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단방향 연속 섬유 복합재 횡단면에서 섬유 배열에 따른 응력 분포 변화
최수훈 ( Soohoon Choi ),지우석 ( Wooseok Ji ) 한국복합재료학회 2020 Composites research Vol.33 No.1
단방향 연속 섬유 강화 복합소재에 대하여 섬유 배열에 따른 응력 분포 양상을 연구하기 위해 단면 형상을 대표하는 체적 요소를 생성하였다. 대표 체적 요소에 횡방향 하중을 가하였을 때, 섬유와 기지재 강성의 차이로 인해 섬유 둘레에서 응력 집중 현상이 발생하며, 섬유 간 좁은 간격 때문에 집중된 응력이 중첩되며 섬유 주변에서 높은 응력이 구해질 것이라 쉽게 예측할 수 있다. 본 연구에서는 섬유 둘레 응력 증감이 단순히 섬유 간 간격 뿐 아니라 섬유의 상대적 위치가 하중 방향과 이루는 각도에 의해서도 결정됨을 보여준다. 정규 육각 구조를 가지는 대표 체적 요소의 중앙에 위치한 섬유를 다양한 방향으로 이동시키며 횡방향 하중을 가하여, 섬유 주변 응력이 증가하거나감소하는 양상을 유한요소해석 기법을 이용해 측정하였다. 섬유 간 거리가 최소이면서 두 섬유의 중심을 잇는 선분의 방향이 하중 방향과 일치할 때 응력이 최대로 증가하였으며, 섬유 간 거리가 최소라 하더라도 하중 방향에 수직일 때 최대 응력은 오히려 감소한다는 것을 보여준다. Stress distributions dependent on fiber arrangements are studied using the two-dimensional representative volume element (RVE) model for uni-directionally continuous fiber-reinforced composites subjected to transverse tensile loading. It is easily expected that the stresses around the fibers are concentrated mainly due to the stiffness mismatch between the fiber and matrix materials. In this presentation, it is shown that the stresses are not always increased although the distance between two fibers is shortened. The 2D RVE models, originally having a regular hexagonal fiber array, is utilized to study the effect of the fiber locations on the stress distributions. As the central fiber is relocated, the stress distributions around the fiber are obtained through finite element analysis. It is found that the stresses around the fiber are strongly dependent on the fiber distance as well as the angle between the loading direction and the line connecting two fibers.
김시온 ( Kim Sion ),조은하 ( Jo Eunha ),최수훈 ( Choi Soohoon ) 한국물환경학회 2020 한국물환경학회·대한상하수도학회 공동 춘계학술발표회 Vol.2020 No.-
In the current research, various conditions were evaluated to understand the release of fibrous microplastics and organic leachate from teabags. Six commercial teabags composed of 4 different plastic materials were tested under different temperatures, fiber damages, and water contact times. The main object of the research was to verify the amount of microplastics or organic leachate that may occur in tea consumed in our every day lives. The main focus was to verify the fibrous microplastic release and organic leachate of teabags under different damages. Damages of 1 ~ 10 cm were conducted on the teabags and submerged in glass vials under different temperatures. The teabags were cut with steal scissors of different degrees and the tea leaves were removed. Empty teabags were washed with deionized (DI) water for three trials before the experiments were conducted. Three empty teabags were submerged in every glass vial and submerged under constant temperatures in a water bath. the water bath contained a shaker where the samples were shaked during each trial. After being submerged in the water bath, the water from the teabags were filtered through a cellulous acetate membrane filter with pore sizes of 1 μm. Each filter was rinsed thoroughly and filtered with DI water before filtrations of the teabag samples. Filtered fibrous microplastics were counted with an optical microscope. Residual microplastics in the filtered water were analyzed with a TOC anayzer, dynamic light scattering analyzer, and SEM imaging. Results showed a logametric increase for both fibrous microplastic release and organic leachate with the increase of the damage inflicted on the teabags. Samples under higher temperatures also showed a higher release of the fibrous microplastics and leached TOC matter. The time for which the damaged teabags were submerged under water also showed a strong correlation with plastic release and TOC leaching. The hydraulic size of the filtered microplastics were in the size range of 1 nm to 2.4 μm. SEM resulted also showed similar sizes of microplastics with EDX results indicating the fibers as polymeric matters. The type of teabags and its assembly method also indicated a degree of influence in the release and leachate of the teabags. The current research has showed the amount of potential mircroplastic consumption via tea consumption.