• 제목/요약/키워드: dynamic stress intensity factors

검색결과 41건 처리시간 0.022초

2차원 Laplace 변환 경계요소법에 의한 이종재료 접합면 균열의 충격해석 (The impact analysis of interface crack in dissimilar materials using the 2-D laplace transformed BEM)

  • 김태규;조상봉;최선호
    • 대한기계학회논문집
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    • 제18권5호
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    • pp.1158-1168
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    • 1994
  • For BEM analyses of the impact problems of dissimilar materials, the connected multi-region method using perfect bonded conditions on the interface boundaries was added to two-dimensional Laplace transformed-domain BEM program for a single region analysis. It was confirmed that the BEM results of impact problems of a single-region and multi-regions for a homogeneous isotropic material are agreed well. The two-dimensional Laplace transformed-domain BEM program combined with connected multi-region method was applied to analyse several impact problems of dissimilar materials. Also the feasibility of BEM impact analyses was investigated for dissimilar materials by the analysis of the BEM results for impact problems of dissimilar materials in terms of physical aspects. As for an application, the two-dimensional Laplace transformed BEM concerning impact problems of cracks at the interface of dissimilar materials and the determinating process of the dynamic stress intensity factors by extrapolation method are presented in this paper.

Arias Intensity 액상화 평가기법의 적용성에 관한 연구 (A Study on the Applicability of Arias Intensity Liquefaction Assessment)

  • 황정태;이종근;신은철
    • 한국지반환경공학회 논문집
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    • 제14권6호
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    • pp.13-19
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    • 2013
  • 본 연구에서는 액상화 평가 대상지반을 선정하여 미국, 일본 등 액상화 발생지역에 적용한 사례가 있는 에너지를 기반으로 하는 Arias intensity 액상화 평가법을 적용하고, 적용성을 검토하기 위하여 기존의 원위치시험을 통한 액상화 간편예측법을 수행하여 평가결과를 비교하였다. 대상지반에 대한 액상화 평가결과, Hachinohe 지진과 Ofunato 지진의 실지진기록을 이용한 Arias Intensity 안전율은 간편예측 안전율과 유사하게 산정되었으며, 설계응답스펙트럼으로부터 작성된 인공지진의 경우 Arias Intensity 안전율은 간편예측 안전율과 비교하여 다소 차이가 나타났다. 액상화를 발생시키는 전단응력비와 발생강도는 응력과 에너지라는 서로 다른 개념으로 산정되지만, 간편예측법의 전단저항응력비와 Arias Intensity의 저항강도는 실지진에 따른 액상화 발생지역을 대상으로 한 표준관입시험 등 경험적 도표를 사용한다는 점에서 Hachinohe 지진과 Ofunato 지진의 경우 Arias Intensity 평가법과 응력개념의 간편예측법 사이에 비슷한 결과가 나타난 것으로 판단된다. 따라서, 에너지를 기반으로 하는 Arias Intensity 액상화 평가법은 응력개념의 간편예측법에서 고려하지 않은 실지진 기록에 대한 가속도, 지속시간, 진폭 등의 지진특성으로 야기되는 지반의 동적변화를 표현할 수 있음을 확인할 수 있었다.

Development of a System Observing Worker's Physiological Responses and 3-Dimensional Biomechanical Loads in the Task of Twisting While Lifting

  • Son, Hyun Mok;Seonwoo, Hoon;Kim, Jangho;Lim, KiTaek;Chung, Jong Hoon
    • Journal of Biosystems Engineering
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    • 제38권2호
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    • pp.163-170
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    • 2013
  • Purpose: The purpose of this study is to provide analysis of physiological, biomechanical responses occurring from the operation to lifting or twist lifting task appears frequently in agricultural work. Methods: This study investigated the changes of physiological factors such as heart rate, heart rate variability (HRV) and biomechanical factors such as physical activity and kinetic analysis in the task of twisting at the waist while lifting. Results: Heart rates changed significantly with the workload. The result indicated that the workload of 2 kg was light intensity work, and the workload of 12 kg was hard intensity work. Physical activity increased as the workload increased both on wrist and waist. Besides, stress index of the worker increased with the workload. Dynamic load to herniated discs was analyzed using inertial sensor, and the angular acceleration and torque increased with the workload. The proposed measurement system can measure the recipient's physiological and physical signals in real-time and analyzed 3-dimensionally according to the variety of work load. Conclusions: The system we propose will be a new method to measure agricultural workers' multi-dimensional signals and analyze various farming tasks.

