Complex 3D Geometries Research Articles

Non-Planar Geometrical Effects on the Magnetoelectrical Signal in a Three-Dimensional Nanomagnetic Circuit.

Expanding nanomagnetism and spintronics into three dimensions (3D) offers great opportunities for both fundamental and technological studies. However, probing the influence of complex 3D geometries on magnetoelectrical phenomena poses important experimental and theoretical challenges. In this work, we investigate the magnetoelectrical signals of a ferromagnetic 3D nanodevice integrated into a microelectronic circuit using direct-write nanofabrication. Due to the 3D vectorial nature of both electrical current and magnetization, a complex superposition of several magnetoelectrical effects takes place. By performing electrical measurements under the application of 3D magnetic fields, in combination with macrospin simulations and finite element modeling, we disentangle the superimposed effects, finding how a 3D geometry leads to unusual angular dependences of well-known magnetotransport effects such as the anomalous Hall effect. Crucially, our analysis also reveals a strong role of the noncollinear demagnetizing fields intrinsic to 3D nanostructures, which results in an angular dependent magnon magnetoresistance contributing strongly to the total magnetoelectrical signal. These findings are key to the understanding of 3D spintronic systems and underpin further fundamental and device-based studies.

Integrating ultrasound directed self-assembly and additive manufacturing to fabricate engineered materials

Engineered materials comprising specifically designed patterns of particles embedded in a matrix material can display exotic physical properties when interacting with an external field, such as metamaterials (electromagnetic wave field) and structural materials (force field), to only name a few. Altering the pattern of particles that constitutes the microstructure of the engineered material enables tuning its properties. We describe a fabrication process to implement macroscale engineered materials layer-by-layer using additive manufacturing, where in each layer we organize a user-specified pattern of particles using ultrasound directed self-assembly to tailor the microstructure of the material. In contrast with previous demonstrations of fabricating engineered materials that are limited to laboratory-scale and/or 2D implementations, this process enables fabricating macroscale specimens with complex 3D geometry required for engineering applications. Hence, this platform technology has significant implications for fabricating engineered materials relevant to a wide range of applications including manufacturing of composite materials, engineered materials for acoustic and electromagnetic cloaking and sub-wavelength imaging, and 3D printing structures with embedded electrical wiring, among others.

Shape Optimization of Thermoacoustic Systems Using a Two-Dimensional Adjoint Helmholtz Solver

Abstract Thermoacoustic instabilities, which arise due to the interaction between flames and acoustics, are sensitive to small changes to the system parameters. In this paper, we apply adjoint-based shape optimization to a 2D finite element Helmholtz solver to find accurately and inexpensively the shape changes that most stabilize a 2D thermoacoustic system in the linear regime. We examine two cases: a Rijke tube and a turbulent swirl combustor. Both systems exhibit an unstable longitudinal mode and we suppress the instability by slightly modifying the geometry. In the case of the turbulent swirl combustor, the sensitivities are higher in the plenum and in the burner than in the combustion chamber, mainly due to the effect of the mean temperature. In the cooler regions, the local wavelength is shorter, which means that geometry changes of a given distance have more influence than they do where the local wavelength is longer. This is the first time adjoint-based shape optimization is applied to 2D Helmholtz solvers in thermoacoustics, after being previously applied to low-order thermoacoustic networks. But Helmholtz solvers have an intrinsic advantage: they can handle complex geometries. The easy scalability of this method to complex 3D geometries makes this tool a strong candidate for the iterative design of thermoacoustically stable combustors.

Influence of Surface Preparation and Heat Treatment on Mechanical Behavior of Hybrid Aluminum Parts Manufactured by a Combination of Laser Powder Bed Fusion and Conventional Manufacturing Processes

