Papers by Author: Sam Hong Song

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Authors: Byoung Ho Choi, Dong Ho Joo, Sam Hong Song
Abstract: The fatigue characteristic of triple spot welded SPCC plates with the variation of the thickness and the geometry under tensile-shear loading is studied by finite element analysis (FEA) and the obtained data is compared with experimental data. Using 3-D solid element model and 3-D beam-shell model, the maximum equivalent stress and the beam deformation angle (BDA) for various thickness and geometry is studied. The linear relation between crack opening angle (COA) from experiment and the BDA from FEA for beam-shell model is represented, and the empirical prediction of fatigue lifetime is proposed using the relation between COA and BDA.
Authors: Cheol Woong Kim, Sam Hong Song, Kwang Joon Yoon, Jeong Soon Lee, Houng Kun Ann, Kwan Seob Jang, Tae Gun Um
Abstract: The researches using the Eddy Current Test (ECT) were limited for the particle reinforced metal base composites. It had been impossible to inspect the eddy current since the carbon/epoxy tube had the low electric conductivity of resin layer. However, it has been successful for our previous research to inspect the defect using the EC. In the case of loading to carbon/epoxy tube, the researches of relationship between the failure behavior and the variation of EC signals have not been carried out. Therefore, this research focused on the comparison and the evaluation of the EC signals according to the variation of the defect depth using the unloading and the radial-loading carbon/ epoxy tube. We obtained results are as follow. Firstly, reviewing the stress distribution of carbon/ epoxy tube under the radial-loading, it was known that the defect depth did not have strongly influence on the stress distribution. Therefore, it was believed that the stress distribution was not directly related to the signals of the EC. Secondly, the EC signals similar to that of the unloading specimens could be obtained from the radial-loading specimen of 80 % defect depth. Thirdly, regardless of the unloading and the radial-loading specimens, the defect of 80 % and 100 % depths had the similar phase angles and Lissajous figures. Finally, it was guessed that the length of microcracks distributed at the whole specimens under the radial-loading was less than 60 % defect depth.
Authors: Cheol Woong Kim, Sam Hong Song, Dong Joon Oh
Abstract: The anisotropy of hybrid composite such as Al/GFRP laminates made it possible to control the fiber orientation according to the loading patterns. Therefore, it is important to study the fatigue and delamination behaviors of Al/GFRP laminates by fiber orientation. Al/GFRP laminates of three different fiber orientations (0°, 45°, 90°) were chosen, and the progressive delamination behavior was examined through the fatigue tests. The effects of the fiber orientation on the crack length, the fatigue life, the delamination, the crack growth rate (da/dN), and the stress intensity factor range ( ΔK) were investigated and discussed. The findings led to a conclusion that the effect of fiber orientation should not be ignored in analyzing the progressive damage of Al/GFRP laminates.
Authors: Sam Hong Song, Jeong Moo Lee
Abstract: The need for research on fatigue behavior of mechanical element under mixed-mode loading has been increasing as the user environment today becomes more and more complicated. However there haven’t been enough investigations on behavior in shear loads comparing to those under tensile loading conditions. So, for this paper, we investigated the characteristics and properties of initiation and propagation behavior for fatigue crack observed for different shapes of the initial crack and magnitudes of load in the modified compact tension shear (CTS) specimen subjected to mode II load. In the low-load condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack surface grew to a main crack. In the high-load condition meanwhile, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation was retarded in the initial propagation region due to the decrease in crack driving force and friction on the crack surface. In both cases, however, fatigue cracks grew in tensile mode. The propagation direction of fatigue crack under mode II loading was approximately at a 70 degree angle from the initial crack, regardless of its shape and load magnitude.
Authors: Cheol Woong Kim, Sam Hong Song, Dong Joon Oh
Abstract: If Fiber Reinforced Metal Laminates (FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of Al alloy layers and that it depended on the crack growth. When FRMLs with circular holes was un-cracked but was delaminated, it was impossible to analyze them by conventional fracture parameters expressed as the function of cracks. Therefore, a new analytical model called Pseudo Crack Model (PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack consumption rate (Ccrack) and the delamination consumption rate (Cdel) was discussed and it was also known that the effect of the Ccrack was larger than that of the Cdel.
Authors: Cheol Woong Kim, Sam Hong Song, Dong Joon Oh
Abstract: The applicability of GLARE is restricted due to the frequent delamination of different materials at interlaminar. The previous researches showed that the major parameter to control the delamination of GLARE was a crack (a). On the other hand, it was also shown that a delamination width (b) could strongly effect on the delamination behavior. Therefore, the aim of this research is to define the delamination behavior using the above correlation. In conclusions, it was shown that the delamination aspect ratio (b/a) was slowly decreased and the delamination area rate (ADR) was increased as the normalized crack size (a/W) was increased. The effect of the delamination shape was strong at the beginning of the cyclic loading but it was gradually diminished.
Authors: Cheol Woong Kim, Sam Hong Song, Dong Joon Oh
Abstract: This paper investigates the effect of the defect location on the stress concentration, the stress distribution, and the crack initiation behavior when the defects were made in the vicinity of the circular hole in the monolithic aluminum and the glass fiber reinforced laminates (GLARE). As the defect location in the vicinity of the circular hole was changed from ° = 90 4 q to ° = 0 1 q , the stress concentration was increased. Generally, the stress concentration of GLARE was about 15% greater than that of the monolithic aluminum. When the defect was at ° = 30 2 q , Multi Site Damage (MSD) crack was found in the monolithic aluminum, but just the main cracks existed in GLARE. The delamination instead of MSD crack was made in GLARE, and it resulted in the prevention against the second crack initiation.
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