Optimization for twist chirality of structural materials induced by axial strain

The design of material microstructure may bring novel properties beyond traditional materials. When a tube or beam is composed of a uniform material, it is hardly twisted under axial compression or extension. In this paper, we will propose a systematic topology optimization approach on designing materials of tubes or beams exhibiting the twist deformation under the axial strain. The optimization objective is to maximize the twist angle of a structure constructed by optimally designing microstructures of cellular or composite materials. The proposed two-scale topology optimization problem is then solved by the extended bi-directional evolutionary structural optimization (BESO) method. Numerical results show that various topological patterns of microstructures are achieved and the resulting tubes and beams exhibit the desirable twist chirality. It is also noted that the twist chirality of the structures somewhat depends on the size of the material unit cell. The size effects of the material unit cell are therefore investigated and discussed. The twist chirality of the resulting structures has many potential applications, e.g., sensors and actuators.