• Journal of Mechanical Science and Technology
• /
• 제15권2호
• /
• pp.172-179
• /
• 2001

The effects of the interface and two holes located near the crack path in the hybrid specimen on the dynamic crack propagation behavior have been investigated using dynamic photoelasticity with the aid of Cranz-Shardin type high speed camera system. The dynamic stress field around the dynamically propagating interface crack tip in the three point bending specimens under a dynamic load applied by a hammer dropped from 0.6m high without initial velocity are recorded. The complex stress intensity factors for the dynamically propagating interface crack are extracted by using a overdeterministic least square method. Theoretical dynamic interface isochromatic fringe loops generated by using the numerically determined complex stress intensity factors are compared with the experimental results. Furthermore, the influence of the hole to the dynamic interface crack velocities has been investigated experimentally.

• 대한기계학회논문집
• /
• 제17권7호
• /
• pp.1710-1718
• /
• 1993

This paper investigates the problem of a crack approaching two circular holes in an orthotropic infinite plate. The stress intensity factors were obtained by using the modified mapping-collocation method. The present results show excellent agreement with existing solutions for a crack approaching two circular holes in an isotropic infinite plate. In the numerical examples, various types of cross-ply laminated composites were considered. To investigate the effect of orthotropy and geometry(d/R and a/(d-R)) on crack tip singularity, stress intensity factors were considered as functions of the normalized crack length. It is expected that the modified mapping-collocation method can be applied to the analysis of various kinds of cracks existing around the stress-concentration region of composite laminate.

• Journal of the Optical Society of Korea
• /
• 제19권6호
• /
• pp.673-678
• /
• 2015

Terahertz dual-band frequency selective surface filters made by perforating two different rectangular holes in molybdenum have been designed, fabricated and measured. Physical mechanisms of the dual-band resonant responses are clarified by three differently configured filters and the electric field distribution diagrams. The design process is straightforward and simple according to the physical concept and some formulas. Due to the weak coupling between the two neighboring rectangle holes with different sizes in the unit cell, good dual-band frequency selectivity performance can be easily achieved both in the lower and higher bands by tuning dimensions of the two rectangular holes. Three samples are fabricated, and their dual-band characteristics have been demonstrated by a THz time-domain spectroscopy system. Different from most commonly used metal-dielectric structure or metal-dielectric-metal sandwiched filters, the designed dual-band filters have advantages of easy fabrication and low cost, the encouraging results afforded by these filters could find their applications in dual-band sensors, THz communication systems and other emerging THz technologies.

• 한국유체기계학회 논문집
• /
• 제17권2호
• /
• pp.12-23
• /
• 2014

A parametric study on anti-vortex holes for turbine blade cooling was investigated numerically. Three-dimensional Reynolds-averaged Navier-Stokes equations and shear stress transport turbulence model were used for analysis of anti-vortex film cooling. Validation of numerical results was carried out comparing with experimental data. The cooling performance of anti-vortex holes was assessed by two geometric variables, the ratio of diameters of holes and the lateral distances between the primary hole and anti-vortex hole at blowing ratios of 0.5 and 1.0. The results showed that the spatially-averaged film-cooling effectiveness increases as the ratio of the diameters increases and the distance between the primary hole and anti-vortex hole decreases.

• Steel and Composite Structures
• /
• 제21권6호
• /
• pp.1211-1226
• /
• 2016

In this study, free vibration and damping characteristics of composite beams with holes are investigated, experimentally and numerically. Two types of samples with different fabrics are used: unidirectional and woven. The effects of diameter, number and location of circular holes on the vibration characteristics of composite beams are examined. The effects of rotation angle and minor to major diameter ratio of the elliptical hole are also investigated numerically. Moreover, the mode shapes of all types of beams are obtained numerically. According to the results, the natural frequency decreases with increasing hole diameter but increases very little with increasing the distance between the hole center and the clamped end. Damping ratio decreases by increasing the diameter of hole. But it fluctuates by increasing the diameters of holes of beam having three holes. Furthermore it decreases by increasing the distance between hole center and clamped end except for the range 50 mm to 100 mm.

• 설비공학논문집
• /
• 제11권5호
• /
• pp.692-699
• /
• 1999

The vortex tube is a sample device for separating a compressed gaseous fluid stream into two flows of high and low temperature without any chemical reactions. The phenomena of energy separation through the vortex tube were investigated experimentally, to see the effects of the number of nozzle holes on the energy separation. The experiment was carried out with the number of nozzle holes from 1 to 10 by varying inlet pressure and cold mass fraction. The experimental results were indicated that the effective number of nozzle holes for the best cooling performance was found as 4. Also, to find effective use in a given operation conditions, the temperature difference of cold air and the cooling capacity of vortex tube was compared. The result is that cooling capacity was more important than temperature difference of cold air.

