Lattice structures

AM and in particular EBM results in different type of defects for as-built parts: surface defects (plate-pile like defects, powders stuck to the surface or partially melted) , internal defects (entrapped gas, lack of fusion ...). All these defects are detrimental for mechanical properties. Some post treatments can help : machining, chemical etching or ultrasonic shot peening for surface defects, Hot Isostatic Pressing for internal ones. When considering lattice structures, it is hard if not impossible to apply some of these post-treatments ans some defects may persist. Thanks to X-ray microtomography, we have defined some corrective factors in order to take into account these defects for static (Fig.1) or fatigue (Fig.2) behaviours.


Fig1  - definition of a mechanically equivalent diameter for single struts



Fig.2 Effect of different post-treatments (etching, HIP, Ultrasonic Shot Peening) on the fatigue properties of EBM single struts. Corresponding surface defects.