• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.298-303
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• 2001

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for a compact tension specimen in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives very much. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.141-149
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• 2002

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for three types of specimens, which are very typical ones in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was concluded that shapes of three types of specimens optimized by the growth-strain method prolong their fatigue lives very much.

• Journal of the Korean Society of Safety
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• v.25 no.6
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• pp.161-168
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• 2010

A series of fatigue tests have been performed on the non-load carrying fillet welded joints in order to quantitatively assess the fatigue characteristics due to the grindings and TIG(Tungsten Inert Gas) welding treatments. From the results of fatigue tests, it has been shown that the fatigue strengths at $2{\times}106$ load cycles were improved in the case of the grinding sand TIG welding treatments, and we could know that it is satisfying fatigue strength prescribed in fatigue design standard in general. Besides, from the results of fracture mechanics approaches, the geometric shape correction factors were the most dominant factors in the initial fatigue crack growth, but as the fatigue crack develops, the finite plate correction factor were became the most dominant factor, and the fatigue life on non-load carrying fillet welded joints could be relatively exactly estimated by using the relations between fatigue crack growth rate and stress intensity factor obtained from finite element analysis and existing proposed formulae.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.529-536
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• 2020

This study aims to provide the basic data for coffee intake and health promotion by examining the conditions in which Korean adults consume the most coffee. The study used raw data from the second year of the 7th National Health and Nutrition Examination Survey (2017), and 3,325 subjects who were 19 years of age or older and who were not missing the required values. This number used as the average amount of coffee drank per day in the past year is at least one cup. In order to identify factors that affect coffee intake, the model included general characteristics such as gender, age, household income, education level, occupation, health behaviors such as smoking, drinking, high intensity and moderate intensity exercises, walking, physical activity during work and leisure, sleep time, stress and depression. The results showed that coffee intake was lower among women than men, coffee intake was higher for people 40-64 years than people 20-39 years old, physical occupations rather than non-physical occupations, smokers rather than non-smokers, and for high stress rather than low stress in life. Subjects with these factors are considered to be at risk of excessive caffeine intake from coffee. The risk group of this study should be studied for the effect of excessive consumption of coffee on personal health.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.111-122
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• 2000

In this study, A series of fatigue tests have been performed on the fillet welded joints of cover plates in steel plate girders in order to quantitatively assess the fatigue characteristics according to the shapes of cover plates. From the results of fatigue tests, it has been shown that the fatigue strengths were slightly different according to their shapes, but satisfied the fatigue design curves in Korea and other countries. Also, from the results of beachmark tests, it has been confirmed that the points of fatigue crack initiation were closely related to the shapes of weld bead toes, and fatigue cracks simultaneously initiated from several points in weld bead toes have been grown as semi-elliptical surface cracks, and these cracks have been coalesced each other, and grown as through thickness cracks, and finally reached to fracture. Besides, from the results of fracture mechanics approaches, stress gradient factors were the most dominant factors among crack correction factors obtained from the existing equations and finite element analysis, and the fatigue life on fillet welded joints of cover plates could be estimated using the relations between fatigue crack growth rate and stress intensity factor range obtained from finite element analysis.

• Physical Therapy Korea
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• v.17 no.1
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• pp.53-61
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• 2010

This study investigated the relationships between Work-related musculoskeletal disorders (WMSDs), contributing factors, and the occupational stress of physical therapists. Self-reported questionnaires were given to 180 physical therapists in Gangwon Province. Variables examined included the prevalence of pain sites related to WMSDs; pain intensity; pain pattern; and job stress, which is thought to involve the physical environment; job demand; insufficient job control; interpersonal conflict; job insecurity; organizational system; reward system; and occupational culture. Among physical therapists, work-related musculoskeletal pain commonly affected the low back (30.1%), shoulder (29.3%), and wrist (12.2%). The sites of work-related musculoskeletal pain treated medically were the low back (22.8%), shoulder (19.8%), neck (12.7%), and wrist (12.1%). "Repeating the same work constantly" was suggested to be the major cause of the pain. The younger therapists were significantly more likely to feel high job stress due to the physical environment (p<.05), job demand (p<.05), and organizational system (p<.01). Women were more likely to feel greater job stress related to job demand, insufficient job control, the organization system, and job rewards. Men were more likely to feel greater job stress related to job insecurity. Weak positive relationships were observed between work-related musculoskeletal pain and job stress, which is thought to involve the physical environment; job demand; insufficient job control; interpersonal conflict; job insecurity; organizational system; reward system; and occupational culture. Physical therapists appear to be at higher risk of WMSDs because 80.1% of the physical therapists studied experienced work-related musculoskeletal pain. To reduce the risk, we need intervention strategies such as preventive education, ergonomically designed medical equipment, a psychosocial approach to work conditions, improved mechanical conditions related to therapeutic patterns, and an institutional infrastructure with sufficient personnel and scheduling.

• The Journal of the Korea Contents Association
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• v.10 no.11
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• pp.424-434
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• 2010

Job stress of Korean workers is 87.8% which is the highest level among OECD countries(average 80%), and job satisfaction is 69% which is the lowest satisfaction much lower than the average(81) of OECD. This study aims to analyze the effect of LMX; Leader-Member Exchange regarding job stress and job satisfaction empirically. According to the result of the study of employees in special hotels in capital areas and Jeolla province, the difference between job stress and intensity showed partial differences in marital status. In addition, the mediating roles of the LMX quality showed that the only organization-related stress consisting of role conflicts and role ambiguity factors was found to be mediated by the quality of LMX in terms of the effect on job satisfaction. Also, the effect of job authority-related stress and job environment stress on job satisfaction showed that the quality of LMX didn't have an influence.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.3
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• pp.65-73
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• 1989

Continuum formulations for the expressions of dynamic energy release rates and computational methods for dynamic stress intensity factors are developed for the analysis of dynamic fracture problems subjected to stress wave loading. Explicit volume integral expressions for instantaneous dynamic energy release rates are derived by modeling virtual crack extensions with the dynamic Eulerian-Lagrangian kinematic description. In the finite element applications a finite region around a crack-tip is modeled by using quarter-point singular isoparametric elements, and the volume integrals are evaluated for each crack-tip element during virtual crack extensions while the singularity is maintained. It is shown that the use of the present method is more reliable and accurate for the dynamic fracture analysis than that of other path-independent integral methods when the effects of stress waves are significant.

• Journal of Applied Reliability
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• v.15 no.3
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• pp.154-162
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• 2015

We have performed accelerated photo-degradation test using a 10-Sun level high irradiance $Weather-Ometer^{(R)}$ (10-Sun Ci5000) in an attempt to study acceleration and correlation between accelerated and service conditions for ink-jet ink. The accelerated test was used to predict lifetimes of ink-jet ink through the calculation of scaling factor for intensity of irradiance and duration of usage combined with estimation of lifetime distribution and inverse power model as a life-stress model. The lifetimes and acceleration factors for foreign and domestic inks were compared with each other. The results showed that the failure mechanisms and life-stress models for ink-jet ink were different among the color of ink which means that we might be in need of further study by color of inks.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1012-1020
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• 2006

The crack that occurs on the wheels of railroad cars can be categorized into a surface crack that starts from the surface or a subsurface crack that starts from the inside and can be detrimental to safe railroad operations. Therefore, estimating the growth life span of this type of crack is very important. In this research, the stress distributions, displacements, and the growth-life spans of both surface cracks and subsurface cracks have been studied. By using the finite element analysis, especially in the life span prediction process, the stress conditions and the stress intensity factors of the crack tip have been discovered. The Paris formula has been used to analyze the growth-life span prediction.