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Acoustic performance of flexible polyurethane composite foams filled with melamine particles
윤동주,김정현 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.12
PU foams are widely used in the automobile industry not only for their lightweight properties, but also as sound-absorbing and seat cushioning materials. The effects of particles on the sound absorption properties of PU composite foams were investigated. PU foams containing 3 wt% melamine particles showed excellent sound absorption properties. However, when the particle content exceeded 3 wt%, particle agglomeration occurred, leading to reduced sound absorption. A dispersant was added during the fabrication process to improve the interfacial compatibility between the PU matrix and melamine particles, resulting in a well-developed cavity and pore structure. The sound absorption characteristics of the PU composite foams were significantly improved in the frequency range below 2,000 Hz. Our study highlights the importance of adjusting the concentration of particles and optimizing the cavity and pore structure of the material for achieving better sound absorption properties in PU composite foams.
부분 오스테나이트화 후 항온 변태한 1.0C-1.5Cr 베어링강의 미세조직 특성
윤동주,최병영 ( Dong Joo Yoon,Byung Young Choi ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.1
Metallographic observation was carried out by scanning and transmission electron microscopy to evaluate microstructural characteristics of partially austenitized and isothermally transformed 1.0C-1.5Cr bearing steel. It was observed that lower bainite formed in the local region of specimen partially austenitized and isothermally held at 250℃ for 1/3hr and formed in almost all area of the specimen isothermally held at 250℃ for 2hrs. Lower bainitic carbides with midrib was also observed in the specimen partially austenitized and isothermally held at 250℃ for 4hrs. Midrib was nearly carbide-free region and thicker in the vicinity of spherical carbides than the other region. Lengthening speed of lower bainitic carbides was remarkabey increased at isothermal holding time ranging from 2hrs to 4hrs.
고정성 보철물을 지지하는 골유착성 임풀란트의 위치에 따른 지지조직에서의 유한요소적 응력분석
尹東柱,申相完,徐室源 대한치과이식임플란트학회 1992 The Korean Academy of Implant Dentistry Vol.12 No.1
Many studies have been reported on the successful replacement of missing teeth with osseointegrated dental implants. However, little research has been carried out on the biomechanical aspect of the stress on the surrounding bone of the free-standing type of dental implant prostheses. This experimental study was aimed to analyze the stress distribution pattern on the supporting tissues depending upon the position of osseointegrated implants supporting fixed bridges. In the cases of unilateral partially edentulous mandible (the 2nd premolar and the 1st and 2nd molars missing), two osseointegrated implants were placed at the 2nd premolar and 2nd molar sites (Model A ), the 1st and 2nd molar sites (Model B, Anterior cantilevered type), the 2nd premolar and 1st molar sites (Model C, Posterior cantilevered type). Chewing forces of dentate patients and denture wearer were applied vertically on the 2nd premolar, the 1st molar, and the 2nd molar of each model. A 3 —Unit fixed partial denture was constructed at each model and cantilevered extension parts were involved in Model B and Model C. Two dimensional finite element analysis was undertaken. The commercial software (Super SAP) for IBM 16 bit personal computer was utilized. The results were as follows : 1. The magnitude of applied load influenced on the total value of stresses, but did not influence on the pattern of stress distribution. 2. The magnitude of stress developed from the supporting tissues were in order of Model C,Model A,Model B. 3. High stresses were concentrated on the cervical and apical portion of the implant/bone interface. 4. A difference of the stress magnitude on the implant/bone interface between mesial and distal implant was most prominant in Model C and in order of Model A and Model B. 5. The stresses developed in Model A were evenly distributed throughout both implants. 6. The stresses concentrated on the cervical portion of cantilevered side were higher in the posterior cantilevered type than in the anterior cantilevered type.