Добірка наукової літератури з теми "Printed Periodic Metallic Geometries"

Membrane filtration process can be intensified by using static mixers inside tubular membranes. Most of commercial static mixers are optimized for mixing fluids, not for membrane filtration. We have developed new turbulence promoter geometries designed for intensification of permeate flux and retention without significant pressure drop along the membrane. In previous experiments, we used metallic turbulence promoters, but in this work, FDM 3D printing technology was used to create these improved geometries, which are new in membrane filtration and they have the same geometry as existing metallic versions. New 3D printed objects were tested with filtration of stable oil-in-water emulsion. Our experiments proved that 3D printed static mixers might be as effective as metallic versions. The effect on initial flux and retention of oil was very similar. Pressure drop along membrane was slightly higher (but significantly lower from pressure drop along the membrane resulted by commercial static mixers, designed only for mixing fluids). Higher pressure drop may be the result of rougher surface due the layer-technology of 3D printing. This negative effect can be reduced by using a smaller nozzle (which will produce smaller layers) or smoothing the surface. PLA is material easier for printing, but from these two materials, PETG is a better choice due its higher operating temperature and better water-resist properties too.

Additive manufacturing allows for the fabrication of large-sized metallic glasses with complex geometries, which overcomes the size limitation due to limited glass-forming ability. To investigate the effect of synthesis parameters on the Mg-based metallic glasses, Mg65Cu20Zn5Y10 was fabricated by laser-based powder bed fusion under different scanning speeds and laser powers. For high energy density, the samples showed severe crystallization and macrocracks, while for low energy density, the samples contained pore defects and unfused powders. Three-dimensionally printed samples were used for the compression test, and the mechanical properties were analyzed by Weibull statistics. Our work identifies proper parameters for 3D printing Mg-based metallic glasses, which provide a necessary, fundamental basis for the fabrication of 3D-printed Mg-based metallic glass materials with improved performance.

Purpose This paper aims to clarify the relationship between mechanical behaviors and the underlying geometry of periodic cellular structures. Particularly, the answer to the following research question is investigated: Can seemingly different geometries of the repeating unit cells of periodic cellular structure result in similar functional behaviors? The study aims to cluster the geometry-functional behavior relationship into different categories. Design/methodology/approach Specifically, the effects of the geometry on the compressive deformation (mechanical behavior) responses of multiple standardized cubic periodic cellular structures (CPCS) at macro scales are investigated through both physical tests and finite element simulations of three-dimensional (3D) printed samples. Additionally, these multiple CPCS can be further nested into the shell of 3D models of various mechanical domain parts to demonstrate the influence of their geometries in practical applications. Findings The paper provides insights into how different CPCS (geometrically different unit cells) influence their compressive deformation behaviors. It suggests a standardized strategy for comparing mechanical behaviors of different CPCS. Originality/value This paper is the first work in the research domain to investigate if seemingly different geometries of the underlying unit cell can result in similar mechanical behaviors. It also fulfills the need to infill and lattify real functional parts with geometrically complex unit cells. Existing work mainly focused on simple shapes such as basic trusses or cubes with spherical holes.

AbstractPlasmonic nanostructures have garnered tremendous interest in enhanced light–matter interaction because of their unique capability of extreme field confinement in nanoscale, especially beneficial for boosting the photoluminescence (PL) signals of weak light–matter interaction materials such as transition metal dichalcogenides atomic crystals. Here we report the surface plasmon polariton (SPP)-assisted PL enhancement of MoS2 monolayer via a suspended periodic metallic (SPM) structure. Without involving metallic nanoparticle–based plasmonic geometries, the SPM structure can enable more than two orders of magnitude PL enhancement. Systematic analysis unravels the underlying physics of the pronounced enhancement to two primary plasmonic effects: concentrated local field of SPP enabled excitation rate increment (45.2) as well as the quantum yield amplification (5.4 times) by the SPM nanostructure, overwhelming most of the nanoparticle-based geometries reported thus far. Our results provide a powerful way to boost two-dimensional exciton emission by plasmonic effects which may shed light on the on-chip photonic integration of 2D materials.

The building construction sector is undergoing one of the most profound transformations towards the digital transition of production. In recent decades, the advent of a novel technology for the 3D printing of clay opened up new sustainable possibilities in construction. Some architectural applications of 3D-printed clay bricks with simple internal configurations are being developed around the world. On the other hand, the full potential of 3D-printed bricks for building production is still unknown. Scientific studies about the design and printability of 3D-printed bricks exploiting complex internal geometries are completely missing in the related literature. This paper explores the new boundaries of 3D-printed clay bricks realized with a sustainable extrusion-based 3D clay printing process by proposing a novel conception, design, and analysis. In particular, the proposed methodological approach includes: (i) conception and design; (ii) parametric modeling; (iii) simulation of printability; and (iv) prototyping. The new design and conception aim to fully exploit the potential of 3D printing to realize complex internal geometry in a 3D-printed brick. To this aim, the research investigates the printability of internal configuration generated by using geometries with well-known remarkable mechanical properties, such as periodic minimal surfaces. In conclusion, the results are validated by a wide prototyping campaign.

Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well.

Abstract This paper describes a new design method for generating a compact heat exchanger (CHX) computational model consisting of triply periodic minimal surface (TPMS) core structures. These TPMS-based core structures are not easy to design using existing CAD systems, especially in the case of CHXs with complex 3D geometries. In this paper, we introduce a novel CHXs design strategy based on the calculation of volumetric distance fields (VDFs). All geometric components, including TPMS-based core structure, heat exchanger exterior shape, and a set of parts for inlet and outlet, are expressed as VDFs in a given design domain. This VDF-based geometric components description allows for the computationally efficient design of a complex-shaped CHX computational model with high levels of geometric complexity. In conjunction with several TPMS-based CHX prototypes built with additive manufacturing (AM) technologies, we describe and discuss the design and manufacturing results for a wide range of CHXs with various geometries to validate the effectiveness of the newly proposed design method. Besides, by examining the heat transfer performance experimental data, we show that the innovative CHX production method using the combination of VDF-based Boolean operations, TPMS-based core structures, and AM technologies proposed in this paper can create an ultra-efficient CHX while maintaining an allowable pressure drop.

A uniplanar millimeter-wave broadband printed log-periodic dipole array (PLPDA) antenna fed by coplanar waveguide (CPW) is introduced. This proposed structure consists of several active dipole elements, feeding lines, parallel coupled line, and the CPW, which are etched on a single metallic layer of the substrate. The parallel coupled line can be optimized to act as a transformer between the CPW and the PLPDA antenna. Meanwhile, this transform performs the task of a balun to achieve a wideband, low cost, low loss, simple directional antenna. The uniplanar nature makes the antenna suitable to be integrated into modern printed communication circuits, especially the monolithic millimeter-wave integrated circuits (MMIC). The antenna has been carefully examined and measured to present the return loss, far-field patterns, and antenna gain.

To meet the demand of continuously growing RF and microwave technologies, scientists and engineers have developed innovative materials consisting of conducting and dielectric materials that overcome limitations in the properties of natural materials. Over the last decades, the development of these artificial materials has evolved to be a new field. An artificial material is a synthesized material that gains its electromagnetic properties from its structure rather than inheriting them directly from those it is composed of. Planar versions of these artificial materials are often characterized by small periodic conducting patches over a dielectric substrate. In addition to the periodicity, the interaction of these structures with the electromagnetic waves depends on the shape and size of the small patches. Planar artificial materials pursued in electromagnetics include frequency selective surfaces (FSS), high impedance surfaces (HIS), artificial magnetic conductors (AMC), and electromagnetic bandgap (EBG) materials, which are characterized by periodic unit cells whose lattice constant is comparable with the operational wavelength. One of the very commonly seen geometry is the mushroom structure, which has a patch array with each element connected to the metal on the other side of the dielectric with a via. These metalbacked configurations are used in various antenna applications. Some narrowband absorbers have also been suggested using these configurations. This thesis investigates new artificial materials consisting of one- and two- layer of metal patch arrays that overcome the requirement for vias, and examines their design and analysis for four different applications (i) Circularly polarized antennas (ii) Surface wave suppression of microstrip antennas (iii) In-phase reflection surface and (iv) Thin radar absorbing material. Artificial materials with square patch arrays with or without vias can be designed as artificial magnetic conductors. Arrays of rectangular patches with vias or square patches with two vias or slots have been proposed for polarization sensitive reflectivity characteristics. In this thesis we propose a simple geometry for polarization sensitive reflection characteristics. This consists of a modification to square patches with variants of fractal Minkowski curves as boundaries on two of its sides, printed over a metal backed dielectric substrate without vias. The structure is compact, and due to its planar nature, it can be fabricated easily using planar technology. Properties and performance of the structure is analyzed numerically through simulations by varying fractal properties of the sides. The asymmetry in the patch causes the reflection phase of the proposed structure to depend on the polarization state of the incident wave and frequency. A phase difference above 200 degrees between the x- and y-polarized reflected waves has been achieved with small unit cells. Application of the proposed via-less structure to generate circular polarization using simple dipole antenna is also demonstrated in this thesis. Square patches arrays with vias have been proposed as high impedance surfaces (HIS) with in-phase reflection and as electromagnetic bandgap (EBG) structures for suppressing surface waves in microstrip antenna applications. The second structure proposed in this thesis is an alternative for these mushroom structures, and consists of a periodic array of square metal patches (on the top surface) and square metal rings (embedded within the dielectric substrate). This structure does not require any vias for effective operation and is analyzed extensively by numerical simulations. In-phase reflections due to high surface impedance and surface-wave suppression characteristics similar to the mushroom structure proposed by Sievenpiper have been validated. Application of the structure to reduce mutual coupling between microstrip antennas and to improve the radiation pattern are demonstrated through simulations. The structure is fabricated and experimental measurements have been made to confirm surface wave suppression characteristics. A waveguide-based experiment was done to demonstrate the in-phase reflection characteristics. One of the main advantages of the proposed structure is that it is planar in nature and easily fabricated using planar technology, without the need for any via connections across dielectric layers. Another feature is that it exhibits in-phase reflection and surface wave suppression bands at the same frequency band as in mushroom structure. The scalability of this structure to operate in different frequency ranges is also demonstrated in this thesis. Modifications to EBG using either resistive patches or surface mounted resistors have been used as absorber. In this thesis, we propose the use of the above ring-patch structure printed on a moderately lossy substrate such as FR4, as a near-perfect electromagnetic absorber. It is demonstrated that input impedance of the structure can be configured to match the free space impedance by varying the width of the ring to result in near-perfect absorption. This configuration causes a concentration of electric fields in the dielectric region between the ring and patch, thereby enhancing the dissipation of the energy. Monostatic and Bistatic radar cross section measurements have been used to ensure that there are no scattered fields in other directions. The structure is thin, easy to fabricate, and is scalable to operate at different frequencies. This does not use any resistive materials for absorption. It is shown that 99% of the incident power is dissipated by either dielectric or metal losses. The performance of this structure is analyzed using an equivalent circuit approach. A method for improving the bandwidth of this absorber by combining four unit cells and optimizing the dimensions of this sub-array is also proposed here. The performance of this EBG based absorber configuration is similar to the metamaterial based absorbers proposed recently with much smaller unit cells. To summarize, this thesis investigates electromagnetic behavior of single and stacked twolayer periodic metal patches without any interconnects, which are simple and easy to fabricate using planar approaches. It has been established that the configurations proposed in this thesis are equally effective for various electromagnetic applications as previously reported geometries, often characterized by vias or surface mount components.

