Control Of Length Scale Research Articles

Eliminating occluded voids in additive manufacturing design via a projection-based topology optimization scheme

Design for additive manufacturing (AM) requires knowledge of the constraints associated with your targeted AM process. One important design concern is the unintentional trapping of parasitic mass in occluded void geometries with either uncured or non-solidified material, or in some cases, sacrificial support material. These occluded features create the need to physically alter the optimal topology to remove the material. In this work, a projection-based topology optimization design formulation is proposed to eliminate occluded void topological features in optimal AM designs. The algorithm is based on the combination and enhancement of two existing algorithms: a projection-based, overhang-constrained algorithm to design self-supporting structures in AM, and a void projection algorithm to design topologies through control of the void phase. The combined algorithm results in topologies with void regions that always possess an exit path to predefined outer surfaces – i.e. drainage pathways. Solutions are first demonstrated in two dimensions, with increasing design freedom allowed through algorithm enhancements. The algorithm is then adapted to 3D, adopting a multi-phase TO approach to not only regain control of the solid phase length scale, but also to drive toward superior performing topologies with minimal impact on the part performance.

Architected porous metals in electrochemical energy storage

Porous metallic structures are regularly used in electrochemical energy storage devices as supports, current collectors or active electrode materials. Bulk metal porosification, dealloying, welding or chemical synthesis routes involving crystal growth or self-assembly for example, can sometimes provide limited control of porous length scale, ordering, periodicity, reproducibility, porosity and surface area. Additive manufacturing and 3D printing has shown the potential to revolutionize the fabrication of architected metals many forms, allowing complex geometries not usually possible by traditional methods, but enabling complete design freedom of a porous metal based on the required physical or chemical property to be exploited. We discuss properties of porous metal structures in EES devices and provide some opinions on how architected metals may alleviate issues with electrochemically active porous metal current collectors, and provide opportunities for optimum design based on electrochemical characteristics required by batteries, supercapacitors or other electrochemical devices.

A new quasi-dimensional flame tracking combustion model for spark ignition engines

A new quasi-dimensional combustion model based on the flame tracking approach is described and presented in the paper. The new quasi-dimensional flame tracking model is able to simulate the turbulent combustion process in premixed fuel/air/residual gas mixtures. A new method for the description of the geometry of the combustion chamber and flame front was developed enabling the visualisation of flame front movement across the combustion chamber. The control of local turbulence quantities in the flame front near the wall enables that the developed flame tracking model can predict the entire turbulent combustion process after the flame kernel development in spark-ignition engines without case-dependent calibration requirement. The developed quasi-dimensional combustion model was validated with the experimental and results of multidimensional model of a single cylinder spark ignition engine on averaged cycles. The model was integrated with the previously developed ignition, mixture stratification and cyclic variability sub-model that enable the simulation of cyclic combustion variability triggered by the stochastic variations of flow angle at the spark plug, mixture stratification and in-cylinder turbulence level. Due to the novelty of the model which includes the control of local integral length scale and turbulent kinetic energy in the flame segments the predictive capability of quasi-dimensional model is achieved with the application of single set of parameters related to average cycle and cyclic combustion variability. Flame tracking model with the low computational time represents a promising tool to calculate the turbulent combustion process including cyclic combustion variability in modern spark ignition engines.

Constraints of distance from boundary to skeleton: For the control of length scale in level set based structural topology optimization

Abstract A method is proposed for the control of minimum/maximum length scale in the level set based structural topology optimization. The minimum/maximum length scale of structure is characterized by using the concept of smallest/biggest maximal inscribable ball. In order to prevent trivial zero minimum length scale, the skeleton of structure is utilized and trimmed. The control of length scale is realized by constraining the distance from boundary to skeleton, and the distance is explicitly constructed by using the highly efficient fast marching method. Numerical examples in two dimensions are investigated.

