Simultaneous optimization of topology and print orientation for transversely isotropic fatigue

Recent developments in additive manufacturing technologies have made it viable to manufacture the highly complex designs obtained via topology optimization. However, additively manufactured metals are complex compared to traditionally manufactured metals in that they often behave transversely isotropic, depending on the chosen print plane orientation, which further complicates design. Many of these additively manufactured metals have approximately isotropic stiffness but transversely isotropic strength properties, in particular those manufactured by powder-bed fusion methods, which are treated in this work. To account for this behavior in high-cycle fatigue, a criterion is formulated with basis in the orientation of the print plane, such that the orientation-dependent strength is taken into account. The criterion uses orientation angles, which can be included as design variables for simultaneous optimization of topology and print plane orientation. Furthermore, an improved formulation for the fatigue damage is proposed to achieve a good combination of accuracy and computational efficiency. These methods are demonstrated by solving both two- and three-dimensional problems, and the 3D design is subsequently verified using commercial finite element software.