• Title/Summary/Keyword: Fatigue loading variation

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A Study on the Variation of the Mechanical Properties and Mode of the Hot-Rolled Mild Stell plate under Fatigue Loading (피로 하중을 받는 열간 압연 연강판재의 기계적 성질과 모우드 변화에 관한 연구)

  • Kim, Hak-Yoon;Lee, Seong-Ho
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.4
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    • pp.326-332
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    • 1995
  • Using natural frequency measurement method, which is one of NDT method, natural frequency of the hot-rolled mild steel plate(specimen) under fatigue loading was measured. Between the degradation of the specimen under fatigue loading and the variation of the natural frequency of the specimen was investigated. As a result, the degradation of the specimen was described and monitored as variation of natural frequency of specimen. The natural frequency of specimen decreased gradually under fatigue loading. This means the variation of material properties of specimen. Especially. It means the variation of Young's modulus of specimen.

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Effects with the Variation of Single Overload mode on Propagation Behavior of Fatigue Crack (단일과대하중의 작용모드 변화가 피로균열의 전파거동에 미치는 영향)

  • 송삼홍;이정무;신승만;홍석표;서기정
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2003.06a
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    • pp.1508-1512
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    • 2003
  • In this study, retardation behavior of fatigue crack under single overloading of the mixed mode state was experimentally investigated. To produce single overload in the mixed mode I+II state, the compact tension shear (CTS) specimen and loading device were used. The propagation tests for fatigue crack were performed under mode I and mixed-mode loading overloading afterwards. We examined the observed deformation aspects, the variation of fatigue life and crack propagation rate, and the aspects of retardation behavior from tests. The retardation effect of mixed-mode single overload on fatigue crack propagation behavior was smaller than that of mode I single overload. Also the loading modes of variable and constant amplitude loads have influence on the retardation behavior of fatigue cracks.

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The Analysis of Fatigue Damage of Connecting Rod under Various Load (다양한 하중을 받는 커넥팅 로드의 피로 파손 해석)

  • Cho, Jae-Ung;Choi, Doo-Seuk;Kim, Key-Sun
    • Transactions of the Korean Society of Automotive Engineers
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    • v.13 no.6
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    • pp.154-162
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    • 2005
  • This study investigates the fatigue life and the damage possibility of connecting rod by the fatigue tool of Ansys workbench. The case of constant fatigue loading variation 'Sine' becomes more stable than that of nonconstant loading but the magnitude of constant load becomes larger than that of nonconstant load. Among nonconstant fatigue loads, the case of 'SAE Bracket History' which is severest at the variation of load tends to be most unstable. The case of 'Sample History2' which becomes a little slow at the variation of load tends to be most stable. The maximum relative damage in case of 'SAE Bracket History' is occurred near the average stress '0' and this case can be shown to have the possibility to take more damage than another case.

The Mixed Mode fatigue Crack Propagation Behavior with the Variation of Stress Ratio (응력비 변화에 따른 혼합모드 피로균열 전파거동)

  • Song, Sam-Hong;Choi, Ji-Hoon;Lee, Jeong-Moo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.11
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    • pp.2287-2296
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    • 2002
  • Most cracks in the structure occur under mixed mode loading and those fatigue crack propagation behavior heavily depends on the stress ratio. So, it is necessary to study the fatigue behavior under mixed mode loading as the stress ratio changes. In this paper, the fatigue crack propagation behavior was respectively investigated at stress ratio 0.1, 0.3, 0.5, 0.7 and we changed the loading application angle into 0$^{\circ}$, 30$^{\circ}$, 60$^{\circ}$ to apply various loading mode. The mode I and II stress intensity factor of CTS specimen used in this study was calculated by the displacement extrapolation method using FEM (ABAQUS). Using both the experiment and FEM analysis, we have concluded the relationship between crack propagation rate and stress intensity factor range at each loading mode due to the variation of stress ratio. Also, when the crack propagated under given stress ratio and loading mode condition, we have concluded the dominant factors of the crack propagation rate at each case.

Effect of Mode II in The Fatigue Crack Propagation Behavior by Variation of Multilevel Loading Direction (다단계 하중방향 변화에 의한 피로균열 전파거동에서의 모드II 영향)

  • 홍석표;송삼홍
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.725-728
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    • 2004
  • In this study, the effect of mode II by variation of multilevel loading direction was experimentally investigated in the fatigue crack propagation behavior. To generate mixed-mode I+II loading state, the compact tension shear(CTS) specimen and loading device were used in this tests. The experimental method divided into three steps and three cases that were step I(0$^{\circ}$), step II(30$^{\circ}$, 60$^{\circ}$, 90$^{\circ}$),step III(0$^{\circ}$) and case I(0$^{\circ}$ ⇒ 30$^{\circ}$ ⇒ 0$^{\circ}$), case II(0$^{\circ}$ ⇒ 60$^{\circ}$ ⇒ 0$^{\circ}$), case III(0$^{\circ}$ ⇒ 90$^{\circ}$ ⇒ 0$^{\circ}$). The result of test, the step II affected to the step III in the all case. Specially, The fatigue crack propagation rate was faster and the fatigue life was smaller than of mixed mode I+II(30$^{\circ}$,60$^{\circ}$) due to the effect of mode II in the step III of the case III

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Study on the mechanical properties and rheological model of an anchored rock mass under creep-fatigue loading

