• 대한기계학회논문집A
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• 제38권2호
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• pp.121-127
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• 2014

단층 그래핀 시트(Single layer graphene sheet, SLGS)의 찢어짐 모드(모드 III) 파괴 예측을 위한 원자 기반 미세결합요소모델이 개발되었다. 이 모델은 그래핀 시트의 최대 변형률 관계를 예측하기 위해 수정된 모스포텐셜을 사용한다. 면외 전단하중 조건에서 그래핀의 모드 III 파괴를 광범위한 분자역학(Molecular mechanics, MM) 시뮬레이션으로 조사하였다. 분자역학은 원자의 균열선단 근처 원자의 변위를 설명하기 위해 사용되었고, 선형탄성파괴역학은 이 영역 바깥의 영역을 설명하기 위해 사용되었다. 해석 결과 분자역학 방법이 SLGS의 전단 물성 계산뿐만 아니라 armchair 및 zigzag 방향 모드 III 파괴인성 연구에도 단순하면서도 신뢰할만하다는 것을 보여준다. SLGS 의 모드 III 파괴인성은 zigzag 방향에 대해 $0.86MPa{\sqrt{m}}$, armchair 방향에 대해 $0.93MPa{\sqrt{m}}$로 예측되었다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.373-378
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• 2002

Metal matrix composites have a great interest in recent years because high specific strength, high specific stiffness characteristics, and application ranges of the composites are extend to variety industry. In this paper, an investigation was performed on the plane strain fracture toughness and slinding wear properties of AC4CH alloy(Al-Si-Mg line) reinforced with 20wt% aluminum borate whisker expect one, which contained a inorganic binder($TiO_2$). the binder led to the formation of strengthen the whisker each other. The test of fracture toughness was using CT(half size) specimen of thickness 12.5mm, width 25mm. and test of slinding wear of using tribo a pin-on-disk machine and lubricant is used without paraffine 8.2CST at room temperature. As results, Fracture toughness $K_{IC}$ is $8.7MPa-m^{05}$ for ABOw/AC4CH, $9.28MPa-m^{05}$ for ABOw/AC4CH added $TiO_2$. but AC4CH alloy was violated the critical stipulated by ASTM standard for valid measurement of $K_{IC}$. In case of, it was performed $J_{IC}$ test instead of $K_{IC}$ based on ASTM E 1820.

• 열처리공학회지
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• 제9권3호
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• pp.161-168
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• 1996

The purpose of this study is to investigate the effect of impurity level and fabrication processes on the strength, fracture toughness and fatigue resistance of 7075, 7050 and 7175 high strength aluminum forgings. It has been verified that plane strain fracture toughness and fatigue characteristics of a specially processed 7175S-T74 alloy is superior to a conventionally processed 7075-T6/T73, 7050-T74 and 7175-T74 alloys. These beneficial effects primarily arise from two view points, i.e., the effect of reducing the impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as $Al_7Cu_2Fe$ and $Mg_2Si$. Futher reduction of the amount of nonequilibrium second phase particles has been observed by applying a special fabrication process.

• Restorative Dentistry and Endodontics
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• 제18권1호
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• pp.1-26
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• 1993

The purpose of this study was to investigate the effect of acid etching on the surface appearance and fracture toughness of five glass ionomer cements. Five kinds of commercially available glass ionomer cements including chemical curing filling type, chemical curing lining type, chemical curing metal reinforced type, light curing tilling type and light curing lining type were used for this study. The specimens for SEM study were fabricated by treating each glass ionomer cement with either visible light curing or self curing after being inserted into a rubber mold (diameter 4mm, depth 1mm). Some of the specimens were etched with 37% phosphoric acid for 0, 15, 30, 60, go seconds, at 5 minutes, 1 hour and 1 day after mixing of powder and liquid. Unetched ones comprised the control group and the others were the experimental groups. The surface texture was examined by using scanning electron microscope at 20 kV. (S-2300, Hitachi Co., Japan). The specimens for fracture toughness were fabricated by curing of each glass ionomer cement previously inserted into a metal mold for the single edge notch specimen according to the ASTME399. They were subjected to a three-point bend test after etching for 0, 30, 60, and 90 seconds at 5 minutes-, 1 hour-and 1 day-lapse after the fabrication of the specimens. The plane strain fracture toughness ($K_{IC}$) was determined by three-point bend test which was conducted with cross-head speed of 0.5 mm/min using Instron universal testing machine (Model No. 1122) following seven days storage of the etched specimens under $37^{\circ}C$, 100% humidity condition. Following conclusions were drawn. 1. In unetched control group, crack was present, but the surface was generally smooth. 2. Deterioration of the surface appearance such as serious dissolving of gel matrix and loss of glass particles occured as the etching time was increased beyond 15 s following Immediate etching of chemical curing type of glass ionomer cements. 3. Etching after 1 h, and 1 d reduced surface damage, 15 s, and 30s etch gave rough surface appearance without loss of glass particle of chemical curing type of glass ionomer cements. 4. Light curing type glass ionomer cement was etched by acid, but there was no difference in surface appearances according to various waiting periods. 5. It was found that the value of plane stram fracture toughness of glass ionomer cements was highest in the light curing filling type as $1.79\;MNm^{-1.5}$ followed by the light curing lining type, chemical curing metal reinforced type, chemical curing filling type and chemical curing lining type. 6. The value of plane stram fracture toughness of the chemical curing lining type glass ionomer cement etched after 5 minutes was lower than those of the cement etched after 1 hour or day or unetched (P < 0.05). 7. Light curing glass ionomer cement showed Irregular fractured surface and chemical curing cement showed smooth fractured surface.

