• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.215-228
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• 2017

A new approach for measuring the specific fracture energy of concrete denoted modified disk-shaped compact tension (MDCT) test is presented. The procedure is based on previous ideas regarding the use of compact tension specimens for studying the fracture behavior of concrete but implies significant modifications of the specimen morphology in order to avoid premature failures (such as the breakage of concrete around the pulling load holes). The manufacturing and test performance is improved and simplified, enhancing the reliability of the material characterization. MDCT specimens are particularly suitable when fracture properties of already casted concrete structures are required. To evaluate the applicability of the MDCT test to estimate the size-independent specific fracture energy of concrete ($G_F$),the interaction between the fracture process zone of concrete andthe boundary of theMDCTspecimens at the end of the test is properly analyzed. Further, the experimental results of $G_F$ obtained by MDCT tests for normal- and high-strength self-compacting concrete mixes are compared with those obtained using the well-established three-point bending test. The procedure proposed furnishes promising results, and the $G_F$ values obtained are reliable enough for the specimen size range studied in this work.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.7-14
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• 1999

TiZrB2 solid solution was synthesized using fine powders of Ti, Zr and B by SHS microwave process. The characterization of the synthesized powder and sintered bodies ws investigated. The combustion temperature and rate were increased with increasing the mole ratio of Zr in temperature profile, and showed the maximum combustion temperature and velocity values of 285$0^{\circ}C$ and 14.6mm/sec in Ti0.2Zr0.8B2 composition. Phase separation has been occured into a composite with TiB2 and ZrB2 phases from TiZrB2 solid solution, which was hot pressed sintering at 30 MPa for an hour at 190$0^{\circ}C$. At the composition of Ti0.8Zr0.2B2 the best properties has been obtained in relative density, bending strength, fracture toughness and hardness, with 99%, 680 MPa, 7.3MPa.m1/2 and 2750 Kg/$\textrm{mm}^2$ respectively.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.87-97
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• 1992

Of various design factors affecting icebreaking capability of an icebreaker, the stem angle(i.e., angle between bow stem and ice sheet) is the most important one under continuous icebreaking operation. This study focuses on the relationship between the bow stem angle of an icebreaker and its icebreaking capability. Considering relatively high loading-rate conditions with typical advancing speed of 3 to 4 knots, the material properties and deformation characteristics of sea ice are regarded as entirely elastic and brittle. In this paper the interaction process of icebreaker with level ice is simplified as a beam of finite length supported by Winkler-type elastic foundation simulating water buoyancy. The wedge type ice beam is loaded by the vertical impact forces due to the inclined bow stem of icebreaking vessels. The numerical model provides locations of maximum bending moment where extreme tensile stress arises and also possible fracture occurs. The model can predict a characteristic length of broken ice sheet upon the given environmental and design parameters.

• Computational Structural Engineering
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• v.10 no.2
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• pp.255-263
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• 1997

The optimum design of most structural systems used in practice requires considering design variables as discrete quantities. The present paper shows that the linear approximation method is very effective as a tool for the discrete optimum designs of unsymmetric composite laminates. The formulated design problem is subjected to a multiple in-plane loading condition due to shear and axial forces, bending and twisting moments, which is controlled by maximum strain criterion for each of the plys of a composite laminate. As an initial approach, the process of continuous variable optimization by FDM is required only once in operating discrete optimization. The nonlinear discrete optimization problem that has the discrete and continuous variables is transformed into the mixed integer programming problem by SLDP. In numerical examples, the discrete optimum solutions for the unsymmetric composite laminates consisted of six plys according to rotated stacking sequence were found, and then compared the results with the nonlinear branch and bound method to verify the efficiency of present method.

• Advances in nano research
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• v.3 no.2
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• pp.97-109
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• 2015

