• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.4
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• pp.447-451
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• 2015

The objective of this study is to predict the structural characteristics of a heat exchanger mounted on an aircraft engine using finite element analysis. The plastic fracture and life of the heat exchanger were estimated by a thermo-mechanical analysis. Tensile tests were conducted under high temperature conditions (700, 800, 900, 1000 K) using five specimens to obtain the mechanical properties of the Inconel 625 tubes. To assess the structural characteristics of the heat exchanger, the full and partial models were applied under the operating conditions given by the thermo-mechanical and inertial load. As a result, the case, tubesheet, flange, and mounting components have a reasonable safety margin to the allowable stress assuming a fatigue strength of Inconel 625 of 10000 cycles under 1000 K.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.1
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• pp.117-125
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• 2014

The temperature distribution of steady state rolling tires with detailed tread blocks is numerically predicted using the three dimensional full patterned tire model. A three dimensional periodic patterned tire model is constructed by copying 1-sector mesh in the circumferential direction. Using the static tire contact analysis, the strain cycles during one revolution are approximated with the strains at Guassian points of the elements which are sector-wise repeated within the same circular ring of elements, by neglecting the tire rolling effect. Based upon the multi-axial fatigue theory, the maximum principal strain is used to represent the combined effect of six strain components on the hysteretic loss. In the following, the deformation due to the inflation and vertical load is calculated using ABAQUS. Then heat generation rate in each element is calculated using an in-house code. Lastly, temperature distribution is calculated using ABAQUS again. Through the numerical experiments, the validity of the proposed prediction method is examined by comparing with the experiment and the temperature distribution of a patterned tire model is compared with those of the main-grooved simple tire model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.5669-5675
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• 2012

To reduce the cost and the time of transport in Eurasian railroad networks such as TKR(Trans-Korea Railway), TCR(Trans-China Railway) and TSR(Trans-Siberia Railway) owing to the problem of different track gauges (narrow/standard/broad gauge), it is important to develop the gauge-adjustable wheelset(GAW) system to adapt easily to these gauges. The Korean GAW system is developing and will be adapting to the brand new freight trains' to improve the conventional overseas GAW system. In this study, structural and durability analyses are performed from the viewpoint of the safe-life design. The core parts of the system might be safe in range of $1{\times}10^7$ cycles from the result of durability analysis. Moreover, to examine the safety of the system while running on a track, rig fatigue test was performed according to UIC code. The safety of the Korean GAW system is demonstrated through testing that all safety-relevant conditions are satisfied.

• 연구논문집
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• s.23
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• pp.127-140
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• 1993

The drive pulley, which is employed for loading and unloading raw materials in a steel mill, is usually manufactured by use of various welding processes. In this study the weldment in the pulley, in which TIG and $CO_2$ welding processes are used, has been analyzed from view point of fracture mechanics. Fracture toughness tests have been performed according to ASTM E813. A servo-hydraulic testing machine (10kN) has been employed. Also the crack propagation tests (Mode I) have been performed with compact tension specimen in compliance with ASTM E647. To predict the critical crack size in the weldment, finite element stress analysis for the drive pulley under real operating conditions have been performed. In addition, the residual stresses at the weldment and in heat-affected zone have been obtained by hole drilling method. The planar critical crack size have been predicted for the drive pulley by considering the stress analysis results and the residual stresses due to welding process. For the drive pulley considered in this study, it has been concluded that the most important factor in determining the critical crack size is the welding residual stress in the transverse direction. Also the effect of stress concentration at the root of the weldment have been noticeable. For the planar crack, the fatigue crack growth life from an initial crack size of 2mm to the critical crack size obtained as in the above have been predicted. The predicted lives were between 55, 900 and 72, 000 cycles depending on the shape of the elliptical crack. The predicted lives were in fairly good agreement for the drive pulley considered in this study.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.3
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• pp.298-306
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• 2008

