  The present paper introduces a hybrid explicit-implicit topology optimization
method for shell-infill composite structure design. The proposed approach
effectively combines the advantages of the explicit Moving Morphable Component
(MMC) method, which describes structural topology only using a set of geometric
parameters, and the implicit Solid Isotropic Material with Penalization (SIMP)
method, which offers greater design freedom for characterizing the structural
features. Compared to the existing methods for shell-infill structure design,
the proposed approach can obtain optimized shell-infill structures with complex
infill topology without resorting to complex filtering/projection operations.
Numerical examples demonstrate the effectiveness of the proposed approach.
