• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.73-78
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• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys, which were casted by mold with Mg-3%Zn-1%Mn and Mg-3%Zn-1%Mn-0.2%Ca, were done under the temperature range of 473-573K and the stress range of 23.42-78.00Mpa. The activation energies and the stress exponents were measured to investigate the creep plastic deformation of those alloys, and the rupture lifes of Mg-Zn-Mn alloy were also measured to investigate the fracture behavior. From the results, the activation energy of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys under the temperature range of 473-493K were measured as 149.87, 145.98KJ/mol, respectively, and the stress exponent were measured as 5.13, 6.06 respectively. Also the activation energies Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys under the temperature range of 553-573K were obtained as 134.41, 129.22KJ/mol, respectively, and tress exponent were obtained as 3.48, 4.63, respectively. Finally stress dependence of rupture life and the activation energy of rupture life of Mg-Zn-Mn under the temperature range of 473-493K was measured as 8.05, 170.0(KJ/mol), respectively, which were a little higher than the results of steady state creep.

• Structural Engineering and Mechanics
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• v.81 no.5
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• pp.565-574
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• 2022

The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (𝚫K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (𝚫K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation's Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).

• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.137-145
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• 2003

In this study, direct tensile fatigue tests of the PS bar were performed in terms of diameter, minimum stress level, and maximum stress level. In the static test, the stress - strain curve and ultimate streng th of the PS bar were determined. Results of the fatigue test indicate that the diameter of the PS bar was not influenced by fatigue life. Minimum stress also had quite an influence on the fatigue of the PS bar. Thus, the fatigue characteristic equation was proposed in terms of stress range and minimum stress through statistical process. Strains on specimen that loaded direct tension were measured in the fatigue test, with the secant modulus of elasticity calculated from measured strains. The strain development consisted of three different stages, i.e., rapid increases during the initial fatigue life, uniform increases during the middle stage, and rapid increases until failure. The secant modulus of elasticity decreased during the fatigue life with increasing strain. However, stress level seemed to have no influence on the secant modulus of elasticity.

• Archives of Reconstructive Microsurgery
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• v.10 no.1
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• pp.18-22
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• 2001

Purpose : The purpose of this study was to evaluate stress fracture of vascularized fibular grafts(VFG) by analyzing factors associated with stress fracture and the treatment results. Materials and Methods : From June 1985 to May 1998, 7 patients with stress fractures in the 38 patients with long bone defect who had vascularized fibular graft were evaluated with clinical and radiologic methods including grafted fibular length and hypertrophic index of de Boer. The average age of the patients was 35 years(range, $14{\sim}60$ years). The mean follow-up period was 20 months(range, $16{\sim}32$ months). Results: 7(18.4%) stress fractures occurred in 38 patients. Characteristics of the fractures were (1) all occurred at lower extremity of male patients treated with VFG for long bone defected caused by infected nonunion; (2) all occurred 10 months at the average(range, $4{\sim}17$ months) after VFG; and (3) the length and hypertrophic index of grafted fibula had no influence on the incidence of stress fracture. Union was obtained in 3 patients by conservative treatment. 4 patients obtained union by internal fixation; one at immediately onset of fracture; and three after failure of conservative treatment who had fracture around the knee joint. Conclusion : Stress fracture may occur during the first one year after vascularized fibular graft and more attention must be paid for prevention of it, especially in the cases of infected nonunion. Stress fracture around the knee joint was expected to lead to a good result of early union by operative treatment.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.3
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• pp.177-182
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• 2005

The steady state cyclic mechanism, and the behaviour of Nicoseal(Fe-29Ni-17Co) have been examined under the condition of square wave stress cyclic tension creep test at the temperature, stress and frequency range of $430{\sim}470^{\circ}C$($0.41{\sim}0.43T_m$), 353~383 MPa, and 3 cpm, respectively. Also, the relationship between cyclic creep and static creep have been examined. The stress exponents(n) for the static creep deformation of this alloy were 11.6, 10.0, 8.4 and 7.9 at the temperature of 430, 445, 460 and $470^{\circ}C$, respectively. The apparent activation energies (Q) for the static creep deformation were 54.2, 51.8, 49.7 and 46.8 kcal/mole for the stress of 353, 363, 373 and 383 MPa, From the above results, it could be considered that the cyclic creep accelaration phenomena was obtained and that the cyclic deformation for Nicoseal seemed to be controlled by dislocation climb over the range of experimental conditions. Nicoseal alloy under the cyclic creep conditions was obtained as P=(T+460)(logt+17). The failure plane observed by SEM showed up transgranular fracture at all range.

