• Title/Summary/Keyword: fatigue behaviors

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Effect of Cast Microstructure on Fatigue Behaviors of A356 Aluminum Alloy for Automotive Wheel (자동차휠용 A356 알루미늄 합금의 주조조직이 피로특성에 미치는 영향)

  • Song, Jeon-Young;Park, Joong-Cheol;Ahn, Yong-Sik
    • Journal of Korea Foundry Society
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    • v.30 no.1
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    • pp.46-51
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    • 2010
  • Recently, automotive industry is attempting to replace steels for automotive parts with light-weight alloys such as aluminum alloy, because of the growing environmental regulations governing exhaust gas and the engine effectiveness of a vehicle. The low cycle fatigue (LCF) and high cycle fatigue (HCF) properties as well as the microstructure and tensile property were investigated on the low pressure cast A356 aluminum alloy wheel, which was followed by T6 heat treatment. The cast microstructure of the alloy influenced significantly on the low cycle and high cycle fatigue behaviors. The rim part of cast aluminum alloy wheel showed higher low cycle and high cycle fatigue strength compared with the spoke part, which should be caused by higher cooling rate of rim part. The spoke part of the wheel showed coarser dendrite arm spacing (DAS) and wide eutectic zone in the microstructure, which resulted in the partial brittle fracture and lower fatigue life time.

Relationships between Sleep Quality, Fatigue and Depression on Health Promoting Behavior by Shift-Work Patterns in University Hospital Nurses (교대근무 형태에 따른 대학병원 간호사의 수면 질, 피로, 우울 및 건강증진 행위 간의 관계)

  • Son, Youn-Jung;Park, Young-Rye
    • Journal of Korean Biological Nursing Science
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    • v.13 no.3
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    • pp.229-237
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    • 2011
  • Purpose: The objective of this study was to investigate the relationships between sleep quality, fatigue, depression and health promoting behavior by shift-work patterns in university hospital nurses. Methods: A cross-sectional, descriptive survey was conducted using a convenient sample. The self-administered questionnaires were given to 165 nurses (shift workers 91, non-shift workers 74) employed in two university hospital located in Seoul and Gyeunggi-do. Data were collected from February to March, 2010. Results: The shift workers showed significantly lower sleep quality and health promoting behavior, and higher fatigue than non-shift workers. There were significant correlations between fatigue, depression and health promoting behavior in shift workers. There were significant correlations between sleep quality, fatigue, depression and health promoting behavior in non-shift workers. In multiple linear regression analysis, after controlling for total work experiences, predictor of health promoting behavior in shift workers was only fatigue (${\beta}$=-.29, p<.001). Predictors of health promotion behavior in non-shift workers were depression (${\beta}$=-.37, p=.002) and fatigue (${\beta}$=-.27, p=.023). Conclusion: This study failed to provide a clear explanation why sleep quality does not have a comparable effect on health promotion behaviors of shift-workers as well as non-shift workers. However, future research is needed to determine the various risk factors influencing on health promotion behaviors by which shift-work pattern exacerbates fatigue.

A Study on the Effect of the Buliding Up by Welding on the Fatigue Fracture Behaviors for the Forged Steel (축계용 단조강재 보수 용접부의 피로 파괴 특성에 관한 연구)

  • 김영식;김종호;한명수;손병영
    • Journal of Ocean Engineering and Technology
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    • v.5 no.1
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    • pp.97-105
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    • 1991
  • In this paper, the fatigue strength and the fatigue crack propagation behaviors of the round bar specimens which were spirally built up by welding and subsequently hardened by quenching were investigated. The material used was SF60 which was whdely employed in mechanical components, especially shafts. Fatigue tests were conducted at the fully reversed condition(R=-1) and axial and load control in the room temperature ahd air environment. The experimental results were expressed by both the range of stress intensity factor ($\Delta{K}$) and the effective range of stress intensity factor ($\Delta{K}_{eff}$). It was clarified that applying of quenching after the building up welding process improved the fatigue strength and the gatigue crack propagation property in the low range of $\Delta{K}$ of the built up round bar specimen.

