• Title/Summary/Keyword: 피로평가

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Measurement and Assessment of Mental Fatigue using Biosignals during Monotonuous Task (I) (생리신호를 사용한 단조 작업 수행시 정신 피로도의 측정과 평가(I))

  • 고한우;윤용현;이창미;김동윤
    • Science of Emotion and Sensibility
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    • v.3 no.1
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    • pp.1-6
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    • 2000
  • 단조 작업에 의한 정신적 피로도의 평가를 위하여 피험자에게 1자릿수 숫자 3개를 더하는 연산 작업을 수행하게 하였다. 주관적 평가를 통해 단조작업임이 확인된 task를 사용하여 작업 시간이 증가함에 따라 단조감이 증가하도록 실험과정을 설계하고 생리신호를 측정하였다. 측정된 생리신호 중 심전도, 피부온도, 호흡을 분석하였다. 단조 작업을 수행함에 따라 피부온도의 증가 경향이 나타났으며, 심박 변화율의 전력스펙트럽 분석결과 고주파성분의 감소와 Power spectrum balance가 증가하였다. 특히 power spectrum balance와 주관적 평가치의 상관관계가 높게 나타났다. 또한 상관관계가 높은 생리신호를 사용하여 정신피로를 예측한 결과 (R=0.945)가 정신피로를 잘 나타낼 수 있음을 알 수 있었다.

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A Study on Fatigue Safety Estimation of Cross Frame of Suspension Bridge(I) - Estimation by Nominal Stress - (현수교 횡프레임의 피로안전성 평가에 관한 연구(I) - 공칭응력에 의한 평가 -)

  • Kyung, Kab Soo;Jeon, Jun Chang;Su, Seok Ku;Yong, Hwan Sun
    • Journal of Korean Society of Steel Construction
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    • v.11 no.4 s.41
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    • pp.397-407
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    • 1999
  • In this paper, the fatigue safety in the suspension bridge is investigated by using nominal and variable stress, respectively. The technique on structural modeling and the fatigue evaluation using nominal stress are mainly dealt with in this paper. To make the finite element analysis model reflecting the actual structural behavior of the suspension bridge with cross frame, the parametric study is carried out. In this study, the influence of supporting condition. the difference of the results of 2- and 3-D analysis and the number of cross frames modelled in are considered. The nominal stress under the real traffic flow of the bridge is calculated by the combination of the stresses due to the unit DB-24 loading. The nominal stresses for details under consideration are compared with allowable stress ranges specified in the codes and the results are discussed.

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Evaluation of Fatigue Crack Growth Rate on the Surface of Steel Members Using COD(Crack Opening Displacement) Measurement (COD(Crack Opening Displacement) 측정에 의한 강재표면의 피로균열진전속도 평가)

  • Kim, Kwang Jin;Kim, In Tae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.2
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    • pp.179-188
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    • 2011
  • Steel structures have been allowed to have fatigue damage tolerance in fact. If it would be assessed whether fatigue crack is growing or not and How fast fatigue crack is propagating, we should make a rational decision on methods and a period of reinforcement in the maintenance. In this study, fatigue crack growth tests on two kinds of through-thickness cracked steel plates and a out-of-plane gusset welded joint were conducted to evaluate fatigue crack growth rate using the COD(Crack Opening Displacement), and COD measurement using strain gauges was examined to offer a practical method. As a result, we proposed a reasonable assessing method for fatigue crack growth rate using the COD and it was experimentally proved practical to estimate the COD through measuring strains.

Study on the Determination of Fatigue Damage Parameter for Rubber Component under Multiaxial Loading (다축하중이 작용하는 방진고무부품 피로손상 파라미터 결정에 관한 연구)

  • Moon, Seong-In;Woo, Chang-Su;Kim, Wan-Doo
    • Elastomers and Composites
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    • v.47 no.3
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    • pp.194-200
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    • 2012
  • Rubber components have been widely used in automotive industry as anti-vibration components for many years. These subjected to fluctuating loads, often fail due to the nucleation and growth of defects or cracks. To prevent such failures, it is necessary to understand the fatigue failure mechanism for rubber materials and to evaluate the fatigue life for rubber components. The objective of this study is to develop the durability analysis process for vulcanized rubber components, which is applicable to predict fatigue life at initial product design step. The determination method of nonlinear material constants for FE analysis was proposed. In order to investigate the applicability of the commonly used damage parameters, fatigue tests and corresponding finite element analyses were carried out and strain energy density was proposed as the fatigue damage parameter for rubber components. The fatigue analysis for automotive rubber components was performed and the durability analysis process was reviewed.

A Study on Fatigue Characteristics under Residual Stress by Cold Expansion (홀 확장 잔류응력하의 피로특성에 관한 연구)

  • Heo, Seong Pil;Kim, Cheol;Jeong, Gi Hyeon;Go, Myeong Hun;Yang, Won Ho
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.2
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    • pp.35-40
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    • 2003
  • Cold expansion method is an effective process to retard the crack initiation at a hole and to improve fatigue life by developing the compressive residual stress around the hole. Several researches have been treated for the crack propagating toward a hole around which the residual stress by cold expansion exists. The objective of this paper is to evaluate the fatigue characteristics under the residual stress by cold expansion. Fatigue tests are performed for the plate with a central hole to which cold expansion has been applied, and the effects of the residual stress on the fatigue life are evaluated. Also the fatigue crack growth tests are conducted for the CT specimen in which the residual stress by cold expansion has been generated. The change of fatigue crack growth characteristics by the residual stress is investigated and the effects of cold expansion ratio are evaluated.

