scholarly journals Assessment of the Dimensional and Geometric Precision of Micro-Details Produced by Material Jetting

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1989
Author(s):  
Miguel Silva ◽  
António Pereira ◽  
Álvaro Sampaio ◽  
António Pontes
Keyword(s):  
Numerical Models ◽  
Three Dimensions ◽  
Material Distribution ◽  
Micro Scale ◽  
Geometric Precision ◽  
Hexahedral Meshes ◽  
Sample Test ◽  
Repeatability And Reproducibility ◽  
Complex Parts ◽  
Distorted Geometry

Additive Manufacturing (AM) technology has been increasing its penetration not only for the production of prototypes and validation models, but also for final parts. This technology allows producing parts with almost no geometry restrictions, even on a micro-scale. However, the micro-Detail (mD) measurement of complex parts remains an open field of investigation. To be able to develop all the potential that this technology offers, it is necessary to quantify a process’s precision limitations, repeatability, and reproducibility. New design methodologies focus on optimization, designing microstructured parts with a complex material distribution. These methodologies are based on mathematical formulations, whose numerical models assume the model discretization through volumetric unitary elements (voxels) with explicit dimensions and geometries. The accuracy of these models in predicting the behavior of the pieces is influenced by the fidelity of the object’s physical reproduction. Despite that the Material Jetting (MJ) process makes it possible to produce complex parts, it is crucial to experimentally establish the minimum dimensional and geometric limits to produce parts with mDs. This work aims to support designers and engineers in selecting the most appropriate scale to produce parts discretized by hexahedral meshes (cubes). This study evaluated the dimensional and geometric precision of MJ equipment in the production of mDs (cubes) comparing the nominal design dimensions. A Sample Test (ST) with different sizes of mDs was modeled and produced. The dimensional and geometric precision of the mDs were quantified concerning the nominal value and the calculated deviations. From the tests performed, it was possible to conclude that: (i) more than 90% of all analyzed mDs exhibit three dimensions (xyz) higher than the nominal ones; (ii) for micro-details smaller than 423 m, they show a distorted geometry, and below 212 m, printing fails.

Analysis and Modeling of Defects in Unsupported Overhanging Features in Micro-Stereolithography

2016 ◽  
Author(s):  
Vito Basile ◽  
Francesco Modica ◽  
Irene Fassi
Keyword(s):  
Finite Element ◽  
Numerical Models ◽  
Numerical Approach ◽  
Fe Analysis ◽  
Test Cases ◽  
Layer By Layer ◽  
Failure Condition ◽  
Micro Scale ◽  
Part Geometry ◽  
Shape Component

In the present paper, a numerical approach to model the layer-by-layer construction of cured material during the Additive Manufacturing (AM) process is proposed. The method is developed by a recursive mechanical finite element (FE) analysis and takes into account forces and pressures acting on the cured material during the process, in order to simulate the behavior and investigate the failure condition sources, which lead to defects in the final part geometry. The study is focused on the evaluation of the process capability Stereolithography (SLA), to build parts with challenging features in meso-micro scale without supports. Two test cases, a cantilever part and a bridge shape component, have been considered in order to evaluate the potentiality of the approach. Numerical models have been tuned by experimental test. The simulations are validated considering two test cases and briefly compared to the printed samples. Results show the potential of the approach adopted but also the difficulties on simulation settings.

2-D and 3-D resistivity image reconstruction using crosshole data

Geophysics ◽  
1992 ◽  
Vol 57 (10) ◽  
pp. 1270-1281 ◽  
Author(s):  
Hiromasa Shima
Keyword(s):  
Field Test ◽  
Numerical Models ◽  
Electrical Potential ◽  
Nonlinear Least Squares ◽  
Three Dimensions ◽  
Inversion Method ◽  
Good Resolution ◽  
Inversion Algorithm ◽  
Linear Inversion ◽  
Resistivity Model