살물선의 피로균열 전파해석과 피로강도 평가에 대한 연구 (A Study on Fatigue Crack Propagation Analysis and Fatigue Strength Evaluation for Bulk Carrier)

  • 엄동석;김충희
    • Journal of Welding and Joining
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    • 제11권4호
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    • pp.112-124
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    • 1993
  • It has been reported that fatigue damage sometimes occurred at the stress concentrated and dynamic loaded structural members of bulk carrier. In this paper, studies on fatigue strength of hull structures are reviewed, and the program for evaluating fatigue strength is developed. And the fatigue crack initiation and propagation on the end part of cargo hold frame of bulk carrier were calculated by FEM stress analysis and the fatigue strength evaluation program. These method can be applied not only to the crack initiation life but also to crack propagation life for the hull structural members at the hull design stage and be effective as the guideline to prevent the crack initiation or to estimate the fatigue strength for repairing of the fatigue damaged structures of real ships.

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Application of Mechanoluminescence for the Dynamic Visualization of an Alumina Fracture

  • Kim, Ji-Sik
    • Journal of Information Display
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    • 제11권1호
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    • pp.33-38
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    • 2010
  • The propagation of cracks was quantitatively analyzed in $Al_2O_3$ ceramic using the mechanoluminescence (ML) of $SrAl_2O_4$:Eu,Dy. The bridging zones behind the crack tip were clearly detected in the crack path of $Al_2O_3$ within a realistic time frame. The magnitudes and shapes of the bridging stress distributions changed with the advancing cracks. They continued to change with the change in the applied load even after the cessation of crack propagation. Effective toughening then commenced, and the applied stress intensity factors dramatically increased up to ~50 MPa $\sqrt{m}$. The expected $K_{Tip}$ values based on the instantaneous bridging stress distributions obtained from the ML observations deviated greatly from those obtained from the measurement using the conventional crack tip lengths; rather, they support the results obtained when bridging tips were used in the quasidynamic crack propagations.

Transient Response of a Permeable Crack Normal to a Piezoelectric-elastic Interface: Anti-plane Problem

  • Kwon, Soon-Man;Lee, Kang-Yong
    • Journal of Mechanical Science and Technology
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    • 제18권9호
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    • pp.1500-1511
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    • 2004
  • In this paper, the anti-plane transient response of a central crack normal to the interface between a piezoelectric ceramics and two same elastic materials is considered. The assumed crack surfaces are permeable. By virtue of integral transform methods, the electro elastic mixed boundary problems are formulated as two set of dual integral equations, which, in turn, are reduced to a Fredholm integral equation of the second kind in the Laplace transform domain. Time domain solutions are obtained by inverting Laplace domain solutions using a numerical scheme. Numerical values on the quasi-static stress intensity factor and the dynamic energy release rate are presented to show the dependences upon the geometry, material combination, electromechanical coupling coefficient and electric field.

Transient analysis of two dissimilar FGM layers with multiple interface cracks

  • Fallahnejad, Mehrdad;Bagheri, Rasul;Noroozi, Masoud
    • Structural Engineering and Mechanics
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    • 제67권3호
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    • pp.277-281
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    • 2018
  • The analytical solution of two functionally graded layers with Volterra type screw dislocation is investigated under anti-plane shear impact loading. The energy dissipation of FGM layers is modeled by viscous damping and the properties of the materials are assumed to change exponentially along the thickness of the layers. In this study, the rate of gradual change ofshear moduli, mass density and damping constant are assumed to be same. At first, the stress fields in the interface of the FGM layers are derived by using a single dislocation. Then, by determining a distributed dislocation density on the crack surface and by using the Fourier and Laplace integral transforms, the problem are reduce to a system ofsingular integral equations with simple Cauchy kernel. The dynamic stress intensity factors are determined by numerical Laplace inversion and the distributed dislocation technique. Finally, various examples are provided to investigate the effects of the geometrical parameters, material properties, viscous damping and cracks configuration on the dynamic fracture behavior of the interacting cracks.

Effect of Multiple Circular Holes on Fatigue Crack Growth Path

  • Won, Young-Jun;Nishioka, Toshihisa
    • Journal of Advanced Marine Engineering and Technology
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    • 제33권1호
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    • pp.112-119
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    • 2009
  • The mechanical fastening has some advantages in respect of the fastening strength and disassemble of the fastened parts. However, at the same time it has some dangerous factors, can cause fatigue crack initiation and propagation due to not only the static loading such as cargo and passengers but also the dynamic loading like vibrations which occur in the engines and the propellers. For this reason, the strength evaluation for the mechanical fastenings along with the sophisticated and detailed mechanical design and the safety evaluation should be executed, In this paper, we were carried out experiments to study fatigue crack growth paths in structures containing the multiple circular holes. It was investigated that how circular holes are affected on fatigue crack growth paths using the specimen consists of A5052-H112, which is widely used as the ship materials. It was found from the experimental results that the fatigue crack as if it is drawn to circular holes when crack tip approach to circular holes. However, it did not go into circular hole if there is the next circular hole. Therefore, the clarification of mechanism on the fatigue crack initiation and the propagation in structures containing the multiple circular holes can be expected in this study.

