• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.255-260
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• 2003

Most of the fatigue test were achieved in fully reversed condition that mean stress is zero. But, generally, mean stress can not be zero. This research was achieved the bending fatigue test that changes mean stress to spring steel and was studied relation with the mean stress and the fatigue life. The method to search effect about mean stress was extended S-N graph in two cases. One method was extended S-N graph using modified Miner's rule with considering damage. Another was extended using tendency of S-N graph. The exponential value(${\alpha}$) of mean stress-alternating stress equation is converged between the Goodman's and the Gerber's value even if fatigue life increases.

• 한국항공우주학회지
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• 제39권7호
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• pp.612-617
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• 2011

동합금 Elbrodur-NIB 재질에 대해 평균응력을 포함한 응력제어시험을 수행하였으며, 그 결과 라체팅 거동에 응력진폭, 평균응력, 응력속도가 어떠한 영향을 주는지에 대해 시험을 통해 알 수 있었다. 라체팅 변형률은 같은 평균응력에서 응력진폭이 증가할수록, 또한 같은 응력진폭에서 평균응력이 증가함에 따라 같이 증가하는 것을 볼 수 있었다. 그러나, 응력속도가 증가함에 따라 라체팅 변형률은 감소하는 것을 알 수 있었다. $10^2-10^5$ 영역에서 3가지 평균응력을 포함한 피로수명예측모델을 검토하였으며, 그 결과 Smith-Watson-Topper가 제안한 모델과 Walker가 제안한 모델이 매우 신뢰성 있는 결과를 보여주었다.

• Steel and Composite Structures
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• 제27권1호
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• pp.89-94
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• 2018

Uniaxial ratcheting behavior of Z2CND18.12N austenitic stainless steel used nuclear power plant piping material was studied. The results indicated that ratcheting strain increased with increasing of stress amplitude under the same mean stress and different stress amplitude, ratcheting strain increased with increasing of mean stress under the same stress amplitude and different mean stress. Based on least square method, a suitable method to arrest ratcheting by loading the materials was proposed, namely determined method of zero ratcheting strain rate. Zero ratcheting strain rate occur under specified mean stress and stress amplitudes. Moreover, three dimensional ratcheting boundary surface graph was established with stress amplitude, mean stress and ratcheting strain rate. This represents a graphical surface zone to study the ratcheting strain rates for various mean stress and stress amplitude combinations. The graph showed the ratcheting behavior under various combinations of mean and amplitude stresses. The graph was also expressed with the help of experimental results of certain sets of mean and stress amplitude conditions. Further, experimentation cost and time can be saved.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.133-141
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• 2006

The Low cycle fatigue behavior of 11.7Cr-1.1Mo heat-resisting steel has been investigated under strain-controlled conditions with mean stresses at room temperature and $300^{\circ}C$. For the tensile mean stress test, the initial high tensile mean stress generally relaxed to zero at room temperature, however, at $300^{\circ}C$ initial tensile mean stress relaxed to compressive mean stress. Low cycle fatigue lives under mean stress conditions are usually correlated using modifications to the strain-life approach. Based on the fatigue test results from different stain ratio of -1, 0, 0.5, and 0.75 at room temperature and $300^{\circ}C$, the fatigue damage of the steel was represented by using cyclic strain energy density. Total strain energy density considering mean stress indicated well better than not considering mean stress at $300^{\circ}C$. Predicted fatigue life using Smith-Watson-Topper's parameter correlated fairly well with the experimental life at $300^{\circ}C$.

• Advances in materials Research
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• 제3권3호
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• pp.163-174
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• 2014

In this study, fatigue properties and crack growth characteristics of a polycarbonate (PC) were examined during cyclic loading at various mean stress (${\sigma}_{amp}$) and stress amplitude (${\sigma}_{mean}$) conditions. Different S vs. N and da/dN vs. ${\Delta}K$ relations were obtained depending on the loading condition. The higher fatigue strength and the higher resistance of crack growth are seen for the PC samples cyclically loaded at the higher mean stress and lower stress amplitude due to the low crack driving force. Non-linear S - N relationship was detected in the examination of the fatigue properties with changing the mean stress. This is attributed to the different crack growth rate (longer fatigue life): the sample loaded at the high mean stress with lower stress amplitude. Even if the higher stress amplitude, the low fatigue properties are obtained for the sample loaded at the higher mean stress. This was due to the accumulated strain energy to the sample, where severe plastic deformation occurs instead of crack growth (plasticity-induced crack closure). Shear bands and discontinuous crack growth band (DGB) are observed clearly on the fracture surfaces of the sample cyclically loaded at the high stress amplitude, where the lower the ${\sigma}_{mean}$, the narrower the shear band and DGB. On the other hand, final fracture occurred instantly immediately after the short crack growth occurs in the PC sample loaded at the high mean with the low ${\sigma}_{amp}$, i.e., tear fracture, in which the shear bands and DGB are not seen clearly.