Today, in industry, laser-based additive manufacturing (LAM) is used to produce high-value parts of very complex designs that are not manufacturable by conventional technologies; this process’ low production throughput and high cost prevent it from being used more extensively. One way to exploit the benefits of LAM in industry is to have it combined with lower-cost manufacturing technologies. In a hybrid approach, LAM can be integrated within an assembly line’s welding station to complete the manufacturing of a product by depositing a foreign material on a substrate only where needed, or by building structures of complex 3D geometries (e.g., lattice structures) directly onto inexpensive preforms. To pave the way for using a hybrid approach design in real applications, as a prime requirement, the chosen technology must grant comparable structural integrity to its products with respect to its conventional counterparts. In this work, different types of surface pretreatments for substrates were investigated as a key enabling factor to tailor the bi-material system’s mechanical properties in use. Hybrid samples were made by depositing AlSi10Mg by direct metal laser sintering onto A356-T6 aluminum bases prefabricated by casting and forging, and their properties were compared with fully homogeneous samples that were conventionally produced. Specifically referring to the automotive use case, both these alloy grades were chosen for their extensive use in the production of motor vehicles. The testing campaign, characterized by microscopy, mechanical testing, and fatigue, revealed that the structural integrity of the hybrid samples is comparable with the benchmarks when standard heat treatments are adopted. This result makes the prospect of the exploitation of the hybridization concept as conceived very promising for the future.

Three-Dimensional Printing of Double-Network Hydrogels: Recent Progress, Challenges, and Future Outlook.

Hydrogels are widely used materials due to their biocompatibility, their ability to mimic the hydrated and porous extracellular microenvironment, as well as their ability to tune both mechanical and biochemical properties. However, most hydrogels lack mechanical toughness, and shaping them into complicated three-dimensional (3D) structures remains challenging. In the past decade, tough and stretchable double-network hydrogels (DN gels) were developed for tissue engineering, soft robotics, and applications that require a combination of high-energy dissipation and large deformations. Although DN gels were processed into simple shapes by using conventional casting and molding methods, new 3D printing methods have enabled the shaping of DN gels into structurally complex 3D geometries. This review will describe the state-of-art technologies for shaping tough and stretchable DN gels into custom geometries by using conventional molding and casting, extrusion, and optics-based 3D printing, as well as the key challenges and future outlook in this field.

An unfitted RBF-FD method in a least-squares setting for elliptic PDEs on complex geometries

Radial basis function generated finite difference (RBF-FD) methods for PDEs require a set of interpolation points which conform to the computational domain Ω. One of the requirements leading to approximation robustness is to place the interpolation points with a locally uniform distance around the boundary of Ω. However generating interpolation points with such properties is a cumbersome problem. Instead, the interpolation points can be extended over the boundary and as such completely decoupled from the shape of Ω. In this paper we present a modification to the least-squares RBF-FD method which allows the interpolation points to be placed in a box that encapsulates Ω. This way, the node placement over a complex domain in 2D and 3D is greatly simplified. Numerical experiments on solving an elliptic model PDE over complex 2D geometries show that our approach is robust. Furthermore it performs better in terms of the approximation error and the runtime vs. error compared with the classic RBF-FD methods. It is also possible to use our approach in 3D, which we indicate by providing convergence results of a solution over a thoracic diaphragm.

Increasing the performance of continuous compression moulding by local pressure adaption

Continuous compression moulding (CCM) is an efficient process for manufacturing endless fibre-reinforced thermoplastic composites, so called organic sheets. The semi-finished products are fully impregnated and consolidated and can be thermoformed into complex 3D-geometries. Applications benefit from excellent weight-specific features as well as functional integration. Nevertheless, limited production speed and lower than acceptable manufacturing quality are still a challenge, especially with the use of high shrinkage polymers. Hence, porosities and defects due to pressure drops inside the laminate during impregnation and solidification can cause degradation in material properties. With the integration of an active adaptive pressing tool and an inline pressure measurement system, the process can be optimised towards guided impregnation and improved pressure distribution. A calculation method based on the B-factor method by Mayer has been adapted for the CCM process in order to enhance the tool design. Both, production speed as well as organic sheet quality can be improved with the optimised processing system presented in the following work.

Nanoscale 3D Electroforming by Template Pyrolysis

A novel approach is demonstrated that extends the resolution of 3D electroforming. Photoresist templates with complex 3D geometries are generated using two‐photon lithography are shrunken by a factor of ≈5 through pyrolysis. A key discovery is that pyrolysis at 500 °C, instead of the higher temperatures normally used for pyrolysis, still shrinks the template by a significant amount but keeps the template nonconductive. This shrunken template is used for electroforming, or template‐assisted electrodeposition, and then etched away to reveal complex 3D structures of pure metal (>99 at%) with linewidths below 200 nm. The versatility of the technique is demonstrated by fabricating octet truss nanolattices from either nanocrystalline gold or microcrystalline copper. In situ micromechanical tests are used as an analytical technique to reveal that these lattices have yield strengths of 325 and 190 MPa for the gold and copper, therefore verifying the fidelity of the architecture.

