• 제목/요약/키워드: fatigue behaviors

검색결과 298건 처리시간 0.025초

SiC 입자 강화 알루미늄기 복합재료의 표면미소 피로균열 발생 및 초기진전거동 (Initiation and Growth Behavior of Small Surface Fatigue Crack on SiC Particle Reinforced Aluminum Composite)

  • 이상협;최영근;김상태;이문환
    • Composites Research
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    • 제21권6호
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    • pp.15-22
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    • 2008
  • 본 연구는 SiC입자를 20% 강화된 알루미늄기 복합재료를 이용해서 평면굽힘피로시험을 향했다. 표면미소피로균열의 발생 및 진전거동은 레프리카법으로 연속관찰을 했고 파괴원인과 파괴기구를 규명하기 위해서 주사전자현미경을 이용했다. da/dn-$K_{max}$ 관계에서 저응력 레벨에서는 여러 개의 균열이 진전하고, 합체 등이 일어나는 것으로부터 진전속도는 꽤 분산(흐트러짐)이 심하고, 고응력 레벨에서는 비교적 흐트러짐은 적게 나타나는 것을 알 수 있었다.

철도 구조물용 맞대기 용접시편 가공에 의한 피로수명 영향 및 용접부 형상을 이용한 피로수명 예측 연구 (A Study on the Effects of the Fatigue Life due to the Processing of the Butt Weld Specimens and the Fatigue Life Estimation due to the Weld Zone Profiles)

  • 김재훈
    • 한국철도학회논문집
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    • 제9권4호
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    • pp.371-378
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    • 2006
  • This study investigates the effects of the material properties and the fatigue behaviors in the SM490A material butt weld specimens due to the heat-treatment and the grinding. In the fatigue behavior, the heat-treatment affects the fatigue life. The S-N curves of both matrix specimen and butt weld specimen are reversed at some cycle by the existence or nonexistence of heat-treatment. The grinding on the bead makes the fatigue limit decrease in the all specimens. But the reinforcement removed, the fatigue limit increases at the high cycle. Also, this study investigates the fatigue life estimation by examining butt weld bead profiles. The butt weld beads, which are welded by semi-robot method, have non-uniform bead profiles described by $\theta,\;\rho$ and h. The stress concentration factors $K_t$, are changed by each different $\theta,\;\rho$ and h from 1.395 to 2.863. Hence, the sensitivity of $K_t$ is changed by each $\theta,\;\rho$ and h. As $\theta$ becomes lower and $\rho$ and h become higher, $K_t$ increases. The fatigue life can he estimated very closely for the AAY specimens without residual stress using only butt weld bead profiles. But, fur the AAN specimens with residual stress, the fatigue life must be estimated by considering both the weld bead profiles and the residual stress data.

제조업 근로자의 건강행위와 직무로 인한 스트레스 자각증상의 관련성 (Effects of Health Behaviors on Perceived Physical and Psychological Job Stress Among Korean Manufacturing Workers)

