Morphological characterization of concave particle based on convex decomposition

Particle morphology is an important factor affecting the mechanical properties of granular materials. However, it is difficult to quantify the morphology characteristics of the complex concave particle. Fortunately, complex particle can be segmented by convex decomposition, so a new shape index named convex decomposition coefficient (CDC) related to the number of segmentations is proposed. First, the pocket concavity was introduced to simplify the morphology hierarchically. Second, the cut weight linked to concavity was defined and convex decomposition was linearly optimised by maximizing the total cut weights. Third, the CDC was defined as the minimum block number where the block area ratio cumulatively exceeded 0.9 in descending order. Finally, the proposed index was used to quantify the particle morphology of coral sand. The results demonstrate that the CDC of coral sands mainly ranges from 2 to 6, with a positively skewed distribution. Furthermore, CDC correlates well with three shape indices: sphericity, particle size, and convexity. Larger CDC is associated with smaller sphericity, larger particle size, and smaller convexity. The index has certain scientific research value and practical significance.