Abstract The concept of a new piezoelectric actuator design is the focus of an ongoing smart structures research at DLR. It envisages actuator geometries, that have their template in nature and are aimed at optimally transfering their mechanical power to the structure in which they are integrated. The second aspect can only be achieved in case of an impedance matching. We found out, that these very specific designs have highly interesting differential geometry descriptions and that these geometries can be realized in a congenial combined manufacturing procedure: we start with 3D-printed filigree lightweight structures and continue with self-organizing processes. The results are simply, doubly and triply periodic piezoelectric membranes, grids and truss elements. One of their essential properties is their almost perfect stress distribution under mechanical loads. Any notch stresses are prevented. In this paper the first example is the modified catenoid piezoactuator. We continue with a doubly periodic honeycomb structure and finish with triply periodic modified gyroid and diamond-like actuators.

Bio-inspired materials have shown to have outstanding mechanical properties over man-made materials and are becoming of increasing interest in many fields of practical applications. Additionally, recent advances in materials and fabrication technologies allow for the design and fabrication of micro- and nano-scale structures to serve as cellular units in macro-scale materials. The mechanical behaviors of cellular solids, including stiffness and strength, can be tuned by simply tailoring the underlying geometry of the structure. In this paper the answer to the following research question is investigated: Can seemingly different bio-inspired geometries of cellular solids result in similar mechanical behaviors? Specifically, the effects of geometry on the compressive deformation responses of multiple bio-inspired periodic cubic cellular structures at macro scale are investigated both through physical tests and FE simulations of 3D printed specimens. The paper outlines standardization of specimens and tests for such a study. Additionally, a $1 recognizer based classification process is used on curves representing compressive deformation behaviors of different bio-inspired geometries to cluster them into same group.

Abstract In recent times, interest in the fabrication of porous NiTi structures have grown significantly. Porous structures have remarkable potential to be used in the areas of tissue engineering, impact absorption, and fluid permeability. However, fabrication of NiTi structures poses challenges such as poor machinability, high work hardening, and inherent springback effects, which render them difficult to tackle through conventional manufacturing routes. Additive manufacturing (AM) can alleviate the aforementioned issues associated with NiTi shape memory alloys (SMAs). In addition, this technology can be employed for producing metallic scaffolds and porous structures of complex architectural details. Recently, a class of minimal surface topologies, known as triply periodic minimal surface (TPMS) structures has emerged as an attractive configuration for building architected constructs. Very little work can be found in the literature addressing the fabrication of NiTi TPMS structures and investigating their behaviors. The complex geometries of these structures may influence the dynamics of the melt pool in beam-based AM processes as well as the solidification rate within different regions of a product, thereby affecting the microstructures of fabricated parts. An inhomogeneity in microstructures of fabricated parts was observed, which motivated a detailed examination of these structures. The novelty of the present work lies in studying the influence of geometries of NiTi TPMS lattices along with laser process parameters.