  • 박경옥;김인석;오영아
    • 보건교육건강증진학회지
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    • 제21권3호
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    • pp.195-211
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    • 2004
  • Stress is a primary health promotion issue in worksite research because psychological distress is closely related not only to workers' health status but also to their job performance. This study identified the significant health behaviors affecting workers' job-related stress in Korean manufacturing industry with the national survey data conducted by the Korean Occupational Safety and Health Agency in 2003. A total of 7,818 factory workers in 1,562 manufacturing companies participated in the Korean nation-wide occupational health survey and 3,390 workers answered that they had any stressors in their workplace among the 7,818 workers finally participated in the analysis. Participants were selected by the stratified proportional sampling process by manufacturing industry classification, company size, and company locations (8 metropolitan and 8 non-metropolitan regions) in Korea. Trained interviewers visited the target companies and interviewed the factory workers randomly selected in each company. Smoking, drinking, weight control, exercise, sleeping, break time at work, and perceived fatigue were included in the health behavior construct. Stress symptoms was consisted of physical and psychological stress with 8 items. All survey responses were anonymously coded into the SPSS statistical program and testified using stepwise multiple regression analysis. Male workers were 73.5% and the 30s were 40.0% among the age groups. The married and the high school graduate were majority with 52.1% and 61.8% each. Current smokers were 44.7% and More than 50% of the participants drank alcohol sometimes. No exercise group was 59.3% and the participants who dissatisfied with their daily sleeping hours were 43.5%. In t-test and analysis of variance, the significant general characteristics associated with physical and psychological job stress were young age (p<0.001), single marital status (p<0.001), and short working period at the present company (p<0.001). The health behaviors related to physical job stress were current smoking, weight change during the past one year (p<0.001), weight control effort (p<0.001), exercise (p<0.001), daily sleeping dissatisfaction (p<0.001), break time, and perceived fatigue (p<0.001). All 10 health behavior factors were significantly associated with psychological job stress (p<0.05). Weight change, weight control effort, exercise, daily sleeping dissatisfaction, little break at work, and high perceived fatigue were significant factors affecting job stress. Daily sleeping dissatisfaction, little break at work, little exercise, weight change for the past one year and young age were selected as the significant health behavior and general factors affecting physical job stress symptoms in stepwise multiple regression analysis. The five factors explained 18.9% of the physical stress score variance. Six factors were selected as the significant health behaviors affecting psychological job stress: daily sleeping dissatisfaction, little exercise, frequent drinking alcohol, high perceived fatigue, little break at work, and little weight control effort. The six factors explained 10.6% of the psychological stress score variance.

직무긴장 모형을 이용한 치과위생사의 직무스트레스와 반응 (Job stress and reaction of dental hygienist by using the job strain model)

  • 최미숙;안권숙
    • 한국치위생학회지
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    • 제10권4호
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    • pp.595-605
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    • 2010
  • Objectives : A precedent research has documented that occupational stress is closely associated with increased the risk of fatigue and decreased in job satisfaction. This study was conducted in an effort to assess the relationship of occupational stress to self-perceived fatigue and job satisfaction by using job strain model. Methods : The number of respondents was 122 dental hygienist who work in dental clinic and period of the investigation was July 2009 through september 2009. A structured questionnaire was employed to evaluate the participants' sociodemographics, job-related factors, health-related behaviors, occupational stress, job satisfaction and self-perceived fatigue. Occupational stress and self-perceived fatigue were assessed using the Korean Occupational Stress Scale-Short form (KOSS-SF) and the Multidimensional Fatigue Scale (MFS), respectively. Results : In job strain model, the ratio of Q2(High Strain Job) group that more susceptible to disease by stress than other group was 16% and the proportion of high fatigue group(Q3, Q4 group) and low job satisfaction group(Q3, Q4 group) was 48%, 45% respectively. In logistic regression analyses, a High Strain Job group was associated with higher odds of react factor(fatigue, job satisfaction) and the odds was down by 3.3%~7.5% after adjustment for age, smoking, alcohol drinking, regular exercise. So the effective strategy for fatigue, job satisfaction reduction for dental hygienist requires additional program focusing on innovated work environment that provide a enough leisure time and exercise program considering the personality traits. Conclusions : The results of this study suggest that occupational stress is a determinant predictor of self perceived fatigue and job satisfaction. Thus, a stress management program for the reduction of occupational stress, and the promotion of dental hygienist impact assessment health and quality of life is strongly recommended.

