Documents published in Scipedia

• 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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• The Effect of Geometrical Imperfections on the Mechanical Properties of Lattice Structures Produced by the Powder Bed Fusion (PBF) Process

  K. Hamasaki, K. Ushijima

  SIM-AM2023.

  
  

  Abstract

  In this paper, the effects of geometrical imperfections observed in a lattice structure fabricated by metal 3D printer on the compressive response were investigated by using FE simulation. Geometrical imperfections which are due to excessive heat transfer and the melting of unnecessary metal powder during the fabrication process was observed using a 3D X-Ray microscope (XRM) machine. Based on the observation, two types of geometrical imperfections (strut diameter deviation and the center-axis offset) were measured, and the quantities of these imperfections on the mechanical properties of lattice block were discussed. By introducing imperfections to the FE model, a likelihood of reduced mechanical properties can be potentially adverted. In addition, by comparing the amount of geometrical imperfections, the initial stiffness and plastic collapse strength in the models based on different strut diameters, we proposed appropriate manufacturing conditions for the lattice blocks that would minimize the reduction of their mechanical properties.

  Abstract
  In this paper, the effects of geometrical imperfections observed in a lattice structure fabricated by metal 3D printer on the compressive response were investigated by using [...]

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• Numerical Investigation of Vibration Properties of Chiral Structures with Artifical Structural Anisotropy

  S. Noguchi, K. Ushijima

  SIM-AM2023.

  
  

  Abstract

  The dynamic vibration response of sandwich beams with an anti-tetra-chiral lattice as a lightweight sandwiched core have been studied by using a nonlinear finite element analysis (FEA). Since the anti-tetra-chiral structure has a weak shear stiffness, its vibration response is strongly affected by the shear deformation. In our calculation, a 3-point bending flexural test was conducted for calculating the effective shear stiffness as well as the effective Young’s modulus of the chiral core. The natural frequency of the sandwich beam has been calculated by FEA, and predicted by using the Rayleigh-Ritz method, assuming that the sandwich beam is composed of composite continuum materials with equivalent Young’s modulus and shear modulus. Moreover, the natural frequency and damping ration of the sandwich beam produced by a 3D printer bas been measured through a vibration test, and compared with numerical results in order to clarify the effectiveness of the chiral sandwich beam as a mechanical component.

  Abstract
  The dynamic vibration response of sandwich beams with an anti-tetra-chiral lattice as a lightweight sandwiched core have been studied by using a nonlinear finite element analysis [...]

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• Towards neuronal network enhanced finite element simulations in additive manufacturing

  C. Behrens, V. Ploshikhin

  SIM-AM2023.

  
  

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• Parametric Study of Directed Energy Deposition Of Duplex Stainless Steels To Optimize Ferrite-Austenite Phase Ratio And Residual Stresses

  D. Weisz-Patrault

  SIM-AM2023.

  
  

  Abstract

  Optimal material properties of duplex stainless steels generally require near 50-50 ferrite-austenite microstructures. The development of additive manufacturing of duplex steels is hindered by difficulty in controlling cooling conditions to ensure a balanced phase ratio. In addition, non-uniform phase distribution is usually observed. Thus, sufficiently fast part scale process simulations are interesting to optimize process parameters to better predict and control the temperature history during fabrication and therefore solid-state phase transitions. Furthermore, stresses should also be taken into account in the optimization of the phase field in order to avoid cracking, buckling or excessive distortions. Numerical results obtained from a fast modeling of directed energy deposition including thermal analysis, diffusion of alloying element to account for phase transitions, and stress computation are analyzed. On this basis, we investigate the effect on stresses of an optimized fabrication strategy designed to target uniform and balanced ferrite-austenite ratio with respect to a reference printing strategy

  Abstract
  Optimal material properties of duplex stainless steels generally require near 50-50 ferrite-austenite microstructures. The development of additive manufacturing of duplex [...]

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• Closed-walled topology optimization of an additively manufactured motor bracket for an unmanned cargo aerial vehicle

  J. Rieser, M. Zimmermann

  SIM-AM2023.