The Effect of Al on Phase Stability and Oxidation Behavior in Ternary Nb-Ti-Si Alloys

In this paper, we report a significant improvement in mechanical and oxidation properties of near eutectic Nb–Si alloys by the addition of aluminum (Al) and control of microstructural length scale. Thus in order to develop new alloys, we have to choose proper alloying elements keeping all the above issues in mind. Among the non-transition elements such as Al, Ga, Ge, Sn, and Al is most attractive from the point of view of enhancing the oxidation resistance and room temperature ductility due to substitution of Si with metallic Al . Al forms oxides which are even more thermodynamically stable than Si and Nb based oxides. Al is also soluble in Nb to a greater degree in conjunction with other refractory elementsFig.1 The figure shows composite X-ray diffraction patterns of each sample exposed to air for one hour in a TGA furnace at above mention temperatures.

Study on the Microstructure and Oxidation Properties of near Eutectic Nb-Si Alloys

In this paper, we report a significant improvement in Microstructure and oxidation roperties of near eutectic NbSi alloys by the addition of aluminum (Al) and control of microstructural length scale. A comparative study of two alloys Nb-18.79at%Si and Nb-12.3at%Si-9at%Al were carried out. The processing for microstructure refinements were carried out by vacuum suction casting in water cooled thick copper mould. It is shown that addition of Al suppresses Nb3Si phase and promotes βNb5Si3phase under nonequilibrium solidification condition. The microstructural length scale and in particular eutectic spacing reduces significantly to 50100 nm in suction cast ternary alloy. The indentation fracture toughness of Al containing suction cast alloy shows a value of 20.2±0.5 MPam which represents a major improvement over bulk NbSi eutectic alloy. The detailed thermal studies confirm a multifold improvement in oxidation resistance up to 1000°C.

Phase Selection in a Laser Surface Melted Zr-Cu-Ni-Al-Nb Alloy

The present work explores the use of the LENS™ (laser engineered net shaping) powder deposition technique in combination with laser surface melting to evaluate the formation–properties–production of bulk metallic glass-forming systems. A model Zr-Cu-Ni-Al-Nb alloy was subjected to a number of laser surface melting experiments to remelt and rapidly solidify a thin surface layer (the laser power varied from 150 W to 450 W and the travel speed of the substrate surface relative to the laser beam varied from 8 mm/s to 170 mm/s). Detailed SEM/TEM evaluation of the microstructure formed under selected laser surface melting conditions was conducted. A marked transition in the microstructure was observed as a result of phase selection, driven by the undercooling manifest under the different imposed solidification conditions. It is considered that such a technique provides valuable insight into the scope for microstructure manipulation through the precise control of the processing variables. The control of the microstructural length scale and the tuning of the intrinsic elastic constants of the constituent phases have been identified as being paramount, for example, in the alloy design of amorphous matrix composites.

A Significant Improvement in Mechanical Properties of near Eutectic Nb-Si Alloys

In this paper, a significant improvement in mechanical and oxidation properties of near eutectic Nb–Si alloys by the addition of aluminum (Al) and control of microstructural length scale were studied. A comparative study of two alloys Nb-18.79at%Si and Nb-12.3at%Si-9at%Al were carried out. Compression test yields the ultimate strength of 1.8±0.1 GPa and engineering strain of 2.3±0.03%. In comparison, the binary Nb-18.79 at% Si alloy possesses an ultimate strength of 1.35±0.1 GPa and strain of 0.2±0.01% when processed under identical conditions. The indentation fracture toughness of Al containing suction cast alloy shows a value of 20.2±0.5 MPa which represents a major improvement over bulk Nb–Si eutectic alloy

Microstructure and mechanical properties of oxidation resistant suction cast Nb–Si–Al alloy