• 대한기계학회논문집
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• 제11권3호
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• pp.376-385
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• 1987

본 연구에서는 평면응력 파괴인성치의 거동에 관한 일련의 연구로서 위와 같 은 점을 고려하여 얇은 두께의 시험편을 이용하여 z의 변화에 대한 평면응력 파괴인성 치와 J저항곡선을 실험적으로 고찰하였으며 크랙성장을 고려한 J적분식도 검토하였다. 크랙길이는 하중제거 컴플라이언스법에 의하여 구하였고, ASTM E813의 방법으로J= .sigma.$_{f}$ .DELTA.(2ａ)인 크랙둔화선과 J저항곡선의 교점에서 구한 J적분값을 J$_{c}$로 정 의하였다. 또한, 재료를 변형경화재료로 가정하여 HRR응력변형율장의 특성을 이용 하여 J적분값을 구한 후 실험치와 상호 비교 검토하였다.이때 입력자료는 실험치의 그것과 동일하게 하였다. 동시에 z의 변화에 대한 T의 변화도 함께 고찰하였다.다.

• 한국주조공학회지
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• 제11권4호
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• pp.331-337
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• 1991

Various test specimens were prepared by austempering low alloyed Mo-Ni-Cu ductile iron blocks of high graphite nodule count at 270, 320 or $370^{\circ}C$ for 0.5, 1, 3 or 9hrs. Tensile test, CVN impact test and plane-strain fracture toughness test(compact tension specimen of 50mm W) were done for each heat treatment condition at room temperature. X-ray diffractometer and optical microscope were used to investigate the change of microstructure and relationships between microstructure and test results. The highest retained austenite volume percent at each austempering temperature was corresponded to the highest mechanical property. The highest elongation value of 17%, U.T.S. value of 1,600 MPa or $K_{IC}$ value of 90MPa${\surd}$m were reached at each optimum condition. The best heat treatment condition for fracture toughness were 3hrs' holding time combined with the austempering temperature of 270 and $320^{\circ}C$, and 1hr's of $370^{\circ}C$.

• 대한기계학회논문집
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• 제18권12호
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• pp.3136-3148
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• 1994

This paper proposed the method of fracture integrity evaluation for semi-elliptical crack. Plane strain fracture toughnesses are used to compare with the thermal shock stress intensity factors for semi-elliptical crack obtained by Vainshtok weight function method. The method is applied to the finite Cr Mo V and 2.25Cr Mo steel plates with semi-elliptical crack under the thermal shock. For the purpose, tensile property and fracture toughness with respect to the temperature are measured. To verify the method, thermal shock experiments are carried. The theoretical predictions are in good agreement with the experiments.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.335-340
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• 2002

In recent years, the study of metal matrix composite has increased specially, aluminum alloy, research and development are briskly progress to find new metal matrix composite. this study is following the this purpose; This study is used metal matrix composite that was produced by matrix, AC4CH. and reinforcement $A_{18}B_4O_{33}$ metal matrix composite to add $Al_2O_3,\;TiO_2$ for strengthen of binding together among the Whisker. Each Metal matrix composite is produced using the squeeze casting method. Fracture tounghness test was in accordance with the provisions of ASTM E399; Specimen was produced half-size CT specimen W=25mm, B=12.5mm, Cross head speed 0.05mm/min in room temperature. The plane strain fracture toughness $K_{IC}$ is $8.7MPa-m^{0.5}$ for $Al_{18}B_4O_{33}$/AC4CH., $9.28MPa-m^{0.5}$ for $Al_{18}B_4O_{33}$/AC4CH added $TiO_2$. and $Al_2O_3$ but AC4CH alloy was violated the critical stipulated by ASTM standard for a valid measurement of $K_{IC}$. In case of, it was performed $I_{IC}$ test instead of $K_{IC}$ based on ASTM E 1820

• 한국재료학회지
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• 제3권3호
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• pp.253-260
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• 1993

용해와 주조, 압출과 열처리 기술의개선으로 고강도, 고파괴인성의 AI-Li-Cu 합금(2090 AI합금)을 제조하였다. 또한 준 산업용 규모(20kg)의 잉고트 제조공정을 확립하기 위해서 (1)선 (2)기계적 성질들에 미치는 열처리 영향 (3) 인장시험, 파괴인성 시험($K_{Ic}$) 및 피로균열 전파시계를 갖고 있으며 최종 제품의 인장강도는 최대시효 조건에서 534MPa부터 566MPa이었고 연신율은 9%에서 11.9%정도였다. C-T 시편을 이용한 파괴인성 시험 결과 최대시효 조건에서 평면변형 파괴인성 ($K_{Ic}$)값은 39MPa$\surd$m였고 미시효 조건에서는 23MPa$\surd$m였다. 또한 0.1, 0.3, 0.5의 하중비에서 피로균열 전파시험을 행하였을때 임계응력 확대계수(${\Delta}K_{th}$)는 각각 6.0, 5.3, 4.3 MPa$\surd$m이었다.

• 한국해양공학회지
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• 제15권3호
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• pp.75-80
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• 2001

The elastic plastic fracture toughness of this material is evaluated by the an unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the material tearing modulus and characterizes the crack tip field under the plane stress and strain. SG-365 steel is observed that J-R curve and Tmat value decrease as 0%, 20%, 30%, and 40%. The 40% side grooved specimen is very useful in estimation of the $J_IC$. Because it is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides. it improves the accuracy of toughness values, decreases the scattering the them and tunneling and shear lip by the side groove. Applicability of tearing modulus($T_J$ proposed by paris et al as instability panameter for this material is investigated.