Theoretical changes in the distribution of electrical potential near subsurface resistivity anomalies have been studied using two resistivity models. The results suggest that the greatest response from such anomalies can be observed with buried electrodes, and that the resistivity model of a volume between boreholes can be accurately reconstructed by using crosshole data. The distributive properties of crosshole electrical potential data obtained by the pole‐pole array method have also been examined using the calculated partial derivative of the observed apparent resistivity with respect to a small cell within a given volume. The results show that for optimum two‐dimensional (2-D) and three‐dimensional (3-D) target imaging, in‐line data and crossline data should be combined, and an area outside the zone of exploration should be included in the analysis. In this paper, the 2-D and 3-D resistivity images presented are reconstructed from crosshole data by the combination of two inversion algorithms. The first algorithm uses the alpha center method for forward modeling and reconstructs a resistivity model by a nonlinear least‐squares inversion. Alpha centers express a continuously varying resistivity model, and the distribution of the electrical potential from the model can be calculated quickly. An initial general model is determined by the resistivity backprojection technique (RBPT) prior to the first inversion step. The second process uses finite elements and a linear inversion algorithm to improve the resolution of the resistivity model created by the first step. Simple 2-D and 3-D numerical models are discussed to illustrate the inversion method used in processing. Data from several field studies are also presented to demonstrate the capabilities of using crosshole resistivity exploration techniques. The numerical experiments show that by using the combined reconstruction algorithm, thin conductive layers can be imaged with good resolution for 2-D and 3-D cases. The integration of finite‐element computations is shown to improve the image obtained by the alpha center inversion process for 3-D applications. The first field test uses horizontal galleries to evaluate complex 2-D features of a zinc mine. The second field test illustrates the use of three boreholes at a dam site to investigate base rock features and define the distribution of an altered zone in three dimensions.

Investigation of Parameter Spaces for Topology Optimization With Three-Dimensional Orientation Fields for Multi-Axis Additive Manufacturing

2020 ◽  
Vol 143 (5) ◽  
Author(s):  
Joseph R. Kubalak ◽  
Alfred L. Wicks ◽  
Christopher B. Williams
Keyword(s):  
Topology Optimization ◽  
Additive Manufacturing ◽  
Design Space ◽  
Mechanical Performance ◽  
Unit Length ◽  
Three Dimensions ◽  
Layer By Layer ◽  
Material Distribution ◽  
Orientation Fields ◽  
Material Orientation

Abstract The layer-by-layer deposition process used in material extrusion (ME) additive manufacturing results in inter- and intra-layer bonds that reduce the mechanical performance of printed parts. Multi-axis (MA) ME techniques have shown potential for mitigating this issue by enabling tailored deposition directions based on loading conditions in three dimensions (3D). Planning deposition paths leveraging this capability remains a challenge, as an intelligent method for assigning these directions does not exist. Existing literature has introduced topology optimization (TO) methods that assign material orientations to discrete regions of a part by simultaneously optimizing material distribution and orientation. These methods are insufficient for MA–ME, as the process offers additional freedom in varying material orientation that is not accounted for in the orientation parameterizations used in those methods. Additionally, optimizing orientation design spaces is challenging due to their non-convexity, and this issue is amplified with increased flexibility; the chosen orientation parameterization heavily impacts the algorithm’s performance. Therefore, the authors (i) present a TO method to simultaneously optimize material distribution and orientation with considerations for 3D material orientation variation and (ii) establish a suitable parameterization of the orientation design space. Three parameterizations are explored in this work: Euler angles, explicit quaternions, and natural quaternions. The parameterizations are compared using two benchmark minimum compliance problems, a 2.5D Messerschmitt–Bölkow–Blohm beam and a 3D Wheel, and a multi-loaded structure undergoing (i) pure tension and (ii) three-point bending. For the Wheel, the presented algorithm demonstrated a 38% improvement in compliance over an algorithm that only allowed planar orientation variation. Additionally, natural quaternions maintain the well-shaped design space of explicit quaternions without the need for unit length constraints, which lowers computational costs. Finally, the authors present a path toward integrating optimized geometries and material orientation fields resulting from the presented algorithm with MA–ME processes.

Recent advances on bedform research and application: Process-based to machine learning

2021 ◽  
Author(s):  
Sanjay Giri ◽  
Amin Shakya ◽  
Mohamed Nabi ◽  
Suleyman Naqshband ◽  
Toshiki Iwasaki ◽  
...  
Keyword(s):  
Machine Learning ◽  
Sediment Transport ◽  
Flow Resistance ◽  
Large Scale ◽  
Data Science ◽  
Numerical Models ◽  
Hybrid Approach ◽  
Water Model ◽  
Micro Scale ◽  
Cfd Models

