• 대한기계학회논문집A
• /
• 제31권7호
• /
• pp.732-738
• /
• 2007

Effects of melt-mixing conditions on fracture properties of hydroxyapatite filled bioabsorbable poly(L-lactic acid)(HA/PLLA) composites was investigated by measuring the firacture toughness value of HA/PLLA composites prepared under different mixing time and rotor speed. The fracture surface morphology was also examined by profile measurement and scanning electron microscopies. It was found that the fracture toughness of HA/PLLA composites decreases due to decrease of ductile deformation of PLLA matrix and debonding of interfaces with increase of the rotor speed and mixing time. Effect of mixing process on neat PLLA was also assessed, and it was found that the fracture toughness of PLLA decreases due to disappearance of multiple craze formation and increase of defects. Such thermal and shear-stress degradation were found to be the primary mechanisms of the degradation of HA/PLLA composites during melt-mixing process.

• Korea-Australia Rheology Journal
• /
• 제15권4호
• /
• pp.173-178
• /
• 2003

Boron nitride is a new processing aid that is capable of eliminating gross melt fracture in several polymer processing operations. Its combinations with other processing aids i.e. fluoropolymers offer additional possibilities of obtaining enhanced processing aids that may take the processes to rates not realized before. A variety of different such combinations are discussed in this paper. The essential componenets are (1) boron nitride capable of eliminating gross melt fracture and (2) suitable lubricant capable of eliminating surface melt fracture such as stearates for the polyolefin processing and polyethylenes for the processing of fluoropolymers.

• Elastomers and Composites
• /
• 제22권3호
• /
• pp.213-218
• /
• 1987

고무중에서 polymer melt와 가장 유사한 유변학적 거동을 보이는 EPDM을 택하여, 가황반응속도를 조사하였으며, 이에 따라 부분적으로 가교도를 달리한 시편의 유변학적 특성을 capillary rheometer를 사용하여 검토하였다. 가교도가 0, 1.5, 3, 6%로 증가함에 따라 die 입구 및 출구에서의 압력 손실은 커지고, melt fracture가 일어나는 전단속도는 낮아지며 특히 die swell은 거의 직선적으로 증가하였다. 본 연구를 통하여 die swell, melt fracture, end effects등의 근원이 고분자 사슬의 탄성변형에 있음을 확인하였으며, 또한 압출, 압연등에서 흔히 관측되는 die swell의 요동이 가공중 발생할 수 있는 가황반응에 기인할 수도 있음을 보여준 것이다.

• 한국결정성장학회지
• /
• 제11권6호
• /
• pp.239-245
• /
• 2001

뮬라이트 preform과 비정질 실리카를 알루미늄 용융체에서 $1100^{\circ}C$, 5시간 동안 반응시켜 $Al/Al_2O_3$복합체가 제조되었다. 뮬라이트 preform과 알루미늄 용융체 간의 화학적 반응은 상호 연결된 미세구조를 형성하였다. $Al/Al_2O_3$복합체의 금속의 양은 뮬라이트 preform의 소결 온도($1600^{\circ}C$, $1625^{\circ}C$, $1650^{\circ}C$, $1700^{\circ}C$)에 따른 겉보기 기공율의 변수로서 조절되었으며, 복합체의 기계적 특성들은 알루미늄 양에 따라 조사되었다. $1600^{\circ}C$ 이상의 온도에서 소결된 뮬라이트 preform은 침투된 알루미늄 용융체와 화학반응을 이루었으나, $1600^{\circ}C$에서 소결된 뮬라이트 소결체는 알루미늄 용융체에 대해 젖음이 이루어지지 않아 화학반응이 진행되지 않았다. 알루미늄 용융체의 침투 방향에 따른 복합체의 기계적 특성에 대한 영향은 알루미늄 용융체의 수직, 평행한 침투 방향 패턴의 두 가지 다른 모델들에 의해 고려되었다. $Al/Al_2O_3$복합체에서 알루미늄의 양의 증가에 따라 파괴강도는 감소하였으며, 파괴인성은 증가하는 경향을 나타냈다.$ Al/Al_2O_3$복합체의 미세구조는 금속의 침투 방향에 의해 결정되었지만, 복합체의 파괴강도와 파괴인성은 금속 침투 방향에 대한 의존성은 나타내지 않았다.

• 한국세라믹학회지
• /
• 제49권4호
• /
• pp.287-294
• /
• 2012

Ceramic Matrix Composites (CMCs) represent a class of non-brittle refractory materials for harsh and extreme environments in aerospace and other applications. The quasi-ductility of these structural materials depends on the quality of the interface between the matrix and the fiber surface. In this study, a manufacture route is described where in contrast to most other processes no additional fiber coating is used to adjust the fiber/matrix interfaces in order to obtain damage tolerance and fracture toughness. Adapted microstructures of uncoated carbon fiber preforms were developed to permit the rapid infiltration of molten alloys and the subsequent reaction with the carbon matrix. Furthermore, any direct reaction between the melt and fibers was minimized. Using pure silicon as the reactive melt, C/SiC composites were manufactured with an aim of employing the resulting composite for friction applications. This paper describes the formation of the microstructure inside the C/C preform and resulting C/C-SiC composite, in addition to the MAX phases.

