1 Copyright © 2016 by ASME Proceedings of the ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference IDETC/CIE 2016 August 21-24, 2016, Charlotte, North Carolina, USA IDETC2016-59494 Optimization for Anisotropy in Additively Manufactured Lattice Structures Tino Stanković Engineering Design and Computing Laboratory Dept. of Mechanical and Process Engineering ETH Zürich, Switzerland tinos@ethz.ch Jochen Mueller Engineering Design and Computing Laboratory Dept. of Mechanical and Process Engineering ETH Zürich, Switzerland jm@ethz.ch Kristina Shea Engineering Design and Computing Laboratory Dept. of Mechanical and Process Engineering ETH Zürich, Switzerland kshea@ethz.ch ABSTRACT The build orientation of fabricated parts is one the most influential factors affecting material properties in many Additive Manufacturing (AM) processes. Applications such as the optimization of lattice structures for AM, are particularly affected as knowledge of the anisotropy model of the material is crucial. The investigation in this paper shows the influence of material anisotropy and build orientation on the optimized lattice structure designs. First, a material property characterization study for both compression and tension states of a single material is carried out for the example of inkjet 3D printing. Then, a generalized optimality criteria method is extended for the optimal sizing of single material and fixed topology lattice structures with respect to displacement, stress and Euler buckling constraints. The stress and Euler buckling constraints are formulated as side constraints that are handled in combination with fully-stressed design recursion. The results demonstrate the effect of anisotropy on the optimized designs caused by individual struts’ build orientation. This demonstrates the need to include anisotropic models in the optimization in order to produce solutions that can be fabricated and tested. 1.0 INTRODUCTION The build orientation of additively manufactured (AM) parts plays an important role in the optimization of lattice structures for inkjet 3D printing and any AM process with known anisotropic material properties. Knowledge of the anisotropy model of the material is crucial since the local load direction in each strut differs based on the topology and rotating the whole structure rotates all struts. In a recently published article, it has been shown that the effect of build orientation of 3D printed parts from the inkjet 3D printing process is non- linear [1]. Due to interactions among many struts and non- linear material properties in a three-dimensional space, the optimization of such structures is not trivial and accurate material data is required. It has also been shown that the weakest mechanical properties are not only found along the z- axis, as assumed in many other works, but at an angle of approximately 45° in relation to the three axes of the printers’ coordinate system as shown in [1][2]. This discovery is particularly important for lattice structures where different angles of the discrete struts in the structure always occur and thus their axial loads are also at many different angles in the structure. Lattice structures are growing in interest due to their favorable strength-to-weight ratio allowing for efficient load carrying and energy absorption properties [3][4]. Multi-material lattices are beneficial because they can alter the product’s performance capabilities without altering the dimensions of the topology and individual struts [5]. Optimizing for anisotropy in such complex structures with often hundreds or thousands of members is, however, a large-scale optimization problem. Few methods exist to deal with such large-scale optimization problems for AM, most notably is the application of the optimality criteria as demonstrated in the recent publications by Stanković et al. [5] and [6] to tackle the problem of optimal