Abstract
A comparison of mode shapes in isotropic structures can be efficiently performed using the modal assurance criterion (MAC) to determine the similarity between mode shape vectors. However, the unidirectional, carbon-based composite (UCBC) structure shows different dynamic characteristics according to the carbon fiber orientation, even for the same structural configuration. The MAC of a certain mode may result in a poor value for the CBC structures in the case of the existence of the distorted mode shape vector from reinforced carbon fibers. In this study, the mode tracking of the UCBC structure is proposed using the MAC value only under the modified mode shape vector to enhance the MAC value between relevant modes. Because the mode shape vectors of the UCBC structure are altered from those of the isotropic structure owing to the reinforced stiffness along the carbon fiber orientation, the modified mode shape vectors are calculated by multiplying the original vectors with the proposed modification window. The proposed method was verified for simple UCBC structures with five different carbon fiber orientations, from 0° to 90°. The UCBC structures were tracked for five modes, three bending and two torsional, and the results were discussed with reference to earlier study results.
Highlights
Crystals 2022, 12, 236. https://Carbon-based composite (CBC) materials have been used in industries owing to their high specific stiffness and adequate damping qualities, and rigorous studies have been focused on the development of lightweight products or manufacturing processes
Structure are altered from those of the isotropic structure owing to the reinforced stiffness along the carbon fiber orientation, the modified mode shape vectors are calculated by multiplying the original vectors with the proposed modification window
Some jobs were devoted to identifying the structural strength or damping properties; the bending resonance method [6] was proposed for the directional-dependent dynamic material property, and damping coefficients were measured for flax-epoxy composite plates [7], thermoplastic organic sheets [8]; the characterization of failure strain was conducted for three reinforcements, woven jute, carbon (3k), and glass fibers under the on- and off-axis [9]
Summary
Carbon-based composite (CBC) materials have been used in industries owing to their high specific stiffness and adequate damping qualities, and rigorous studies have been focused on the development of lightweight products or manufacturing processes. The sensitivity of modal parameters was discussed for a simple UCBC specimen over different five carbon fiber orientations in a previous study [25], and the relationship between the structural stiffness and the viscous damping coefficient was investigated for the same composite structure [26]. The tracking method of identified modes of interest is essential to provide reliable FRFs or modal information of the UCBC structure, so a direct investigation of the mode-tracking method was developed using multiple indicators, such as the MAC value, resonance frequency, and viscous damping coefficient in a recent study [27]. Because the modified mode shapes were derived from the modification window compensating for the distorted behavior from the carbon fibers, the proposed method is surely independent of the dynamics of the system and can be extended into general composite structures. The best study results may be successfully obtained using the tracking strategy with only the modified MAC values, and this study is the first step towards finding dynamic variations in composite structures using the modification of mode shapes in composite structures
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