• Title/Summary/Keyword: Creep Deformation

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Time-dependent creep analysis of a functionally graded beam with trapezoidal cross section using first-order shear deformation theory

  • Mirzaei, Manouchehr Mohammad Hosseini;Loghman, Abbas;Arefi, Mohammad
    • Steel and Composite Structures
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    • v.30 no.6
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    • pp.567-576
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    • 2019
  • Time-dependent creep analysis of a rotating functionally graded cantilever beam with trapezoidal longitudinal cross section subjected to thermal and inertia loading is investigated using first-order shear deformation theory (FSDT). The model described in this paper is a simple simulation of a turbine blade working under creep condition. The material is a metal based composite reinforced by a ceramic where the creep properties of which has been described by the Sherby's constitutive model. All mechanical and thermal properties except Poisson's ratio are assumed to be variable longitudinally based on the volume fraction of constituent. The principle of virtual work as well as first order shear deformation theory is used to derive governing equations. Longitudinal distribution of displacements and stresses are investigated for various volume fractions of reinforcement. Method of successive elastic solution is employed to obtain history of stresses and creep deformations. It is found that stresses and displacements approach their steady state values after 40000 hours. The results presented in this paper can be used for selection of appropriate longitudinal distribution of reinforcement to achieve the desired stresses and displacements.

Modified 𝜃 projection model-based constant-stress creep curve for alloy 690 steam generator tube material

  • Moon, Seongin;Kim, Jong-Min;Kwon, Joon-Yeop;Lee, Bong-Sang;Choi, Kwon-Jae;Kim, Min-Chul;Han, Sangbae
    • Nuclear Engineering and Technology
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    • v.54 no.3
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    • pp.917-925
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    • 2022
  • Steam generator (SG) tubes in a nuclear power plant can undergo rapid changes in pressure and temperature during an accident; thus, an accurate model to predict short-term creep damage is essential. The theta (𝜃) projection method has been widely used for modeling creep-strain behavior under constant stress. However, many creep test data are obtained under constant load, so creep rupture behavior under a constant load cannot be accurately simulated due to the different stress conditions. This paper proposes a novel methodology to obtain the creep curve under constant stress using a modified 𝜃 projection method that considers the increase in true stress during creep deformation in a constant-load creep test. The methodology is validated using finite element analysis, and the limitations of the methodology are also discussed. The paper also proposes a creep-strain model for alloy 690 as an SG material and a novel creep hardening rule we call the damage-fraction hardening rule. The creep hardening rule is applied to evaluate the creep rupture behavior of SG tubes. The results of this study show its great potential to evaluate the rupture behavior of an SG tube governed by creep deformation.

Creep Deformation Characteristics of Polycrystalline Ice and its Numerical Simulation in the Flow of Polar Glaciers (극지 빙하유동에 있어서 Polycrystalline Ice의 Creep 변형특성 수치 시뮬레이션)

  • 최경식
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.2 no.2
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    • pp.59-66
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    • 1990
  • Various types of ice distribution under low temperature greatly influence the environment of the Arctic and Antarctic Oceans. To understand fundamentals of ice properties such as Polar glaciers, icebergs and sea ice, this study focuses on the material behaviors and failure mechanisms of polycrystalline ice. Utilizing the continuum damage theory, a three-dimensional constitutive model to describe creep deformation characteristics in the glacial flow is developed in consideration of micro-cracking as the major physical process of ice deformation. The numerical model is compared with the published experimental data especially in uniaxial constant stress creep tests. The model can simulate primary and secondary creeps as well as tertiary creep characteristics due to the microcrack accumulation.

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Creep analysis of a rotating functionally graded simple blade: steady state analysis

  • Mirzaei, Manouchehr Mohammad Hosseini;Arefi, Mohammad;Loghman, Abbas
    • Steel and Composite Structures
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    • v.33 no.3
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    • pp.463-472
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    • 2019
  • Initial thermo-elastic and steady state creep deformation of a rotating functionally graded simple blade is studied using first-order shear deformation theory. A variable thickness model for cantilever beam has been considered. The blade geometry and loading are defined as functions of length so that one can define his own blade profile and loading using any arbitrary function. The blade is subjected to a transverse distributed load, an inertia body force due to rotation and a distributed temperature field due to a thermal gradient between the tip and the root. All mechanical and thermal properties except Poisson's ratio are assumed to be longitudinally variable based on the volume fraction of reinforcement. The creep behaviour is modelled by Norton's law. Considering creep strains in stress strain relation, Prandtl-Reuss relations, Norton' law and effective stress relation differential equation in term of effective creep strain is established. This differential equation is solved numerically. By effective creep strain, steady state stresses and deflections are obtained. It is concluded that reinforcement particle size and form of distribution of reinforcement has significant effect on the steady state creep behavior of the blade.