주철의 피로전파거동에 미치는 미세조직의 영향 (The Effects of the Microstructures on the Fatigue Crack Propagation Behaviors of Cast Irons)

  • 김석원;박진성;이형철;김동건;우기도
    • 한국주조공학회지
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    • 제25권1호
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    • pp.16-22
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    • 2005
  • This study aims to investigate the effects of the microstructures and nodule type on the fatigue characteristics of cast iron. Fatigue tests were carried out in tension-tension mode using a servo-hydraulic testing machine with load control mode operating at a frequency of 15 Hz. The tests were conducted at stress ratio R=Kmin/Kmax, of 0.1. Initial crack ${\Dalta}K$ values were highly performed with increase in tensile strength of DCI fatigue specimens. ${\Dalta}K_{th}$ region, fatigue crack propagation was primarily advanced through cell boundary and in periphery of near nodule. Fatigue crack propagation rate of D2 consisted with 2Phase(Ferrite+Pearlite) was slow due to crack closure enhanced by crack deflection and occurred crack branching. The generation of crack branch was occurred due to interaction of crack-nodule. At Threshold and Paris zone, the fractographs of the fatigue fracture surface for DCI show typical striations of a ductile fracture and isolated cleavage planes near graphite. The effect of microstructure on fatigue crack propagation of GC strongly depends on the type of flake. The generation of crack branch occurred due to interaction of crack-nodule. The fractographs of the fatigue fracture surface for GC show cleavage plane along the flake graphite.

Very long life fatigue behaviors of 16Mn steel and welded joint

  • Liu, Yongjie;He, Chao;Huang, Chongxiang;Khan, Muhammad K.;Wang, Qingyuan
    • Structural Engineering and Mechanics
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    • 제52권5호
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    • pp.889-901
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    • 2014
  • Very long life fatigue tests were carried out on 16Mn steel base metal and its welded joint by using the ultrasonic fatigue testing technique. Specimen shapes (round and plate) were considered for both the base metal and welded joint. The results show that the specimens present different S-N curve characteristics in the region of $10^5-10^9$ cycles. The round specimens showed continuously decreasing tendency while plate specimens showed a steep decreasing step and an asymptotic horizontal one. The fatigue strength of round specimen was found higher than plate specimen. The fatigue strength of as-welded joint was 45.0% of the base material for butt joint and 40% for cruciform as-welded joint. It was found that fracture can still occur in butt joint beyond $5{\times}10^6$ cycles. The cruciform joint has a fatigue limit in the very long life fatigue regime ($10^7-10^9$ cycles). Fatigue strength of butt as-welded joint was much higher as compared to cruciform as-welded joint. Improvement in fatigue strength of welded joint was found due to UPT. The observation of fracture surface showed crack mainly initiated from welded toe at fusion areas or geometric discontinuity sites at the surface in butt joint and from welded toe in cruciform joint.

The Relationships among Postpartum Fatigue, Depressive Mood, Self-care Agency, and Self-care Action of First-time Mothers in Bangladesh

  • Fahima, Khatun;Lee, Tae Wha;Ela, Rani;Gulshanara, Biswash;Pronita, Raha;Kim, Sue
    • 여성건강간호학회지
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    • 제24권1호
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    • pp.49-57
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    • 2018
  • Purpose: Postpartum fatigue can impact maternal well-being and has been associated with levels of perceived self-care. This study aimed to examine the relationship among fatigue, depressive mood, self-care agency, and self-care action among postpartum women in Bangladesh. Methods: A descriptive cross sectional survey was done with 124 first-time mothers from two tertiary hospitals in Dhaka, Bangladesh. The Modified Fatigue Symptoms checklist, Denyes' Self Care Instrument, the Edinburgh Postnatal Depression Scale, and items on sociodemographic and delivery-related characteristics, were used in Bengali via translation and back-translation process. Results: High fatigue levels were found in 18.5% (n=23) and 73.4% had possible depression (n=91). There was a significant negative relationship between fatigue and self-care agency (r=-.31, p<.001), and self-care action (r=-.21, p<.05). Fatigue differed by level of self-care agency (t=4.06, p<.001), self-care action (t=2.36, p=.023), newborn's APGAR score (t=-2.93, p=.004), parental preparation class participation (F=15.53, p<.001), and postpartum depressive mood (t=-4.64, p<.001). Conclusion: Findings suggest that high level of self-care efficacy and behaviors can contribute to fatigue management, and highlight the need for practical interventions to better prepare mothers for postpartum self-care, which may, in turn, alleviate postpartum fatigue.