Modeling of liquid lithium flow in porous plasma facing material

Abstract Flowing liquid lithium can, in principle, create a renewable surface interacting with the plasma, providing protection for the underlying solid substrate. Recent experiments [1] showed that liquid lithium supplied through a porous medium can limit the plasma facing surface temperature, even at high heat flux values in excess of 10 MW/m2. The use of new 3D printing techniques allows creation of plasma facing components that supply liquid lithium through capillary channels. Numerical analysis can be used to develop and optimize porous plasma facing component using virtual prototyping. The present contribution introduces a numerical model of liquid metal flow in a porous structure, interacting with the plasma. The model uses computational fluid dynamics (CFD) to model a flow through a complex 3D geometry including magneto-hydrodynamics (MHD) effects. The CFD set-up covers the liquid metal, plasma and solid structures, simultaneously, connected by realistic interfaces. Small scale interface structures are modeled separately to obtain a self-consistent interface functions. Customized version of the general-purpose CFD is used to handle complex 3D geometries, and efficient pre- and post-processing. MHD is introduced using the magnetic vector potential approach, allowing precise fluid–solid interface treatment. Special stabilization procedures were derived and applied to improve convergence of the momentum balance equations with source terms due to Lorentz force and surface tension. Conjugate heat transfer analysis was performed in the plasma, liquid metal and solid components. The customized code was validated using analytical results for high Hartmann number flow. Results of the validation and numerical analysis of liquid lithium plasma facing components using porous walls will be presented.

Highly uniform polycrystalline diamond coatings of three-dimensional structures

Diamond is highly desirable as a conformal thin-film coating for three-dimensional (3D) devices due to its extreme hardness, durability and biocompatibility, especially in the case of implantable medical devices and prosthetics. Recent advances in microwave plasma chemical vapour deposition (CVD) have enabled conformal coating of such 3D structures with nanodiamond films. However, these techniques have not been extended to micro-crystalline diamond, due to interactions between the 3D substrates and resonant microwave cavity. Here we demonstrate more uniform growth of CVD polycrystalline diamond (PCD) coatings on complex-shaped structures, with the use of in-cavity Faraday cages, to isolate the 3D sample from the microwave cavity. While this does disrupt the distribution of the microwave plasma, which surrounds the 3D structure, we show that growth of relatively uniform micro-crystalline and faceted PCD films is possible over the entirety of the exposed 3D sample surface. The resultant technique opens possibilities for the coating of complex 3D geometries with a wider range of diamond materials than has been possible to date.

3D Interactive Segmentation With Semi-Implicit Representation and Active Learning.

Segmenting complex 3D geometry is a challenging task due to rich structural details and complex appearance variations of target object. Shape representation and foreground-background delineation are two of the core components of segmentation. Explicit shape models, such as mesh based representations, suffer from poor handling of topological changes. On the other hand, implicit shape models, such as level-set based representations, have limited capacity for interactive manipulation. Fully automatic segmentation for separating foreground objects from background generally utilizes non-interoperable machine learning methods, which heavily rely on the off-line training dataset and are limited to the discrimination power of the chosen model. To address these issues, we propose a novel semi-implicit representation method, namely Non-Uniform Implicit B-spline Surface (NU-IBS), which adaptively distributes parametrically blended patches according to geometrical complexity. Then, a two-stage cascade classifier is introduced to carry out efficient foreground and background delineation, where a simplistic Naïve-Bayesian model is trained for fast background elimination, followed by a stronger pseudo-3D Convolutional Neural Network (CNN) multi-scale classifier to precisely identify the foreground objects. A localized interactive and adaptive segmentation scheme is incorporated to boost the delineation accuracy by utilizing the information iteratively gained from user intervention. The segmentation result is obtained via deforming an NU-IBS according to the probabilistic interpretation of delineated regions, which also imposes a homogeneity constrain for individual segments. The proposed method is evaluated on a 3D cardiovascular Computed Tomography Angiography (CTA) image dataset and Brain Tumor Image Segmentation Benchmark 2015 (BraTS2015) 3D Magnetic Resonance Imaging (MRI) dataset.

