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On Ultrasonic Techniques of Fiber Orientation in CFRP Composite Laminates
임광희(Kwanghee Im),김영남(Youngnam Kim),나승우(Seoungwoo Na),이길성(Kilsung Lee),David K. Hsu,박제웅(Jewoung Park),심재기(Jaeki Sim),양인영(Inyoung Yang) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The layup of a CFRP (carbon-fiber reinforced plastics) composite laminates affects the properties of the laminate, including stiffness, strength and thermal behavior. It is very important to detect ply error before the laminate is cured for both manual procedure and fiber placement procedure. An ultrasonic technique would be very beneficial, which could be used to test the part after and before curing laminates and requires less time than the optical test. Also cross-polarized scan is very sensitive to the layup errors and ply misorientations. Scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. Firstly, a manual scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers to find the effect of fiber misorientations of composite laminates. Also a method for nondestructively determining the ply layup in a composite laminate is presented. The method employs a normal-incidence longitudinal ultrasound to perform C-scan of ply interfaces of the laminate. And a ply-by-ply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. Test results between after and before curing laminates with model data were compared for a fiber orientation of the laminates.
곡률을 갖는 복합재 적층쉘의 충격거동에 관한 실험적 고찰
김영남(Youngnam Kim),김지훈(Jihoon Kim),이현(Hyun Lee),나승우(Seoungwoo Na),심재기(Jaeki Sim),양인영(Inyoung Yang) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Composites are considered for many structural applications structural weight. These materials have high strength-to-weight and stiffness-to-weight ratios. However, they are susceptible to impact loading because they are laminar systems with weak interfaces. Matrix cracking and delamination are the most common damage mechanisms of low velocity impact and are dependent on each other. This paper is to study the behavior of composite shell under transverse impact loading. In this study, carbon-epoxy composite laminates with various curvatures was used. Low velocity impact tests were performed using a drop weight testing machine. The 100㎜×100㎜ shells were clamped in order to produce a central circular area (Φ=80㎜). An hemispherical impactor (m=0.1㎏ and Φ=10㎜) was used and the tests were done with velocities ranging from 2.8 to 4.8 ㎧. The real curve force/time was registered in order to obtain the maximum contact force and contact time. And then, we know that contact force and delamination area of flat-plate is higher than cylindrical shell panel in the same kinetic energy level, and flat-plate is easily penetrated than cylindrical shell panel. And contact force, deflection and delamination area decrease as the curvature increase.