An isogeometric approach to topology optimization of multi-material and functionally graded structures

A new isogeometric density-based approach for the topology optimization of multi-material structures is presented. In this method, the density fields of multiple material phases are represented using the isogeometric non-uniform rational B-spline-based parameterization leading to exact modeling of the geometry, removing numerical artifacts and full analytical computation of sensitivities in a cost-effective manner. An extension of the perimeter control technique is introduced where restrictions are imposed on the perimeters of density fields of all phases. Consequently, not only can one control the complexity of the optimal design but also the minimal lengths scales of all material phases. This leads to optimal designs with significantly enhanced manufacturability and comparable performance. Unlike the common element-wise or nodal-based density representations, owing to higher order continuity of density fields in this method, their gradients required for perimeter control restrictions are calculated exactly without additional computational cost. The problem is formulated with constraints on either (1) volume fractions of different material phases or (2) the total mass of the structure. The proposed method is applied for the minimal compliance design of two-dimensional structures consisting of multiple distinct materials as well as functionally graded ones. Copyright (C) 2016 John Wiley & Sons, Ltd.