미시역학적 파손이론을 이용한 복합재 적층판의 피로수명 예측 = Prediction of Fatigue Life of Composite Laminates using Micromechanics of Failure

국문 초록 (Abstract)

복합재 적층판의 피로수명을 평가하는 것은 여러 가지 재료와 섬유적층각에 따라 수많은 인증실험이 요구된다. 본 논문에서는 미시역학적 파손이론을 이용하여 복합재의 구성재료인 섬유, 기지 및 섬유/기지 경계면의 피로수명 예측를 통해 복합재적층판의 피로수명 평가를 할 수 있는 방법을 제시하였다. 기지는 다축응력상태을 고려할 수 있는 일반적인 등방성 재료의 등가응력파손식을 이용하였고, 섬유는 이방성 재료이지만 섬유방향의 응력이 주요하므로 섬유방향의 응력만 고려한 최대응력파손식을 사용하였다. 섬유/기지 경계면에서는 임계단면파손식을 사용하였고, 경계면의 피로강도가 크다고 가정하여 경계면에서의 피로파손는 무시하였다. 인장과 압축강도가 다른 재료의 평균응력효과를 고려할 수 있도록 수정된 Goodman 식을 이용하였다. 순수 기지의 피로실험 데이터를 기반으로 미시역학적 파손이론을 이용하여 단일 플라이와 복합재 적층판인 UDT[90°2], BX[±45°]S와 TX[0°2/±45°]S의 피로수명을 예측해 보았고, 실험 데이터와 잘 일치함을 확인하였다.

다국어 초록 (Multilingual Abstract)

Many tests are required to predict the fatigue life of composite laminates made of various materials and having different layup sequences. Aiming at reducing the number of tests, a methodology was presented in this paper to predict fatigue life of composite laminates based on fatigue life prediction of constituents, i.e. the fiber, matrix and interface, using micromechanics of failure. For matrix, the equivalent stress model which is generally used for isotropic materials was employed to take care of multi-axial fatigue loading. For fiber, a maximum stress model considering only stress along fiber direction was used. The critical plane model was introduced for the interface of the fiber and matrix, but fatigue life prediction was ignored for the interface since the interface fatigue strength was presumed high enough. The modified Goodman equation was utilized to take into account the mean stress effect. To check the validity of the theory, the fatigue life of three different GFRP laminates, UDT[90°2], BX[±45°]S and TX[0°2/±45°]S was examined experimentally. The comparison between predictions and test measurements showed good agreement.

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