• 한국산업융합학회 논문집
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• 제7권4호
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• pp.317-324
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• 2004

The purpose of this study was to provide basic data for nursing intervention in patient undergoing angiocardiography. Method: The subjects of this study were 60 patients undergoing angiocardiography. The data were analyzed using mean, percentage and pearson correlation Coefficient. Result 1) The mean score of the affective stress(anxiety) was $48.00{\pm}12.24$ and behavioral stress was $1.98{\pm}1.97$. The mean score of the physiologic stress(vital sign) was systolic pressure $124.10{\pm}17.72$, diastolic pressure $79.71{\pm}12.68$, pulse: $81.03{\pm}12.16$, respiration: $21.21{\pm}1.40$ 2) The mean score of the pain was $1.40{\pm}0.67.$ 3) There was a significant positive correlation between stress and pain. Conclusion : The result of this study show that stress is very important factor that effect on the pain therefore it will be considered stress in patient undergoing angiocardiography.

• 한국직업건강간호학회지
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• 제8권2호
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• pp.141-155
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• 1999

For the purpose of disclosing the mental health status as well as its stress factors of female workers in industry, a questionaire survey was carried out on 283 female workers, namely. 134 of a service industry(department store) in seoul and 149 of a manufacturing industry(food) in Kyunggi-do district from 24 to 29 January, 1994. The result were as follows : 1. The mean scores of poor mental health indicator showed no significant difference between service industry and manufacturing industry, while the mean scores of good mental health indicator showed a significant difference between those two industries. 2. The mean scores of work stress as social stress factors showed a significant difference between service industry and manufacturing industry. However, no significant difference was observed between the mean scores of personal stress factor between those two industries. 3. In general, the work stress factor was more significantly contributed by marital status, while the social stress as well as the personal stress factor were contributed more by monthly income. 4. The major contributing factor to the poor mental health was the personal stress factor in general, followed by the work stress factor. However, the weight of these two stress factors was reversed according to the type of industries.

• Nuclear Engineering and Technology
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• 제38권3호
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• pp.277-284
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• 2006

In order to ensure the structural integrity of nuclear welded structures during design life, the fatigue life has to be evaluated by fatigue analysis procedures presented in technical codes such as ASME B&PV Code Section III. However, existing fatigue analysis procedures do not explicitly consider the presence of welded joints. A new fatigue analysis procedure based on a structural stress/fracture mechanics approach has been recently developed in order to reduce conservatism by erasing uncertainty in the analysis procedure. A recent review of fatigue crack growth data under various mean loading conditions using the structural stress/fracture mechanics approach, does not consider the mean loading effect, revealed some significant discrepancies in fatigue crack growth curves according to the mean loading conditions. In this paper, we propose the use of the stress intensity factor range ${\Delta}K$ characterized with loading ratio R effects in terms of the structural stress. We demonstrate the effectiveness in characterizing fatigue crack growth and S-N behavior using the well-known data. It was identified that the S-N data under high mean loading could be consolidated in a master S-N curve for welded joints.

• 한국정밀공학회지
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• 제16권3호통권96호
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• pp.145-153
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• 1999

This study has been performed to investigate the stress distribution around defects that behave as stress concentrators and fracture mechanical analysis for cracks initiatiating at stress concentrators. The stress distribution was analyzed using Finite Element Method and non dimensional stress intensity factor was determined by the mean stress method. In addition, stress interaction effects around defects and cracks were compared.

• Journal of Mechanical Science and Technology
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• 제19권5호
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• pp.1065-1071
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• 2005

In this study, residual stress distribution in multi-stacked film by MEMS (Micro-Electro Mechanical System) process is predicted using Finite Element method (FEM). We evelop a finite element program for residual stress analysis (RESA) in multi-stacked film. The RESA predicts the distribution of residual stress field in multi-stacked film. Curvatures of multi­stacked film and single layers which consist of the multi-stacked film are used as the input to the RESA. To measure those curvatures is easier than to measure a distribution of residual stress. To verify the RESA, mean stresses and stress gradients of single and multi layers are measured. The mean stresses are calculated from curvatures of deposited wafer by using Stoney's equation. The stress gradients are calculated from the vertical deflection at the end of cantilever beam. To measure the mean stress of each layer in multi-stacked film, we measure the curvature of wafer with the left film after etching layer by layer in multi-stacked film.