• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 The 8th Asian Symposium on Precision Forging ASPF
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• pp.26-30
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• 2003

Since the dimension of cold forged part is larger than the cavity size of forging die, the difference results from the various features, such as, the elastic characteristics of die and workpiece, thermal influences, and machine-elasticity. All of these factors should be considered to get more accurate prediction of the dimension of forged part. In this paper, severe FE techniques are proposed to improve the prediction accuracy of dimension for cold forged part. To validate the importance of the above mentioned factors, and the estimated results are compared with the experimental results. The used model is a closed die upsetting of cylindrical billet. The calculated dimensions are well coincided with .the measured values based on the proposed techniques. The proposed techniques have put two simple but important points into Fe simulation. One is the separation of forging stages into 3 steps, from a loading through punch retraction to ejecting stage. The other is the dimensional change, according to the temperature changes due to the deformation. The FE analysis could predict the dimension of cold forged part within the $10{\mu}m$, based on the more realistic consideration.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1705-1712
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• 2001

Mechanical component has striation with constant width and SEM can estimate fracture type and loading condition. SEM has benefit to fatigue fracture analysis but striation can be observed according to the kind of material and range of crack growth rate and can't. In this case, it needs AFM that can measure 3-dimensional surface profile with resolution of atomic size. In this study. to find fracture reason of torsion-mounted blade in nuclear plant, we estimate the relation between stress intensity factor range and root mean square roughness in 12% Cr steel by AFM and predict in-service loading condition of turbine blade. failure analysis is performed by finite element method and Goodman diagram on torsion-mounted blade.

• 한국공작기계학회논문집
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• 제17권1호
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• pp.50-58
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• 2008

The SM45C metallic coupons have been tested under static tensile loading with acoustic emission (AE) as the load-deflection curve mainly. In this study, we used AE to detect the yielding of material and AE techniques was applied to rapidly estimate the mechanical characteristics of a material. First, coupons without an artificial defect were tested at different cross-head speed. For all cases in this analysis, yielding point of SM45C coupons did not appear definitely compared to mild steel, whereas coupons start to generate AE counts upon yielding. So all cases are normalized to know the possibility of accelerated life test of a material. And next, coupons with different from sizes of circular hole defects were tested at the same cross-head speed of 5 mm/min. Results were classified into 3 classes and analyzed by AE amplitude & signal strength as a function of time. Summarizing the specific conclusions, we need to additional research considering plate with width-ratio in order to estimate the fracture mechanism.

• 한국공간정보시스템학회 논문지
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• 제9권2호
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• pp.81-91
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• 2007

본 논문에서는 공간 데이터 웨어하우스에서 시공간 분석지원을 위한 공간 데이터의 비중복 적재 기법을 제안한다. SDW는 이기종의 다양한 서비스를 지원하는 SDBMS로부터 공간 데이터를 추출한다. 제안 기법에서는 SOW에 소스로 참여하는 SDBMS에서 변경된 부분만을 추출하고, 이를 공간연산을 통해 중복된 데이터를 제거한 후 통합된 형태로 적재함으로써 빠른 공간 데이터 분석을 지원할 수 있으며, 저장 공간의 낭비를 줄일 수 있다. 이는 공간 마이닝등의 시간에 따른 분석 및 예측 분야에 효율적인 형태로 공간 데이터를 적재한다.

• 대한기계학회논문집A
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• 제35권4호
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• pp.367-374
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• 2011

마찰 스프링은 부하가 가해질 때와 가해지지 않을 때 서로 다른 특성을 가지고 있다. 마찰스프링의 이러한 특성으로 인해 충격 시스템에 주로 사용된다. 본 논문에서는 마찰 스프링을 포함한 발사장치의 주퇴복좌기 설계 연구가 수행되었다. 마찰 스프링의 강성을 결정하기 위해서는 충격량과 운동량 관계를 고려한 단순한 발사장치 모델의 운동방정식이 개발되었다. 발사장치의 동적 거동시뮬레이션 결과에 기초하여, 주퇴복좌 시스템의 마찰 스프링의 지름을 결정하였다.

• Steel and Composite Structures
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• 제33권3호
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• pp.433-444
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• 2019

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

• Geomechanics and Engineering
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• 제34권5호
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• pp.561-575
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• 2023

This study investigates to provide a fast solution to the problem of bearing capacity in layered soils with easily obtainable parameters that does not require the use of any charts or calculations of different parameters. Therefore, a hybrid approach including both the finite element (FE) method and machine learning technique have been applied. Firstly, a FE model has been generated which is validated by the results of in-situ loading tests. Then, a total of 192 three-dimensional FE analyses have been performed. A data set has been created utilizing the soil properties, footing sizes, layered conditions used in the FE analyses and the ultimate bearing capacity values obtained from the FE analyses to be used in multigene genetic programming (MGGP). Problem has been modeled with five input and one output parameter to propose a bearing capacity formula. Ultimate bearing capacity values estimated from the proposed formula using data set consisting of 20 data independent of total data set used in MGGP modelling have been compared to the bearing capacities calculated with semi-empirical methods. It was observed that the MGGP method yielded successful results for the problem considered. The proposed formula provides reasonable predictions and efficient enough to be used in practice.

