단일방향 탄소섬유복합재료 적층 판에서 전파 방향에 따른 램파 S0 모드의 군속도의 변화
Variation of the Group Velocity of Lamb Wave S0 Mode with the Propagating Direction in the Laminated Unidirectional CFRP Plates
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초록
본 연구에서는 단일방향 탄소섬유강화복합재료 판에서 대칭모드의 군속도 분선곡선을 전파 방향을 변화시키면서 계산하였다. 그리고 속도 분산 곡선에서 첫 번째 단절주파수 이하인 0.2 MHzmm에 해당하는 S0 대칭모드 군속도를 가지고서 위상속도 곡선을 얻고 slowness 곡선을 도입하여 군속도 곡선으로 교정하였다. 단일방향 섬유강화복합재료 판에서 대칭모드의 속도를 전파 방향을 변화시키면서 측정하였고 교정된 군속도 곡선과 비교하였다. 측정된 속도는 섬유 방향 근처의 cusp 영역을 제외하고는 교정된 군속도 곡선과 잘 일치하였다. 이것은 단일방향 탄소섬유강화복합재료 판에서 속도가 빠른 방향으로 에너지를 더 잘 전파하기 때문에 전파 방향이 주축방향과 일치하지 않을 때 군속도 방향은 섬유 방향 쪽으로 기울어지는 결과로 나타난 것이다.
Abstract
In this paper, the group velocity dispersion curves of the symmetric mode in unidirectional CFRP plate was calculated as varying the propagating direction. The group velocity curve was obtained with the group velocities of the symmetric mode corresponding to 0.2 MHzmm under the first cut-off frequency in the dispersion curves, and corrected by introducing the slowness curve. The velocities of the S0 symmetric mode in the unidirectional CFRP plate were measured as varying the propagating direction and compared with the corrected group velocity curve. The measured velocities were good agreement with the corrected group velocity curve except near the fiber direction which was called the cusp region. It implies that the direction of the group velocities incline toward the fiber direction of the unidirectional CFRP plates when the propagation direction is not accorded with the principal axis. It is supposed that this phenomenon results from the preferential propagating the energy toward the direction with the faster propagation velocity.
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