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Analysis of Composite Microporosity according to Autoclave Vacuum Bag Processing Conditions

오토클레이브 진공포장법의 공정 조건에 따른 복합재의 미세기공률 분석

  • Yoon, Hyun-Sung (Research Center for Aircraft Parts Technology, School of Mechanical and Aerospace Engineering, Gyeongsang National University) ;
  • An, Woo-Jin (Research Center for Aircraft Parts Technology, School of Mechanical and Aerospace Engineering, Gyeongsang National University) ;
  • Kim, Man-Sung (Research Center for Aircraft Parts Technology, School of Mechanical and Aerospace Engineering, Gyeongsang National University) ;
  • Hong, Sung-Jin (Research Center for Aircraft Parts Technology, School of Mechanical and Aerospace Engineering, Gyeongsang National University) ;
  • Song, Min-Hwan (Research Center for Aircraft Parts Technology, School of Mechanical and Aerospace Engineering, Gyeongsang National University) ;
  • Choi, Jin-Ho (Research Center for Aircraft Parts Technology, School of Mechanical and Aerospace Engineering, Gyeongsang National University)
  • Received : 2019.04.04
  • Accepted : 2019.08.26
  • Published : 2019.10.31

Abstract

The composite material has the advantage that the fibers can be arranged in a desired direction and can be manufactured in one piece. However, micro voids can be formed due to micro air, moisture or improper curing temperature or pressure, which may cause the deterioration in mechanical strength. In this paper, the composite panels with different thicknesses were made by varying the curing pressure in an autoclave vacuum bag process and their microporosities were evaluated. Microporosity was measured by image analysis method, acid digestion method, and combustion method and their correlation with ultrasonic attenuation coefficient was analyzed. From the test results, it was found that the acid digestion method had the highest accuracy and the lower the curing pressure, the higher the microporosity and the ultrasonic attenuation coefficient. In addition, the microporosity and the ultrasonic attenuation coefficient were increased as the thickness of the composite panel was increased at the same curing pressure.

복합재는 원하는 방향으로 섬유를 배열하여 일체형으로 제조할 수 있는 장점이 있다. 그러나, 복합재는 제작과정에서 층(ply)과 층 사이에 있는 미세 공기, 소재 내부의 수분 또는 경화 중의 부적절한 온도와 압력 등으로 인하여 미세기공이 형성될 수 있으며, 이는 복합재 부품의 기계적 강도저하의 주요 원인으로 평가되고 있다. 본 논문에서는 오토클레이브 진공백 성형법을 이용하여 복합재 두께 별로 공정 조건(경화압력, 압밀시간, 압밀압력, 진공압력)을 변화시켜가며 복합재 패널을 제작하여 미세기공률을 분석하였다. 미세기공률은 이미지 분석법, 용해법, 연소법을 이용하여 평가하였으며, 초음파 감쇠계수와의 연관성을 분석하였다. 실험결과, 미세기공률 분석의 정확도는 용해법이 가장 우수한 것으로 나타났으며, 경화압력이 낮아질수록 미세기공률이 증가하고 높은 초음파 감쇠계수 값을 가짐을 확인하였다. 또한, 동일한 경화압력이라도 적층두께가 증가할수록 초음파 감쇠계수가 증가하고 기공률이 증가됨을 확인하였다.

Keywords

References

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