The Effect of Fiber Orientation and Crack on Dynamic Characteristics of a Unidirectional Composite Cantilevered Wing Plate

Composite materials are becoming key elements in constructing advanced structures such as aircraft. These structures offer the benefit in terms of optimization between strength, stiffness, and weight. In recent studies, the concern of composite structures applications is the understanding of their failure modes such as crack and delamination, including complex fiber orientations. The presence of crack with various fiber orientations may affect the stiffness of the structure. In aircraft applications, particularly wing structures, the issue is more challenging due to the coupling of aerodynamic load and flexible structure which leads to aeroelastic phenomenon of flutter. Therefore, this study aimed to investigate the effect of crack on dynamic characteristics of a unidirectional composite simplified wing-like structure. The experiment was conducted by constructing the finite element model of a simplified wing-like structure as the basis, which was modeled as a unidirectional composite plate structure with some predefined fiber directions. To model the damage, a chordwise crack was inserted into the structure, whose length and location could be varied. Modal analysis was conducted to obtain dynamic characteristics of the composite structure, namely natural frequencies and mode shapes. The changes in natural frequencies and mode shapes for different combinations of fiber directions, crack lengths, and crack locations, are quantified and analyzed. Modal Assurance Criteria (MAC) was used to quantitatively evaluate the similarity of the mode shapes for different fiber orientation settings. The results showed that the order of the first six vibration modes, namely bending and torsion, was not altered by the change of fiber orientations but affected the value of natural frequencies. Furthermore, the existence of crack could reduce the natural frequencies significantly. MAC evaluation also showed that crack length could change the order of the mode shapes and the natural frequency of particular modes. For the fundamental modes, first bending and torsion, the natural frequencies decrease by approximately 20% as crack moves closer to the root. The changes in natural mode order and frequencies influenced the occurrence of couplings between modes capable of affecting the stability boundary in aeroelastic case.