In this paper, we report a significant improvement in mechanical and oxidation properties of near eutectic Nb–Si alloys by the addition of aluminum (Al) and control of microstructural length scale. A comparative study of two alloys Nb-18.79at%Si and Nb-12.3at%Si-9at%Al were carried out. The processing for microstructure refinements were carried out by vacuum suction casting in water cooled thick copper mould. It is shown that addition of Al suppresses Nb3Si phase and promotes βNb5Si3 phase under nonequilibrium solidification condition. The microstructural length scale and in particular eutectic spacing reduces significantly to 50–100nm in suction cast ternary alloy. A detailed TEM study shows the presence of δ-Nb11Si4 phase in Nb matrix. The hardness of Nb solid solution can be increased as a consequence to a level observed in Nb3Si intermetallic due to the well oriented precipitates. Compression test yields the ultimate strength of 1.8±0.1GPa and engineering strain of 2.3±0.03%. In comparison, the binary Nb-18.79at% Si alloy possesses an ultimate strength of 1.35±0.1GPa and strain of 0.2±0.01% when processed under identical conditions. The latter exhibits coarser microstructural length scale (300–400nm) and a brittle behavior. The indentation fracture toughness of Al containing suction cast alloy shows a value of 20.2±0.5MPa√m which represents a major improvement over bulk Nb–Si eutectic alloy. The detailed thermal studies confirm a multifold improvement in oxidation resistance up to 1000°C.

Effect of Gallium on microstructure and mechanical properties of Nb–Si eutectic alloy

In this paper, we report a significant improvement in mechanical properties of near eutectic Nb–Si alloys by addition of Gallium (Ga) and control of microstructural length scale. A comparative study of two alloys Nb-18.79 at.%Si and Nb-20.2 at.%Si–2.7 at.%Ga were carried out. The microstructure refinements were carried out by vacuum suction casting in water cooled thick copper mold. It is shown that addition of Ga suppresses Nb3Si phase and promotes β-Nb5Si3 phase. The microstructural length scale and in particular eutectic spacing reduces significantly to 50–100 nm in suction cast ternary alloys. Compression test shows a strength of 2.8 ± 0.1 GPa and plasticity of 4.3 ± 0.03%. In comparison, the binary Nb-18.79 at.%Si alloy processed under identical conditions exhibit coarser length scale (300–400 nm) and brittle behavior. The fracture toughness of Ga containing suction cast alloy shows a value of 24.11 ± 0.5 MPa√m representing a major improvement for bulk Nb–Si eutectic alloy.

Stability and Dewetting of Metal Nanoparticle Filled Thin Polymer Films: Control of Instability Length Scale and Dynamics

We investigate the influence of gold nanoparticle addition on the stability, dewetting, and pattern formation in ultrathin polymer-nanoparticle (NP) composite films by examining the length and time scales of instability, morphology, and dynamics of dewetting. For these 10-50 nm thick (h) polystyrene (PS) thin films containing uncapped gold nanoparticles (diameter approximately 3-4 nm), transitions from complete dewetting to arrested dewetting to absolute stability were observed depending on the concentration of the particles. Experiments show the existence of three distinct stability regimes: regime 1, complete dewetting leading to droplet formation for nanoparticle concentration of 2% (w/w) or below; regime 2, partial dewetting leading to formation of arrested holes for NP concentrations in the range of 3-6%; and regime 3, complete inhibition of dewetting for NP concentrations of 7% and above. Major results are (a) length scale of instability, where lambdaH approximately hn remains unchanged with NP concentration in regime 1 (n approximately 2) but increases in regime 2 with a change in the scaling relation (n approximately 3-3.5); (b) dynamics of instability and dewetting becomes progressively sluggish with an increase in the NP concentration; (c) there are distinct regimes of dewetting velocity at low NP concentrations; (d) force modulation AFM, as well as micro-Raman analysis, shows phase separation and aggregation of the gold nanoparticles within each dewetted polymer droplet leading to the formation of a metal core-polymer shell morphology. The polymer shell could be removed by washing in a selective solvent, thus exposing an array of bare gold nanoparticle aggregates.