• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.397-398
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• 2006

The advanced piezoelectric ceramic composite actuator, which is called LIPCA with the FRP and the optimization of the laminate configuration, was performed to maximize the stress transfer and the fiber bridging effect. This study evaluated the effect of variable electric fields on the PZT characteristic, laminate configuration and fatigue characteristics under the resonance frequency, which meant the largest performance range and the changes of its interlaminar phase were also evaluated by stages. In conclusions, Comparing with the fatigue lift of intact LIPCA, the fatigue life of LIPCA embedded by the artificial delamination was decreased up to 50%. The micro void growth and the coalescence of epoxy were actively made at the interlaminar phase subject to the large tensile stress.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.756-757
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• 2006

P/M enables the economical production of components for many kinds of gears. Functionally, the sub gear requires high tooth accuracy and bending fatigue strength. The whole tooth profile was sized after sintering to satisfy the gear tooth accuracy specification. The part was redesigned to reduce machining requirements. The required bending fatigue strength was achieved through appropriate material choice and induction of compressive residual stress by shotpeening after carburizing. The P/M sub gear replaced a forged steel gear, satisfied performance requirements, expanded the use of P/M applications and provided over 30% cost reduction.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.558-567
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• 2003

The catenary wires are damaged by periodic running of train as well as repeated stress. The wires are also degraded by atmosphere corrosion at fields. Corrosion of wires increased surface roughness and deteriorated mechanical properties by providing fatigue crack initiation sited resulting in a bad effect on service life of the wires. Fatigue test of catenary wires performed to estimate service lifetime. Also, simulation to analyze stress on catenary wires was conducted through modelling the finite elements for dynamic behaviors of wires. Fatigue life of catenary wires was estimated with fatigue and simulation tests.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.400-405
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• 2004

In this study, the optimal welding condition of the input power was selected experimentally through the ERW simulator, which is equal to welding status of ERW part in pipe. This condition is the input power 250kW in the heat treatment of the $900^{\circ}C$ normalizing derived from the nondestructive technique and impact energy. In order to evaluate the variation of the fatigue life in the pipe, fatigue surface crack growth test of base and optimal welded metal were performed statistically. As stress intensity factor range (${\Delta}K_s$) increases, the fatigue crack propagation rate (da/aN) of the base metal is faster than that of the welded joint. The variation of the fatigue life in the ERW pipe was estimated statistically using Monte-Carlo simulation with the standard deviation of material constants (C and m) of the paris law in the specimen.

• Korean Journal of Metals and Materials
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• v.46 no.6
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• pp.363-369
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• 2008

Effects of top coat morphology and thickness on thermal fatigue behavior of thermal barrier coatings (TBC) were investigated in this study. Thermal fatigue tests were conducted on three coating specimens with different top coat morphology and thickness, and then the test data were compared via microstructures, cycles to failure, and fracture surfaces. In the air plasma spray specimens (APS1, APS2), top coat were 200 and $300{\mu}m$ respectively. The thickness of top coat was about $700{\mu}m$ in the perpendicular cracked specimen (PCS). Under thermal fatigue condition at $1,100^{\circ}C$, the cycles to top coat failure of APS1, APS2, and PCS were 350, 560 and 480 cycles, respectively. The cracks were initiated at the interface of top coat and thermally grown oxide (TGO) and propagated into TGO or top coat as the number of thermal fatigue cycles increased. For the PCS specimen, additive cracks were initiated and propagated at the starting points of perpendicular cracks in the top coat. Also, the thickness of TGO and the decrease of aluminium concentration in bond coat do not affect the cycles to failure.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.794-799
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• 2001

For the development of an electric molding machine with low energy, high performance, and high reliability, characterization, finite element analysis and fatigue strength analyses were performed. Strain was measured by strain gages bonded on electric molding machine and compared with stress analysis results using I-DEAS. The analyses showed good agreement with test results. By means of the comparison, we could draw an adequate boundary condition for the stress analysis of the components of electric molding machine. Additionally, we could verify the load distribution mechanism among the parts. The life prediction results for tie bar and thread zone showed infinite life.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1657-1659
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• 1996

The objective of this study is to provide a life prediction of isothermal fatigue using strain partitioning of high temp. steel for power plants. The experimental system was composed of Instron 8501, induction heating system, extensometer and pyrometer with hydraulic power system

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.461.2-461
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• 2001

• Proceedings of the Korean Nuclear Society Conference
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• 2005.10a
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• pp.709-710
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• 2005

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.1
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• pp.198-207
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• 1996

The effect of temperature, frequency and microstructure on fatigue crack propagation property of Ti-6A1-4V alloy has been investigated. The temperatures employed were room temperature, 20$0^{\circ}C$ and 40$0^{\circ}C$. The frequencies were 20Hz and 8 Hz. The microstructures tested were equiaxed and bimodal microstructures. Mechanical properties and fatigue crack growth rates were measured in different test conditions. From the experimental results, following conclusions were obtained. Bimodal microstructure showed superior fatigue crack growth resistance to equiaxed microstructure. Under all test conditions, fatigue crack growth rate increased with test temperature. Wine the frequency decreasing from 20Hz to 8Hz, fatigue crack growth rate increased.