Topology and orientation optimization of multi-material hinge-free composite compliant mechanisms under multiple design-dependent loadings

Compliant mechanisms with multiple input loads and output ports are commonly applied in micro-electromechanical systems (MEMS), while compliant mechanisms under design-dependent pressure loadings (such as pneumatic or hydraulic) can generate smooth and compatible deformations. Combining these two types of problems, we propose the design problem of compliant mechanisms under multiple design-dependent loadings. To potentially improve the structural performances, fiber-reinforced composite materials are introduced, and multi-material topology optimization and material orientation optimization are considered simultaneously, which enables the materials to be anisotropic and heterogeneous. Since compliant mechanisms utilize elastic deformation to transmit input forces or displacements to output forces or displacements, anisotropic and heterogeneous material can increase the freedoms in displacement and force transmissions compared to conventional homogeneous isotropic material. The topology optimization is implemented via an extended moving iso-surface threshold (MIST) method for multi-material, in which a novel element-based searching scheme is employed for tracking multiple fluid–structure interfaces. The orientation optimization is achieved via an analytical solution derived for fully anisotropic materials and multi-input-multi-output compliant mechanisms. Numerical examples are presented to show the validity of the present MIST method to design multi-material hinge-free compliant mechanisms under multiple design-dependent loadings.