• Journal of Biosystems Engineering
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• 제15권3호
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• pp.207-218
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• 1990

Grains display characteristics of both elastic bodies and viscous fluids when they are subjected to mechanical treatments in harvesting, handling, and processing. This viscoelastic behavior of grains when mechanically stressed must be fully understood to establish maximum machine efficiency and have a minimum degree of grain damage and the highest quality of the final product. The studies were conducted to examine the effect of the moisture content, the loading rate and the initial deformation on the stress relaxation behavior of whole kernel of rough rice, and develop the rheological model to represent its stress relaxation behavior. The following results were obtained from the study. 1. Moisture content had the greatest influence on the initial portion of the relaxation curve. With elapsing time the lower moisture content resulted in the lower residual stress for the Japonica-type rough rice and vice versa for the Indica-type rough rice. But within the ranges of moisture content tested, the degree of stress relaxation per unit strain on the Indica-type rough rice was a little higher than those on the Japonica-type rough rice. 2. The slower loading rate resulted in less initial stress. The decreasing trend of residual stress for all the samples tested with increasing loading rate was shown. 3. The higher initial deformation for all the samples resulted in less initial stress. The increasing of amount of stress relaxation per unit strain with increase of initial stress indicated that viscoelastic properties of rough rice depended not only upon duration of load applied but also initial stress applied. This means that rough rice is nonlinear viscoelastic material. 4. The compression stress relaxation properties of rough rice kernel can be described by a generalized Maxwell model representing by the Maxwell elements.

• 한국구조물진단유지관리공학회 논문집
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• 제14권4호
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• pp.119-125
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• 2010

화재시 콘크리트의 성능저하는 재하조건, 열팽창 및 크리프 등과 같은 여러 가지 요인에 대하여 영향을 받을 수 있다. 1950년대부터 일본, 유럽, 미국과 같은 선진외국에서는 고온을 받은 콘크리트의 특성에 관하여 많은 연구들이 행해지고 있으나 재하조건, 가열방법, 시험체의 크기 및 가열장치의 성능 등과 같은 다양한 요인들이 연구자들의 독자적인 방법에 의해 실험이 진행되고 있다. 이에 본 연구에서는 시험체 크기, 가열속도, 시험방법이 유사한 일본 및 국내의 연구를 바탕으로 가열 및 재하를 받은 콘크리트의 역학적 성능에 대하여 분석하였으며, 상온 및 고온에서의 상관관계분석, 압축강도 추정곡선을 산출하여 CEN 및 CEB code와 비교 평가하였다. 그결과 재하가열을 받은 콘크리트는 $100^{\circ}C{\sim}400^{\circ}C$의 범위에서 역학적 특성에 대한 재평가의 필요성을 확인하였다.

• Advances in concrete construction
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• 제13권1호
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• pp.83-99
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• 2022

The two, NBD and SCB tests using gypsum circular discs each containing a single notch have been experimentally accomplished in a rock mechanics laboratory. These specimens have also been numerically modelled by a two-dimensional particle flow which is based on Discrete Element Method (DEM). Each testing specimen had a thickness of 5 cm with 10 cm in diameter. The specimens' lengths varied as 2, 3, and 4 cm; and the specimens' notch angles varied as 0°, 45° and 90°. Similar semi-circular gypsum specimens were also prepared each contained one edge notch with angles 0° or 45°. The uniaxial testing machine was used to perform the experimental tests for both NBD and SCB gypsum specimens. At the same time, the numerical simulation of these tests were performed by PFC2D. The experimental results showed that the failure mechanism of rocks is mainly affected by the orientations of joints with respect to the loading directions. The failure mechanism and fracturing patterns of the gypsum specimens are directly related to the final failure loading. It has been shown that the number of induced tensile cracks showing the specimens' tensile behavior, and increases by decreasing the length and angle of joints. It should be noted that the fracture toughness of rocks' specimens obtained by NBD tests was higher than that of the SCB tests. The fracture toughness of rocks usually increases with the increasing of joints' angles but increasing the joints' lengths do not change the fracture toughness. The numerical solutions and the experimental results for both NDB and SCB tests give nearly similar fracture patterns during the loading process.