Citrate ion is a commonly used reductant in metal colloid synthesis, undergoes strong surface interaction with silver nanocrystallites. The slow crystal growth observed as a result of the interaction between the silver surface and the citrate ion makes this reduction process unique compared to other chemical and radiolytic synthetic methods. The antimicrobial effects of silver (Ag) ion or salts are well known, but the effects of citrate coated Ag nanoparticles (CAgNPs) are scant. Herein, we have isolated biofilm causative bacteria and fungi from drinking water PVC pipe lines. Stable CAgNPs were prepared and the formation of CAgNPs was confirmed by UV-visible spectroscopic analysis and recorded the localized surface plasmon resonance of CAgNPs at 430 nm. Fourier transform infrared spectroscopic analysis revealed C=O and O-H bending vibrations due to organic capping of silver responsible for the reduction and stabilization of the CAgNPs. X-ray diffraction micrograph indicated the face centered cubic structure of the formed CAgNPs, and morphological studies including size (average size 50 nm) were carried out using transmission electron microscopy. The hydrodynamic diameter (60.7 nm) and zeta potential (-27.6 mV) were measured using the dynamic light scattering technique. The antimicrobial activity of CAgNPs was evaluated (in vitro) against the isolated fungi, Gram-negative and Gram-positive bacteria using disc diffusion method and results revealed that CAgNPs with 170ppm concentration are having significant antimicrobial effects against an array of microbes tested.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2007.11a
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• pp.358-363
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• 2007

Reinforcing steel work plays an important role in terms of its structural performance or weight of construction cost for reinforced concrete structures. Precise estimation of re-bar quantity gives a basis for managing the reinforcing steel work effectively. However, the estimation process is still performed ineffectively based upon the expert's experience or manpower in spite of the advanced technology or improvement efforts. Therefore, the purpose of this research is to develop a prototype system for taking-off the quantity of reinforcing steel bars quickly and accurately in an order consistent with the specific members identified on the drawings. An estimate algorithm considering the connection, settlement and coating thickness of re-bars was suggested regarding to their replacement conditions which places more emphasis on constructibility. Also, this system produces the shop drawings automatically with the calculation results.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.289-293
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• 2003

This study dealt with the characterization of $MoSi_2$ based composites containing three types of additive materials such as SiC, $NbSi_2\;and\;ZrO_2$ particles have been investigated, based on the detailed examination of their microstructures and fracture surfaces. The effects of reinforcing materials on the high temperature strength of $MoSi_2$ based composites have been also examined. $MoSi_2$ based composites were fabricated by the hot press process under the vacuum atmosphere. The volume fraction of reinforcing materials in the composite system was fixed as 20 %. The microstructures and the mechanical properties of $MoSi_2$ based composites were investigated by means of SEM, EDS, XRD and three point bending test.

• Journal of Sensor Science and Technology
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• v.19 no.5
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• pp.375-384
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• 2010

In this paper, we proposed a new shaft distortion correction system having an adaptive PID controller using displacement sensors, which is adaptively reflecting variations of shaft strength owing to irregular heat treatment during an annealing process and sensitivity to the seasonal temperature changes. Generally, the shafts are annealed by heat treatment in order to enlarge the strength of the shaft, which causes an distortion of a shaft such as irregular bending of the shaft. In order to correct such a distortion of the shaft, a mechanical pressure is properly impacted to the distorted shaft. However, the strength of every shaft is different from each other owing to irregular annealing and seasonal temperature changes. Especially, the strength of a thin shaft such as a car transmission shaft is much more sensitive than that of a thick shaft. Therefore, it is very important for considering the strength of each shaft during correction of the car transmission shaft distortion in order to generate proper mechanical pressure. The conventional PID controller for the shaft distortion correction system does not consider each different strength of each shaft, which causes low productivity. Therefore, we proposed a new PID controller considering variations of shaft strength caused by seasonal temperature changes as well as irregular heat treatment and different cooling time. Three displacement sensors are used to measure a degree of distortion of the shaft at three different location. The proposed PID controller generates adaptively different coefficients according to different strength of each shaft using appropriately obtained pressure times from long-term experiments. Consequently, the proposed shaft distortion correction system increases the productivity about 30 % more than the conventional correction system in the real factory.

• Resources Recycling
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• v.12 no.3
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• pp.46-53
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• 2003

Recycling of aluminum dross is an important issue in the secondary aluminum industries. In this study, aluminum dross generated in the domestic secondary aluminum industry was processed to use it as raw material for producing alumina refractories. Sample dross was classified according to its size. The dross smaller than 1 mm was leached with sodium hydroxide solution to extract the remained aluminum from the dross into the solution. and then aluminum hydroxide precipitate was recovered from the leach liquor. The waste residue in the leaching was washed, dried and roasted. Most remained metallic components in the residue was changed into oxide through the processes. The roasted dross was made into alumina castable refractories by mixing with aggregates and a binder. Bending strength of the tested castable specimen was over $25\;kg/\textrm{m}^2$ and compressive strength over $80\;kg/\textrm{cm}^2$, which satisfied the Korean Standard value respectively. From the results, it was suggested that this process could be applicable to recycling of aluminum dross.

• 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.