• Journal of the Korean Wood Science and Technology
• /
• 제35권2호
• /
• pp.69-78
• /
• 2007

The mechanical properties of wood flour, Hwangto (325 and 1,400 mesh per 25,4 mm) and coupling agent-reinforced HDPE composites were investigated in this study. Hwangto and maleated polyethylene (MAPE) were used as an inorganic filler and a coupling agent, respectively. The addition of Hwangto and MAPE to virgin HDPE also increased the Young's modulus in the smaller degree. The addition of wood flour and Hwangto to virgin HDPE increased the tensile strength, due to the high uniform dispersion of HDPE by high surface area of Hwangto in HDPE and wood flour. MAPE also significantly increased the tensile strength. When wood flour was added, there was no notable difference on the tensile properties, in terms of Hwangto particle size. Hwangto also improved the flexural modulus and strength of reinforced HDPE composites. With different particle sizes of Hwangto, there was no considerable difference in flexural modulus and strength of reinforced HDPE composites. The addition of Hwangto showed slightly lower impact strength than that of wood flour. However, the particle size of Hwangto showed no significant effect on the impact strength of reinforced composites. In conclusion, reinforced HDPE composites with organic and inorganic fillers provide highly improved mechanical properties over virgin HDPE.

• 폴리머
• /
• 제25권5호
• /
• pp.679-690
• /
• 2001

폴리에테르형 기포개방제를 사용한 고탄성 폴리우레탄 발포체의 제조에서 기포개방제의 농도변화가 계의 반응속도, 유변학적 성질, 발포체의 구조적인 안정성, 형태학적 성질 및 개방기포의 함량 등에 미치는 영향을 조사하고 이를 통하여 기포개방에서 기포개방제의 역할을 알아보았다. 또한 기포개방제의 농도에 따른 발포체의 기계적 물성을 관찰하였다. 기포개방제의 높은 친수성으로 인해 우레아 생성반응이 지연됨을 관찰하였다. 유변학적 성질의 관찰을 통하여 기고개방제의 농도 증가에 따라 계의 점도저하와 tan $\delta$의 증가를 확인하였고 이로 인해 얻어진 발포체는 낮은 구조적인 안정성과 높은 개방기포 함량을 나타내었다. 기포개방제의 농도 증가에 따라 matrix의 파괴와 matrix내 수소결합된 우레아의 고른 분산을 발포체의 형태학적 성질의 관찰로 확인할 수 있었다. 결론적으로 고탄성 폴리우레탄 발포체의 제조시 기포개방제의 높은 친수성에 기인하여 matrix의 탄성특성 저하가 일어나고 이로 인해 높은 개랑기포 함량을 가진 발포체가 형성됨을 알 수 있었다. 발포체의 경도, 인장강도, 인열강도, 신율 등은 기포개방제의 농도 증가에 따라 저하하였다.

• 한국식품과학회지
• /
• 제31권1호
• /
• pp.99-105
• /
• 1999

Methylcellulose (MC), hydroxypropylmethylcellulose-15 (HPMC-15)와 hydroxypropyl-methylcellulose-50 (HPMC-50)필름과 이에 칼슘을 첨가한 식용필름을 제조하여 이화학적 특성을 비교 연구하였다. 제조된 필름은 모두 $2.38{\sim}3.55$의 운도를 나타내며, 백색의 투명한 필름을 형성하였다. 인장강도는 MC필름이 HPMC필름보다 높았으며, 칼슘의 첨가에 의하여 증가하였고, 신장율은 HPMC-15와 이에 칼슘을 첨가한 필름군만 유의적으로 낮았다. 용해도는 HPMC의 점도의 증가에 따라 감소하였으며, MC필름과 HPMC-15필름 사이에는 유의적인 차이를 나타내지 않았고 칼슘의 첨가에 의하여 영향을 나타내지 않았다. 칼슘첨가에 의하여 투습도는 유의적인 차이를 나타내지 않았으며, MC필름이 HPMC-50 필름보다 낮았고, HPMC필름은 점도의 증가에 따라 증가하였다. 가스투과도는 MC필름이 HPMC필름보다 적었으며, 칼슘 첨가로 이산화탄소와 산소의 투과계수의 비가 낮게 측정되었다. 주사현미경으로 표면형상을 관찰한 결과 칼슘을 첨가한 MC필름이 더욱 균일한 표면형상을 나타냄을 알 수 있었다. 이상의 결과로서 HPMC와 MC필름은 Ca을 첨가함으로서 제조방법의 차이는 없었으나 인장강도가 증가하고 균일한 표면형상을 나타내어 HPMC와 MC필름 보다 내구성이 있는 필름을 제조할 수 있었다.

