• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.499-504
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• 2003

Future bridge decks must have high load-resistance capacity as well as fatigue strength to withstand the increase in traffic loading and the increase in span length between girders due to the decrease in the number of main girders. Steel-concrete composite bridge decks may be proper deck types to satisfy such requirements. To promote the application of composite bridge decks, a rational process to predict and evaluate the fatigue behavior of steel concrete composite bridge deck is required. Various types of steel-concrete composite bridge decks have been developed in many countries. In this study, combining advantages of the existing composite deck types, a new type of composite bridge deck is proposed. An experimental study is performed to examine the fatigue behavior of the proposed composite bridge deck. This composite bridge deck consists of corrugated steel sheet, welded T-beams, stud-type shear connectors and reinforced concrete filler. The fatigue tests are conducted under four-point bending test with three different stress ranges in constant amplitude. The fatigue category of the fillet welding between corrugated steel sheet and the T-beam is evaluated based on the S-N data obtained from the experiment.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.337-341
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• 2004

Engineering ceramics have superior heat resistance, corrosion resistance, and wear resistance. Consequently, these art significant candidates for hot-section structural components of heat engine and the inner containment of nuclear fusion reactor. Besides, some of them have the ability to heal cracks and great benefit can be anticipated with great benefit the structural engineering field. Especially, law fracture toughness of ceramics supplement with self-healing ability. In the present study, we have been noticed some practically important points for the healing behavior of silicon nitride, alumina, mullite with SiC particle and whisker. The presence of silicon carbide (SiC) in ceramic compound is very important for crack-healing behavior. However, self-healing of SiC has not been investigated well in detail yet. In this study, commercial SiC was selected as sample, which can be anticipated in the excellent crack healing ability. The specimens were produced three-point bending specimen with a critical semi-circular crack of which size that is about $50-700{\mu}m$. Three-point bending test and static fatigue test were performed cracked and healed SiC specimens. A monotonic bending load was applied to cracked specimens by three-point loading at different temperature. The purpose of this paper is to report Strength Properties and Elastic Waves Characteristics of Silicon Carbide with Crack Healing Ability.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.287-290
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• 2005

Once hot forgings for automotive parts such as wheel bearing flange to which cyclic asymmetric bending stress is continuously applied are produced, it is necessary to control their microstructure to obtain superior mechanical properties. It is however hard to control the microstructure uniformly because the strength is reduced as coarsening of ferrite grains. To investigate the microstructural alteration according to process variables during hot working, the variation of the ferrite grain size was studied by utilizing of the computer aided servo-hydraulic Gleeble tester which is hot deformation behavior reproduction equipment. In addition, the effect of the ferrite grain size of raw material on the austenite grain behavior of hot forgings was also examined. The rolling contact fatigue resistance of the induction hardened SAE 1055 steel was compared with the occasion of the same condition of SAE52100 bearing steel. As a result, it was confirmed that the ferrite grain sizes of the forgings depend on the heating temperature and cooling start temperature during hot forging and cooling processes. The induction hardened SAE1055 steel showed a superior rolling contact fatigue resistance to the induction hardened SAE52100 steel. The reason is that SAE1055 steel is freer from the material defect such as segregation than the comparative steel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.753-764
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• 1996

The metal matrix composites(MMC) are currently receiving a great deal of attention. These composites possess exellent mechanical and physical properties such as modulus, strength, wear resistance and thermal stability, which make them very attractive for use in automotive piston. In this study, $Al/{Al_2}{O_3}$(15%) composites are fabricated by the squeeze casting method. Mechanical properties such as tensile strength and ductility are performed at room and elevated temperature($250^{\circ}C$ and $350^{\circ}C$), respectively. Through thermomechanical analyser, thermal expansion coefficient of $Al/{Al_2}{O_3}$ composites are conducted for ranging from room temperature to ($400^{\circ}C$.And bending fatigue tests are also performed by the rotary bending machine at room temperature.The tensile strength and elastic modulus have been improved up to 38% and 35% by the addition of the reinforcements, respectively. Thermal expansion coefficients of MMCs which is located normal and parralel to the applied pressure are showed slightly different less than 10%. Fatigue strengh of the composite was improved by about 20% compared with that of unreinforced Al alloy. The results of this study will be used to understand the basic fracture behavior of MMCs and eventually to expand the applocation of MMCs as a machine parts undertaken various loadings.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.5
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• pp.2511-2515
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• 2013