  
  

  Abstract

  Compared to conventional intuition-based design, topology optimization (TO) provides considerable mass savings by clearing excess material from lightly loaded regions of a structural part. The remaining material may be distributed in a purely truss-like fashion, or in the form of a closed-walled design consisting of flat plates or curved shells with variable thickness. Unless buckling is of critical concern, closed-walled designs are in general more efficient than trusses which makes them particularly interesting for challenging applications in lightweight design. However, closed-walled designs obtained by topology optimization are still the exception rather than the rule. This paper investigates the applicability of the recently developed selective penalization approach to the design of a motor bracket for an unmanned aerial vehicle (UAV) to deliver defibrillators which is currently being developed by the HORYZN student initiative at the Technical University of Munich. The optimization results are closed walled designs as desired. A comparison to a truss-like design as well as to a conventional off-the-shelf motor bracket reveals that the closed-walled design even outperforms the topology optimized truss-like design by additional 3% in terms of stiffness-to-weight ratio. Moreover, it provides a streamlined housing protecting the motor cables and contributing to the reduction of aerodynamic drag at cruise speed. Another key finding of this case study is: Depending on the specific optimization problem, and a suitable build orientation provided, closed-walled designs may lower the amount of necessary sacrificial support structures or may even be almost self-supporting. For the closed-walled motor bracket design we found a reduction by more than 25% compared to the truss-like design. This did not require limiting the freedom of design by imposing any additional constraints. The motor bracket was successfully manufactured from aluminium alloy using laser powder bed fusion (LPBF) followed by removal of support structures and CNC machining of functional surfaces.

  Abstract
  Compared to conventional intuition-based design, topology optimization (TO) provides considerable mass savings by clearing excess material from lightly loaded regions of a [...]

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• Incremental Viscoelasticity for 3D Concrete Printing: Finite Strain Modeling and Parametric Studies

  B. NEDJAR, Z. Awada, J. Torrenti

  SIM-AM2023.

  
  

  Abstract

  Within a 3D concrete printing process, concrete is still fresh and possible collapse may occur due to its own weight and lack of formwork. On the other hand, the mechanical characteristics of the material are continuously evolving due to hydration during curing. Withina predictive theory, the constitutive relation of the early age concrete is to be defined in rate form. In this contribution, and due to the soft nature of the problem at hand, a finite strainincremental viscoelastic modeling is adopted. A generalized Maxwell rheological model is used together with a Saint-Venant-like incremental elasticity. A parametric study is conducted on simulated slump-tests to highlight the abilities of the present framework. Clearly, the early age rheology and mechanical properties have a great impact on the buildability of the fresh concrete. A set of simulations is then given for the purpose of demonstration.

  Abstract
  Within a 3D concrete printing process, concrete is still fresh and possible collapse may occur due to its own weight and lack of formwork. On the other hand, the mechanical [...]

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• Effect of Residual Stresses on the Mechanical Properties of TPMS Lattice Structures Manufactured Using 316L Stainless Steel

  H. Mapari, H. Kruse, E. Escobar, A. Matei, J. Schleifenbaum

  SIM-AM2023.

  
  

  Abstract

  In recent years, the use of Triply Periodic Minimal Surface (TPMS) lattice structures has gained popularity due to their advantages like high surface to volume ratio and their lightweight potential. Nowadays, TPMS lattice structures can be seen in many fields, including aerospace and medical applications, which can be fabricated using AM methods like Laser Powder Bed Fusion (PBF-LB/M) process. During the PBF-LB/M process, the transient emperature change is caused by the cyclic nature of the thermal load resulting in the accumulation of residual stresses (RS). These RS can cause dimensional inaccuracies, warpageand have a severe impact on the loading capacity and quality of the PBF-LB/M part. In this paper, the effect of RS on the mechanical properties of primitive and gyroid TPMS lattice structures of volume fraction 20%, 30% and 40% undergoing compression testing is studied using Finite Element Analysis (FEA) and experiments. The sequentially coupled thermomechanical finite element model is used to account for the RS accumulation and its effect on Young’s modulus, yield strength and Specific Energy Absorption (SEA).

  Abstract
  In recent years, the use of Triply Periodic Minimal Surface (TPMS) lattice structures has gained popularity due to their advantages like high surface to volume ratio and their [...]

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