<p>Evolution and transition of bedforms in lowland rivers are micro-scale morphological processes that influence river management decisions. This work builds upon our past efforts that include physics-based modelling, physical experiments and the machine learning (ML) approach to predict bedform features, states as well as associated flow resistance. We revisit our past works and efforts on developing and applying numerical models, from simple to sophisticated, starting with a multi-scale shallow-water model with a dual-grid technique. The model incorporates an adjustment of the local bed shear stress by a slope effect and an additional term that influences bedform feature. Furthermore, we review our work on a vertical two-dimensional model with a free surface flow condition. We explore the effects of different sediment transport approaches such as equilibrium transport with bed slope correction and a non-equilibrium transport with pick-up and deposition. We revisit a sophisticated three-dimensional Large Eddy Simulation (LES) model with an improved sediment transport approach that includes sliding, rolling, and jumping based on a Lagrangian framework. Finally, we discuss about bedform states and transition that are studied using laboratory experiments as well as a theory-guided data science approach that assures logical reasoning to analyze physical phenomena with large amounts of data. A theoretical evaluation of parameters that influence bedform development is carried out, followed by classification of bedform type by using a neural network model.</p><p>In second part, we focus on practical application, and discuss about large-scale numerical models that are being applied in river engineering and management practices. Such models are found to have noticeable inaccuracies and uncertainties associated with various physical and non-physical reasons. A key physical problem of these large-scale numerical models is related to the prediction of evolution and transition of micro-scale bedforms, and associated flow resistance. The evolution and transition of bedforms during rising and falling stages of a flood wave have a noticeable impact on morphology and flow levels in low-land alluvial rivers. The interaction between flow and micro-scale bedforms cannot be considered in a physics-based manner in large-scale numerical models due to the incompatibility between the resolution of the models and the scale of morphological changes. The dynamics of bedforms and the corresponding changes in flow resistance are not captured. As a way forward, we propse a hydrid approach that includes application of the CFD models, mentioned above, to generate a large amount of data in complement with field and laboratory observations, analysis of their reliability based on which developing a ML model. The CFD models can replicate bedform evolution and transition processes as well as associated flow resistance in physics-based manner under steady and varying flow conditions. The hybrid approach of using CFD and ML models can offer a better prediction of flow resistance that can be coupled with large-scale numerical models to improve their performance. The reseach is in progress.</p>

A Spectral Boundary-Integral Method for Quasi-Dynamic Ruptures of Multiple Parallel Faults

2021 ◽  
Author(s):  
Sylvain Barbot
Keyword(s):  
Integral Method ◽  
Numerical Models ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Three Dimensions ◽  
Power Law Distribution ◽  
Slow Slip Events ◽  
Multiple Faults ◽  
Rupture Dynamics ◽  
Wide Range

ABSTRACT Numerical models of rupture dynamics provide great insights into the physics of fault failure. However, resolving stress interactions among multiple faults remains challenging numerically. Here, we derive the elastostatic Green’s functions for stress and displacement caused by arbitrary slip distributions along multiple parallel faults. The equations are derived in the Fourier domain, providing an efficient means to calculate stress interactions with the fast Fourier transform. We demonstrate the relevance of the method for a wide range of applications, by simulating the rupture dynamics of single and multiple parallel faults controlled by a rate- and state-dependent frictional contact, using the spectral boundary integral method and the radiation-damping approximation. Within the antiplane strain approximation, we show seismic cycle simulations with a power-law distribution of rupture sizes and, in a different parameter regime, sequences of seismogenic slow-slip events. Using the in-plane strain approximation, we simulate the rupture dynamics of a restraining stepover. Finally, we describe cycles of large earthquakes along several parallel strike-slip faults in three dimensions. The approach is useful to explore the dynamics of interacting or isolated faults with many degrees of freedom.

Structure Analysis with 3D Hexahedral Meshes Generated by a Label-Driven Subdivision

2018 ◽  
Vol 12 (1) ◽  
pp. 113-122
Author(s):  
Bo Liu ◽  
◽  
Kenjiro T. Miura ◽  
Shin Usuki
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Structure Analysis ◽  
Three Dimensions ◽  
Two Dimensional ◽  
The Finite Element Method ◽  
Hexahedral Element ◽  
Hexahedral Meshes ◽  
Subdivision Algorithm ◽  
Element Method

For structure analysis with the finite element method (FEM), the hexahedral element is preferable to the tetrahedral one from the viewpoint of accuracy. Previously, we had introduced a label-driven subdivision method for a two-dimensional mesh and showed that the meshes generated by our method were useful for structural analyses. In this study, we extend our two-dimensional algorithm to three-dimensions and verify that the meshes generated by the proposed mesh-subdivision algorithm are useful for structural analyses.

