Issue 53

P. Ferro et alii, Frattura ed Integrità Strutturale, 53 (2020) 252-284; DOI: 10.3221/IGF-ESIS.53.21 256 Figure 4: Multi scale modeling approach P OWDER - SCALE MODELS Powder deposition nce the power quality is defined, the powder coating characteristics are the first variables affecting final product quality. By using powder-scale models it is possible to predict the distribution of packing density and microstructure as well as the interaction between the coater arm and the base material [32,33]. The discrete element model (DEM) is used in literature to simulate the powder deposition [34]. The model is based on the solution of the Newton’s second law (Eqs. 2 and 3) of motion and rigid body dynamics equation: (2) (3) In Eqs. 2 and 3, m i is the mass of the particle i, is the translational acceleration of particle i, g is the gravity constant, and F ij is the force acting on particle i, given by particle j. For the rotational motion, I i is the moment of inertia of particle i, is the angular acceleration of particle i, ∑ i (r ij x F ij ) represents the total rotational force acting on particle i from the rest of the system. The interaction of particles is calculated basing on Hertzian contact force, F hz [35,36]: F hz   R i R j R i  R j [(k n  n ij  m eff  n v n )  (k t  s t  m eff  t v t )] (4) with R i and R j radii of particle i and j, respectively, δ the overlap distance of two particles, k the elastic constant, γ the viscoelastic damping constant, n ij the unit vector along the line connecting the centers of the two particles, v the component of the relative velocity of the two particles; indices n and t refer to normal and tangential contact respectively. Finally, m eff is the effective mass of two particles. One has to define the particle size distribution, the layer thickness and the rigid box where the particles are inserted. The DEM output is the location and radius of each particle that is transferred to the CFD model as initial conditions. Using DEM and input parameters taken from literature [37, 38], O