• 한국정밀공학회지
• /
• 제13권12호
• /
• pp.70-77
• /
• 1996

Fatigue tests were carried out at high temperature on a Cr-Mo-V steel in order to assess the fatigue life of components used in power plants. The characteristics of high temperature fatigue were divided in terms of cycle-dependent fatigue and time-dependent fatigue, each crack propagation rate was examined with respect to fatigue J-integral range, .DELTA. J$_{f}$and creep J-integral range, .DELTA. J$_{c}$. The fatigue life was evaluated by analysis of J-integral value at the crack tip with a dimensional finite element method. The results obtained from the present study are summarized as follows : The propagation characteristics of high temperature fatigue cracks are determined by .DELTA. J$_{f}$for the PP(tensile plasticity-compressive plasticity deformation) and PC(tensile plasticity - compressive creep deformation) stress waveform types, and by .DELTA. J$_{c}$for the CP(tensile creep- compressive plasticity deformation) stress waveform type. The crack propagation law of high temperature fatigue is obtained by analysis of J-integral value at the crack tip using the finite element method and applied to examine crack propagation behavior. The fatigue life is evaluated using the results of analysis by the finite element method. The predicted life and the actual life are close, within a factor of 2.f 2.f 2.

• 대한토목학회논문집
• /
• 제3권4호
• /
• pp.143-148
• /
• 1983

크리이프, 건조수축(乾燥收縮), 노화현상(老化現象), 온도변형등(溫度變形等) 콘크리트구조물(構造物)의 시간의존성변형(時間依存性變形)에 대한 일반적(一般的) 수치해석법(數値解析法)을 제시(提示)하였다. 크리이프는 콘크리트의 연령(年齡)과 온도변화(溫度變化)의 함수인 중량적분(重量積分)으로 표시하였는데 특수(特殊)한 형태(形態)의 크리이프함수(凾數)를 사용함으로써 효과적(効果的)인 수치해석(數値解析)이 가능(可能)하게 되었다. 수치해석예(數値解析例)를 통하여 이 방법(方法)의 정확성(正確性)을 입증하였다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
• /
• pp.147-148
• /
• 2010

콘크리트 구조물의 재령종속적 거동에 대한 유도된 구성관계의 예측특성과 정도 분석을 목적으로 세 종류의 실험을 수행하였다. 이 실험은 구성관계를 정의하기 위해 요구되는 건조수축과 크리프 및 탄성계수발현에 관한 세 기본관계식을 유도하기 위한 원통형 공시체 실험과 원통형공시체 내에 축방향 철근을 매립한 철근매립형 공시체 축하중 실험 및 자중과 함께 등분포하중을 받는 RC 보 실험으로 구성하였다.

• Geomechanics and Engineering
• /
• 제21권2호
• /
• pp.215-226
• /
• 2020

The magnitude and distribution of tunnel deformation were widely discussed topics in tunnel engineering. In this paper, a three-dimensional (3D) finite element program was used for the analysis of various horseshoe-shaped opening expressway tunnels under different geologies. Two rock material models - Mohr-Coulomb and Hoek-Brown were executed in the process of analyses; and the results show that the magnitude and distribution of tunnel deformation were close by these two models. The tunnel deformation behaviors were relevant to many factors such as cross-sections and geological conditions; but the geology was the major factor to the normalized longitudinal deformation profile (LDP). If the time-dependent factors were neglected, the maximum displacements were located at the distance of 3 to 4 tunnel diameters behind the excavation face. The ratios of displacement at the excavation face to the maximum displacement were around 1/3 to 1/2. In general, the weaker the rock mass, the larger the ratio. The displacements in front of the excavation face were decreased with the increasement of distance. At the distance of 1.0 to 1.5 tunnel diameter, the displacements were reduced to one-tenth of the maximum displacement.

