• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 춘계학술대회 논문집
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• pp.454-459
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• 2003

The paper will present chip formation mechanism and surface integrity generation mechanism based on the systematical experimental tests. Some basic factors such as the end milling cutter tooth number, cutting forces, cutting temperature, cutting vibration, the chip status, the surface roughness, the hardness distribution and the metallographic texture of the machined surface layer are involved. the chip formation mechanism is typical thermal plastic shear localization at high cutting speed with less number og shear ribbons and bigger shear angle than at low speed, which means lack of chip deformation. The high cutting speed with much more cutting teeth will be beneficial to the reduction of cutting forces, enlarge machining stability region, depression of temperature increment, auti-fatigability as well as surface roughness. The burrs always exists both at low cutting speed and at high cutting speed. So the deburr process should be arranged for milling titanium alloy in any case.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.397-402
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• 2003

This paper presents strut-and-tie models for predicting shear strength of RC interior beam-column joints considering the plastic hinge rotation of adjacent beams. On seismic design of frame system, it is controlled beams to occur plastic hinges and to be ductile so as to dissipate earthquake energy efficiently. The plastic hinge deformation of beams is used as analysis parameter in terms of strain of beam tensile bars at column face. The shear strengths of beam-column joints are evaluated by combining direct strut mechanism with truss mechanism. It is assumed that the max force transferred by direct strut mechanism is based on the strength of cracked concrete element, and that by truss mechanism is based on bond capacity.

• Steel and Composite Structures
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• 제48권2호
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• pp.131-143
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• 2023

The CFRP bar was used to achieve more ductile and durable headed-stud shear connectors in composite components. Three series of push-out tests were firstly conducted, including specimens reinforced with pure steel fibers, steel and CFRP bars. The distributed stress was measured by the commercial PPP-BOTDA (Pre-Pump-Pulse Brillouin optical time domain analysis) optical fiber sensor with high spatial resolution. A series of numerical analyses using non-linear FE models were also made to study the shear force transfer mechanism and crack response based on the test results. Test results show that the CFRP bar increases the shear strength and stiffness of the large diameter headed-stud shear connection, and it has equivalent reinforcing effects on the stud shear capacity as the commonly used steel bar. The embedded CFRP bar can also largely improve the shear force transfer mechanism and decrease the tensile stress in the transverse direction. The parametric study shows that low content steel fibers could delay the crack initiation of slab around the large diameter stud, and the CFRP bar with normal elastic modulus and the standard reinforcement ratio has good resistance to splitting crack growth in headed stud shear connectors.

• Computers and Concrete
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• 제14권1호
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• pp.19-40
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• 2014

Reinforced concrete deep beams are structural beams with low shear span-to-depth ratio, and hence in which the strain distribution is significantly nonlinear and the conventional beam theory is not applicable. A strut-and-tie model is considered one of the most rational and simplest methods available for shear strength prediction and design of deep beams. The strut-and-tie model approach describes the shear failure of a deep beam using diagonal strut and truss mechanism: The diagonal strut mechanism represents compression stress fields that develop in the concrete web between diagonal cracks of the concrete while the truss mechanism accounts for the contributions of the horizontal and vertical web reinforcements. Based on a database of 406 experimental observations, this paper proposes a new strut-and-tie-model for accurate prediction of shear strength of reinforced concrete deep beams, and further improves the model by correcting the bias and quantifying the scatter using a Bayesian parameter estimation method. Seven existing deterministic models from design codes and the literature are compared with the proposed method. Finally, a limit-state design formula and the corresponding reduction factor are developed for the proposed strut-andtie model.

• 한국정밀공학회지
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• 제4권3호
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• pp.44-51
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• 1987

In metal cutting various types of chips are produced in consequence of cutting conditions. Flow-type chips have been studied in most cases because they are easier to be analyzed, but the actual surfaces of chips are not smooth, but crushed. This paper deals with saw-toothed chips, special types of flow-type chips, which have deep concaves and high convexes and sharp angles on the free surface. I tried to establish the theory of saw-toothed chip mechanism through experimental observation, that is, the mathmatical model of the cutting energy and cutting mechanism through the geometrical observation of the chips by using a microscope. The results obtained are as follows: 1. The mechanism of saw-toothed chips is diffenent from that of general flow-chips. 2. In the case of saw-toothed chips, the shear angle must be measured by the hypotenuse angle and the rake angle, and the shear angle is more affected by the rake angle than by the hypotenbuse angle. 3. The friction angle is represented by .beta. = . pi. /4+ .alpha./ sub n/- .phi. which is different from Merchant's equation. 4. The pitch and the slip are greatly influenced by depth of cut, but the influence of the rake angle on it is small. 5. The normal stress and the shear stress on the shear plane decrease with the increase of the cutting depth, and they are almost independent on the variation of a rake angle. 6. The unit friction energy on the tool face, the unit shear energy on the shear plane, and the total cutting energy per unit volume decrease with the increase of rake angle and cutting depth.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.375-378
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• 2005

In the mechanism of beam shear failure, beam action and arch action always exist simultaneously. According to a/d ratio, the proportion and contribution between these two actions to shear capacity are merely changed. Moreover, the current codes recommendations are founded on the experimental results with normal strength concrete, the applicable range of $f'_{c}$ must be extended. Based on this mechanism and new requirement, an analytical equation is proposed for shear capacity prediction of reinforced concrete beams without stirrups. To reflect contribution change of two actions, stress variation in longitudinal reinforcement along the span is considered with Jenq and Shah Model. Dowel action and shear friction are also taken into account. Size effect is included to derive more precise equation. It is shown that the proposed equation is more accurate than other empirical equations and codes. So, it can be possible that wide range of a/d ratio is considered by one equation.

