• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.564-573
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• 2001

The mechanical properties of short carbon/glass fiber reinforced polypropylene are experimentally measured as functions of fiber content and nozzle diameter. Also, these properties are compared with the survival rate of reinforced fibers and fiber volume fraction using image analysis after pyrolytic decomposition. The survival rate of fiber aspect ratio as well as fiber volume fraction is influenced by injection processing condition, the used materials and mold conditions such as diameter of nozzle, etc. In this study, the survival rate of fiber aspect ratio is investigated by nozzle size variations in injection/mold sides. It is found that the survival rate of glass fiber is higher that the survival rate of glass fiber is higher than that of carbon fiber. Both tensile modulus and strength of short-fiber reinforced polypropylene are improved s the fiber volume fraction and nozzle diameter are increased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.318-324
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• 2005

Theoretical efforts are performed to extend the formulation of NSLT(New Shear Lag Theory) for the prediction of the elastic modulus in short fiber composite. The formulation is based on the elastic stress transfer considering the stress concentration effects influenced by elastic modulus ratio between fiber and matrix. The composite modulus, thus far, is calculated by changing the fiber aspect ratio and volume fraction. It is found that the comparison with FEA(Finite Element Analysis) results gives a good agreement with the present theory (NSLT). It is also found that the NSLT is more accurate than the SLT(Shear Lag Theory) in short fiber regime when compared by FEA results. However, The modulus predicted by NSLT becomes similar values that of SLT when the fiber aspect ratio increases. Finally, It is shown that the present model has the capability to predict the composite modulus correctly in elastic regime.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.5 s.248
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• pp.543-549
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• 2006

The bursting properties under various conditions were investigated to ascertain the optimum conditions to yield the best properties. Fiber aspect ratio (AR: length of fiber/diameter of fiber), interphase condition and fiber content were considered as variables which impact the bursting pressure, bulge constant, torsional rigidity ratio. The bursting pressure of reinforced rubber increases up to 8.73 times compared to the virgin material. The better interphase condition shows the higher bursting pressure at given AR and fiber content. The bulge constant and torsional rigidity highly decrease with increasing AR and better interphase condition at same fiber content. The bulge constant and torsional rigidity reveal the minimum of 11% and 0.6% of the matrix, respectively. The bursted shape after test shows the different patterns between unfilled and reinforced rubbers. The case of virgin rubber shows a radiating shape while that of reinforced rubber shows a fluctuating straight line. Overall, it was found that the fiber AR and interphase condition have an important effect on bursting properties.

• Journal of the Mineralogical Society of Korea
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• v.23 no.1
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• pp.73-84
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• 2010

We studied the geological occurrence, associated minerals, mineralogical properties and formation process of tremolites from two abandoned asbestos mines, Jungang (Sinsuk) and Daebosuksan, located in Boryoung area, Chungnam. Morphologically different tremolites such as long fibrous, needle-like, bladed and prismatic forms coexisted. Fibrous tremolite, known for its high toxieity to human health, was systematically analyzed by polarized light microscopy and scanning electron microscopy. The average length of tremolite fibers was 31.2 ${\mu}m$ although the maximum length of some asbestos was 210.0 ${\mu}m$. The average width and aspect ratio were 1.6 ${\mu}m$ and 19.9, respectively. Tremolite showed inclined extinction in the range of 6.1~20.2$^{\cric}$. X-ray diffraction patterns were slightly different between fibrous (asbestiform) and prismatic (non-asbestiform) tremolites. EPMA analysis of tremolites in the study area indicated extremely high Mg content with very low Fe content, close to the composition of tremolite in end-member in the tremolite-actinolite solid solution series. The formational conditions of asbestiform and non-asbestiform tremolite appear to be different. Asbestiform tremolite was estimated to have been formed in later stage.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.126-130
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• 1993

소경드릴가공은 많은 기계가가공중에서도 가장 곤란한 가공의 하나이다.그것은 가공구멍단면 이하의 공간속에서 공구강성이나 칩처리들이 고려되어야 한다는 엄격한 제한이 소경이란 형태에서 한층 어려워지기 때문이다.소경의 구멍가공은 최근 전자제품,우주항공기 부품,소형정밀부품, 섬유산업의 광섬유관련품 등에 까지 수요가 증가함에 따라 레이져가공,전자빔가공,전해가공과 같은 전기물리적가공법이 많이 사용되고 있지만 생산성 및 가공정밀도의 관점에서 만족스러운 결과를 얻을 수 없는 실정이다, 이에반해 기계가공인 소경드릴가공은 공구강성저하로 인해 쉽게 파손된다는 점은 있지만 가공정도가 양호하고 종횡비가 높은 가공이 가능하여 실용화가 가장 좋은 분야라고 할수 있다. 이로 인해 최근에는 여기에 관한 많은 연구가 지행되고 있다. 또한 기계가공의 자동화가 진전됨에 따라서 단일공국의 대표적 공구인 바이트의 결함을 검출하는것 못지않게 드릴의 마멸이나 절손의 검출 또는 예측이 중요한 문제로 부각됨에 따라 절삭저항의 이용이 증가할 것으로 생각된다. 따라서 본 연구에서는 ADI에 포함된 Si량이 드릴가공시 ADI의 피삭성에 미치는 영향을 절삭조건을 변화시켜 고찰함과 동시에 공구수명에 대하여 고찰하였다.