지진하중을 받는 I형 곡선거더 단경간 교량의 대리모델 기반 전역 민감도 분석 (Surrogate Model-Based Global Sensitivity Analysis of an I-Shape Curved Steel Girder Bridge under Seismic Loads)

  • 전준태;손호영;주부석
    • 한국재난정보학회 논문집
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    • 제19권4호
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    • pp.976-983
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    • 2023
  • 연구목적: 지진하중을 받는 교량 구조물의 동적 거동은 지진파의 특성 혹은 재료 및 기하학적 특성과 같은 많은 불확실성에 영향을 받는다. 하지만 모든 불확실성 인자가 교량 구조물의 동적 거동에 중요한 영향을 미치진 않는다. 영향성이 낮은 불확실성 인자까지 고려한 확률론적 내진성능 평가는 많은 계산비용이 요구되기 때문에 교량의 동적 거동에 미치는 영향을 고려하여 불확실성 인자는 식별되어야 한다. 따라서 본 연구는 I형 곡선 거더를 갖는 단경간 교량의 동적 거동에 영향을 미치는 주요 매개변수를 식별하기 위해 전역민감도 분석을 수행하였다. 연구방법: 지진파의 불확실성과 곡선 교량의 재료 및 기하학적 불확실성을 고려하여 유한요소 해석을 수행하였으며 해석결과를 기반으로 대리모델을 작성하였다. 결정계수와 같은 성능평가지료를 이용하여 대리모델을 평가하였으며 최종적으로 대리모델 기반의 전역 민감도 분석을 수행하였다. 연구결과: 지진하중을 받는 I형 곡선 거더의 응력응답에 가장 큰 영향을 미치는 불확실성 인자는 최대지반가속도(PGA), 교각의 높이(h), 강재의 항복응력(fy) 순으로 나타났다. PGA, h, fy의 주효과 민감도 지수는 각각 0.7096, 0.0839, 0.0352로 나타났으며 총 민감도 지수는 각각 0.9459, 0.1297, 0.0678로 나타났다. 결론: I형 곡선 거더의 응력응답은 입력운동의 불확실성에 대한 영향성이 지배적이며 각 불확실성 인자 사이의 교호작용에 큰 영향을 받는다. 따라서 입력운동의 개수 및 intensity measure과 같은 입력운동의 불확실성에 대한 추가적인 민감도 분석과 곡선거더의 개수 및 곡률과 같은 구조적 불확실성까지 고려한 총 민감도 분석은 필요하다.

베이지안 분류 기반 통합가뭄지수를 활용한 낙동강 유역의 미래 가뭄에 대한 수문학적 위험도 분석 (Evaluation of Future Hydrologic Risk of Drought in Nakdong River Basin Using Bayesian Classification-Based Composite Drought Index)

  • 김혁;김지은;김지영;유지영;김태웅
    • 대한토목학회논문집
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    • 제43권3호
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    • pp.309-319
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    • 2023
  • 최근 기후변화로 인해 기상재해의 발생빈도와 강도가 증가하고 있다. 우리나라는 지역별 기후 특성의 편차로 인해 기후변화에 따른 취약성 및 대응능력이 지역별로 차이가 크다. 특히 가뭄은 다양한 요인에 의해 발생하고, 기상학적, 수문학적, 농업적 영향 범위가 광범위하다. 따라서 가뭄에 효과적으로 대응하기 위해서는 다양한 요인을 고려할 수 있는 통합가뭄지수를 활용할 필요가 있으며, 기후변화를 고려한 미래 가뭄을 종합적으로 평가해야 한다. 본 연구에서는 베이지안 분류(DNBC) 기반의 통합가뭄지수를 활용하여 낙동강 유역의 미래 가뭄에 대한 수문학적 위험도(${\bar{R}}$)를 평가하였다. 우선, 관측자료와 기후변화 시나리오 자료를 이용하여 부문별 가뭄지수(SPI, SDI, ESI, WSCI)를 DNBC에 적용하여 통합가뭄지수를 산정하였다. 산정된 통합가뭄지수의 심도와 지속기간을 대상으로 이변량 가뭄빈도분석을 실시하고, 이변량 재현기간을 활용하여 수문학적 위험도를 산정하였다. 그 결과, S2(2021-2040) 기간에서 위험도가 가장 높게 나타났으며(${\bar{R}}$=0.572), 평균적으로 위험도가 가장 높은 지역은 밀양강(#2021)이었다(${\bar{R}}$=0.94). 단기 미래(2021-2040) 기간 동안 낙동강 유역의 수문학적 위험도는 전반적으로 큰 폭으로 상승하였으며, 중·장기 미래(2041-2070, 2071-2099) 기간 동안 낙동강 유역 북부의 위험도는 감소하고 남부의 위험도는 상승하였다.