Effect of shape parameters of fiber on the packing structure

Employing the discrete element method with a multi-sphere model, this paper presents a numerical analysis of the packing structure of fibers during the preparation of the fiber porous blank, in which effects of such shape parameters of fibers as the aspect ratio and the curl index have been taken into account. For ten kinds of straight fibers and eight kinds of curved fibers with different aspect ratios and curl indexes, the microstructure of fiber packing formed by gravity settling is quantified in terms of the packing porosity, coordination number, contact orientation and fiber orientation. The results show that a larger packing porosity can be realized by increasing the aspect ratio or decreasing the curl index. Similarly, an individual fiber with a large aspect ratio in the packing structure can have more lap joints by increasing the curl index. Meanwhile, the phenomenon that curved fiber can fit better in an interstice than straight fibers is the main cause for the sharp increase of the mean coordination number when the shape of fiber changes from straight to curved. With regard to straight fibers, a preferable contact angle of 15° is confirmed almost for all cases while the intersection angle is in the vicinity of 50° on the whole. Correspondingly, the curvature has a significant influence on the heterogeneity of the contact orientation, and a strong tendency of horizontal alignment can be found for both straight and curved fibers. It is noted that the predictions of the packing porosity for straight fibers in this work are comparable to available experimental data and simulations. Those finds would be useful for a better understanding of the packing structure of fibers at the particle scale.