Piton de la Fournaise, elasto-plastic models of stresses and deformation accounting for the topographic load and a magmatic injection

2020 ◽  
Author(s):  
Muriel Gerbault ◽  
Fabrice Fontaine ◽  
Aline Peltier ◽  
Lydie Gailler ◽  
Riad Hassani ◽  
...  
Keyword(s):  
Large Scale ◽  
Numerical Models ◽  
Three Dimensions ◽  
Stress Fields ◽  
Volcanic Complex ◽  
Test Cases ◽  
Magma Storage ◽  
Arbitrary Geometry ◽  
Piton De La Fournaise ◽  
Central Cone

<p><span>Building on previous work aimed at identifying and characterizing the potential mechanical </span><span>trigger</span><span> controlling eruptions and destabilization at Piton de la Fournaise, we study the mechanical behavior of the </span><span>volcanic edifice</span><span> on a crustal scale. Do </span><span>the</span> <span>recurrent </span><span>earthquake </span><span>pattern</span><span> correspond to a destabilization structure, precursor </span><span>of</span><span> a large-scale flank slid</span><span>ing</span><span>? </span><span>Or instead to a</span><span> reactivated </span><span>area of </span><span>magma storage (partially crystallized “sill”)? To answer these questions, we design numerical models which estimate the stress field associated with the volcanic complex. We use the ADELI finite element method in three dimensions, which handles</span> <span> elasto-visco-plastic rheolog</span><span>ies</span><span>. In these models, we take into account 1) the topographic </span><span>load</span><span>, 2) the major density and resistance heterogeneities within the volcano obtained from previous studies, and 3) the </span><span>overpressure induced by the </span><span>in</span><span>tr</span><span>usion of a dike of arbitrary geometry.<br>The model</span><span>ed dike </span><span>injection generates deformation and stress fields such that their </span><span>isocontours</span><span> highlight an ellipsoidal cup structure </span><span>extending </span><span>from the central cone to a depth close to 0 and reaching the ends of the eastern flank. This zone could be assimilated to the zone of seismicity observed and described previously. </span><span>Toget</span><span>h</span><span>er with several systematic test cases, w</span><span>e will discuss the significance of these results, </span><span>such as whether</span><span> it </span><span>reveals</span><span> a rheological delimitation zone of the hydrothermalized </span><span>bed</span><span>rock, </span><span>resulting from</span><span> the combin</span><span>ed</span><span> influence of the topographic load and that of a magmatic injection.</span></p>

scholarly journals Image-based modelling of lateral magma flow: the Basement Sill, Antarctica

2017 ◽  
Vol 4 (5) ◽  
pp. 161083 ◽  
Author(s):  
Nick Petford ◽  
Seyed Mirhadizadeh
Keyword(s):  
Numerical Models ◽  
Mass Density ◽  
Three Dimensions ◽  
Dry Valleys ◽  
Element Mesh ◽  
Magma Flow ◽  
Continental Scale ◽  
Low Viscosity ◽  
High Particle ◽  
High Reynolds

The McMurdo Dry Valleys magmatic system, Antarctica, provides a world-class example of pervasive lateral magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle microstructure of a congested magma slurry. We simulated the flow regime in two and three dimensions using numerical models built on a finite-element mesh derived from field data. The model captures the flow behaviour of the Basement Sill magma over a viscosity range of 1–10 4  Pa s where the higher end (greater than or equal to 10 2  Pa s) corresponds to a magmatic slurry with crystal fractions varying between 30 and 70%. A novel feature of the model is the discovery of transient, low viscosity (less than or equal to 50 Pa s) high Reynolds number eddies formed along undulating contacts at the floor and roof of the intrusion. Numerical tracing of particle orbits implies crystals trapped in eddies segregate according to their mass density. Recovered shear strain rates (10 −3 –10 −5  s −1 ) at viscosities equating to high particle concentrations (around more than 40%) in the Sill interior point to shear-thinning as an explanation for some types of magmatic layering there. Model transport rates for the Sill magmas imply a maximum emplacement time of ca 10 5 years, consistent with geochemical evidence for long-range lateral flow. It is a theoretically possibility that fast-flowing magma on a continental scale will be susceptible to planetary-scale rotational forces.

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