• 한국패류학회지
• /
• 제27권3호
• /
• pp.253-259
• /
• 2011

Boring behaviour and drilling mechanism were investigated by visual observations. In this study, of two kinds of holes (the outer and inner holes) which are formed by drilling of boring gastropod Lunatia fortunei (Naticidae), the diameters of the outer holes are broader and larger than those of the inner holes, and their holes look like the crater in shape, as seen in all valves of bivalves bored by Naticidae species. Two kinds of glands (the accessory boring gland and accessory salivary gland) on the foots of boring gastropods have been investigated. Of them, it has been confirmed that only the accessory salivary glands on the foots secreted sulphuric (acidic) components in the mucus (secretion), while the accessory boring glands on the foots did not secrete their components. In this study, we confirmed that L. fortunei possess the accessory boring gland on the foot, as seen in most species in Naticidae. Accoeding to the results of the experiment of the blue litmus paper tests of the mucus (secretions) secreted from the accessory boring gland the color of the blue litmus paper did not turn red in color because chemical components of mucus (secretion) secreted from the accessory boring gland on the foot of L. fortunei (boring gastropod) were not acidic components. It is supposed that the mucus, which is secreted from the accessory boring gland, contained gelatin-like substances or enzymes without acidic components, as already reported in Naticidae species. Therefore, these substances may be involved in softening the surface of the valves of M. veneriformis. Consequently, it is assumed thar L. fortunei bores holes through the shells of molluscs by means of following 3 methods: (1) a softening of the calcareous shells of M. veneriformis with chemical secretions (including gellatin-like substances or enzyme except for acidic components) from the accessory boring glands, (2) mechanical rasping with the radula, (3) a combination of both. In this study, particularly, acidic components, which are involved in softening the surface of the shells, are not associated with the boring mechanism of L. fortunei because chemical acidic components were not detected in the mucus (secretion), as found in Naticidae species.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.181-186
• /
• 2003

An experimental study has been conducted to measure the temperature fields for two and three staggered rows of the rectangular shaped-holes with high turbulence intensity. 10 % turbulence intensity is obtained by installation of two kinds of grids which have different shapes. One grid which is installed at 30d upstream from center of 1st row of holes is composed of vertical cylinders of which diameter is 10 mm and center to center distance is 18 mm. The other installed 15d apart to upstream from center of 1st row of holes which has square pattern is constructed of 3 rum square bars and bar spacing is 25 mm. Temperature fields are measured by using a thermocouple rake which is attached on three-axis traversing system. The results show that the overall values are decreased and the thicker film of coolant is fanned downstream of rows of holes for high mainstream turbulence intensity.

• 한국항공우주학회지
• /
• 제31권3호
• /
• pp.79-84
• /
• 2003

홀 확장법은 홀 주위에 압축 잔류응력층을 생성시킴으로서 균열 발생을 지연시키는 방법으로 항공산업 분야에서 널리 사용되고 있다. 홀 확장 잔류응력의 분포는 홀 확장률, 맨드럴 삽입방향, 재료 물성치 등 여러 가지 홀 확장 피라미터에 따라 달라진다. 홀 확장 잔류응력층의 정확한 파악은 항공산업의 실제 설계에 있어서 매우 중요함에도 불구하고 이에 대한 연구는 상대적으로 부족하였다. 본 연구에서는 유한요소해석을 통하여 두 개의 인전한 홀에 홀 확장법을 적용하는 경우 대한 잔류응력 분포를 구하였다. 연구 결과 두개 홀에 동시에 홀 확장을 하는 경우가 순차적으로 홀 확장으로 하는 경우보다 더 유리한 잔류응력 분포를 얻을 수 있었다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집A
• /
• pp.304-310
• /
• 2001

Cracks at mechanical fastener holes usually nucleate as elliptical comer cracks at the faying surface of the mechanical joints and grow as elliptical arc through cracks after penetrating the opposite surface. In this study mode I, II and III stress intensity factors at two surface points of elliptical arc through cracks at mechanical fastener holes are analyzed by applying weight function method. The weight function method for two dimensional mixed-mode problem is extended to three dimensional one and it is verified.