compression strength was not changed after solution heat treatment but the flow curve after ultimate strength showed very smooth and uniform plateau region. This change of flow curve means that the deformation mechanism is altered from brittle fracture to ductile deformation and the energy absorption property of Al foam is dramatically improved. The improvement of energy absorption without any detriment of mechanical properties is due to that the very brittle precipitation like Al-Cu and Al-Mg was uniformly dissolved in Al matrix after solution heat treatment. And various mechanical properties of Al alloy porous material were improved by 40% with aging of $200^{\circ}C$ and 50min. These improvements are ascribe to the various fine precipitates like $\Omega$ and $\theta$'.

• Transactions of Materials Processing
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• v.20 no.5
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• pp.362-368
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• 2011

For the purpose of improving crashworthiness qualities and maximizing weight saving efficiency, TWB's(tailor welded blanks) of quench-hardenable boron steel sheet formed by hot stamping processes has been used for automotive BIW (body in white) applications. In this work, the flow behaviors of TWB of quench-hardenable boron steel sheet were investigated in uniaxial tension tests at elevated temperature. TWB's having a uniform thickness of 1.4mm were fabricated by laser welding. Specimens with two weld line directions were used to test the mechanical property and reliability of the weld zone. After heating at $950^{\circ}C$ for 5min, the specimens were subjected to tension test at 650, 700 and $800^{\circ}C$ with a strain rate of 0.01 /s and at $700^{\circ}C$ with strain rates of 0.01, 0.1 and 1/s. The ultimate strength of the weld zones was higher than that of the base materials at 650 and $700^{\circ}C$, but was similar to the base metal at $800^{\circ}C$. Fracture occurred at the base material at 650 and $700^{\circ}C$, but at the weld zone at $800^{\circ}C$.