• Journal of the Korean Society for Heat Treatment
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• v.6 no.4
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• pp.237-242
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• 1993

The fatigue behaviors of mechanically alloyed Al-4Mg alloys dispersed with either $Al_2O_3$ or $MgAl_2O_4$ oxide particles were investigated. This study maily concerned with the role of coherency of dispersed particles with the matrix on the fatigue behavior of the alloys. The $MgAl_2O_4$ which has a spinel structure with the lattice parameter of exactly the twice of Al showed the habit relation with the matrix. The mechanically alloyed Al-4Mg alloys showed stable stress responses with fatigue cycles from start to failure regadless of strain amplitudes and of existence of dispersoids. The Al-4Mg alloy dispersed with $MgAl_2O_4$ showed not only the better static mechanical properties but also the better low cycle fatigue resistance than that with $Al_2O_3$, i.e., much higher plastic strain energy dissipated to failure, at low strain amplitude. However, this alloy showed inferior fatigue resistance to that dispersed with $Al_2O_3$ or that without dispersion at high strain amplitude. These results imply that $MgAl_2O_4$ may promote lowering the stacking fault energy of the alloy inherited from the coherency with the matrix so that dislocations shuttle back and forth on the same slip plane without cross slipping to other planes during fatigue at low strain amplitude resulting in long fatigue life.

• Journal of the Korean Society of Safety
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• v.31 no.4
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• pp.9-14
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• 2016

STS304L of membrane structure has been used for a LNG storage tank and has exposed long time under the cryogenic temperature. The purposes of this study are to evaluate the mechanical properties of base and used materials for STS304L of membrane. The tensile and high cycle fatigue tests were investigated for STS304L of membrane used over 20 years at room temperature and $-162^{\circ}C$. In addition, the test of base STS304L was performed in order to compare with used material properties. The chemical composition and phase change were investigated from EDS and XRD. From results of tensile test, yield and ultimate tensile strengths of used STS304L are smaller than those of base STS304L. S-N curves were obtained from fatigue tests at both temperatures. Also, P-S-N curves were presented with statistical method recommend by JSME-S002. Fractography was conducted for analysis of fracture mechanisms.

• 연구논문집
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• s.32
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• pp.85-94
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• 2002

Even in the world wide automobile companies where a few simple modules are put into practical use, the front subframe modules of which performances of durability, NVH and crash are significantly important are under planing. In this study, design technology for the automobile front subframe module, which consists of an engine, a transmission and steering parts, structural components (frame, upper arm, lower arm and brake etc.) and rubber components(engine mount, axle mount and rubber disc etc.), was developed. A FEM-based analytical approach was used to evaluate the multiaxial high cycle fatigue damage of the front subframe module. Strain-life fatigue database system and expert system for fatigue properties of welded materials were developed. Stiffness values of the various rubber bushes mounted on the front subframe were evaluated by experimental method and FEM. TWB(Tailor Welded Blank) technology was applied to forming the cross member of the front subframe. Performance evaluations in relation to NVH and crash were conducted by using CAE technologies.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.11
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• pp.919-925
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• 2016

In this study, multibody dynamic and mechanical analyses were conducted for the structure of roller chain bucket elevator system. The fatigue life of the roller chain elevator system was determined under static and fatigue loadings. Results of multibody dynamic analysis suggested that the maximum contact force occurred at the drive sprocket engagement point with the roller chain due to maximum tension. Fatigue analysis results suggest that the high load roller chain system is durable and safe because its life time is more than 700,000 cycles, close to its designed value (1,000,000 cycle). However, the contact portion of plate and pin needed a safety factor. The dynamic analysis of the heavy load roller chain was conducted with a multibody dynamic analysis program. The results obtained in this study can be utilized for dynamic analysis of roller chain systems in all industries.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.5
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• pp.1-8
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• 2000

Fatigue and data retention characteristics of the Pt/PZT/Pt structure using single grain PZT thin films by PZT seeding method were investigated. In case of fatigue, there is no loss in switched polarization up to 2$\times$10$^{11}$ cycles using 1MHz square wave form at $\pm$10V and no data loss after 30000sec of memory retention at room temperature. From the activation energy measured at high temperatures, the time required 20% loss in remanent polarization is estimated to be 6.6$\times$10$^{7}$ years at room temperature.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.245-247
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• 2017

