• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.10a
• /
• pp.354-357
• /
• 2005

When Ti-6Al-4V is used in long steam turbine blades, the main issues are how to improve the fatigue strength as a problem of internal quality and how to forge the thinnest possible blades as problem of dimensional precision. To assure an excellent fatigue strength, it is important to make the two phase fine and equiaxial structure by providing enough plastic deformation in the two phase$(\alpha\;phase/\beta\;phase)$ temperature region. Accordingly, it needs to predict that forging temperature, preform design and forging velocity in forging process. To achieve this end, the two steps forging process was suggested to forge the thin and twisted blades with a precision hammer considering die forces and metal flow. Two steps forging process consists of the flattening forging process and finishing forging process. Process in forging of a 1016mm long steam turbine blade is designed by the finite element method. This study attempts to derive systematic design procedures for process design in the forging. Forging parameters was analyzed in two-dimensional plane-strain simulation and two steps forging process carried out in three-dimensional simulation. Consequently, optimal forging process parameters of long steam turbine blades in Ti-6Al-4V with a high dimensional precision are selected in the hammer die forging.

• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.468-472
• /
• 2010

To develop the Exhaust Maniverter(Manifold and converter) it needs to consider flow characteristics related to durability and performance of the catalyst, manufacturability, etc. This paper presents the analysis results regarding to flow characteristics such as flow uniformity, tangential speed, O2 sensor sensitivity and CHT (conjugate heat transfer) for the LCF(Low Cycle Fatigue) for gasoline 2.0 liter engine. The results are satisfactorily corresponded to the general criteria. Also skin temperature and pressure drop wire measured at the Engine Bench. These results can be useful for the design guide for Exhaust Maniverter.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.11 no.5
• /
• pp.42-47
• /
• 2012

Construction equipment is heavily loaded during normal operation. In recent years, there is a trend that lower gear noise levels are demanded for drivers to avoid annoyance and fatigue during operation. For articulated hauler's final drive, meshing transmission error(T.E.) is the excitation that leads the tonal noise known as gear whine, and radiated gear whine is also the dominant source of noise in the whole gearbox. This paper presents a method for the analysis of the tooth profile modification, and the prediction of transmission error under the loaded torques for the spur gear pair of the articulated hauler's final drive. And the transmission error, transmission error harmonics and contact stress are also calculated and compared before and after tooth modification under one torque. The simulation result shows that the transmission error and contact stress under the loads can be minimized by the appropriate tooth profile modification.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2002.05a
• /
• pp.39-39
• /
• 2002

In order to improve wear and fatigue resistance of the structural materials, especially cold work roller for 304 stainless steel, an eco-super-finishing and surface hardening treatment using ultrasonic vibration energy was developed and applied to the SKD-ll roller. The eco-super-finishing machine was designed and fabricated by DesignMecha Co, by its own technology. It was observed that the surface roughness, hardness and residual stress were changed from $Ra{\;}={\;}O.25\mu\textrm{m}$, Hv=710 and ${\sigma}$={\;}+400{\;}MPa{\;}to{\;}Ra{\;}={\;}0.165\mu\textrm{m}$, Hv = 1200 and ${\sigma}=-610$ MPa after 20 KHz micro-cold forging, which means almost equal to the 300 % improvement of life-time.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.9
• /
• pp.1027-1032
• /
• 2012

Two types of very small multiplying gears and arrays have been developed for new dental hand-pieces, and the increased speed ratios, modules, number of teeth, gear diameters, and gear types were calculated based on the dynamics of the machinery. The contacting and bending strengths were evaluated for gear teeth with two design concepts using AGMA equations and finite element analyses, and the contacting stresses on teeth with and without DLC (diamond-like-carbon) coating layers were calculated. Fatigue and tension tests were performed to obtain an S-N curve, the Young's modulus, and the strength of the gear material, and these were utilized in the analyses. Slightly larger stresses were found for 2-axis-type gears than for other types of gears, and the S-N curves showed that a gear lifetime of 109 cycles was satisfied. The contacting stresses in gears coated with DLC were reduced by 30%. A new prototype model of a hand-piece with small gears was successfully fabricated and tested.

• Journal of Korean Academy of Fundamentals of Nursing
• /
• v.10 no.2
• /
• pp.163-170
• /
• 2003

Purpose: This study was done to identify stress, fatigue, and self efficacy in patients on dialysis and identify their effect on quality of life. Method: The participants (n=149) who agreed to participate in the research were selected from among those who were on dialysis treatment at C University Medical Centers in Seoul and Inchon, and at C University Medical Center in Jeju. The data were collected from July, 2001 to March, 2002 using interviews. Data analysis was done with t-test, ANOVA, and multiple stepwise regression using the SAS program. Result: Quality of life was significantly different according to economic status, and type of dialysis. Quality of life for the group with higher economic status was better than for the group with lower economic status, and the group on peritoneal dialysis had higher quality of lift scores than the group on hemodialysis. As for self-efficacy, there were significant difference according to duration of disease, type of dialysis, and duration of dialysis. Stress was significantly different according to marital status. Quality of life was significantly predicted by stress (40.02%) and fatigue (3.85%). Conclusion: To improve quality of life for people on dialysis, their stress should be treated positively, also multi-dimensional nursing interventions to provide emotional support and nursing interventions to diminish fatigue are required.

