• 대한가정학회지
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• 제39권9호
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• pp.63-78
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• 2001

The purpose of this study is to compare how different the belief, social support, stress, coping and motivation between the Korean and American children. The data was collected from 157 Korean and 114 American students (5·8th grade). The resets were as follows: 1. Korean children's other dependency and pessimism level was significantly higher than those of American children. Also Korean children perceived higher than American children in the control-pressure stress and elf-respect stress. 2. Pessimism was observed the highest effect factor on Korean children's stress. 3. Korean students tried various coping under the relationship stress. 4. Problem oriented coping was found as an effective coping in Korean children. But the pursuit of support was found as an effective coping in American children.

• 한국기계가공학회지
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• 제14권2호
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• pp.112-120
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• 2015

In this study, the growth rate of surface cracks (da/dN) during the retardation period was analyzed in terms of effective stress intensity factor range(${\Delta}K_{eff}^*$) obtained by using the proposed effective plastic zone concept. Effective stress intensity factors obtained by using the effective plastic zone concept were smaller than those obtained by using Willenborg analysis. On the growth rate of surface cracks analyzed by ${\Delta}K$, the dependence of overload stress levels appears. On the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a linear relationship with two different slops between da/dN and ${\Delta}K_{eff}$. However, on the growth rate by ${\Delta}K_{eff}^*$ obtained by the proposed effective plastic zone concept, there is a linear relationship between da/dN and ${\Delta}K_{eff}^*$ that coincides with the results of constant amplitude loading.

• 한국학교보건학회지
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• 제19권2호
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• pp.25-36
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• 2006

Purpose : To investigate academic stress, coping method, and stress symptoms of high school students. Methods : Four hundreds-forty five high school students were studied from 14th July to 21th July, 2006. All subjects were in 1st, 2nd and 3rd grade of two high school in Seoul. The academic stress, coping method and stress symptoms were evaluated by questionnaire. Results : Male students showed more academic stress than female students. There was a significant difference in the academic stress according to sex. The 2nd grade students show the highest score of academic stress in the 3 factors(parents, teacher, and friend). Male students used more active coping methods to academic stress than female students. There was a significant difference in the coping methods to academic stress according to sex. There were positive correlations between the academic stress and the stress symptoms. Among the academic stress factors, parents and teacher factor influenced physiologic, psychologic, and behavioral symptom of stress symptoms. The friend factor influenced psychologic and behavioral symptom of stress symptoms. Conclusion : According to the study results, we must provide high school students more effective coping methods to academic stress at school environment.

• 한국보건간호학회지
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• 제28권2호
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• pp.285-297
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• 2014

Purpose: The purpose of this study was to investigate the structural relationship among the life stress, depression, suicidal ideation of adolescent. Methods: Participants for this study included 285 students from five middle schools located in Seoul and Gyeongsangbukdo, Korea. The SPSS 18.0 program and AMOS 18.0 program were used for analysis of data. Results: The characteristics of this study were to analyze causal relationship with latent variables by considering measurement error and to grasp direct effect, indirect effect and total effect. Life stress and depression were found to be factors influencing suicidal ideation. Depression was a direct factor and life stress was a indirect factor. The effects of depression as a mediator between life stress and suicidal ideation were significant statistically. Conclusion: The findings of this study may provide useful assistance in development of effective nursing interventions for prevention and management of middle school students' suicidal ideation.

• 대한기계학회논문집A
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• 제25권5호
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• pp.797-804
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• 2001

To obtain representative fatigue crack growth characteristic curve in residual stress field, fatigue crack growth test was carried out at various stress ratio and fatigue crack growth characteristic curve was represented using crack closure concept. Obtained results are as follows;K(sub)op/K(sub)max was independent of K(sub)max when R was lower than 0.5 and crack closure phenomenon was not observed when R is higher than 0.5. therefore neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated. Thus, considering crack closure phenomenon, fatigue crack growth characteristics curve of A 106 Gr B Steel weldment can be effectively estimated.