Carbon black from pyrolysis of waste tires was used to modify and improve the fatigue properties and low temperature cracking of asphalt binder. 0%, 5%, 10%, 15% and 20% of pyrolyzed carbon black was mixed. Couple of laboratory tests, such as dynamic shear rheometer test and bending beam rheometer test, were carried out. The use of pyrolyzed carbon black decreased the fatigue at room temperature and improved the resistance of low temperature cracking up to $-12^{\circ}C$, but, was off the criteria at $-18^{\circ}C$.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2153-2162
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• 2011

The goal of this Paper is to reduce rail's wear in curved track by applying an additional surface layer material(High hardness and High resistance capacity of wear) on the top of the railhead. In order to evaluate appropriation of a coating material, experimental tests such as the varieties of fundamental properties tests (hardening, wear, tensile, and bending) and RCF(rolling contact fatigue)test were performed to establish fatigue wear and damage mechanism. As a result, wear performance of coating rail is better than heated rail about 6times and normal rail about 8~9times.

• Proceedings of the KWS Conference
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• 1999.05a
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• pp.233-236
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• 1999

The welding residual stress should be considered in fatigue stress analysis because it develope during the process of the electric resistance spot welding and it causes bad affect on the fatigue crack initiation and growth at nugget edge of spot welded points. Therefore the accurate estimation of residual stress is crucial. In this study, nonlinear finite element analysis on welding residual stress generated during the process of the spot welding was conducted, and their results were compared with the experimental data measured by X-ray diffraction method. From the results, it was found that welding residual stress existed as tension in the nugget center and as compression around the nugget edge.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.743-751
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• 2000

Because welding residual stress is formidable result in electric resistance spot welding process, and it detrimentally affect to fatigue crack initiation and growth at nugget edge of spot welded la p joints, it should be considered in fatigue analysis. Thus, accurate prediction of residual stress is very important. In this study, nonlinear finite element analysis on welding residual stress generated in process of the spot welding was conducted, and their results were compared with experimental data measured by X-ray diffraction method. By using their results, the maximum principal stress considered welding residual stress at nugget edge of the spot welded lap joint subjected to tension-shear load was calculated by superposition method. And, the $\Delta$P- $N_f$ relations obtained through fatigue, tests on the IB-type spot welded lap joints was systematically rearranged with the maximum principal stress considered welding residual stress. From the results, it was found th2at fatigue strength of the IB-type spot welded lap joints could be systematically and more reasonably rearranged by the maximum principal stress($\sigma$1max-res considered welding residual stress at nugget edge of the spot welding point.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.93-99
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• 2016

In this paper, we investigated the mechanical and electrical reliability of silver nanowire (AgNW) films. In particular, the durability and reliability of AgNW films were studied when the AgNW film was subjected to the bending deformation under current flow. The electrical durability of AgNW was evaluated by observing changes in heat generation and current density occurring in AgNW through voltage and current tests. The AgNW film showed a constant resistance change up to a bending radius of 2 mm and 200,000 cycles in the bending fatigue tests. The over-coating layer has an effect of improving the durability of the AgNW film. In the case of AgNW with the over-coating layer, heat was uniformly dissipated on the surface of AgNW film, whereas in the case of AgNW film without the over-coating layer, heat was generated locally. In the bending test under the current flow, the current density of the AgNW film was continuously decreased up to 52.4%. During bending, the AgNW was deformed due to mechanical deformation such as tensile, bending and sliding of the AgNW, consequently contact resistance of the AgNW was increased, leading to a electrical breakdown of AgNW by Joule heating. It was found that the application of the over-coating layer can improve the electrical and mechanical reliability of the AgNW film.

• Composites Research
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• v.26 no.1
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• pp.1-6
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• 2013

CNT-polypropylene (PP) composites were compounded by solvent dispersion method with uniform dispersion by using twin screw extruder. Damage sensing effects based on conductive carbon nanotubes (CNT) were evaluated to monitor the internal damage of CNT-PP composites using electrical resistance measurement. Mechanical and interfacial properties of CNT-PP composites were investigated and compared with neat PP. The mechanical properties of PP matrix were improved after adding CNT, because of the reinforcing effect of CNT fillers. In order to monitor the internal damage of CNT-PP composite, the change in electrical resistance of the composites was measured under fatigue loading and bending tests. CNT fillers exhibited good sensing under electrical resistance measurements. It is shown that CNT-PP composites with low CNT contents allow identifying critical cyclic loading, which are found to be accompanied with the internal failure.