DEM powder spreadingand SPH powder melting models for additive manufacturing processsimulations

Particle-based numerical methods enable different process simulations for powder bed additive manufacturing. Two examples are the simulation of powder spreading and the simulation of melting and re-solidification. From these simulations, several material properties can be extracted such as packing density after spreading, porosity and surface properties after re-solidification and, ultimately, indicators for the strength of the component. In this work simulations of powder spreading using the Discrete Element Method (DEM) as well as simulations of the melt pool dynamics by means of SmoothedParticle Hydrodynamics (SPH) are presented. Surface tension material properties are varied and the influence on the resulting surface shape is discussed. The occurrence of different surface roughness patterns can be addressed to certain dimensionless numbers, namely the Capillary number, the Marangoni number and the ratio of the laser scan speed to a characteristic Marangoni current surface velocity

Magnetization models for particle-based simulations of magnetorheological fluids

In this study, three-dimensional particle-based simulations are used to model magnetorheological fluids. The numerical model of the MRF is implemented in the framework of the Discrete Element Method (DEM) and takes into account the coupling of the magnetic dipoles, the hydrodynamic drag forces and steric forces between particles. To accurately treat the magnetic interaction between particles, the magnetic field at the particles’ position is computed and an appropriate magnetization model is implemented. DEM simulations with different volume fractions of the MRF are carried out and the resulting magnetization curves are put in comparison with experimental data

Magnetization models for particle-based simulations of magnetorheological fluids

In this study, three-dimensional particle-based simulations are used to model magnetorheological fluids. The numerical model of the MRF is implemented in the framework of the Discrete Element Method (DEM) and takes into account the coupling of the magnetic dipoles, the hydrodynamic drag forces and steric forces between particles. To accurately treat the magnetic interaction between particles, the magnetic field at the particles’ position is computed and an appropriate magnetization model is implemented. DEM simulations with different volume fractions of the MRF are carried out and the resulting magnetization curves are put in comparison with experimental data

Particle-Based Numerical Simulation Study of Solid Particle Erosion of Ductile Materials Leading to an Erosion Model, Including the Particle Shape Effect

Solid particle erosion inevitably occurs if a gas–solid or liquid–solid mixture is in contact with a surface, e.g., in pneumatic conveyors. Having a good understanding of this complex phenomenon enables one to reduce the maintenance costs in several industrial applications by designing components that have longer lifetimes. In this paper, we propose a methodology to numerically investigate erosion behavior of ductile materials. We employ smoothed particle hydrodynamics that can easily deal with large deformations and fractures as a truly meshless method. In addition, a new contact model was developed in order to robustly handle contacts around sharp corners of the solid particles. The numerical predictions of erosion are compared with experiments for stainless steel AISI 304, showing that we are able to properly predict the erosion behavior as a function of impact angle. We present a powerful tool to conveniently study the effect of important parameters, such as solid particle shapes, which are not simple to study in experiments. Using the methodology, we study the effect of a solid particle shape and conclude that, in addition to angularity, aspect ratio also plays an important role by increasing the probability of the solid particles to rotate after impact. Finally, we are able to extend a widely used erosion model by a term that considers a solid particle shape

Reorientation of Suspended Ceramic Particles in Robocasted Green Filaments during Drying

This work considers the fabrication of ceramic parts with the help of an additive manufacturing process, robocasting, in which a paste with suspended particles is robotically extruded. Within the final part, the material properties depend on the orientation of the particles. A prediction of the particle orientation is challenging as the part usually undergoes multiple processing steps with varying contributions to the orientation. As the main contribution to the final particle orientation arises from the extrusion process, many corresponding prediction models have been suggested. Robocasting involves, however, further processing steps that are less studied as they have a smaller influence on the orientation. One of the processing steps is drying by natural convection, which follows directly after the extrusion process. A quantification of the reorientation that occurs during drying is mostly unknown and usually neglected in the models. Therefore, we studied the amount of reorientation of suspended particles in robocasted green filaments during drying in detail. For our study, we applied the discrete element method, as it meets various requirements: The exact particle geometry can be resolved precisely; particle–particle interactions can be described; the paste composition is reproduced exactly; the initial particle orientation can be set in accordance with the prediction from the analytical models for the extrusion part; macroscopic force laws exist to represent capillary forces due to the remaining fluid phase that remains during drying. From our study, we concluded that the magnitude of particle reorientation during drying is small compared to the orientation occurring during the extrusion process itself. Consequently, reorientation during drying might further be neglected within analytical orientation prediction models