  • Song, Yang;Li, Yong qi
    • Geomechanics and Engineering
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    • v.23 no.6
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    • pp.535-546
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    • 2020
  • The stress environment of deep rock masses is complex. Under the action of earthquakes or blasting, the strength and stability of anchored rock masses in fracture zones or faults are affected. To explore the variation in anchored rock masses under creep-fatigue loading, shear creep comparative testing of anchored marble specimens with or without fatigue loading is performed. Considering the damage variable of rock under fatigue loading, a rheological model is established to characterize the whole shear creep process of anchored rock masses under creep-fatigue loading. The results show that (1) the overall deformation of marble under creep-fatigue loading is larger than that under only shear creep loading, and the average deformation is increased by 18.3%. (2) By comparing the creep curves with and without fatigue loading, the two curves basically coincide when the first level stress is applied, and the two curves are stable with the increase in stress level. The results show that the strain difference among the specimens increases gradually in the steady-state stage and reaches the maximum at the fourth level. (3) The shear creep is described by considering the creep mechanical properties of anchored rock masses under fatigue loading. The accuracy of this creep-fatigue model is verified by laboratory tests, and the applicability of the model is illustrated by the fitting parameter R2. The proposed model provides a theoretical basis for the study of anchored rock masses under low-frequency earthquakes or blasting and new methods for the stability and reinforcement of rock masses.

Fatigue Life Predication of Impacted Laminates Under Block Loading (블록하중을 받는 충격손상 적층복합재료의 피로수명 예측)

  • Kim, Jeong-Gyu;Gang, Gi-Won;Yu, Seung-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.7
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    • pp.1089-1096
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    • 2001
  • This paper presents the fatigue behavior of composite materials with impact-induced damage under 2 level block loading. For this purpose, the 2 level block loading fatigue tests were performed on the impacted composite laminate. The fatigue life of the laminate under the block loading is greatly influenced by the impact damage; the effect of impact damage can be characterized by the present impact damage parameter. Based on this parameter, the model is developed to predict the fatigue life under block loading and the results by this model agree well with experimental results regardless of applied impact energy. Also, stochastic model is established to describe the variation of cumulative damage behavior and fatigue life due to the material nonhomogeneity.

Fatigue Crack Propagation Behavior in CTS Specimen Under Mixed-Mode Loading with Hole Defefects (원공 결함을 갖는 CTS 시험편의 혼합모드 하중 하에서의 피로균열 전파거동)

  • Song, Sam-Hong;Shin, Seung-Man;Lee, Jeong-Moo;Seo, Ki-Jeong
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.137-142
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    • 2003
  • In this study, the propagation behavior of fatigue crack effected hole defects was investigated under mixed-mode I+II loading. To create mixed-mode stress field at crack tip, the compact tension shear (CTS) specimen and loading device were used in this tests. The propagation experiments of fatigue crack were performed by changing of the loading application angle(${\phi}$) and the distance(L) estimated from pre-crack tip to hole center located side by side by side with a pre-crack. As L changes, the variation for propagation aspect of fatigue crack, fatigue life and crack propagation rate were examined under mixed-mode loading. Under mixed-mode loading, the propagation rate of fatigue crack increased while the propagation direction changed dramatically because of the interference of hole defects.

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Mixed Mode Fatigue Crack Propagation Behavior due to The Variation of Stress Ratio (응력비의 변화에 따른 혼합 모드 피로 균열 전파 거동)

  • Song, Sam-Hong;Choi, Ji-Hoon;Lee, Jeong-Moo
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.286-291
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    • 2001
  • Most cracks in the structure occur under mixed mode loadings and those propagation depend on the stress ratio very much. So, it is necessary to study the fatigue behavior under mixed mode loading as stress ratio changes. In this paper, fatigue crack propagation behavior was investigated respectively at stress ratio 0.1, 0.3, 0.5, 0.7 and we change loading application angle to $0^{\circ},\;30^{\circ},\;60^{\circ}$ to apply various loading. mode. The mode I and II stress intensity factors of CTS specimen used in this study were calculated by displacement extrapolation method using FEM(ABAQUS). Using both the study through the experiment and the theoretical study through FEM analysis, we studied the relation between crack propagation rate and stress intensity factor range at each loading mode due to the variation of stress ratio. Also, when the crack propagated under given stress condition and given loading mode condition, we studied what the dominant factors of the crack propagation rate were at each case.

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A Study on the Safety of Reinforced Concrete Structures under Fatigue Load (피로 하중을 받는 철근콘크리트 구조물의 안전성에 관한 연구)

  • 채원규
    • Journal of the Korean Society of Safety
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    • v.9 no.2
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    • pp.18-25
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    • 1994
  • In this thesis, the fatigue tests were performed on a series of reinforced concrete to Investigate the variation of strength and the safety of reinforced concrete structures under fatigue load. The specimens were of the same rectangular cross-section, of effective height 24cm and width 30cm and their span was 330cm. The three point loading system is used in the fatigue tests. In these tests, the fracture mode of reinforced concrete structures under fatigue load, relationship between the repeated loading cycles and the mid-span displacement of the specimens were observed. According to the test results, the following fatigue behavior of reinforced concrete specimens were observed. By increasing of the number of repeated loading cycles, the mid-span displacement became greater, however the Incremental amounts of the displacement were reduced. It could be also known that the inelastic strain energy of the doubly reinforced rectangular beams was larger than that of the singly reinforced rectangular beams as increasing the number of repeated loading cycles. Compliance of reinforced concrete structures tended to be reduced as increasing the repeated loading cycles, and the compliance of the doubly reinforced rectangular beams was generally smaller than that of the singly reinforced rectangular beams. Based on the above investigation, it could be concluded that the doubly reinforced rectangular beams under fatigue load were more efficient to resist the brittle fracture than the singly reinforced rectangular beams.

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