• 대한기계학회논문집
• /
• 제14권6호
• /
• pp.1365-1381
• /
• 1990

본 연구에서는 Kant 등이 제안한 고차판이론의 C연속변위 유한요소 모델을 사 용하여 충격자와 적층판의 저속 충격 응답에 대하여 연구하여 그 결과를 Mindlin의 판 이론에 의한 계산 결과와 비교하고, 경계 조건의 영향 및 충격자의 충격속도, 질량변 화에 대한 접촉력의 변화를 고찰하고자 한다.

• Structural Engineering and Mechanics
• /
• 제22권5호
• /
• pp.563-574
• /
• 2006

This paper studies mechanical behavior of the superelastic shape memory alloy (SMA) rods in terms of local deformations and time via tensile loading-unloading cycles for both ends fixed end constraints. Besides the unique stress induced martensitic transformation (SIMT), SMA's time dependent behavior when it is in mixed-phase condition upon loading and unloading, also need careful attention with a view of investigating the local deformation of the structural elements made of the same material. With this perspective, the so-called stress-relaxation tests have been performed to demonstrate and investigate the local strains-total strains relationships with time, particularly, during the forward SIMT. Some remarkable phenomena have been observed pertaining to SIMT, which are absent in traditional materials and those unique phenomena have been explained qualitatively. For example, at the stopped loading conditions the two ends (fixed end and moving end of the tensile testing machine) were in fixed positions. So that there was no axial overall deformation of the specimen but some notable increase in the axial local deformation was shown by the extensometer placed at the middle of the SMA specimen. It should be noted that this peculiar behavior termed as 'inertia driven SIMT' occurs only when the loading was stopped at mixed phase condition. Besides this relaxation test for the SMA specimens, the same is performed for the mild steel (MS) specimens under similar test conditions. The MS specimens, however, show no unusual increase of local strains during the stress relaxation tests.

• 한국자동차공학회논문집
• /
• 제18권4호
• /
• pp.121-126
• /
• 2010

The automotive weather strip has functions of isolating of water, dust, noise and vibration from outside. To achieve good sealing performance, weather strip should be designed to have the high contact force and wide contact area. However, these design causes excessive permanent deformation of weather strip. The causes of permanent deformation is generally explained to be the chemical material detrioration and physical variation and cyclic loading, etc. This paper introduces a numerical method to predict the permanent deformation using the time dependent viscoelastic model which is represented by Prony series in ABAQUS. Uniaxial tension and creep tests were conducted to obtain the material data. And the lab. test for the permanent deformation was accelerated during shorter time, 300 hours. The permanent deformation of weather strip was successfully predicted under the different loading conditions and different section shapes using the suggested numerical process.

• Geomechanics and Engineering
• /
• 제4권1호
• /
• pp.67-78
• /
• 2012

Soil foundations exhibit significant creeping deformation, which may result in excessive settlement and failure of superstructures. Based on the theory of viscoelasticity and fractional calculus, a fractional Kelvin-Voigt model is proposed to account for the time-dependent behavior of soil foundation under vertical line load. Analytical solution of settlements in the foundation was derived using Laplace transforms. The influence of the model parameters on the time-dependent settlement is studied through a parametric study. Results indicate that the settlement-time relationship can be accurately captured by varying values of the fractional order of differential operator and the coefficient of viscosity. In comparison with the classical Kelvin-Voigt model, the fractional model can provide a more accurate prediction of long-term settlements of soil foundation. The determination of influential distance also affects the calculation of settlements.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.1407-1412
• /
• 2003

In MEMS devices, packaging induced stress or stress induced structure deformation become increasing concerns since it directly affects the performance of the device. In this paper, deformation behavior of MEMS gyroscope package subjected to temparature change is investigated using high-sensitivity $Moir{\acute{e}}$ interferometry. Using the real-time $Moir{\acute{e}}$ setup, fringe patterns are recorded and analyzed at several temperatures. Temperature dependent analyses of warpages and extensions/contractions of the package are presented. Linear elastic behavior is documented in the temperature region of room temperature to $125^{\circ}C$. Analysis of the package reveals that global bending occurs due to the mismatch of thermal expansion coefficient between the chip, the molding compond and the PCB.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2009년도 춘계 학술발표회
• /
• pp.164-178
• /
• 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.