• 유변학
• /
• 제7권3호
• /
• pp.173-180
• /
• 1995

LLDPE/LDPE 혼합물의 유변 물성과 필름가공특성 필름 물성 및 LLDPE의 extrudate 표면상태를 살펴보았다. LLDPE에 LDPE를 혼합함으로써 용융 강도가 크게 향상 되는 것을 볼수 있었으며 혼합비에 따라 필름의 기계적 물성이 변화하는 것을 볼수 있었다. 즉 최고의 물성을 나타내는 적절한 혼합비율이 존재하였다. 본논문에 사용된 LLDPE/LDPE 혼합물에 있어서는 LDPE의 함량이 15∼30wt%일 때 가장 우수한 기계적 물성을 얻을수 있 었다. LLDPE 필름의 표면 불량 문제를 보기위하여 capillary를 이용하여 LLDPE extrudate 의 표면 튀틀림(distortion)의 진행순서를 살펴본 결과, 전단 응력이 0.23MPa 일때 sharkskin이 발현함을 볼수 있었다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
• /
• pp.554-554
• /
• 2000

To improve mechanical properties of Cu-Al-Ni alloy by the grain refinement, Cu-Al-Ni SMA ribbons were fabricated by melt spinning apparatus. The variations of microstructure, mechanical properties and transformation characteristics with the condition of rapid solidification and annealing time-temperature were investigated in Cu-Al-Ni SMA ribbons. The ribbons fabricated by melt spinning obtained around 1.5nm in width and 50-60${\mu}{\textrm}{m}$ in thickness. With increasing wheel speed in order of 10m/s, 15m/s, 20m/s, 30m/s and 3m/s, the grain size was decreased in order of 10${\mu}{\textrm}{m}$, 6.25${\mu}{\textrm}{m}$, 5.5${\mu}{\textrm}{m}$, 3${\mu}{\textrm}{m}$ and 3${\mu}{\textrm}{m}$. $M_{s}$ and $A_{s}$ temperature were decreased with decreasing grain size. By X-ray diffraction test, ordered $\beta$$_1$ phase was observed in all the SMA ribbons and the volume friction of it was increased with increasing wheel speed. With increasing wheel speed, strain was increased from 4.2% to 5.8% and fracture mode has changed from mixture of intergranular and dimple fracture to mixture of fiber structure and dimple fracture. The grain size of ribbon heat-treated at $600^{\circ}C$ was increased with increasing time. In the heat-treated ribbons at 55$0^{\circ}C$, ${\gamma}$$_2$ phases were observed.d.d.

• 연구논문집
• /
• 통권22호
• /
• pp.127-139
• /
• 1992

The mechnial properties such as fracture strength, ductility and fatigue strength of Cu shape memory alloy are lower than those of Ti-Ni SMA, because of their high elastic anisotropy and large grain size. And in order to improve the mechanical property of Cu SMA, some techniques such as casting method by addition of refining element, powder metallurgy and rapid solidification process have been studied on the refinement of the grain size of Cu SMA. This study was carried out to refine the grain size of CuAlNi SMA by applying the melt spinning method. According to this study, the conclusions are as follows; - grain size of the melt-spun ribbon was about $1\mum$ - there was not change in grain size, although increasing of hot pressing temperature -grain size of the hot-extruded specimen was about $30-40\mum$, it is more refiner than that of castings

• 폴리머
• /
• 제31권5호
• /
• pp.399-403
• /
• 2007

폴리카보네이트/폴리(부틸렌 테레프탈레이트)(PC/PBT) 블렌드에 대해 용융혼합 과정에서 에스테르 교환반응 거동을 조사하였고, PC/PBT 혼합비에 따른 유변학적 특성, 파괴거동 및 파단면 모폴로지를 조사하였다. FT-IR 및 $^1H-NMR$ 분석을 통해 용융혼합 중에 PC와 PBT간 에스테르화 반응이 일어남을 확인하였다. PC 함량이 증가할수록 용융지수(MI)는 감소하여 PC의 높은 흐름저항성을 확인하였다. 또한 PC 함량이 증가할수록 저장 및 손실 탄성률은 증가하였고, Cole-Cole 도시로부터 PC/PBT 블렌드의 경우 혼합비에 관계없이 유변학적 상용성은 나타내지 않은 것으로 나타났다. 인장강도는 PC 함량이 증가함에 따라 선형적인 증가를 나타내었다. 충격강도의 경우 PC 함량이 증가함에 따라 증가하였는데, 약 $30{\sim}40wt%$ 범위에서 가장 급격한 증가폭을 나타내었고, 50 wt% 이상의 범위에서는 거의 일정한 값을 나타내었다. 충격 파단면을 관찰한 결과 약 40 wt% 이상의 범위에서부터 충격방향으로 거친 파괴 릿지(ridge)가 형성되어서 높은 충격강도를 나타낸 것으로 판단된다.

• 한국세라믹학회지
• /
• 제33권5호
• /
• pp.536-546
• /
• 1996

The TiC-Ni/Al reaction-bonding composites were prepared by the infiltration of Ni/Al melt into the TiC preforms. The microstructure the reaction composition crystalline phase and the mechanical properties of the composites were investigated. During the reaction-bonding Ni/Al mixture had a good wettability and per-meability with TiC preform and pore-free and fully dense sintered bodies were produced. In the case of the Ni/Al atomic ratio of 0.3 and 0.5 TiC raw particle shape was changed to irregular particles because of the decomposition in the liquid matrix and its phenomena was more distinguished in the Al-rich liquid matrix. With increasing more than 1 of the Ni/Al atomic ratio the sample of TiC grain shape was changed from spherical to palatelet particles. Also with increasing the atomic ratio of Ni/Al bending strength and fracture spherical to palatelet particles. Also with increasing the atomic ratio of Ni/Al bending strength and fracture toughness were increased and its maximum value was 1073 MPa and 11 MPa.m1/2 respectively.