• Title/Summary/Keyword: fatigue Model

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The Structural Equation Model of Burnout of the Critical Care Nurses Based on the Job Demand-Resource Model (직무요구-자원 모델에 기반을 둔 중환자실 간호사의 소진 구조모형)

  • Park, Ok Kyoung;Son, Myeong Hee;Park, Mi Youn;Baek, Eun Sun;Kim, Phill Ja
    • Journal of Korean Clinical Nursing Research
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    • v.22 no.1
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    • pp.88-98
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    • 2016
  • Purpose: The purpose of this study was to construct and test a structural equation model of burnout of the critical care nurses based on the job demand-resource model. Methods: A structured questionnaire was completed by 414 critical care nurses. The relationships between concepts of job stress, empathic ability, resilience, job satisfaction, compassion fatigue and burnout were analyzed. Using SPSS WIN 22.0 and AMOS 22.0 programs, the direct and indirect effects of factors affecting burnout among critical care nurses were calculated and modelled. Results: The modified model was yielded as follows: Chi-square= 216.59, GFI= .93, AGFI= .89, NFI= .90, CFI= .93, RMSEA= .07, SRMR= .06 and showed good fit indices. Job satisfaction and compassion fatigue had mediation effects between other three exogenous variables and burnout. Conclusion: The major findings of this study indicate that it is important to develop a support program for critical care nurse in order to improve their job satisfaction and ameliorate their compassion fatigue.

A Study on the Fatigue Reliability of Structures by Markov Chain Model (Markov Chain Model을 이용한 구조물의 피로 신뢰성 해석에 관한 연구)

  • Y.S. Yang;J.H. Yoon
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.2
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    • pp.228-240
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    • 1991
  • Many experimental data of fatigue crack propagation show that the fatigue crack propagation process is stochastic. Therefore, the study on the crack propagation must be based on the probabilistic approach. In the present paper, fatigue crack propagation process is assumed to be a discrete Markov process and the method is developed, which can evaluate the reliability of the structural component by using Markov chain model(Unit step B-model) suggested by Bogdanoff. In this method, leak failure, plastic collapse and brittle fracture of the critical component are taken as failure modes, and the effects of initial crack distribution, periodic and non-periodic inspection on the probability of failure are considered. In this method, an equivalent load value for random loading such as wave load is used to facilitate the analysis. Finally some calculations are carried out in order to show the usefulness and the applicability of this method. And then some remarks on this method are mentioned.

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Seismic assessment of steel structures through a cumulative damage

  • Perera, R.;Gomez, S.;Alarcon, E.
    • Steel and Composite Structures
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    • v.1 no.3
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    • pp.283-294
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    • 2001
  • In the present work a constitutive model is developed which permits the assessment of the structural performance through a criterion based on cumulative damage. For it, a damage index is defined and is evaluated through the application of the Miner's rule in low-cycle fatigue. However, the damage index is not considered as a posteriori variable since is incorporated explicitly as an internal variable in the constitutive equations which produces a direct coupling between the damage and the structural mechanical behaviour allowing the possibility of considering as a whole different coupled phenomena. For the elaboration of this damage model, the concepts of the mechanics of continuum medium are applied on lumped dissipative models in order to obtain a coupled simplified model. As a result an elastoplastic model coupled with damage and fatigue damage is obtained.

Prediction of Crack Growth Retardation Behavior by Single Overload (단일 과대 하중에 의한 균열 성장 지연 거동 예측)

  • 송삼흥;최진호;김기석
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.11a
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    • pp.928-932
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    • 1996
  • Single overload fatigue tests with overload sizes ranging from 50% and 100% have been performed to investing ate the fatigue crack growth retardation behavior. A modified and experimental method of Willenborg's model for prediction of crack growth retardation behavior has been developed, based on evaluations of equivalent plastic zone size (EPZS) changing its size along the overload plastic zone boundary. The minimum crack growth rates of each overload size are linearly decreased with overload size increasing, but fatigue lives extended by single overload are increasing much more unlike the crack growth rates. Comparisons of crack growth behavior predicted by EPZS model and Willenborg model have shown that the EPZS model accounts for overload effects better than Willenborg model. These effects include delayed retardation, large retardation region, minimum crack growth rate, and the increase rate of crack growth rate in the region crack growth rate recovered.

