• 한국소음진동공학회논문집
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• 제18권1호
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• pp.101-109
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• 2008

The stability of a rotating cantilever pipe conveying fluid with a crack and tip mass is investigated by the numerical method. That is, the effects of the rotating angular velocity, mass ratio, crack severity and tip mass on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating pipe are derived by using the Euler-Bernoulli beam theory and the extended Hamilton's principle. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. Also, the crack is assumed to be in the first mode of fracture and always opened during the vibrations. When the tip mass and crack are constant, the critical flow velocity for flutter is proportional to the rotating angular velocity of pipe. In addition, the stability maps of the rotating pipe system as a rotating angular velocity and mass ratio ${\beta}$ are presented.

• International Journal of Concrete Structures and Materials
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• 제19권1E호
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• pp.25-32
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• 2007

The fracture energy evaluated from the previous experimental results can be simulated by using the modified singular fracture process zone (S-FPZ) model. The fracture model has two fracture properties of strain energy release rate for crack extension and crack close stress versus crack width relationship $f_{ccs}(w)$ for fracture process zone (FPZ) development. The $f_{ccs}(w)$ relationship is not sensitive to specimen geometry and crack velocity. The fracture energy rate in the FPZ increases linearly with crack extension until the FPZ is fully developed. The fracture criterion of the strain energy release rate depends on specimen geometry and crack velocity as a function of crack extension. The behaviors of micro-cracking, micro-crack localization and full development of the FPZ in concrete can be explained theoretically with the variation of strain energy release rate with crack extension.

• 대한기계학회논문집
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• 제13권5호
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• pp.947-951
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• 1989

본 연구에서는 디지틀식 균열속도 측정장치를 보완, 확장시켜 몇몇 고분자 (polymer)재료에 있어서의 동적 균열전파속도를 측정하였으며, 다른 연구자들의 실험 데이터와 비교하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.383-388
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• 2001

Effects of particle property variation of cone crack shape according to impact velocity in silicon carbide materials were investigated. The damage induced by spherical impact having different material and size was different according to materials. The size of ring cracks induced on the surface of specimen increased with increase of impact velocity within elastic contact conditions. The impact of steel particle produced larger ring cracks than that of SiC particle. In case of high impact velocity, the impact of SiC particle produced radial cracks by the elastic-plastic deformation at impact regions. Also percussion cone was formed from the back surface of specimen when particle size become large and its impact velocity exceeded a critical value. Increasing impact velocity, zenithal angle of cone cracks in SiC material was linearly decreasing not effect of impact particle size. An empirical equation, $\theta=\theta_{st}-\upsilon_p(180-\theta_{st})(\rho_p/\rho_s)^{1/2}/415$, was obtained from the test data as a function of quasi-static zenithal angle of cone crack($\theta_{st}$), the density of impact particle(${\rho}_p$) and specimen(${\rho}_s$). Applying this equation to the another materials, the variation of zenithal angle of cone crack could be predicted from the particle impact velocity.

• 대한기계학회논문집A
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• 제25권3호
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• pp.434-442
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• 2001

When the interfacial crack of two dissimilar isotropic bi-materials is propagated with constant velocity along the interface, stress and displacement components are derived in this research. The dynamic photoelastic experimental hybrid method for bimaterial is introduced. It is assured that stress components and dynamic photoelastic hybrid method developed in this research are valid. Separating method of stress component is introduced from only dynamic photoelastic fringe patterns. Crack propagating velocity of interfacial crack is 80∼85% (in case of aluminum, 24.3∼25.9%) of Rayleigh wave velocity of epoxy resin. The near-field stress components of crack-tip are similar with those of pure isotropic material under static or dynamic loading, but very near-field stress components of crack-tip are different from those.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.689-694
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• 2003

An iterative modal analysis approach is developed to determine the effect of transverse open cracks on the dynamic behavior of simply supported pipe conveying fluid subject to the moving mass. The equation of motion is derived by using Lagrange's equation. The influences of the velocity of moving mass and the velocity of fluid flow and a crack have been studied on the dynamic behavior of a simply supported pipe system by numerical method. The presence of crack results in higher deflections of pipe. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. Totally, as the velocity of fluid flow and the crack severity are increased, the mid-span deflection of simply supported pipe conveying fluid is increased. The time which produce the maximum dynamic deflection of the simply supported pipe is delayed according to the increment of the crack severity.