피로효과를 고려한 레일패드의 정적스프링계수 변화에 따른 콘크리트 슬래브 제도의 거동분석 (A Behavior Analysis of HSR Concrete Slab Track under Variety of Rail Pad Static Stiffness on Fatigue Effect)

  • 박용걸;강기동;최정열
    • 한국철도학회논문집
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    • 제10권5호
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    • pp.499-505
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    • 2007
  • 본 연구의 주목적은 고속선 콘크리트 슬래브 궤도시스템에서 레일패드의 피로효과에 따른 영향을 분석하는 데에 있다. 이에 3차원 해석모델 및 실내시험을 통해 도출된 레일패드의 피로효과(경화, 스프링계수 증가)가 고속선 궤도의 역학적 거동에 미치는 영향을 분석하였다. 본 연구에서는 콘크리트 슬래브 궤도의 적정 탄성력 확보여부를 의미하는 레일패드의 적정스프링계수 산정에 관한 연구의 일환으로 고속철도 콘크리트 슬래브 궤도에 적용된 레일체결시스템에 대한 실내시험을 통한 레일패드의 정적스프링계수를 산정하고 체결시스템에 대한 피로시험을 통해 도출된 피로효과가 고려된 레일패드의 스프링계수 변화를 해석모델에 적용함으로써 향후 고속선 콘크리트 슬래브 궤도운영에서의 열차 주행안정성 확보 및 합리적인 궤도유지관리를 위한 기초데이터를 확보하고자 한다.

Environmental fatigue correction factor model for domestic nuclear-grade low-alloy steel

  • Gao, Jun;Liu, Chang;Tan, Jibo;Zhang, Ziyu;Wu, Xinqiang;Han, En-Hou;Shen, Rui;Wang, Bingxi;Ke, Wei
    • Nuclear Engineering and Technology
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    • 제53권8호
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    • pp.2600-2609
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    • 2021
  • Low cycle fatigue behaviors of SA508-3 low-alloy steel were investigated in room-temperature air, high-temperature air and in light water reactor (LWR) water environments. The fatigue mean curve and design curve for the low-alloy steel are developed based on the fatigue data in room-temperature and high-temperature air. The environmental fatigue model for low-alloy steel is developed by the environmental fatigue correction factor (Fen) methodology based on the fatigue data in LWR water environments with the consideration of effects of strain rate, temperature, and dissolved oxygen concentration on the fatigue life.

틸팅차량용 KTX 차체의 하니컴복합재 측벽판 체결부의 피로파괴평가 (Fatigue Fracture Assessment of Honeycomb Composite Side-Wall Panel Joint for the KTX Tilting Car Body)

  • 정달우;김정석;최낙삼
    • 대한기계학회논문집A
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    • 제34권1호
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    • pp.55-60
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    • 2010
  • 틸팅형 고속열차의 차체에 적용되는 하니컴 복합재 조인트 구조물의 경우 운행중 외팔보형 굽힘하중을 받게된다. 하이브리드 복합재 조인트 구조물에 대한 굽힘시험평가를 수행하기 위해 실제 틸팅열차 차체 구조물에서 조인트부를 절단 채취하여 시험편으로 제작하였다. 굽힘시험결과 시험편의 파괴거동은 정적하중과 피로하중하에서 확연히 달라짐을 보였다. 정적굽힘하중 하에서는 하니컴 코어 영역에서 전단변형과 파괴가 발생하였으며, 피로굽힘하중 하에서는 복합재 표피층과 하니컴 코어층 사이에서 계면분리가 발생하거나, 또는 금속재 언더프레임과의 용접부에서 파괴가 발생하였다. 이러한 파괴거동은 다른 산업분야에서 사용되는 유사한 구조의 하니컴 복합재 조인트 구조물에서도 발생할 수 있기 때문에, 본 실험 결과를 하니컴 복합재 조인트 구조물의 설계변수를 개선하기 위해 이용될 수 있다.