Experimental Study on Evaluation of Fatigue Crack Growth Rate of Steel Plates using Crack Opening Displacement (COD(Crack Opening Displacement) 측정을 통한 강재의 피로균열진전속도 추정에 관한 실험적 연구)

  • Kim, Kwang-Jin;Kim, In-Tae;Ryu, Yong-Yeol
    • Journal of Korean Society of Steel Construction
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    • v.22 no.6
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    • pp.589-597
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    • 2010
  • Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

Durability Assessment of Polyoxymethylen Using Ultrasonic Fatigue Testing (초음파 피로시험법을 이용한 엔지니어링 플라스틱 (Polyoxymethylen ; POM)의 내구성 평가)

  • Cho, In Sik;Hwang, Jung Ho;Oh, Joo Yeon;Kim, Hyun Chang;Oh, Sae Hoon;Lee, Chang Soon;Park, In Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.8
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    • pp.781-785
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    • 2015
  • In this study, a newly developed ultrasonic fatigue test was performed for durability assessment of polyoxymethylene engineering plastic, which has a high crystallization rate and degree of crystallization. Fatigue strength of POM (polyoxymethylene) was performed on a piezoelectric UFT developed by Mbrosia Co., Ltd(1), operating at a high frequency of 20 kHz. The test results showed a fatigue limit of 5.0~6.0 MPa under fatigue testing at R = -1, 20kHz; and, electron microscopy revealed the size effect by risk volume and fractured dimple structure after the coalescence of micro-voids through the crazing effect, which occurs during the failure of a polymer.

Evaluation of Statistical Fatigue Life of Hybrid Composite Joints in Low-Floor Bus (저상버스용 하이브리드 복합재 조인트부의 통계적 피로수명평가)

  • Jung, Dal-Woo;Choi, Nak-Sam
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.11
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    • pp.1705-1713
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    • 2010
  • The reliable fatigue life for hybrid composite joint structures was estimated by a statistical method for evaluating fatigue life; the results of the fatigue test varied widely. Cyclic bending tests were performed on a cantilever beam with a hybrid composite joint, which was developed for the body of a low-floor bus. In order to estimate the fatigue life of the hybrid composite joint structure by comparing the data obtained during the fatigue tests, the most suitable probabilistic density function among the normal, lognormal, and Weibull distributions was selected. The probabilistic-stress-life (P-S-N) curves calculated by using the selected Weibull distribution was suggested for process of statistical fatigue life estimation and reliability design.

A Study on Statistical Characteristics of Fatigue Life of Carbon Fiber Composite (탄소섬유 복합재 피로수명의 통계적 특성 연구)

  • Joo, Young-Sik;Lee, Won-Jun;Seo, Bo-Hwi;Lim, Seung-Gyu
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.1
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    • pp.35-40
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    • 2019
  • The objective of this paper is to identify the fatigue properties of carbon-fiber composite which is widely applied for the development of aircraft structures and obtain data for full-scale fatigue test. The durability and damage tolerance evaluation of composite structures is achieved by fatigue tests and parameters such as fatigue life factor and load enhancement factor. The specimens are made with carbon-fiber/epoxy UD tape and fabric prepreg. Fatigue tests are performed with several stress ratios and lay-up patterns. The Weibull shape parameters are analyzed by Sendeckyj model and individual fatigue lives with Weibull distribution. And the fatigue life factor and load enhancement factor considering reliability are evaluated.

Current Knowledge on Fatigue in Advanced Cancer Patients (진행된 암환자에서 피로의 최신지견)

  • Kim, Jung-Hyun;Choi, Youn-Seon
    • Journal of Hospice and Palliative Care
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    • v.11 no.4
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    • pp.175-180
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    • 2008
  • 진행된 암환자에서 피로는 70% 이상이 경험하게 되는 흔한 증상이며 삶의 질을 저하시키는 주된 요인이다. 피로에 대한 선별검사는 "피곤하거나 지친감이 있나요?"라는 단순한 질문으로 가능하며 이미 개발된 평가도구를 사용하여 평가할 수 있다. 동반 질환이나 피로의 원인을 알기 위한 병력청취와 검사실 검사가 필요할 수 있으며 결과에 따라 가역적 인자를 치료하는 과정이 우선되어야 한다. 적절한 약물치료를 시행하여 증상을 호전시킬 수 있으며 이중 methylphenidate는 암 연관 피로를 호전시키고 마약성 진통제에 의한 진정에 효과가 입증되었다. 환자의 여명에 따라 부신 피질 호르몬제도 사용할 수 있고, 운동 및 환자의 교육과 영양관리 또한 중요하다.

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