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A Study on the Shear Fatigue Damage Behavior of the Reinforced Concrete Beams Subject to Repeated Loading Using the Strut-Tie Model (스트럿-타일 모델을 이용한 반복하중을 받는 철근 콘크리트 보의 전단피로손상거동에 관한 연구)

  • Oh, Byung-Hwan;Han, Seung-Hwan;You, Young
    • Proceedings of the Korea Concrete Institute Conference
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    • 1997.04a
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    • pp.430-435
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    • 1997
  • This paper represents the investigation of the shear fatigue behavior and damage procedure of reinforced concrete beams subject to repeated loading using the strut-tie model. Damage Index is defined as the ratio of deflection at each cycle to the ultimate deflection of inelastic region. Two types of strut-tie model are designed according to the inclined angles of concrete-struts and the consideration of concrete-ties. In one model, aggregate interlock and resistance of uncracked concrete are regarded as the main sheat resisting mechanism and in the other, stirrup is. The results show that the strut-tie model combined with damage index can describe the shear fatigue behavior of RC beams subject to repeated loading effectively.

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Corrosion-Fatigue Reliability-Based Life Cycle Cost Analysis of High-Speed Railway Steel Bridges (고속철도 강교량의 부식.피로신뢰성 기반 생애주기비용 분석)

  • Jeon, Hong-Min;Sun, Jong-Wan;Cho, Hyo-Nam
    • Proceedings of the KSR Conference
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    • 2007.11a
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    • pp.1132-1140
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    • 2007
  • As it recently appears that Life Cycle Cost Analysis may be considered as new methodology for economic valuation of infrastructure many researches have been made to assess LCC(Life Cycle Cost) of each facility based on a reasonable methods. In general, LCC is composed of construction cost and expected maintenance repair cost. And especially, maintenance repair cost must be estimated to enhance the reliability through systematic and reasonable methods. However in Korea, because high speed railway steel bridges are recently constructed no direct statistical data are available for the account of the maintenance cost and then their maintenance characteristics are not linear yet. Therefore, the approach proposed in the paper utilizes a theoretical determination and degradation of the corrosion and fatigue of the bridges based on Rahgozar et al.(2006)'s model on fatigue notch factor considering into the corrosion to incorporate the corrosion effect into the fatigue strength reduction model. And then, the corresponding probability of failure is calculated in terms of the reliability index using S-N curve to formulate the fatigue limit state. Therefore, this paper proposes the minimum Life Cycle Cost through optimum maintenance plan analysis of high-speed railway steel bridges under construction. Finally, this paper reviews the proposed model in oder to confirm the applicability and feasibility by appling it to high speed railway steel bridges under construction

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Composite material optimization for heavy duty chassis by finite element analysis

  • Ufuk, Recep;Ereke, Murat
    • Advances in Automotive Engineering
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    • v.1 no.1
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    • pp.41-59
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    • 2018
  • In the study, investigation of fiber- reinforced composite materials that can be an alternative to conventional steel was performed by finite element analysis with the help of software. Steel and composite materials have been studied on a four axle truck chassis model. Three-dimensional finite element model was created with software, and then analyzes were performed. The analyses were performed for static and dynamic/fatigue cases. Fatigue cases are formed with the help of design spectra model and fatigue analyses were performed as static analyses with this design spectra. First, analyses were performed for steel and after that optimization analyses were made for the AS4-PEEK carbon fiber composite and Eglass-Epoxy fiber composite materials. Optimization of composite material analyzes include determining the total laminate thickness, thickness of each ply, orientation of each ply and ply stacking sequence. Analyzes were made according to macro mechanical properties of composite, micromechanics case has not been considered. Improvements in weight reduction up to %50 provided at the end of the composite optimization analyzes with satisfying stiffness performance of chassis. Fatigue strength of the composite structure depends on various factors such as, fiber orientation, ply thickness, ply stack sequence, fiber ductility, ductility of the matrix, loading angle. Therefore, the accuracy of theoretical calculations and analyzes should be correlated by testing.

