Documents published in Scipedia

• Comparison of Incompressible and Weakly-Compressible SPH for the Simulation of Laser Beam Welding

  D. Sollich, P. Eberhard

  particles2023.

  
  

  Abstract

  The process of laser beam welding is simulated using the Weakly-Compressible Smoothed Particle Hydrodynamics (WCSPH) and the Incompressible SPH (ISPH) methods. The presented models consider significant physical effects such as heat conduction, temperature-dependent surface tension with wetting, the phase transitions melting and solidification, and an evaporation-induced recoil pressure. Here, particular emphasis is placed on the modeling differences between the WCSPH and ISPH methods. Then, both methods are evaluated in terms of their accuracy and performance in the simulation of deep penetration laser beam welding with oscillating laser power.

  Abstract
  The process of laser beam welding is simulated using the Weakly-Compressible Smoothed Particle Hydrodynamics (WCSPH) and the Incompressible SPH (ISPH) methods. The presented [...]

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• Calibration of AM powders for Optimization of Recoating Applications using DEM

  N. Sani, J. Quist, K. Jarateg, A. Bilock, L. Cordova, F. Edelvik

  particles2023.

  
  

  Abstract

  Additive Manufacturing (AM) has been a subject of significant attention from both industrial manufacturers and research communities. However, several challenges hinder the widespread implementation of this technology in the industry. Powder recoating is a crucial step in powder-bed AM process that involves achieving a uniformly packed bed of powder particles that are later melted by an energy source, such as a laser or electron beam. One of the main challenges is calibrating the contact model parameters accurately to match the flowability and spreadability of specific powder alloys. This paper proposes a Discrete Element Method (DEM) model calibration framework based on surrogate model optimisation. The study utilises a Revolution Powder Analyser (RPA) as the experimental reference system. The proposed method is demonstrated with two AM powder samples, Ti64 and Inconel 718. The results indicate that particle-particle friction, rolling resistance, and van der Waals (vdW) surface energy significantly affect the system responses. Furthermore, the validation results show good correspondence between the simulation with calibrated parameters and experimental data. Overall, proposed calibration framework has the potential to optimise powder recoating and to improve the accuracy and effectiveness of the additive manufacturing.

  Abstract
  Additive Manufacturing (AM) has been a subject of significant attention from both industrial manufacturers and research communities. However, several challenges hinder the [...]

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• How the Packing Density and Penetration Resistance is Influenced by Particle Shape: DEM Modelling of Plate Penetration in Granular Media

  G. van Selm, M. Mohajeri, H. Shi, D. Schott

  particles2023.

  
  

  Abstract

  Granular materials play a crucial role in various geotechnical, mining, and bulk handling applications. Understanding their mechanical properties is essential for optimal use in these industries. Traditional experimental methods like Cone Penetration Test (CPT) and open pile testing have limitations on their repeatability and offer little insight into the contact mechanics. The Discrete Element Method (DEM) is a powerful tool for investigating and simulating granular material behaviour at the element scale and provides deeper understanding in geometry-material interactions. However, due to computational costs, spherical particles are often preferred, though they may not always capture realistic particle interactions. In the current study, the packing density and the penetration resistance of particle beds with different particle shapes, including sphere, multi-spheres and polyhedrons, are compared using a plate penetration test modelled in DEM. Sensitivity analyses are performed for sliding friction, consolidation pressure, and Particle Size Distribution (PSD). Results indicate that polyhedral shapes show lower penetration resistance compared to spherical and multi-spherical shapes. Sliding friction has the most significant impact on resistance, while consolidation pressure has minimal effect on porosity. The study highlights the importance of particle shape in granular media modelling and emphasizes the need for further research in this area.

  Abstract
  Granular materials play a crucial role in various geotechnical, mining, and bulk handling applications. Understanding their mechanical properties is essential for optimal [...]

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• ISPH with a Geometric Multigrid Preconditioning Solver using Background Cells in GPU environment

  H. Osaki, D. Moriwaka, M. Asai

  particles2023.