Experimental Investigations of Combination Effects of Installation Damage and Creep Deformation on Long-Term Design Strength of Geogrids (지오그리드의 장기설계인장강도에 미치는 시공시 손상 및 크리프 변형 복합효과에 대한 실험적 평가)

  • Cho, Sam-Deok;Lee, Kwang-Wu;Oh, Se-Yong;Lee, Do-Hee
    • Journal of the Korean Geosynthetics Society
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    • v.4 no.4
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    • pp.23-37
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    • 2005
  • The factors affecting the long-term design strength of geogrid can be classified into factors on creep deformation, installation damage, temperature, chemical degradation and biological degradation. Especially, creep deformation and installation damage are considered as main factors to determine the long-term design strength of geogrid. Current practice in the design of a reinforced soil structures is to calculate the long-term design strength of a geosynthetic reinforcement damaged during installation by multiplying the two partial safety factors, $RF_{ID}$ and $RF_{CR}$. This method assumes that there is no evaluation of synergy effect between installation damage and creep deformation of geogrids. This paper describes the results of a series of experimental study, which are carried out to assess the combined effect of the installation damage and the creep deformation for the long-term design strength of geogrid reinforcements. A series of field tests was carried out to assess installation damage of various geogrids with respect to different fill materials, and then creep tests are conducted to evaluate the creep deformation of both undamaged and damaged geogrids. The results indicated that the tensile strength reduction factors, RF, considering the combined effect between the installation damage and the creep deformation is less than that calculated by the current design method.

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Effect of Interaction Between Dislocation and Nitrides on High Temperature Deformation Behavior of12%Cr-15%Mn Austenitic Steels (전위와 질화물의 상호작용이 12%Cr-15%Mn 오스테나이트강의 고온변형거동에 미치는 영향)

  • 배동수
    • Journal of Ocean Engineering and Technology
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    • v.15 no.3
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    • pp.58-62
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    • 2001
  • The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high n austenitic steels. After measuring the internal stress in minimum creep rate state under applied stress of 236MPa at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band widths and values of internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

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Interaction between dislocation and nitride precipitates during high temperature deformation behaviors of 12%Cr-15%Mn austenitic steels (12%Cr-15%Mn 오스테나이트강의 고온변형거동중의 전위와 질화물의 상호작용)

  • 배동수
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.05a
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    • pp.332-337
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    • 2001
  • The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high Mn austenitic steels. After measuring the internal stress in minimum creep rate at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band width of effective stress and internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

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Creep Analysis for the Pressurized Water Reactor Spent Nuclear Fuel Disposal Canister (가압경수로 고준위페기물 처분용기에 대한 크립해석)

  • Ha Joon-Yong;Choi Jong-Won;Kwon Young-Joo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.17 no.4
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    • pp.413-421
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    • 2004
  • In this paper, a structural analysis for the pressurized water reactor(PWR) spent nuclear fuel disposal canister which is deposited under the 500m deep underground is carried out to predict the creep deformation of the canister while the underground water and swelling bentonite pressure are applied on the canister. Usually the creep deformation may be caused due to the Pressure and the high heat applied to the canister even though additional external loads are not applied to the canister. These creep deformations depend on the time. In this paper, oかy the underground water and bentonite swelling Pressure are considered for the creep deformation analysis of the canister, because the heat distribution inside canister due the spent fuel is not simple and depends on time. A proper creep function is adopted for the creep analysis. The creep analysis is carried out during $10^8$ seconds. The creep analysis results show that the creep strains are very small and these strains occur usually in the lid and bottom of the canister not in the cast iron insert. A much smaller strain is found in the cast iron insert. Hence, the creep deformation doesn't affect the structural safety of the canister, and also the creep stress which shows the stress relaxation phenomenon doesn't affect the structural safety of the canister.

Creep Modelling of Reinforced Earth using Power Law-based Creep Models (Power Law 기반의 크리프 모델을 이용한 보강토 구조물의 크리프 모델링)

  • Kim, Jae-Wang;Kim, Sun-Bin;Yoo, Chung-Sik
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.03a
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    • pp.164-178
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    • 2009
  • The importance of long-term performance of reinforced earth structures has been gaining its attention as the use of reinforced earth structures as load supporting structures is increasing. When using reinforced earth structures as loading supporting structures the stability as well as serviceability requirements must be met. In that respect the time-dependent long term deformation characteristics should be well understood. In this study the applicability of power law-based creep models for modeling of creep deformation of the components of reinforced earth structures are examined.

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Dynamic Compressive Creep of Extruded Ultra-High Molecular Weight Polyethylene

  • Lee, Kwon-Yong;David Pienkowski;Lee, Sungjae
    • Journal of Mechanical Science and Technology
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    • v.17 no.9
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    • pp.1332-1338
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    • 2003
  • To estimate the true wear rate of polyethylene acetabular cups used in total hip arthroplasty, the dynamic compressive creep deformation of ultra-high molecular weight polyethylene (UHMWPE) was quantified as a function of time, load amplitude, and radial location of the specimen in the extruded rod stock. These data were also compared with the creep behavior of polyethylene observed under static loading. Total creep strains under dynamic loading were only 64%, 70%, and 61% of the total creep strains under static loading at the same maximum pressures of 2 MPa,4 MPa, and 8 MPa, respectively. Specimens cut from the periphery of the rod stock demonstrated more creep than those cut from the center when they were compressed in a direction parallel to the extrusion direction (vertical loading) whereas the opposite was observed when specimens were compressed in a direction perpendicular to the extrusion direction (transverse loading). These findings show that creep deformation of UHMWPE depends upon the orientation of the crystalline lamellae.