• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.37-42
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• 2003

The problem of an orthotropic material with a central crack is studied. The material is subjected to uniform biaxial loading along its boundary. The normal stress ratio theory is applied to predict fracture strength behavior in cracked orthotropic material. The dependence of the critical stress with respect to the biaxial loading and the crack orientation is discussed. Our analysis shows significant effects of biaxial loading on the critical stress. The additional tenn in the asymptotic expansion of the crack tip stress field appears to provide more accurate critical stress prediction.

• 해양환경안전학회지
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• 제4권2호
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• pp.43-52
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• 1998

Generally, the navigational safety of a ship under various loading conditions is evaluated by a loading manual. However, the loading manual handles only statical factors such as weight and buoyancy of ship without including any wave conditions. Practically ship's safety is much concerned with the occurrences on the rough sea as propeller racing, rolling, deck wetness, vertical acceleration, lateral acceleration, slamming and so on. The purpose of this paper is to present a synthetic and practical evaluation method of navigational safety using the integrated seakeeping performance index(ISPI) under loading conditions of ship in seaways. The method is calculated by means of the ISPI by measuring only vertical acceleration. Judgement of dangerousness is carried out for four lading conditions : homogeneous full loaded, half loaded, heavy ballast loaded, and normal ballast loaded conditions. In developing the practical evaluation system of navigational safety, it is useful to solve the difficulties in measuring factors by sensors. And by applying the evaluation diagrames, navigators are able to avoid dangerousness by keeping away of the danger encountering angle of wave direction which the diagram shows.

• Geomechanics and Engineering
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• 제35권5호
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• pp.475-486
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• 2023

Ballast particles have an irregular shape and are discrete in nature. Due to the discrete nature of ballast, it exhibits complex mechanical behaviour under loading conditions. The discrete element method (DEM) can model the behaviour of discrete particles under a multitude of loading conditions. DEM is used in this paper to simulate a series of three-dimensional direct shear tests in order to investigate the shear behaviour of railway ballast and its interaction at the microscopic level. Particle flow code in three dimension (PFC3D) models the irregular shape of ballast particles as clump particles. To investigate the influence of particle size distribution (PSD), real PSD of Indian railway ballast specification IRS:GE:1:2004, China high-speed rail (HSR) and French rail specifications are generated. PFC3D built-in linear contact model is used to simulate the interaction of ballast particles under various normal stresses, shearing rate and shear box sizes. The results indicate how shear resistance and volumetric changes in ballast assembly are affected by normal stress, shearing rate, PSD and shear box size. In addition to macroscopic behaviour, DEM represents the microscopic behaviour of ballast particles in the form of particle displacement at different stages of the shearing process.

• 한국구조물진단유지관리공학회 논문집
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• 제21권1호
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• pp.9-14
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• 2017

본 연구는 일반철근과 FRPH Bar를 주철근으로 한 철근 콘크리트 보부재를 대상으로 정적실험 및 반복하중 재하실험을 수행하여 에너지 소산성능 및 반복하중 저항성능을 분석하였다. 실험을 위하여 24MPa의 설계강도를 가진 콘크리트 보부재($200{\times}200{\times}2175mm$)를 제작하였으며, 4점 휨 시험을 수행하여 초기균열하중, 항복하중, 파괴하중을 측정하였다. 정적하중 재하실험을 통해 각 시험체에 대한 항복하중과 파괴강도를 측정하였는데, 항복하중은 RC보에서는 48.9kN, FRPH 보에서는 36kN으로 평가되었으며, 파괴하중은 두 시험체 모두 50kN의 강도를 보였다. 정적하중-처짐 결과에서는 FRPH 보는 RC보에 비하여 인장경화특성을 나타내는데, 이는 FRPH bar의 인장경화 특성에 기인한다. 반복하중하에서 FRPH bar를 가진 보에서는 일반 RC보와는 다르게 작은 폭의 균열이 넓게 발생하였으며, 우수한 처짐 복원력을 나타내었다. 정적 동적 에너지 비율을 이용한 에너지 소산능력에서는 RC보에서는 0.62, FRPH 보에서는 0.83으로 평가되었으며, 이를 통해 FRPH를 가진 보부재에서 효과적으로 반복하중에 대하여 저항함을 알 수 있다.

• 한국지반공학회논문집
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• 제30권2호
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• pp.53-64
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• 2014

이 연구에서는, 균질한 재성형 점토를 이용한 실내시험을 통해 정규압밀 영역에서의 하중재하기간이 점성토의 압축 및 장기압밀 특성에 미치는 영향을 명확히 하고자 하였다. 또한 각 하중재하기간에 따른 현장에서의 유효상재하중에 해당하는 초기압밀하중을 변화시킨 장기압밀 시험을 수행하여 표준압밀시험시의 하중단계별 재하방법과 하중재하기간의 증가에 따른 압축곡선의 특성을 비교/분석하여 하중재하기간에 따라 최종침하량을 예측하는 방법을 제안하고자 하였다. 연구 결과 하중재하기간에 따른 점성토의 압축특성은 초기압밀하중을 가한 후 하중재하기간이 증가할수록 주어진 단계에서의 압밀후반부의 2차압밀의 증가로 선행압밀하중이 약간씩 감소하는 경향을 나타내었다. 그와 동시에 2차압밀이 유사과압밀 현상 및 점토골격의 안정화를 유발하여 정규압밀영역에서의 압축지수에 미치는 영향은 미미했으며 과압밀영역에서는 유사과압밀 현상으로 재압축지수의 증가를 유발하는 것으로 나타났다.