• 한국안전학회지
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• 제6권4호
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• pp.81-87
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• 1991

We propose the crack growth rate equation which will model fatigue crack growth rate behavior such that constant stress amplitude fatigue crack growth behavior can be predicted. Constant stress amplitude fatigue tests are conducted for four materials under three stress ratios of R＝0.2, R＝0.4 and R＝0.6. Materials which have different mechanical properties i.e. stainless steel, low carbon steel, medium carbon steel and aluminum alloy are used. Through constant stress amplitude fatigue test by using unloading elastic compliance method, it is confirmed that crack closure is a close relationship with fatigue crack propagation. We describe simply fatigue crack propagation behavior as a function of the effective stress intensity factor range ($\Delta$ $K_{eff}$＝U .$\Delta$K) for all three regions (threshold region, stable region). The fatigue crack growth rate equation is given by da / dN＝A($\Delta$ $K_{eff}$­$\Delta$ $K_{o}$ )$^{m}$ / ($\Delta$ $K_{eff}$­$\Delta$K) Where, A and m are material constants, and $\Delta$ $K_{o}$ is stress intensity factor range at low $\Delta$K region. $K_{cf}$ is critical fatigue stress intensity factor.actor.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.235-239
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• 1994

In this paper, the fatigue behaviour of typical axisymmetric forward extrusion die is investigated and extrusion process is analyzed by the rigid-plastic finite element method and elasto-plastic finite element method. To approach the crack problem involving crack initiation and propagation in extrusion die, LEFM(Linear Elastic Fracture Mechanics) is introduced and singular element which models stress.strain singularity in the crack tip vincity has been used to obtain an accurate stress intensityu factor values and other results. Form the displacement around the crack tip the stress intensity factor and the effective stress intensity factor at the beginning of the die inlet radius has been calculated. Applying proper fatigue crack propagation criterion such as Paris/Erdogan fatigue law to this data the angle and direction of fatigue crack growth has been simulated and these are compared with some experimental results. Using the computed crack growth rate, fatigue life of the extrusion die has been evaluated.

• Journal of Mechanical Science and Technology
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• 제18권6호
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• pp.961-971
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• 2004

Methods for determination of the crack opening stress intensity factor ($K_{op}$) and for estimation of the effective stress intensity factor range ($\Delta{K}_{eff}$) are evaluated for crack growth test data of aluminum alloys. Three methods of determining $K_{op}$, visual measurement, ASTM offset compliance method, and the neural network method proposed by Kang and Song, and three methods of estimating $\Delta{K}_{eff}$, conventional, the 2/PIO and 2/PI methods proposed by Donald and Paris, are compared in a quantitative manner by using evaluation criteria. For all $K_{op}$ determination methods discussed, the 2/PI method of estimating $\Delta{K}_{eff}$ provides good results. The neural network method of determining $K_{op}$ provides good correlation of crack growth data. It is recommended to use 2/PI estimation with the neural $K_{op}$ determination method. The ASTM offset method used in conjunction with 2/PI estimation shows a possibility of successful application. It is desired to improve the ASTM method.

• 동력기계공학회지
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• 제16권2호
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• pp.43-48
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• 2012

Generally accelerated life test is well known as one method to reduce reliability qualification test period. This test is conducted under the higher stress condition than normal condition. So it can save the test time by calculating the acceleration factor from the relationship between the worst stress condition and normal condition. This paper investigates the worst stress condition for the accelerated life test to increase the acceleration factor. Especially, we focused on the method to obtain effective acceleration factors under the worst stress condition. Moreover, we considered how to decide the worst stress condition by looking for the operating limit of this system. The acceleration factor can be estimated from the ratio of the kinematic viscosity in the normal condition and the worst stress condition, the lowest temperature, by using Arrhenius relationship. Through some experiments for a refrigerator's compressor, we were able to confirm how to increase acceleration factors and how to reduce the reliability qualification test period with minimum samples.

• 대한기계학회논문집
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• 제7권3호
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• pp.270-277
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• 1983

Plastic plane stress solutions are given for a center cracked strip, characterized by the Ramberg-Osgood plastic index, under bi-axial tension. Using a power law hardening stress-strain relation, an incremental plasticity finite element formulation is developed, and simple formulation is given for computing J-integral with nodal displacements. The near tip angular distribution of von Mises effective stress doesn't differ significantly in magnitude according to the change of loading stress and bi-axial load combination factor. But, for smaller plastic index, the location of its maximum value moves vertically at a head of crack. J-integral value, in the plastic zone near crack tip, decreases with load combination factor for large and small plastic index.