• Structural Engineering and Mechanics
• /
• v.74 no.4
• /
• pp.567-576
• /
• 2020

Considerable controversy surrounds the choice of the best abutment type for implant prosthetics. The two most common structures are hex and non-hex abutments. The non-hex abutment typically furnishes a larger contact area between itself and the implant than that provided by a hex structure. However, when a hex abutment is loaded, the position of its contact area may be deeper than that of a non-hex abutment. Hence, the purpose of this study is to determine the different biomechanical behaviors of an internal bone-level implant based on the abutment type-hex or non-hex-and clinical crown length under static and cyclic loadings using finite element analysis (FEA). The hex structure was found to increase the implant and abutment stability more than the nonhex structure among several criteria. The use of the hex structure resulted in a smaller volume of bone tissues being at risk of hypertrophy and fatigue failure. It also reduced micromovement (separation) between the implant components, which is significantly related to the pumping effect and possible inflammation. Both static and fatigue analyses, used to examine short- and long-term stability, demonstrated the advantages of the hex abutment over the non-hex type for the stability of the implant components. Moreover, although its impact was not as significant as that of the abutment type, a large crown-implant ratio (CIR) increased bone strain and stress in the implant components, particularly under oblique loading.

• Journal of the Korean Society for Heat Treatment
• /
• v.13 no.4
• /
• pp.224-230
• /
• 2000

Garbon steel(SM35C) was gas nitrocarburized at $580^{\circ}C$ in $55%N_2-40%NH_3-5%CO_2$ mixed gas atmosphere, and then the steel was induction hardened at $850^{\circ}C$. The microstructure of gas nitrocarburized surface layer was observed by optical microscope and SEM. The phase analysis was carried out by X-ray diffraction method. The mechanical properties of gas nitrocarburized SM35C steel was evaluated by hardness, wear and fatigue test. The thickness of compound and diffusion layer were increased with increasing the gas nitrocarburizing time and the densest compound layer was obtained at 3 hours gas nitrocarburizing time. In case of 15sec induction hardening after gas nitrocarburizing, the surface hardness was decreased from 800Hv to 630Hv owing to the decomposition of compound layer, but wear resistance was increased because of increased hardness of diffusion layer. The fatigue strength of induction hardened steel after gas nitrocarburizing, $58kgf/mm^2$, was higher than $41.5kg/mm^2$ of gas nitrocarburized steel and $45kg/mm^2$ of induction hardened steel, respectively.

• Journal of the Society of Naval Architects of Korea
• /
• v.28 no.1
• /
• pp.108-116
• /
• 1991

In the non-linear behavior of many materials, there is difference between the monotonic behavior by static load and the cyclic behavior by cyclic load. In particular, the short fatigue cracks to propagate in elasto-plastic stress concentrations(notches), are governed significantly by the cyclic behavior of materials. Accordingly, it is needed to investigate and compare the monotonic and cyclic behavior of materials. In the pressent study, the stress-strain relations of materials by monotonic and cyclic load tests were examined for 2 kinds of steels(SS41, HT80) and 5 kinds of Al-alloys(A5083-O, A6N01-T5, A7N01-T4, A7016-T6, A7178-T6). And the constants for mechanical properties of the materials were determined by experimental results, Moreover, when a notch was subjected to cyclic load, the effect of cyclic hardening property of materials on the variation of stress-strain amplitude in the notch tip was discussed by the application of Neuber's rule and experiments for a center notched plate.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.40 no.12
• /
• pp.1700-1707
• /
• 2011

This study evaluated the effect of multigrain supplementation on exercise-related changes in running time and glycogen storage capacity of male SD rats engaged in treadmill exercise. Thirty-six 6-week-old rats were divided into six groups: normal (Nor) fed normal feed, control (Con) fed with 20% normal feed and 80% milled rice, test group one (GI) fed with multigrain feed I, test group two (GII) fed with multigrain feed II, test group three (GIII) fed with multigrain feed III, and test group four (GIV) fed with multigrain feed IV. Endurance tests by treadmill machine were administered after 24 days of multigrain feed supplementation and adaptive training. Running time was extended and glycogen storage capacity increased in the multigrain-treated group compared to the non-treated group. Also, the fatigue indicators of inorganic phosphorous, CPK, and lactate concentration were all reduced in the multigrain feed group compared to the control group after 25 min and/or exhausted exercise. But there was no difference in GOP, GTP, lactate, or LDH concentrations between the groups. Our results demonstrated that endurance improved with multigrain feed in rats. Specifically, running time, glycogen storage capacity, inorganic phosphorous, CPK, and lactate serum concentration increased. Importantly, the improvements in endurance brought about in the GII group fed with waxy barley was the greatest among the experimental groups.