FINITE ELEMENT MODELING AND PARAMETER STUDY OF HALF-BEAD OF MLS CYLINDER HEAD GASKET

  • CHO S. S.;HAN B. K.;LEE J. H.;CHANG H.;KIM B. K.
    • International Journal of Automotive Technology
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    • v.7 no.1
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    • pp.109-114
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    • 2006
  • Half-beads of multi-layer-steel cylinder head gaskets take charge of sealing of lubrication oil and coolant between the cylinder head and the block. Since the head lifts off periodically due to the combustion gas pressure, both the dynamic sealing performance and the fatigue durability are essential for the gasket. A finite element model of the halfbead has been developed and verified with experimental data. The half-bead forming process was included in the model to consider the residual stress effects. The model is employed to assess the dependence of the sealing performance and the fatigue durability on the design parameters of half-bead such as the width and height of bead and the flat region length. The assessment results show that the sealing performance can be enhanced without significant deterioration of the fatigue durability in a certain range of the half-bead width. In the other cases the improvement of sealing performance is accompanied by the loss of the fatigue durability. Among three parameters, the bead width has the strongest influence.

A Study on the Application Method of Steinberg Fatigue Limit Equation for Electronic Part Life Assessment of Fighter Aircraft Radar (전투기 레이다용 전자부품 수명평가를 위한 Steinberg 피로한계식 적용방안 연구)

  • Kim, Deokjoo;Hah, Seung Ryong;Kang, Minsung;Heo, Jaehun
    • Journal of the Korea Institute of Military Science and Technology
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    • v.23 no.4
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    • pp.319-327
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    • 2020
  • In this study a methodology to evaluate fatigue life of the electronic parts for the fighter radar unit under random vibration loading is presented. To do this, one parameter for the 3-σ RMS quation of Steinberg fatigue model is modified to come up with a printed circuit board(PCB) with multiple electronic parts, while fundamental frequency and dynamic deflection of the PCB are calculated from a MATLAB based finite element computer code. For the RIFA structure selected in this study, the 3-σ RMS fatigue limit displacement is reduced to 0.741 times as much as the Steinberg model. This investigation allows to assess the life of multiple electronic parts mounted on the PCB with reinforced metal cover/body showing non-sinusoidal deflection patterns.

Flexural behaviour of GFRP reinforced concrete beams under cyclic loading

  • Murthy, A. Ramachandra;Gandhi, P.;Pukazhendhi, D.M.;Samuel, F. Giftson;Vishnuvardhan, S.
    • Structural Engineering and Mechanics
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    • v.84 no.3
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    • pp.361-373
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    • 2022
  • This paper examines the flexural performance of concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars under fatigue loading. Experiments were carried out on concrete beams of size 1500×200×100 mm reinforced with 10 mm and 13 mm diameter GFRP bars under fatigue loading. Experimental investigations revealed that fatigue loading affects both strength and serviceability properties of GFRP reinforced concrete. Experimental results indicated that (i) the concrete beams experienced increase in deflection with increase in number of cycles and failed suddenly due to snapping of rebars and (ii) the fatigue life of concrete beams drastically decreased with increase in stress level. Analytical model presented a procedure for predicting the deflection of concrete beams reinforced with GFRP bars under cyclic loading. Deflection of concrete beams was computed by considering the aspects such as stiffness degradation, force equilibrium equations and effective moment of inertia. Nonlinear finite element (FE) analysis was performed on concrete beams reinforced with GFRP bars. Appropriate constitutive relationships for concrete and GFRP bars were considered in the numerical modelling. Concrete non linearity has been accounted through concrete damage plasticity model available in ABAQUS. Deflection versus number of cycles obtained experimentally for various beams was compared with the analytical and numerical predictions. It was observed that the predicted values are comparable (less than 20% difference) with the corresponding experimental observations.