  In the present work, a hybrid MMC-MMV approach is developed for designing
additive manufacturing-oriented shell-graded-infill structures. The key idea is
to describe the geometry of a shell-graded-infill structure explicitly using
some geometry parameters. To this end, a set of morphable voids is adopted to
describe the boundary of the coating shell, while a set of morphable components
combing with a coordinate perturbation technique are introduced to represent
the graded infill distribution. Under such treatment, both the crisp boundary
of the coating shell and the graded infill can be optimized simultaneously,
with a small number of design variables. Numerical examples demonstrate the
effectiveness of the proposed approach.