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Evaluation of Influence on the Fatigue Strength of Residual Stresses at the Welded Toe of Welded Structure. (용접구조물 요접토우부의 잔류응력이 피로강도에 미치는 영향 평가)

  • 차용훈;김하식;김일수;성백섭
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.10 no.4
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    • pp.7-13
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    • 2001
  • This Study is to investigate the influence of weld residual stresses on the fatigue crack growth behaviors in pressure ves-sel reinforcement. In order to perform this study, the automatically welded specimens are prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. For pad-on-plate of skip welding continuous welding and PWHT specimen, fatigue crack initiation is generally initiat-ed at weld starting and end toe zone, and ruptured at weld starting toe zone, Fatigue life if pad-on-plate continuous speci-men is increased more than that of pad-on-plate skip fillet welding specimene about 85% under low load, about 20% under high load, and decreased than that of two-pad continuous welding specimen about 85%. In da/dN-$\Delta$ Κ curve under low load, pad-on-plate skip fillet welding specimen showed retardation on the initial crack, and the fatigue crack growth rate at the low region of $\Delta$Κ greater specimene E(3.8{\times}10^{-6}$mm/cycle). And the fatigue life of welding specimen was smaller than that of PWHT specimen.

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Initiation and Propagation Behaviors of Micro-Surface-Fatigue Cracks under In-Plane Tension Fatigue Tests (引張 軸荷重 疲勞 에 의한 微小表面 균열 의 發생 . 成長擧動)

  • 서창민
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.1
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    • pp.1-9
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    • 1985
  • In-plane tension fatigue tests (R = 0.05) were carried out to investigate the initiation and propagation behaviors of micro-surface-fatigue cracks on smooth surfaces of a mild steel. Also, the investigations of saturated cyclic strain which can be obtained by the fatigue tests have been made via the cyclic strain intensity factor, .DELTA. $K_{\epsilon}$/, for the purpose of unifying two approaches of the study of fatigue; the one approach is based on the fracture mechanics concept and the other on lowcycle fatigue concept. Some of the results are as follows; The growth rate, d(2a)/dN, of small cracks cannot be represented by one straight line as a function of .DELTA.K for various of the nominal stress range, .DELTA..sigma., and is higher than that of a larger through crack. The rearrangement of the d(2a)/dN by .DELTA..epsilon..root..pi.s( = .DELTA. $K_{\epsilon}$/) with the stress range .DELTA..epsilon. in .DELTA.K replaced by .DELTA..epsilon., strain range, gives one straight line of the .DELTA. $K_{\epsilon}$-d(2a)/dN relation for various values of stress range .DELTA.$_{\epsilon}$../.X>../.

A Study on the Fatigue Crack Growth Behaviour for the Welded Configuration in Pressure Vessel Stiffener (압력용기 보강재의 용접 형태에 따른 피로균열성장 거동에 관한 연구)

  • 차용훈;김하식;성백섭
    • Journal of the Korean Society of Safety
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    • v.16 no.3
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    • pp.1-6
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    • 2001
  • The study is to investigate the influence on the fatigue crack growth behaviors for the welded configuration in pressure vessel stiffener. In order to perform this goal, the automatic welded specimens were prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. In skip welding of pad-on-plate, continuous fillet welding and PWHT specimen, fatigue crack is generally initiated at the starting and end old toe zone, and ruptured at the starting old toe zone. The fatigue life of pad-on-plate of the continuous fillet welding specimen is larger than that of pad-on-plate skip fillet welding specimen about 85% under low load, about 20% under high load and less than that of two-pad continuous fillet welding specimen about 85%. In da/dN-$\Delta$K curve under low load, skip fillet welding specimen of pad-on-plate showed retardation on the initial crack, and the fatigue crack growth rate at the low region of $\Delta$K greater specimen E($3.8 {\times} 10^{-6}mm/cycle$). And the fatigue life of welding specimen was smaller than that of PWHT specimen.

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Multiaxial fatigue behaviors of open-rib to crossbeam joints in orthotropic bridge structures

  • Yang, Haibo;Qian, Hongliang;Wang, Ping;Dong, Pingsha;Berto, Fillipo
    • Steel and Composite Structures
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    • v.42 no.6
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    • pp.843-853
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    • 2022
  • The fatigue behavior of welded open rib-to crossbeam joints (ORCJ) in orthotropic bridge structures is investigated using a traction structural stress method. The fatigue behaviors of welded open rib-to crossbeam joints have been a subject of study for decades for ensuring operational safety and future design improvement. A mesh-insensitive combination of traction structural stresses in ORCJ was obtained considering the effect of in-plane shear stress and validated by fatigue test results. The proposed method is advantageous for predicting fatigue cracks that initiate from the crossbeam cutout and propagate along the crossbeam. The investigations carried out with the proposed approach reveal that the normal structural stress decreases with the propagation of fatigue cracks, while the ratio of shear stress to normal stress increases. The effect of shear structural stress is significant for the analysis of fatigue behavior of ORCJ in multiaxial stress states.