• 한국환경복원기술학회지
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• 제5권4호
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• pp.19-30
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• 2002

The stability of slope using root-pile like to the reinforcements is affected by the interaction behavior mechanism of soil-reinforcements. Through the studying on the interaction in joint of its, therefore, the control roles can be find out in installed slope. In study, the stress level ratio based on the insert angle of installed reinforcements in soil used to numerical analysis, which was results from the duty direct shear test in Lab. The maximum shear strain variation on the reinforcements was observed at insert angle, which was approximately similar to the calculated angle based on the equation proposed by the Jewell. The elasto-plastic joint model on the contact area of soil-reinforcements was presumed, the reinforced soil assumed non-linear elastic model and the reinforcements supposed elastic model, respectively. The finite element analysis of assumed models was performed. The shear strain variation of non-reinforced state obtained by the FEM analysis including elasto-plastic joint elements were shown the rationality of general limit equilibrium analysis for the slope failure mode on driving zone and resistance zone, which based on the stress level step according to failure ratio. Through the variation of shear strain for the variation of inserting angle of reinforcements, the different mechanism on the bending and the shear resistance of reinforcements was shown fair possibility.

• Steel and Composite Structures
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• 제42권3호
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• pp.299-313
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• 2022

Steel-concrete-steel composite structures with bidirectional webs (SCSBWs) are used in large-scale projects and exhibit good mechanical performances and constructional efficiency. The shear behaviors of SCSBW deep beam members in key joints or in locations subjected to concentrated forces are of concern in design. To address this issue, experimental program is investigated to examine the deep-beam shear behaviors of SCSBWs, in which the cracking process and force transfer mechanism are revealed. Compared with the previously proposed truss model, it is found that a strut-and-tie model is more suitable for describing the shear mechanism of SCSBW deep beams with a short span and sparse transverse webs. According to the experimental analyses, a new model is proposed to predict the shear capacities of SCSBW deep beams. This model uses strut-and-tie concept and introduces web shear and dowel action to consider the coupled multi mechanisms. A stress decomposition method is used to distinguish the contributions of different shear-transferring paths. Based on case studies, a simplified model is further developed, and the explicit solution is derived for design efficiency. The proposed models are verified using experimental data, which are proven to have good accuracy and efficiency and to be suitable for practical application.

• 한국해양공학회지
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• 제22권4호
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• pp.8-13
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• 2008

In this study, an investigation of shear wave ultrasonic technique was carried out to detect stacking orientation error for CF/Epoxy quasi-isotropy composite laminates. The ultrasonic shear wave is particularly sensitive to ply orientation and layup sequence in tire CF/Epoxy composite laminates. In the manufacturing of composite laminates, it is important that layup errors be detected in samples. In this work, an effect was mack to develop shear wave techniques that can be applied to composite laminates. During testing, the mast significant problem is that the couplant conditions do not remain the same because of its changing viscosity. The design and use of a shear ware transducer would greatly alleviate the couplant problem. A pyramid of aluminum, with isosceles triangle (two 45o angles) sides, was made to generate shear waves, using two longitudinal transducers based on an ultrasonic-polarized mechanism. A signal splitter was connected to the pulser jack on a pulser/receiver and to the longitudinal transducers. The longitudinal transducers were mounted with mineral oil, and the shear transducer was mounted with burnt honey on the bottom as a receiver. The shear wave was generated at a maximum and a minimum based on the ultrasonic-polarized mechanism. Results show it is feasible to measure layup error using shear wave transducers on a stacking of prepregs in composites.

• 콘크리트학회논문집
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• 제16권2호
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• pp.163-174
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• 2004

플랫플레이트-기둥 접합부의 뚫림전단강도를 규명하기 위해 그동안 많은 실험연구가 수행되어 왔다. 실험결과에 의하면, 뚫림전단강도는 접합부의 기둥크기, 철근비, 경계조건 등 다양한 설계변수에 따라 크게 변화하는 것으로 나타났다. 하지만 현행 설계기준들은 설계변수의 영향을 정확히 반영하고 있지 못한 실정이다. 본 연구에서는 뚫림전단의 파괴메카니즘을 정의하기 위하여, Rankine의 파괴기준을 이용하는 구조역학적 접근법이 사용되었다. 파괴메카니즘은 접합부에 배치된 하부철근량에 따라 압축지배 전단파괴와 인장지배 전단파괴로 분류되며, 또한 뚫림전단강도는 슬래브의 휨손상에 밀접한 영향을 받는 것으로 밝혀졌다. 이 연구결과에 근거하여 콘크리트의 뚫림전단강도식을 개발하였으며, 제안된 방법은 기존 실험연구결과와 비선형 수치해석결과와의 비교를 통해 타당성이 검증되었다. 비교결과, 다양한 설계변수의 영향을 반영하고 있는 제안된 강도모델은, 현행 설계기준보다 접합부의 뚫림전단강도를 정확히 추정할 수 있는 것으로 밝혀졌다.