• 한국주조공학회지
• /
• 제32권2호
• /
• pp.98-103
• /
• 2012

Recently, development of Al-based alloys for high mechanical performance has been an important issue in automotive industry. The present study focused on the design of a high strength Al-based alloy for rheo-diecasting. The research was based on thermodynamic calculation and experimentals to optimize the alloy compositions. Two important considerations were carried out: i) to obtain uniform slurry with fine and globular microstructures for rheo-diecasting, ii) to be strengthend by T6 heat treatment. In order to evaluate the effect of Si content on the slurry microstructure and castability, thermodynamic calculation and fluidity test were carried out. The effects of various alloying components, such as Mg, Cu and Zn, on age hardenability were also investigated. The mechanical properties of the rheo-diecasting products using the newly developed alloy are 324MPa in tensile strength, 289MPa in yield strength, and 11.2% in elongation after T6 heat treatment.

• 상하수도학회지
• /
• 제20권4호
• /
• pp.545-558
• /
• 2006

The current conditions of large water mains are evaluated by deteriorations and the causes of deterioration are investigated through visual assessments in the field, mechanical tests and analysis of chemical compositions in laboratory for each pipe material, unlined cast iron pipes (CIPs), ductile iron pipes (DCIPs) and steel pipes (SPs) Tubercles and scales from internal and external corrosion of unlined cast iron pipes were identified as the causes of functional performance limitations in large water mains. It is investigated that main causes of internal and external corrosion of water pipes are from lots of depositions of organic and inorganic substances on pipe surface, concentrated pitting, and uniform corrosion by local or global exfoliation or detachment of lining and coatings of DCIPs and SPs. Internal and external corrosion depths of CIPs were higher than those of DCIPs and SPs. Consequently, total corrosion rate summed internal and external corrosion rates of CIPs also were shown to be higher than those of DCIPs and SPs. The failure time from hole generation of CIPs by total corrosion rate was predicted to be taken sixteen years, and DCIPs and SPs were twenty-six years and one hundred and fifty three years. And longitudinal deflection of investigated water mains were not happened and mechanical strengths such as tensile strength, elongation, and hardness also were mostly suited to Korea Standards. It was thought that the weakness of tensile strength of one sample(S-11) was, however, due to higher carbon contents(%) in CIPs. Pipe deterioration score of S-46 was 55.2 and was preferentially assessed to be rehabilitated.

• 한국재료학회지
• /
• 제5권8호
• /
• pp.1005-1112
• /
• 1995

Al-Li-Cu-Mg합금에서 0~9% 범위의 stretching이 석출상 및 기계적성질에 미치는 영향을 조사하였다. Stretching을 하였을 경우 $\delta$'(A1$_3$Li)석출상의 크기는 변화가 없었으나 T$_1$(Al$_2$CuLi)석출상은 미세하고 균일하게 분포하였으며 입계석출물도 비교적 적게 형성되었다. 또한 변형부위에 분포하는 $\delta$'석출상에 의한 planar slip도 감소되었다. 항복강도는 15$0^{\circ}C$에서 120시간 시효처리 하였을때 stretching을 하지 않은 경우 328~342 Mpa에서 6% stretching을 하였을 경우 466~488MPa로 향상되었으며 연신율은 같은 조건에서 각각 9.7~10.4%와 5~5.7%를 나타내었다.