Effect of Microstructural Factors on Fatigue and Fatigue Crack Propagation Behaviors of Mill-Annealed Ti-6Al-4V Alloy (미세조직적 인자가 밀소둔된 Ti-6Al-4V 합금의 피로 및 피로균열전파 거동에 미치는 영향)

  • Park, Sanghoo;Kim, Sumin;Lee, Daeun;Ahn, Soojin;Kim, Sangshik
    • Korean Journal of Metals and Materials
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    • v.56 no.12
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    • pp.845-853
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    • 2018
  • To understand the effect of microstructural factors (i.e., the size of ${\alpha}$ phase, equiaxed vs bimodal structure) on high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of mill-annealed Ti-6Al-4V (Ti64) alloy, three specimens of EQ (equiaxed)-8 (8 indicates the size of ${\alpha}$ grain), BM (bimodal)-8, and BM-16 were studied. The uniaxial HCF and FCP tests were conducted at an R ratio of 0.1 under sinusoidal fatigue loading. The microstructural influence (i.e., EQ vs BM) was not significant on the tensile properties of mill-annealed Ti64 alloy, and showed an increase in tensile strength and elongation with decreasing gauge thickness from 50 mm to 1.3 mm. The microstructure, on the other hand, affected the resistance to HCF substantially. It was found that the EQ structure in mill-annealed Ti64 has better resistance to HCF than the BM structure, as a result of different crack initiation mechanism. Unlike HCF behavior, the effect of microstructural features on the FCP behavior of mill-annealed Ti64 was not significant. Among the three specimens, BM-16 specimen showed the highest near-threshold ΔK value, probably because it had the greatest slip reversibility with large ${\alpha}$ grains. The effect of microstructural factors on the HCF and FCP behaviors of mill-annealed Ti64 alloy are discussed based on fractographic and micrographic observations.

Fatigue Crack Growth Equation considered the Effect of Stress Ratio (응력비의 영향을 고려한 표면피로균열의 균열성장식)

  • 강용구;김대석
    • Journal of Ocean Engineering and Technology
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    • v.12 no.1
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    • pp.39-49
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    • 1998
  • In this work, fatigue tests by axial loading were carried out to investigate the effect of stress ratio on the growth behaviors of surface fatigue crack for SM45C steel and Al 2024-T4 alloy. The growth behaviors of surface crack have been monitored during fatigue process by measuring system attached CCTV and monitor. When the growth rates of surface crack were investigate by the concept of LEFM based on Newman-Raju's .DELTA.K, the dependence of stress ratio appears both SM45C steel and Al 2024-T4 alloy. Therefore, modified stress intensity factor range, .DELTA.K' [=(1+R)/sup n/.DELTA.K] are intorduced to eliminate the dependence of stress ratio. Using .DELTA.K', it is found that the dependence of stress ratio disappears both SM45C steel and Al 2024-T4 alloy.

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Fatigue Life Prediction by Elastic-Plastic Fracture mechanics for Surface Flaw Steel (표면결함재에 관한 탄소성 파괴역학에 의한 피로수명 예측)

  • Gang, Yong-Gu;Seo, Chang-Min;Lee, Jong-Sik
    • Journal of Ocean Engineering and Technology
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    • v.9 no.2
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    • pp.112-122
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    • 1995
  • In this work, prediction of fatigue life and fatigue crack growth are studied. 4th order polynominal function is presented to describe the crack growth behaviors from artifical pit of SM45C steel. Crack growth curves obtained from 4th order polyminal growth equations are in good agreement with experimental data The crack growth behaviors at arbitrary stress levels and investigated by the concept of elastic-plastic fracture mechanics using ${\Delta}J$. Fatigue life prediction are carried out by numerical integral method. Prediction lives obtained by proposed method in this study, is in good agreement with the experimental ones. Life prediction results calculated by using of ${\Delta}J$ better than those of ${\Delta}K$.

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