• Composites Research
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• v.15 no.3
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• pp.11-17
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• 2002

Cracking of the reinforcements is a significant damage mode in particle or short-fiber reinforced composites because the broken reinforcements lose load carrying capacity. This paper deals with elastic stress distributions and load carrying capacity of intact and cracked ellipsoidal inhomogeneities. Three dimensional finite element analysis has been carried out on intact and broken ellipsoidal inhomogeneities in all infinite body under pure shear. For the intact inhomogeneity, the stress distribution is uniform in the inhomogeneity and non-uniform in the surrounding matrix. On the other hand, for the broken inhomogeneity, the stress in the region near crack surface is considerably released and the stress distribution becomes more complex. The average stress in the inhomogeneity represents its load carrying capacity, and the difference of average stresses between the intact and broken inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The broken inhomogeneity with higher aspect ratio maintains higher load carrying capacity.

• Proceedings of the ESK Conference
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• 1997.10a
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• pp.31-34
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• 1997

본 연구에서는 들기 작업 중 특히 2인이 행하는 들기 과업시 신장과 근력의 차이가 작 업 능력에 어떠한 영향을 미치는가를 실험을 통해 심리육체적(Physchophysical approach)/ 생리학적(Physiological approach)으로 분석하였다. 실험은 건설 현장 작업의 Form 들기 작업을 시뮬레이션하였다. 남자 대학생 14명을 대상으로 2인 작업팀을 신장/근력 차이가 있는 팀과 비슷 한 신장/근력 팀으로 설정된 기준에 따라 나누었고 20분간 심리육체적인 실험을 통해 이 두 그룹간 의 최대 허용 하중 (Maximum Acceptable Weight of Load, MAWL)과 생리적인 부하(Load)의 차이를 측정하였다. 생리적 부하는 K4를 신장과 관계없이 근력이 약한 피실험자에게 착용케하여 심박수와 에너지 소비량을 산출하여 두 그룹을 비교하였다. 실험 결과 최대 허용하중의 경우 다른 신장/근력 팀에 분당 2회의 빈도의 경우 각각 16.2kg, 14.0kg, 분당 4회의 경우 각각 12.6kg, 10.6kg으로 비슷 한 신장/근력 팀의 경우가 다른 신장/근력 팀의 경우보다 높은 최대 허용 하중을 보였고, 에너지 소 비량은 다른 신장/근력 팀과 비슷한 신장/근력 팀에 대해 분당 2회의 경우 각각 6.01 kal/분, 5.82 Kal/분, 분당 4회의 경우 각각 7.81 kal/분, 7.43 kal/분, 심박수는 분당 2회의 경우 98.62(회/분), 94.60(회/분), 분당 4회의 경우 122.00(회/분), 117.43(회/분), 으로 다른 신장/근력 팀의 경우가 비슷한 신장/근력 팀의 경우보다 높은 에너지 소비량과 심박수를 보였다.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.106-112
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• 2004

In particle or short-fiber reinforced composites, cracking or debonding of the reinforcements cause a significant damage mode because the damaged reinforcements lose load carrying capacity. The average stress in the inhomogeneity represents its load carrying capacity, and the difference between the average stresses of the intact and broken inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The composite in damage process contains intact and broken reinforcements in a matrix. An incremental constitutive relation of discontinuously-reinforced composites including the progressive cracking damage of the reinforcements have been developed based on the Eshelby's equivalent inclusion method and Mori-Tanaka's mean field concept. Influence of the cracking damage on the stress-strain response of the composites is demonstrated.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.87-90
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• 2001

In particle or short-fiber reinforced composites, cracking of the reinforcements is a significant damage mode because the broken reinforcements lose load carrying capacity. This paper deals with elastic stress distributions and load carrying capacity of intact and cracked ellipsoidal inhomogeneities. Three dimensional finite element analysis has been carried out on intact and broken ellipsoidal inhomogeneities in an infinite body under pure shear. For the intact inhomogeneity, as well known as Eshelby(1957) solution, the stress distribution is uniform in the inhomogeneity and non-uniform in the surrounding matrix. On the other hand, for the broken inhomogeneity, the stress in the region near crack surface is considerably released and the stress distribution becomes more complex. The average stress in the inhomogeneity represents its load carrying capacity, and the difference of average stresses between the intact and broken inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The load carrying capacity of the broken inhomogeneity is expressed in terms of the average stress of the intact inhomogeneity and some coefficients. It is found that the broken inhomogeneity with higher aspect ratio still maintains higher load carrying capacity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.99-103
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• 1991

본 논고에서는 Radial 및 Axial 하중을 동시에 받을 수 있고, 예압에 의해 주축강성을 증대시킬수 있으며, Ball수의 증가로 부하능력을 향상시킨 초정 밀.초고속용 Angular ball bearing을 조합 사용하고, 고속회전에 지금까지 개 발된 ball bearing 윤활방법 중 가장 효과적인 간헐적인 oil 공급과 air 압력 으로, 계속 ball을 냉각, 윤활시켜주는 air oil 윤활법의 채용과, 국내 공작기 계 제조회사들이 주로 사용하는 일본 FAMUC AC Spindle motor(FAMUC-H type : 8000-15000rpm)를 사용해서 초고속 주축의 최적 설계조건을 제시하기 위한 기초연구 단계로 MT40-12000rpm 급의 Machining center용 Cartridge type의 Spindle unit개발을 통해서 주축설계에 따른 문제점과 연구용 주축제작의 생산 기술적 문제점 및 진동특성을 검토 하고자 한다.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.129-139
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• 2016

Cast-in-place concrete-filled hollow PC (HPC) columns are used to reduce lifting load of heavy-weight PC columns and to improve the structural integrity of joints. In the present study, a new type of HPC column was proposed to improve the productivity and structural integrity of the concrete. To form the hollow PC columns, a permanent inner form was prefabricated using structural deck plates and penetrated lateral bars. Half-scale specimens of four HPC columns were tested under combined axial compression and lateral cyclic loading to evaluate the seismic resistance. In the design of test specimens, various parameters such as the spacing of lateral re-bars, the use of steel fiber, and the thickness of PC cover were considered. The test results showed that the proposed HPC columns generally exhibited satisfactory load-carrying capacity and deformation capacity without brittle failure of PC. If closely spaced hoops or fiber reinforcements are used for PC, the deformation capacity can be improved further by restraining PC spalling.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.35-46
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• 2014

Two types of cast-in-place concrete-filled hollow PC (HPC1, HPC2) columns were developed to reduce lifting load of heavy-weight PC columns and to improve the structural integrity of joints. To form the hollow PC columns, a couple of prefabricated PC panels was used for HPC1, and special hoops were used for HPC2. Lateral pressure of wet concrete on PC faces was measured while placing the concrete inside the columns. To evaluate the seismic resistance, full scale specimens of two HPC columns and a conventional RC column were tested under combined axial compression and lateral cyclic loading. The test results showed that the structural performance of the proposed HPC columns such as intial stiffness, maximum strength, and displacement ductility was comparable to that of the conventional RC column, but the energy dissipation of HPC2 slightly decreased after rebar-buckling. However, all the test specimens satisfied the energy dissipation requirement specified in ACI 374.