  
  

  Abstract

  Incompressible fluid analysis using the ISPH or MPS methods requires the solution of the pressure Poisson equation, which takes up most of the overall computation time. In addition, the iteration number for solving pressure Poisson equations may increase as the simulation model scale increases. This is a common problem in particle methods and the other implicit time integration solvers. In different methods, FEM, etc., good quality preconditioning, such as multigrid preconditioning, can significantly improve the convergence of iterative solution methods. There are two types of multigrid preconditioners, algebraic multigrid and geometric multigrid methods, but there are few examples of their application in particle methods. In this study, we attempted to develop a framework for a geometric multigrid preconditioner for solving the pressure Poisson equation in the ISPH. First, we focused on the geometric multigrid preconditioner using background cells, which are used for neighboring particle search, and implemented it on a GPU environment. Through a simple dam-break problem, we compared the computation time between the Conjugate gradient (CG) solver with a traditional preconditioner and the CG solver with a geometric multigrid preconditioner. We confirmed that the background cell-based geometric multigrid preconditioner is practical for the ISPH method.

  Abstract
  Incompressible fluid analysis using the ISPH or MPS methods requires the solution of the pressure Poisson equation, which takes up most of the overall computation time. In [...]

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• A Macro-Meso-Microscale Meshless Model for Multiphysics Particle-Laden Flows

  J. Joubert, D. Wilke, P. Pizette

  particles2023.

  
  

  Abstract

  This work extends a multi-phase mixing model framework designed for a Smoothed Particle Hydrodynamics context. Specifically, we propose a higher-order variation using the first-order accurate Generalised Finite Difference differential operators to construct an incompressible scheme for simulating fluid-solid coupled systems resolved via a continuum mixture model. The proposed scheme incorporates inter-phase shear between phases and the viscosity dependency of the solid phase concentration. The scheme is verified by simulating a modified lid-driven cavity case at Re = 1000. In this simulation, our method was capable of treating initially discontinuous concentration fields with a maximum solid volume concentration of 0.5 and a solid-to-fluid density ratio of 4.

  Abstract
  This work extends a multi-phase mixing model framework designed for a Smoothed Particle Hydrodynamics context. Specifically, we propose a higher-order variation using the [...]

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• Discrete Element Method to simulate the thermo-mechanical behavior of plasma-sprayed thermal barrier coatings during a thermal cycle

  I. Bensemmane, W. Leclerc, N. Ferguen, M. Guessama

  particles2023.

  
  

  Abstract

  Thermal Barrier Coatings (TBCs) are multilayer systems used in Ni-based superalloy components for gas turbine blades submitted to high temperatures resulting in the development of high thermal stresses. The intricacy of their microstructure coupled to severe environmental conditions lead to their premature failure according to complex mechanisms involving notably creep and Coefficient of Thermal Expansion (CTE) mismatch effects. This work aims to investigate the development of thermal residual stress within TBCs during a heating step using a numerical model based on Discrete Element Method (DEM). The suitability of such an approach is investigated in terms of stress field distribution in comparison to Finite Element Method (FEM). Results reveal the capability of the proposed DEM approach to simulate creep phenomenon in a TBC system under thermal loading and predict accurately thermal stresses leading to failure.

  Abstract
  Thermal Barrier Coatings (TBCs) are multilayer systems used in Ni-based superalloy components for gas turbine blades submitted to high temperatures resulting in the development [...]

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• Particle-based Semi-resolved Coupling Model for the Simulation of Internal Erosion in soil structures

  K. Tsuji, M. Asai, K. Kasama

  particles2023.

  
  

  Abstract

  Internal erosion, caused by seepage flow inside the soil, accelerates soil failure during a natural disaster. Numerical simulation can be an effective tool to quantitatively evaluate the relationship between internal erosion and the instability of the ground as a whole. Internal erosion and multiphase flow simulation of fluid and granular materials with a particle size distribution require coupling simulations that can represent the interaction between particles and pore water and the movement of particles. There are two main types of coupling models: ”Resolved coupling model,” which can calculate detailed flow and fluid forces, and ”Unresolved coupling model,” which is based on empirical drag and seepage flow models. Previous studies have indicated that both models should be judged appropriately based on the ratio of particle-fluid spatial resolution. However, applying a resolved coupling model to the vast number of soil particles that make up the ground is impractical from a computational cost perspective, and empirical unresolved coupling model has difficulty in representing localized failures such as internal erosion. Therefore, developing a new coupling model that satisfies both computational accuracy and efficiency is desirable. In this study, we applied ISPH (Incompressible Smoothed Particle Hydrodynamics) for fluid analysis and DEM (Discrete Element Method) for soil particles to develop a fluid-soil coupling simulation model that can directly represent the movement of soil particles during the internal erosion process. Through numerical experiments using a particle layer with the vertical upward flow, we understand the limitations of the conventional coupling model and propose a new hybrid type of semi-resolved coupling model that combines these two models appropriately.