Consistent Thermo-Capillarity and Thermal Boundary Conditions for Single-Phase Smoothed Particle Hydrodynamics

A model for capillary phenomena including temperature-dependency and thermal boundary conditions is presented in the numerical framework of smoothed particle hydrodynamics (SPH). The model requires only a single fluid phase and is therefore computationally more efficient than surface tension schemes which need an explicit fluid-fluid or fluid-gas interface. The model makes use of a surface identification mechanism based on the SPH renormalization tensor. All relevant properties of the continuum surface force (CSF) based approach, i.e., the delta function, normal vector and curvature, are calculated in a consistent manner. The model is parametrized by physical material properties and is successfully validated by means of a large set of analytical test cases. The applicability of the proposed model to more complex scenarios is demonstrated

Auxiliary data tables relating process parameters and parameters of the Herschel-Bulkley rheology model to a deformation profile

This data set contains two files. The first file "process-parameters-to-reach-target-shear-distribution.csv" provides a detailed set of curves in accordance with Figure 3.4 in the linked paper. Here, the first row "PhiGammaSuf" is the ordinate and all following rows are the respective abscissae for a certain pair of sufficient shear (gammaSuf) and flow exponent n. Please refer to the main text of the paper for a detailed explanation. The second file "relation-consistency-to-mean-velocity.csv" consists of the data set in accordance with Figure 3.7. Here, the first column "R-DeltaP-By-L-tau0" is the ordinate and all subsequent columns belong to a certain flow index. The headers have a format of "y-for-n={value}", where "y" is a substitution for $\frac{K}{\tau_0} \left(\frac{v_\text{mean}}{R}\right)^n$ as shown on the abscissa in Figure 3.7 and {value} is the corresponding flow index of interest. Again, please refer to the main text for a detailed explanation.The files are formated in a such a way that they can be easily opened in Microsoft Excel. Please be aware that columns are separated by commas (",") and the dot (".") is used as decimal point

Vorrichtung und Verfahren zum Bestimmen einer Wandschubspannung und System zur Erkennung von Arteriosklerose

Es ist eine Vorrichtung zum Bestimmen einer Wandschubspannung in einem Blutgefäss mit einer Bildanalyseeinheit gezeigt, die ausgebildet ist, basierend auf einer Aufnahme des Blutgefässes eine Geometrie einer Bifurkation des Blutgefässes zu bestimmen. Ferner weist die Vorrichtung eine Auswertungseinheit auf, die ausgebildet ist, basierend auf der bestimmten Geometrie eine Wandschubspannung in dem Blutgefäss zu bestimmen

Dimensionless unified modelling of macroscale electric properties of conductive fibre networks in different regimes

The electric properties of conductive fibre networks, which can be representative of carbon nanotube networks, are investigated by means of numerical simulations and a dimensionless unified macroscale model is developed. Fibres are represented as rigid chains of discrete element method particles and we compress systems of fibres in a representative volume element periodic in three dimensions. In the used electric resistor network method, the particles are used as discretisation points to construct a system of linear equations linking the particle conductivities to their local electric potentials and in turn allowing for predictions on the electric macroscale properties of the fibre system. A carried out dimensional analysis suggests suitable scaling laws to unify different macroscale fibre systems in two different regimes - a percolating and a conductive regime. The dimensionless macroscale conductance is found to depend on the percolation threshold and percolation probability. It is moreover found that the critical solid volume fraction for rigid fibres is not only dependent on the fibre aspect ratio, but can also depend on the compression height of the system. Additionally, correlations between transmittance and solid volume fractions are found allowing for possibly simple solid volume fraction estimations in experiments