This presentation was made at CAASE18, The Conference on Advancing Analysis & Simulation in Engineering. CAASE18 brought together the leading visionaries, developers, and practitioners of CAE-related technologies in an open forum, to share experiences, discuss relevant trends, discover common themes, and explore future issues.
Metal additive manufactured (AM) lattice-type structures are an efficient way of establishing high directional stiffness at a far reduced material volume. This makes them ideal for aerospace applications such as UAVs. Typical manufacturing processes include SLM (Selective Laser Melting) / DMLS (Direct Metal Laser Sintering), and EBM (Electron Beam Melting). When considering real-life applications of these structures, many assumptions are made about the characteristics of the manufactured material. Among others, these include strength, elastic moduli, thermal properties, material density, surface finish, and structural stability. These characteristics are affected by many factors, including laser spot size, laser power, metal powder, build orientation, and feature size.
This paper addresses some of the key problems with characterizing metal AM parts. Specifically investigated are how bulk material properties correlate with lattice feature size (sub 1mm), and why this occurs. Explicit dynamics finite element simulations are used in a novel quasi-static regime to predict the deformations and failure. These simulations are applied to the microscopic features of tensile specimens using 3D models obtained via CT scans. This enables very close observation of the initiation and completion of ductile fractures. Comparisons are drawn between the simulated fractures and the actual test fractures.
Next considered are methods of physically testing the stiffness and strength of built-up lattice structures. Using the material data obtained from size correlated dog-bone specimens, the lattices are simulated with explicit dynamics and self-contact. Observations are made of progressive failure modes for lattices in both tension and compression, and subsequently correlated to the simulations. The load-displacement behavior is also directly correlated to test and shows good accuracy.
The study ultimately presents a method whereby a metal AM lattice can be reliably simulated despite aggressive idealization of the features. The correlation of bulk material properties with AM lattice feature size shows that the properties change at smaller sizes, but become constant at larger sizes. The benefits of using explicit dynamics are explored, particularly for predicting ductile fracture surfaces, and problems with complex contact.
|Date||5th June 2018|