• 소성∙가공
• /
• 제21권1호
• /
• pp.49-57
• /
• 2012

It is difficult to estimate the properties of multilayered sheet because they are composed of one or more different materials. Plastic deformation behavior of the multilayered sheet is quite different as compared to each material individually. The deformation behavior of multilayered sheet should be investigated in order to prevent forming defects and to predict the properties of the formed part. In this study, the mechanical properties and formability of stainless steel-aluminum-magnesium multilayered sheet were investigated. The multilayered sheet needs to be deformed at an elevated temperature because of its poor formability at room temperature. Uniaxial tensile tests were performed at various temperatures and strain rates. Fracture patterns changed mainly at a temperature of $200^{\circ}C$. Uniform and total elongation of multilayered sheet increased to values greater than those of each material when deformed at $250^{\circ}C$. The limiting drawing ratio (LDR) was obtained using a circular cup deep drawing test to measure the formability of the multilayered sheet. A maximum value for the LDR of about 2 was achieved at $250^{\circ}C$, which is the appropriate forming temperature for the Mg alloy. Fracture patterns on a circular cup and thickness of formed part were predicted by a rigid-viscoplastic FEM analysis. Two kinds of modeling techniques were used to simulate deep drawing process of multilayered sheet. A single-layer FE-model, which combines the three different layers into a macroscopic single layer, predicted well the thickness distribution of the drawn cup. In contrast, the location and the time of fracture were estimated better with a multi-layer FE model, which used different material properties for each of the three layers.

• 폴리머
• /
• 제32권5호
• /
• pp.409-414
• /
• 2008

전기방사법으로 이온염을 함유하는 TFE/증류수 혼합용매를 이용하여 젤라틴 나노섬유를 제조하였으며, 얻어진 나노섬유의 평균직경은 $110{\sim}125\;nm$였다. 이온염의 농도가 증가할수록 비드의 발생이 줄어들고 균일한 나노섬유 제조가 가능하였다. 이는 이온염의 첨가에 의한 젤라틴 용액의 점도 및 전도도가 증가함에 기인하는 것으로 확인되었다. 특히 일가이온보다 이가이온을 사용할 경우 점도 및 전도도의 증가에 더 효과적이었으며 이들 이온염은 분자간 소수성 상호작용뿐만 아니라 젤라틴 분자의 입체구조 정렬에도 영향을 주었다. 그러나 이온염 농도에 따른 나노섬유의 직경변화는 관찰되지 않았다. 제조된 나노섬유를 이용한 XRD분석 결과 이온염의 농도가 증가할수록 젤라틴 분자의 재결정화에 의해 나노섬유의 결정화도가 높아졌다.

• 산업식품공학
• /
• 제15권4호
• /
• pp.305-310
• /
• 2011

본 연구에서는 DSM을 이용하여 단백질 추출이나 정제없이 식품에 적용 가능성이 있는 가식성 필름을 개발하였다. HPH 처리는 표면이 매끄럽고 균일한 형태의 필름을 형성시켰고, 필름의 WVP값을 감소시켜 수분 방벽 효과를 높였다. 필름 내 글리세롤 농도 증가는 WVP값을 전반적으로 높였다. 농산물 가공 부산물인 DSM으로 제작된 가식성 필름은 새로운 식품 소재로서 상업적 적용 가능성을 보여주었다.

• Corrosion Science and Technology
• /
• 제21권2호
• /
• pp.130-137
• /
• 2022

In this work, the degradation of high-pressure superheater tubes exposed to the flame of a duct burner in a heat recovery steam generator of a district heating system was evaluated. To assess the deterioration of the used superheater tube, the microstructure, microhardness, and tensile properties were investigated by comparison to an unused tube. The study found that a fin bound at the outer surface of the used tube became fragile only in the location facing the flame. This indicates that the tube was directly exposed to the flame from the duct burner or underwent abnormal overheating. While the unused tube showed a uniform value in hardness and equiaxial grain structure, the used tube revealed a decrease in hardness up to 105 HV and an increase in grain size with a plate-like morphology in the location facing the flame. The coarsening of the grain structure by the flame weakened the mechanical properties of yield strength, tensile strength, and elongation.