• 펄프종이기술
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• 제31권5호
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• pp.57-72
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• 1999

Traditional theories of the tensile failure of paper have assumed that uniform strain progresses throughout the sheet until an imperfection within the structure causes a catastrophic break. The resistance to tensile elongation is assumed to be elastic , at first, throughout the structure, followed by an overall plastic yield. However, linear image strain analysis (LISA) has demonstrated that the yield in tensile loading of paper is quite non-uniform throughout the structure, Traditional theories have failed to define the flaws that trigger catastrophic failure. It was assumed that a shive or perhaps a low basis weight area filled that role. Studies of the fracture mechanics of paper have typically utilized a well-defined flaw around which yield and failure could be examined . The flaw was a simple razor cut normal to the direction of tensile loading. Such testing is labeled mode I analysis. The included fla in the paper was always normal to the tensile loading direction, never at another orientation . However, shives or low basis weight zones are likely to be at random angular orientations in the sheet. The effects of angular flaws within the tensile test were examined. The strain energy density theory and experimental work demonstrate the change in crack propagation from mode I to mode IIas the initial flaw angle of crack propagation as a function of the initial flaw angle is predicted and experimentally demonstrated.

• Structural Engineering and Mechanics
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• 제60권1호
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• pp.1-19
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• 2016

In this study, the supersonic panel flutter of doubly curved composite sandwich panels with variable thickness is considered under aerothermoelastic loading. Considering different radii of curvatures of the face sheets in this paper, the thickness of the core is a function of plane coordinates (x,y), which is unique. For the first time in the current model, the continuity conditions of the transverse shear stress, transverse normal stress and transverse normal stress gradient at the layer interfaces, as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of the sandwich panel are satisfied. The formulation is based on an enhanced higher order sandwich panel theory and the vertical displacement component of the face sheets is assumed as a quadratic one, while a cubic pattern is used for the in-plane displacement components of the face sheets and the all displacement components of the core. The formulation is based on the von $K{\acute{a}}rm{\acute{a}}n$ nonlinear approximation, the one-dimensional Fourier equation of the heat conduction along the thickness direction, and the first-order piston theory. The equations of motion and boundary conditions are derived using the Hamilton principle and the results are validated by the latest results published in the literature.

• Computers and Concrete
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• 제23권6호
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• pp.409-419
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• 2019

In the present study, effect of size and placement of cubic specimens on compressive strength of self-compacting lightweight concrete (SCLC) were considered. To do so, 81 specimens of different sizes (50 mm, 75 mm, 100 mm, and 150 mm) were prepared by using three different mixes of SCLC. Results of the cured specimens were then used in regression analyses to find predictive equations with regard to both the placement direction and the size. Test results showed that the strength ratio in cases in which the direction of loading and placement were parallel, were higher than those specimens, whose configurations were normal between loading and placement. In addition, strength ratios in SCLC mixes were slightly higher than those are for self-compacting normal weight concrete. In order to analyze the effect of size on compressive strength the conventional size effect law as well as the modified size effect law (MSEL) were used. Besides, the convergence criterion of nonlinear regression process of size effect study has been discussed. Analyses of the results showed that the unconstraint nonlinear regression in size effect study of SCLC mixes could lead to erroneous results.

• 한국안전학회지
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• 제37권5호
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• pp.1-6
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• 2022

In this study, to confirm the effects of the mixed load of normal and shear forces acting on a fixing bolt, fatigue design criteria were developed by varying the loading angle and conducting tensile and fatigue tests. After evaluating and comparing the test results under different loading angles, the evaluation criteria were selected. These evaluation criteria were then applied to develop the design criteria. An Arcan fixture was designed and manufactured to simultaneously apply a mixed load of normal and shear forces to the fixing bolt of a turntable, and a fatigue test was conducted. S-N diagrams for various loading angles were obtained, and a 1% P-S-N diagram of failure probability was determined using statistical processing techniques. Our results show that failures of the fixing bolt can be prevented using these diagrams as a basis for developing fatigue design criteria.

• 대한물리치료과학회지
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• 제7권1호
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• pp.285-294
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• 2000

80 persons who don't have past history of cardiopulmonary and neuromuscular disease. The results were as follow; 1. PCI(Physiological Cost Index) value without loading to ankle were significantly increased compared to 1kg, and 2kg (p<0.01). 2. Female Subjects showed more increased PCI value in without loading and lkg, 2kg loading compared to male subjects (p<0.01). 3. In every PCI condition the difference among height groups was observed (p<0.01). 4. The difference among weight groups in each PCI condition was observed (p<0.01). These results showed that energy consumption was increased according to loading on the ankle during gait so weight of orthosis or prosthesis must be considered when choosing them and during gait training with these ones.