STATEMENT OF PROBLEM: Effect of surface treatment of ceramic under loading does not appear to have been investigated. PURPOSE: The aim of this study was to investigate the effect of surface treatment of esthetic ceramic, which is performed to increase the bonding strength, on the fracture stress under controlled cyclic loading condition. MATERIAL AND METHODS: Sixty 1.0 mm-thick specimens were made from Mark II Vitablocs (Vita Zahnfabrik, Germany) and divided into 3 groups: polished (control), sandblasted, and etched. Specimens of each group were bonded to a dentin analog material base including micro-channels to facilitate the flow of water to the bonding interface. Bonded ceramics were cyclically loaded with a flat-end piston in the water (500,000 cycles, 15Hz). Following completion of cyclic loading, specimens were examined for subsurface crack formation and subsequent stress was determined and loaded to next specimen by the staircase method according to the crack existence. RESULTS: There were significant differences of mean fatigue limit in the sandblasted (222.86 ${\pm}$ 23.42 N) and etched group (222.86 ${\pm}$ 14.16 N) when compared to polished group (251.43 ${\pm}$ 10.6 N) (P<.05; Wald-type pair-wise comparison and post hoc Bonferroni test). Of cracked specimens, surface treated group showed longer crack propagation after 24 hours. All failures originated from the radial cracking without cone crack. Fracture resistance of this study was very low and comparable to failure load in the oral cavity. CONCLUSION: Well controlled cyclic loading could induce clinically relevant cracks and fracture resistance of Mark II ceramic was relatively low applicable only to anterior restorations. Surface treatment of inner surface of feldspathic porcelain in the matsicatory area could influence lifetime of restorations.

• The Korean Journal of Ceramics
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• v.3 no.4
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• pp.263-268
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• 1997

RuO$_3$ thin films were deposited on Si(100) substrate at low temperatures by hot-wall metalorganic chemical vapor deposition. Bis(cyclopentadienyl) ruthenium, Ru$(C_5H_5)_2$, was used as the precursor RuO$_2$single phase was obtained at a low deposition temperature of 25$0^{\circ}C$ and the crystallinity of RuO$_2$thin films improved with increasing deposition temperature. RuO$_2$thin films grow perpendicularly to the substrate and show the columnar structure. The grain size of RuO$_2$films drastically increases with increasing the deposition temperature. The resistivity of the 180 nm-thick RuO$_2$thin films deposited at 27$0^{\circ}C$ was 136 $\mu$$\Omega$-cm and increased with decreasing film thickness. SrBi$_2Ta_2O_4$ thin films deposited by rf magnetron sputtering on the RuO$_2$bottom electrodes showed a fatigue-free characteristics up to ~10$^10$ cycles under 5 V bipolar square pulses and the remanent polarization, 2 P$_r$ and the coercive field, 2 E, were 5.2$\mu$C/$\textrm{cm}^2$ and 76.0 kV/cm, respectively, for an applied voltage of 5 V The leakage current density was about 7.0$\times$10$^{-6}$ A/$\textrm{cm}^2$ at 150 kV/cm.

• Journal of Technologic Dentistry
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• v.33 no.3
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• pp.193-202
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• 2011