• Journal of the Mineralogical Society of Korea
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• v.25 no.2
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• pp.95-104
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• 2012

Electron microscopy of the tremolite-actinolite series amphiboles from the naturally occurring asbestos locality showed the morphological diversity including fibrous, acicular, and prismatic. Very thin, long, and flexible fibers of constant width form ropy bundles or mats. Acicular particles are slightly thick, long, elastic, and easily separated from the bundle of parallel rods. Acicular fragments of lower aspect ratio are formed during the crushing of the amphibole prism. Morphological features of the amphiboles are different depending on their localities and vary in a specimen. Morphological continuum between amphibole fiber and prism requires the establishment of reliable identification criterions and sample preparation protocol based on the relation between carcinogenicity and morphological features.

• Journal of the Korean Vacuum Society
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• v.22 no.3
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• pp.156-161
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• 2013

We fabricated transparent conductive electrodes with silver (Ag) nanofibers by electrospinning process. Ag nanofibers have high aspect ratio and fused junctions which result in low sheet resistance. Electrospinning is a fast and efficient process to fabricate continuous one-dimensional (1D) nanofibers. Ag/polymer ink were prepared in polymer matrix solution by a sol-gel method. Then, Ag/polymer nanofibers precursors are heated at $200{\sim}500^{\circ}C$ in air for 2 h to eliminate partially the polymers. The topographical features of the Ag nanofibers were characterized by FE-SEM, and the electrical property was analyzed through I-V measurement system. Finally, optical property was measured using UV/VIS spectroscopy. The transparent conductive electrodes with Ag nanofibers exhibited a sheet resistance (Rs) of $250{\Omega}/sq$ at a transparency (T) of 83%. Transparent conductive films, contain the Ag nanofibers as conductive materials, have good electrical, optical, and mechanical properties. Therefore, it is expected to be useful for the application of flexible display in the future.

• Economic and Environmental Geology
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• v.47 no.5
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• pp.479-488
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• 2014

Naturally occurring asbestos (NOA) from disturbance of rocks and soils has been overlooked as a source of exposure that could potentially have a detrimental impact on human health. But, few researches on mineralogical characteristics of NOA occurred in soils have been reported in Korea. Therefore, the objective of this study was to investigate the mineralogical characteristics of NOA occurred in soils at Daero-ri area, Seosan, Chungnam Province, Korea. Sedimentation method was used for particle size separation of the asbestos-containing soils. XRD and PLM analyses were used to characterize mineralogical characteristics and mineral assemblages in soils. SEM-EDS and TEM-EDS analyses were used to characterize mineral morphology and chemical composition. Particle size analyses of the asbestos-containing soils showed they were composed of 26-93% sand, 4-23% silt and 3-70% clay. Soil texture of the soils was mainly sand, sandy loam, sandy clay, and clay. PLM analyses of the soil showed that most of the soil contained asbestiform tremolite and actinolite. The average content of asbestos in the soil was 1.5 wt. %. Therefore, the soil can be classified into asbestos-contaminated soils based on U. S. Environmental Protection Agency classification (content of asbestos in contaminated soil > 1%). Morphologically different types of tremolite such as long fibrous, needle-like, fiber bundle, bladed and prismatic forms co-existed. Prismatic tremolite was dominant in sand fraction and asbestiform tremolite was dominant in silt fraction. This study indicates that the prismatic form of tremolite transform gradually into a fibrous form of tremolite due to soil weathering because tremolite asbestos was mainly existed in silt fraction rather than sand fraction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.1
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• pp.55-62
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• 2004

Although the previous researches evaluated the fatigue behavior of glass fiber/epoxy laminates using the traditional fracture mechanism, their researches were not sufficient to do it: the damage zone of glass fiber/epoxy laminates was occurred at the delamination zone instead of the crack-metallic damages. Thus, previous researches were not applicable to the fatigue behavior of glass fiber/epoxy laminates. The major purpose of this study was to evaluate delamination behavior using the relationship between crack length and delamination width in hybrid composite material such as Al/GFRP laminate. The details of investigation were as follows : 1) Relationship between crack length and delamination width, 2) Relationship between delamination aspect ratio and delamination area rate, 3) Variation of delamination growth rate is attendant on delamination shape factors. The test results indicated that the delamination growth rate depends on delamination width delamination aspect ratio and delamination shape factors.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.113-116
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• 2003

The investigation of delamination growth behavior in hybrid composite material such as FRMLs should be considered delamination growth rate, dA_D/da$ using the delamination shape factor, $f_S$ instead of traditional fracture mechanics parameters. The main objective of this study is to evaluate the relationship between delamination element (i. e. delamination width, b, delamination contour, c, delamination shape factor, $f_S$ and delamination growth rate, dA_D/da$) and delamination growth in FRMLs under cyclic bending moment. The delamination shape formed along the fatigue crack between aluminum layer and glass fiber/epoxy layer are measured by scanning method. The details of study are as follow : ⅰ) Relationship between crack length, a and delamination width, b. ⅱ) Variation of delamination growth rate, dA_D/da$ was attendant on delamination shape factors, $f_{S1}$, $f_{S2}$, $f_{S3}$. The test result indicated the delamination growth behavior depends in delamination element such as delamination width, b, delamination shape factors, $f_{S1}$, $f_{S2}$, $f_{S3}$.