  Abstract
  Internal erosion, caused by seepage flow inside the soil, accelerates soil failure during a natural disaster. Numerical simulation can be an effective tool to quantitatively [...]

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• Design of Graphical Symbols for Shape Transformations of 4D Printed Parts

  E. Pei, C. Leung

  SIM-AM2023.

  
  

  Abstract

  The term “4D Printing” (4DP) is defined as the ability for a part produced using an additive manufacture process to change its shape when activated by or exposed to one or more stimuli over time. This emerging technology offers unique advantages over conventional Additive Manufacturing (AM) by extending the three dimensions of space into the fourth dimension of time. 4DP parts can be programmed to actuate passively without the need for an external power source such as an electromechanical or other active system, thereby reducing the probability of failure and the complexity of components. This work attempts to address some of the challenges faced by the design engineer in a project team when producing technical documentation to specify the desired shape transformation of a 4DP part with a structured graphical representation at an appropriate level of abstraction. In this paper the requirements for a shape transforming 4DP part are represented as the allowable variation in dimensional size and tolerance in geometric form of the functionally critical features on the part for each function that the transformed shape serves. In this paper, the authors describe how the proposed standard to specify the desired shape transformations of a 4DP part could use graphical symbols in a structured specification by means of a Transformation Control Frame (TCF) to define the rules of transforming between shapes and a Bill of Transformations (BoT) to enumerate all the Transformation Control Frames (TCF) necessary to describe the intended sequence of shape transformations. To illustrate how the graphical symbols could be applied, a SMA actuated gripper is presented as a use-case.

  Abstract
  The term “4D Printing” (4DP) is defined as the ability for a part produced using an additive manufacture process to change its shape when activated by or exposed to one [...]

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• Thermal model for laser-based powder bed fusion of metal process: modelling, calibration, and experimental validation

  M. Carraturo, P. Breese, S. Oster

  SIM-AM2023.

  
  

  Abstract

  In the present contribution, we propose an effective numerical thermal modeling solution for melt pool simulations in Laser-based Powder Bed Fusion of Metals processes. The proposed model employs an anisotropic conductivity to represent melt pool dynamics effectsin a homogeneous material model. The numerical implementation of the proposed physical model is first experimentally calibrated and then validated with respect to a series of melt pool measurements as acquired by using a short-wave infrared (SWIR) camera monitoring system.

  Abstract
  In the present contribution, we propose an effective numerical thermal modeling solution for melt pool simulations in Laser-based Powder Bed Fusion of Metals processes. The [...]

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• Cellular Automata Simulation of Fully Equiaxed Microstructure Formation in Scalmalloy® during Additive Manufacturing with Adjustable Ring Mode Laser

  M. Mohebbi, V. Ploshikhin

  SIM-AM2023.

  
  

  Abstract

  We utilized an Adjustable Ring-Mode (ARM) laser to achieve an almost fully equiaxed microstructure in powder bed Fusion-laser beam Scalmalloy®. ARM laser-built specimens exhibited over 90% fine-grained material, while circular laser-built specimens yielded less than 50% fine-grained material, using the same laser power, speed, and hatch spacing. To gain insights into these interesting results, we employed a Cellular Automata (CA) solidification simulation, incorporating the nucleation role of L12 Al3(ScxZr1-x) precipitates through a particle-based nucleation model. The simulation was coupled with the corresponding temperature field derived from finite difference analyses of the circular and ARM laser beams. The simulation results revealed a significantly thicker precipitation zone (equiaxed grains) under the ARM laser compared to the circular beam, primarily attributed to reduced temperature and cooling rates. The excellent correlation between simulation and experimental results demonstrates promising potential for the predictive application of the developed model. It can be effectively utilized to optimize heat source modulation and process parameters, thereby enabling the adaptation of microstructure and mechanical properties

  Abstract
  We utilized an Adjustable Ring-Mode (ARM) laser to achieve an almost fully equiaxed microstructure in powder bed Fusion-laser beam Scalmalloy®. ARM laser-built specimens [...]

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