• Journal of Korean Clinical Nursing Research
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• v.20 no.2
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• pp.189-199
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• 2014

Purpose: The purpose of this study was to investigate job stress and job satisfaction among nurses in gastrointestinal endoscopy units, and factors related to their job stress and job satisfaction. Methods: The study participants were 153 nurses working in gastrointestinal endoscopy units at eleven general hospitals. Job stress and job satisfaction were measured using nurses's job stress scale and the index of work satisfaction respectively. Results: The average job stress was 3.67 (range 1~5) and job satisfaction was 2.90 (range 1~5). Gastrointestinal endoscopy unit nurses, who were full time worker, having more than 7 years of clinical experiences, having higher incomes, having high subjective work-intensity, and having an intention to change their working units, showed greater job stresses than those of the others. There were significant differences in job satisfaction according to subjective health status, the types of employment, subjective work-intensity, subjective aptitude, intention to change working units, major nursing tasks, and the numbers of major nursing tasks. Also, the subjects's job stress showed a negative correlation with job satisfaction. Conclusion: Findings suggest that management strategies should be developed to increase job satisfaction focusing on general and job characteristics associated with job stress.

• Journal of Korean Academy of Nursing Administration
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• v.15 no.4
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• pp.593-600
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• 2009

Purpose: This study was to examine the relation of nurses' job stress and knowledge, attitude and care behavior for elderly patient in hospitals. Method: One hundred ninety one nurses caring the elderly patients in hospitals in Ilsan, Busan and Gyeongsangnam-do were subjects. The data was collected between Sept. 21 and 31, 2009. Data was analyzed using t-test, ANOVA, Pearson correlation with SPSS/Win 17.0 and the fitness of pathway models with AMOS 5.0. Results: The mean scores of job stress and knowledge were in middle range, and attitude and care behavior were in a little higher range. The fitness of hypothetical model was excellent. Job stress had direct effects on attitude and care behavior, knowledge had direct effect on attitude and attitude had direct effect on care behavior. But the pathways related to job stress and attitude and job stress and care behavior were not significant. In modified model deleted the pathway between job stress and attitude, the pathway related to job stress and behavior also was not significant. Conclusion: Education related to the elderly for nurses to improve care behavior is needed continuously.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.68-77
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• 2014

In this study, polysulfide epoxy polymer concrete was chosen as an ultra thin bridge deck overlay, and the effect of polymer concrete pavement on the fatigue stress range of the orthotropic steel deck was analyzed through the comparative analysis with epoxy asphalt pavement and SFRC pavement. Abaqus was used to estimate the fatigue stress range, and signed von-mises stress was used to estimate fatigue stress range according to pavement materials and thickness, considering there were multi axis stresses which have longitudinal and lateral direction on the welded parts of the steel deck.

• Journal of Korean Society of Steel Construction
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• v.9 no.3 s.32
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• pp.363-375
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• 1997

This study encompasses the performance of static and fatigue test for the 8 large scale test specimens to clarify the fatigue behavior of coped stringer and the effect of the repair and strengthening on the damaged stringer of the floor system in steel railway bridges. For the purpose of the research, the actual stress wave for the existing bridge was measured, the basic stress range frequency histogram was made and the equivalent stress range was calculated. Using the result from the equivalent stress range made by adjusting the stress range, the static and fatigue test was carried out by identifying the previous rehabilitation and after. As the result of the static tests, it was revealed that the level of local stress under the S1 specimen test of the real equivalent stress range was similar to tensile strength of the test material, and it was consistent with the requirement of the initiation condition of the fatigue crack. Through the various rehabilitation methods to the damaged specimens, the effects of the repair and reinforcement were analyzed. According to the results of the repair of effect, bolting the high tension bolt over the stop hole was confirmed to be more adequate method than drilling only stop hole to delay the fatigue crack growth. Futhermore, in case of the stringer subjected by bending moment, the reinforcement over the upper flange side was determined to be a useful strengthening method, and the reinforcement to the web of the stringer was not appropriate to accomodate as a adequate strengthening method. Also it was confirmed that the category of the fatigue design for the coped stringer met with the category E specified on the fatigue design criteria of the Highway Standard Specification in Korea.

• Journal of the Korean Society of Safety
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• v.16 no.1
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• pp.31-36
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• 2001

Surface crack growth characteristics and influence of the stress amplitude in rotary bending fatigue test were evaluated for annealed S35C steel, and than fractal dimensions of fatigue crack paths estimated using the box counting method. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) Crack growth rate ds/dN and db/dN (s : half crack length at the surface crack, b : crack depth) depended on stress amplitude (${\Delta}{\sigma}/2$), stress intensity factor range (${\Delta}K_A, {\Delta}K_C$) and crack length. (2) At the effect area of 0.3 mm hole notch (s＜0.5 mm) crack growth rate did not depend on these factors. (3) The fractal dimensions (D) increased with stress amplitude (${\Delta}{\sigma}/2$) but decreased with cyclic number.