Purpose: The aim of this study was to evaluate the effect of pre-treatment of core and hydrothermal treatment on the bond strength and flexural strength of ceramic veneered zirconia. Methods: 3Y-TZP specimens(KaVo Zr, $25mm{\times}3mm{\times}1mm$)were prepared by five pre-treatment methods and divided into seven groups including control two groups, subsequently the specimens veneered with the E-MAX ceram according to manufacturer's information(total specimen thickness 1.5mm). Two groups from ceramic-zirconia specimens(n=105, n=15 per group)were assigned into two experimental fatigue conditions, namely storage in an autoclave at $134^{\circ}C$ for 5h, thermo-cycling(3,000cycles, between 5 and $55^{\circ}C$, dwell time 45s, transfer time 2s). A flexural strength test was performed in a universal testing machine(crosshead speed: 0.5mm/min). Data were statistically analyzed using one-way ANOVA and Tukey's test(${\alpha}$=0.05). Results: The ceramic-zirconia bond strength value for liner application group(LLW, $27.3{\pm}3.8$) were significantly lower than those of the pre-treatment groups($30.72{\pm}5.3$). The ceramic-zirconia bond strength and zirconia flexural strength was not affected by thermo-cycling(p>0.05), whereas it was affected by storage in an autoclave at $134^{\circ}C$ for 5h(p<0.05). Conclusion: The results indicated that the ceramic-zirconia bond strength and zirconia flexural strength was affected by low temperature degradation.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.4
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• pp.1581-1584
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• 2014

Background: The overall prognosis for cancers of unknown primary (CUP) is poor, median overall survival (OS) being 6-12 months. We evaluated our multicentric retrospective experience for CUP administered docetaxel and cisplatin combination therapy. Materials and Methods: A total of 29 patients that were pathologically confirmed subtypes of CUP were included in the study. The combination of docetaxel ($75mg/m^2$, day 1) and cisplatin ($75mg/m^2$, day 1) was performed as a first line regimen every 21 days. Results: The median age was 51 (range: 27-68). Some 17 patients had multimetastatic disease on the inital diagnosis. Histopathological diagnoses were well-moderate differentiated adenocarcinoma (51.7%), undifferentiated carcinoma (27.6%), squamous cell cancer (13.8%), mucoepidermoid carcinoma (3.4%) and neuroendocrine differentiated carcinoma (3.4%). Median number of cycles was 3 (range: 1-6). Objective response rate was 37.9% and clinical benefit was 58.6%. Median progression free survival (PFS) and overall survival (OS) were 6 months (range: 4.3-7.7 months) and 16 months (range: 8.1-30.9 months), respectively. Fourteen patients (60.8%) were treated in a second line setting. There was no treatment related death. Most common toxicities were nausia-vomiting (44.6%) and fatigue (34.7%), serious cases (grade 3/4) suffering nausia-vomiting (10.3%), neutropenia (13.8%) and febrile neutropenia (n=1). Conclusion: The combination of cisplatin and docetaxel is an effective regimen for selected patients with CUP.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1227-1233
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• 2010

In the hot section of a gas turbine, the turbine blades were protected from high temperature by providing a thermal barrier coating (TBC) as well as by cooling air flowing through internal passages within the blades. The cooling air then passed through discrete holes on the blade surface, creating a film of cooling air that further protects the surface from the hot mainstream flow. The holes are subjected to stresses resulting from the lateral growth of thermally grown oxide, the thermal expansion misfit between the constituent layers, and the centrifugal force due to high-speed revolution; these stresses often result in cracking. In this study, the deformation and cracks occurring near a hole on a heat-resistant alloy subjected to thermo-mechanical cycling were investigated. The experiment showed that cracks formed around the hole depending on the applied stress level and the number of cycles. These results could be explained by our analytic solution.

• Korean Journal of Materials Research
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• v.9 no.8
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• pp.763-767
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• 1999

Composite materials have been increasingly used in automotive and aircraft industries, naturally leading to active researches on the materials. Carbon-epoxy composites, one of major composite materials, are investigated to determine their thermal characteristics. Under conditions of thermal fatigues composed of repeated heatings and coolings, variations of elastic constants are studied for the carbon-epoxy composites to reveal the thermal nature of the composites. In general, composite materials are known to have decreasing elastic constants with increasing temperatures. However, in contrary to this commonly observed behavior, the results obtained in this investigation for the elastic constants of the carbon-epoxy composites show unexpected phenomena in that the elastic constants initially increase with increasing temperatures to certain point and decrease later with further increase in temperatures when the carbon-epoxy composites are subjected to thermal fatigues.