A turbine wheel undergoes high heat flux and centrifugal force when a gas turbine starts. The temperature and stress of the turbine wheel increase rapidly, and the time point and rate of them may not coincident. The difference of heating and rotating rates influences the life of turbine wheel. We conducted thermo-mechanical fatigue analysis with finite element methods to study the influence. The low acceleration and deceleration of the wheel extends the life. If the turbine wheel decelerate faster than cooling, the life increases.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.3
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• pp.184-189
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• 1994

The heat treatment charaterristic of SCM 440 and B 16 steels has been investigated in various condition(A, B and C) to the effect of heat treatment on mechanical properties, and the following results were obtained. 1. We are obtained a good nitriding characteristic in bainitic structure than other heat treatment cycle in our experiment. 2. Fatigue characteristic has shown in order of B)C)A condition as heat treatment cycle. 3. The effective hardening depth and fatigue characteristic has been excellented in B 16 than SCM 440 after the nitriding and Q. T for Band C condition. 4. Nitriding depth has been increased in addition of Cr, V and the nitriding efficiency is increased as easiness of banite formation to wide range of cooling rate by addition of Mo. 5. The depth of compound layer in parallel surface, notched slop plane and notched bottom has been varied to the nitriding depth of 5, 4 and 3 ${\mu}$ in relatively uniform pattern after 10h nitriding treatment for SCM 440 into A condition.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.57-63
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• 2008

The last stage blade of the low pressure steam turbine remarkably affects turbine plant performance and availability Turbine manufacturers are continuously developing the low pressure last stage blades using the latest technology in order to achieve higher reliability and improved efficiency. They tend to lengthen the last stage blade and apply shrouds at the blades to enhance turbine efficiency. The long blades increase the blade tip circumferential speed and water droplet erosion at shroud is anticipated. Parts of integral shrouds of the last stage 40 inch blades were cracked and liberated recently in a combined cycle power plant. In order to analyze the root cause of the last stage blades shroud cracks, we investigated operational history, heat balance diagram, damaged blades shape, fractured surface of damaged blades, microstructure examination and design data, etc. Root causes were analyzed as the improper material and design of the blade. Notches induced by erosion and blade shroud were failed eventually by high cycle fatigue. This paper describes the root cause analysis and countermeasures for the steam turbine last stage blade shroud cracks of the combined cycle power plant.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1257-1263
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• 2010

The naval structure exposes to environmental vibration of shafted propeller propulsion and engine vibration. The shipboard equipments are developed compliance to MIL-STD-167-1A. For this purpose, vibration fatigue life of shipboard equipment for long lives should be estimate via an analytical approach and vibration test. In this paper, High cycle fatigue strength of cast aluminum alloy A356 using shipboard equipment was evaluated by 14 S-N method. The stress applied on the structure is evaluated by an analytical method(frequency response analysis with sinusoidal input and a fatigue evaluation) to simulate a MIL-STD-167-1A test. The frequency with the maximum equivalent stress is shown by Max. test frequency and the vibration fatigue life of shipboard equipment was estimated by Miner's rule.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.185-194
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• 1998

In this study, the rotary bending fatigue test was carried out with two kinds of material, S43C and S50C, using in the Front engine and Front drive wheels(F.F.) of vehicle. The one part of specimens was heated by high frequency induction method(about 1mm depth and $H_RC$ 56~60) and tested environment temperature were $-30^{\circ}C$, $+25^{\circ}C$ and $+80^{\circ}C$ in order to look over the influence of the heat treatment and the temperatures. In the experimented result at $+25^{\circ}C$ and $+80^{\circ}C$, the fatigue life of non-heated specimens were decreased about 35%, but that of heated specimens were decreased about only 5% at $+80^{\circ}C$ more than at $25^{\circ}C$. And in the experiment result at $-30^{\circ}C$ and $+25^{\circ}C$, the non-heated and heated specimens were about 110%, 120% higher fatigue life at $-30^{\circ}C$ than at the $+25^{\circ}C$ each other. On the other hand, the fatigue crack propagation rate of S50C was higher than that of S43C.