• 콘크리트학회논문집
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• 제15권1호
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• pp.52-59
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• 2003

동적 하중이 작용하는 콘크리트 CLWL-DCB 시험편에 대해 변위제어 파괴실험이 실시되었다. 381mm의 균열성장 동안 측정된 균열속도는 0.80mm/sec ~ 215m/sec이었다. 측정된 하중과 하중점-변위로부터 외부일 및 운동에너지와 변형에너지가 유도되었고, 에너지 균형에 필요한 파괴에너지가 각 균열속도의 균열성장에 대해 계산되었다. 실험의 결과에 요구되는 파괴에너지의 회귀식으로부터 연속적으로 성장하는 균열의 파괴저항이 계산되었다. 실험에 요구되는 파괴에너지에 대한 최대 표준오차는 3.2% 이하였다. 균열속도에 관계없이 약 28mm의 초기 균열성장 또는 미소균열의 성장에 대한 파괴저항의 증가율은 상대적으로 작았으며, 이후의 균열성장 또는 미소균열의 국부화에 대해 파괴저항의 기울기는 급격히 증가하여 균열속도에 따라 90∼145mm의 균열성장에서 최대 파괴저항이 되었다. 평균 185mm의 균열성장 동안 최대 파괴저항을 유지한 후 파괴저항은 균열속도가 빠를수록 급속히 감소하였다. 최대 파괴저항은 균열속도가 0.273m/sec보다 빠른 경우에 균열속도의 대수 값에 비례하여 142N/m에서 217N/m까지 증가하며, 균열속도가 빠를수록 관성력이 포함되지 않은 평균 파괴에너지율 215N/m와 유사한 값을 보였다. 콘크리트의 균열성장에 대한 파괴저항을 측정하기 위해서는 균열속도에 따라 최소한 90∼145mm의 안정 균열성장이 필요하다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.111-116
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• 2000

A semi-infinite interfacial crack propagated with constant velocity in two bonded anisotropic strip under out-of-plane clamped displacements is analyzed. The asymptotic stress and displacement fields near the crack tip are obtained, where the results get more general expressions applicable not only to isotropic/orthotropic materials but also to the extent of the anisotropic material having one plane of elastic symmetry for the interfacial crack. The dynamic stress intensity factor is obtained as a closed form, which is decreased as the velocity of crack propagation increases. The critical velocity where the stress intensity factor comes to zero is obtained, which agrees with the lower value between the critical values of parallel crack merged in the material 1 and 2 adjacent to the interface. The dynamic energy release rate is also obtained as a form related to the stress intensity factor.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2000년도 학술발표회 발표논문집
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• pp.284-289
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• 2000

This study is performed to evaluate an the crack properties and repair-reinforcement of concrete introduced crack. Materials used are portland cement, coarse aggregate, fine aggregate, unsaturated polyester resin and fly ash. Specimen is used beam of 76${\times}$76${\times}$412mm for measurement of pulse velocity, dynamic modulus of elasticity and bending strength and is introduced crack artificially. The following conclusions are drawn; Pulse velocity, dynamic modulus of elasticity and bending strength of concrete introduced crack is shown the lower 1.24∼11.91%, 3.42∼17.21% and 38.17∼61.0% than that of the control concrete, respectively. Pulse velocity, dynamic modulus of elasticity and bending strength of concrete repaired and reinforced crack is shown the higher 0.5∼2.60%, 1.57∼3.07% and 28.17∼47.25% than that of the concrete introduced crack and the lower than that of the control concrete, respectively.

• 대한기계학회논문집A
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• 제28권4호
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• pp.419-426
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• 2004

In this paper, studied about the effect of open crack and the moving mass on the dynamic behavior of simply supported pipe conveying fluid. The equation of motion is derived by using Lagrange's equation. The influences of the velocity of moving mass, the velocity of fluid flow and a crack have been studied on the dynamic behavior of a simply supported pipe system by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. Therefore, the crack is modelled as a rotational spring. Totally, as the velocity of fluid flow is increased, the mid-span deflection of simply supported pipe conveying fluid is increased. The position of the crack is located in the middle point of the pipe, the mid-span deflection of simply supported pipe presents maximum deflection.