Abstract Failure Assessment Diagrams (FADs) are, in practice, the main engineering tool for the analysis of structural components containing cracks. They are utilised in well-known structural integrity assessment procedures, such as BS7910 and API 579 1/ASME FFS 1, and their reliability has been proven by numerous laboratory tests and industrial applications. However, they have been defined and validated in metallic materials, so their application in other types of materials requires demonstrating that the different assumptions taken when analysing metals are also valid for the particular material (non-metallic) being analysed. At the same time, additive manufacturing (AM) is a growing technology that allows complex geometries to be fabricated through a quite simple process. Among the different AM techniques, fused deposition modelling (FDM) is one of the most widely used, and consists in the extrusion of heated feedstock plastic filaments through a nozzle tip. The resulting printed materials have quite specific characteristics and properties, which are highly dependent on the printing parameters (e.g., raster orientation, printing temperature, etc.) and on the resulting state of internal defects. This paper provides FAD analyses for two additively manufactured (FDM) polymers: ABS and PLA. The results show that the FAD methodology may be applied for these two particular polymers, as long as linear-elastic fracture toughness values are used.

Abstract Ultrafast laser processing has been widely studied for surface texturing. The complex interaction between the laser energy, plasma, and surface chemistry produces complex morphologies including Laser-Induced Periodic Surface Structures and random higher aspect ratio geometries. Laser texturing allows engineering of metallic surface’s wettability as well as the reflectance on either broadband or narrowband basis. This paper experimentally maps the laser process parameters to the surface morphology and diffuse reflectance for stainless steel, aluminum, and copper substrates. All experiments are conducted with a 1030 nm wavelength, 230 fs pulse length laser in an ambient environment. The results show how the common morphological regimes shift with material and how the reflectance varies with morphology. To further decrease the reflectance, hierarchical structures are generated by first locally micromachining the surface to form a lattice of trenches using the focused laser beam, before texturing the surface with a rastered, defocused laser beam. The micromachined features interact with laser texturing and increase light trapping on the surface. This is a function of the depth and periodicity of the hierarchical structures as well as the surface topography. This approach provides the ability to lower the surface reflectance and add an extra level of control for directing deep micro-cavities along the surface.

Abstract Powder bed fusion (PBF) has become a widely used additive manufacturing (AM) technology to produce metallic parts. Since the PBF process is driven by a moving heat source, consistency in part production, particularly when varying geometries, has proven difficult. Thermal field evolution during the manufacturing process determines both geometric and mechanical properties of the fabricated components. Simulations of the thermal field evolution can provide insight into desired process parameter selection for a given material and geometry. Thermal simulation of the PBF process is computationally challenging due to the geometric complexity of the manufacturing process and the inherent computational complexity that requires a numerical solution at every time increment of the process. We propose a new thermal simulation of the PBF process based on the laser scan path. Our approach is unique in that it does not restrict itself to simulations on the part design geometry, but instead simulates the formation of the geometry based on the process plan of a part. The implication of this distinction is that the simulations are in tune with the as-manufactured geometry, meaning that calculations are more aligned with the process than the design, and thus could be argued is a more realistic abstraction of real-world behavior. The discretization is based on the laser scan path, and the thermal model is formulated directly in terms of the manufacturing primitives. An element growth mechanism is introduced to simulate the evolution of a melt pool during the manufacturing process. A spatial data structure, called contact graph, is used to represent the discretized domain and capture all thermal interactions during the simulation. The simulation is localized through exploiting spatial and temporal locality, which is based on known empirical data. This limits the need to update to at most a constant number of elements at each time step. This implies that the proposed simulation not only scales to handle three-dimensional (3D) printed components of arbitrary complexity but also can achieve real-time performance. The simulation is fully implemented and validated against experimental data and other simulation results.

Laser and electron-beam powder bed fusion (PBF) additive manufacturing (AM) technology has transitioned from prototypes and tooling to production components in demanding fields such as medicine and aerospace. Some of these components have geometries that can only be made using AM. Initial applications either take advantage of the relatively high surface roughness of metal PBF parts, or they are in fatigue, corrosion, or flow environments where surface roughness does not impose performance penalties. To move to the next levels of performance, the surfaces of laser and electron-beam PBF components will need to be smoother than the current as-printed surfaces. This will also have to be achieve on increasingly more complex geometries without significantly increasing the cost of the final component. Unsettled Topics on Surface Finishing of Metallic Powder Bed Fusion Parts in the Mobility Industry addresses the challenges and opportunities of this technology, and what remains to be agreed upon by the industry.