  Permitting multiple materials within a topology optimization setting
increases the search space of the technique, which facilitates obtaining
high-performing and efficient optimized designs. Structures with multiple
materials involving fluidic pressure loads find various applications. However,
dealing with the design-dependent nature of the pressure loads is challenging
in topology optimization that gets even more pronounced with a multi-material
framework. This paper provides a density-based topology optimization method to
design fluidic pressure loadbearing multi-material structures. The design
domain is parameterized using hexagonal elements as they ensure nonsingular
connectivity. Pressure modeling is performed using the Darcy law with a
conceptualized drainage term. The flow coefficient of each element is
determined using a smooth Heaviside function considering its solid and void
states. The consistent nodal loads are determined using the standard finite
element methods. Multiple materials is modeled using the extended SIMP scheme.
Compliance minimization with volume constraints is performed to achieve
optimized loadbearing structures. Few examples are presented to demonstrate the
efficacy and versatility of the proposed approach. The optimized results
contain the prescribed amount of different materials.