An investigation into the challenges of the point grinding machining process

Point grinding is an abrasive machining process that utilises miniature single layer superabrasive tools to remove material. The use of such small diameter tools offers advantages in the manufacturing of small or difficult to access complex 3D geometries, however, in their current state, these tools suffer from several critical challenges preventing their successful implementation. An investigation into the use of a typical commercially available point grinding tool for machining of hardened steel components has been carried out, with the aim of identifying the critical process challenges. The requirement for high rotational speeds, high tool deflection, variation in grit protrusion heights and bond layer thickness, accelerated tool wear, increased sensitivity to runout, zero cutting speed at tooltip and high tool loading have been identified as the main issues affecting the point grinding process. It is crucial that these challenges are correctly understood to facilitate future tool development.

Stimuli Responsive Shape Memory Microarchitectures

AbstractShape memory polymers (SMPs) respond to heat by generating programmable movement in devices that require substantial deformation and operate at transient temperatures, including stents and embolization coils. To enable their use in small‐scale applications like retinal vasculature stenting, shape transformations must occur in SMPs with complex 3D geometries with nanoscale features. This work describes the synthesis and sculpting of a benzyl methacrylate‐based SMP into 3D structures with <800 nm characteristic critical dimensions via two photon lithography. Dynamic nanomechanical analysis of 8 µm‐diameter cylindrical pillars reveal the initiation of this SMP's glass transition at 60 °C. Shape memory programming of the characterized pillars as well as complex 3D architectures, including flowers with 500 nm thick petals and cubic lattices with 2.5 µm unit cells and overall dimensions of 4.5 µm × 4.5 µm × 10 µm, demonstrate an 86 +/− 4% characteristic shape recovery ratio. These results reveal a pathway toward SMP devices with nanoscale features and arbitrary 3D geometries changing shape in response to temperature.

Selective Laser Melting and Electron Beam Melting of Ti6Al4V for Orthopedic Applications: A Comparative Study on the Applied Building Direction.

The 3D printing process offers several advantages to the medical industry by producing complex and bespoke devices that accurately reproduce customized patient geometries. Despite the recent developments that strongly enhanced the dominance of additive manufacturing (AM) techniques over conventional methods, processes need to be continually optimized and controlled to obtain implants that can fulfill all the requirements of the surgical procedure and the anatomical district of interest. The best outcomes of an implant derive from optimal compromise and balance between a good interaction with the surrounding tissue through cell attachment and reduced inflammatory response mainly caused by a weak interface with the native tissue or bacteria colonization of the implant surface. For these reasons, the chemical, morphological, and mechanical properties of a device need to be designed in order to assure the best performances considering the in vivo environment components. In particular, complex 3D geometries can be produced with high dimensional accuracy but inadequate surface properties due to the layer manufacturing process that always entails the use of post-processing techniques to improve the surface quality, increasing the lead times of the whole process despite the reduction of the supply chain. The goal of this work was to provide a comparison between Ti6Al4V samples fabricated by selective laser melting (SLM) and electron beam melting (EBM) with different building directions in relation to the building plate. The results highlighted the influence of the process technique on osteoblast attachment and mineralization compared with the building orientation that showed a limited effect in promoting a proper osseointegration over a long-term period.

Acoustic analysis of ship propeller using CFD

The acoustic levels generated by ship propeller are very much important in the design and development of the propeller from stealth technology point of view. The KCS SVA 1193 model of propeller geometry has been taken from the literature. The complex 3D geometry of the propeller is created using CATIAV5. The propeller geometry, surrounded by the sea water, has been considered by creating the fluid domain around the propeller. The acoustic levels, generated by the propeller, are computed using commercial software package ANSYS FLUENT. The unstructured mesh is generated in the fluid domain. The k–∈ standard turbulence model is selected to capture the viscous effects. The velocity at the inlet, pressure at outlet and moving frame of reference boundary conditions are used for computational analysis. Broadband noise model is used to capture the effects of the acoustic waves. The thrust and torque have been estimated for the chosen propeller. In this analysis, the acoustic power level of the propeller is captured and the non-dimensional coefficients are calculated.

Creation of 3D Geometry in Scan-to-CAD/BIM Environment

Scan-to-BIM brings the documentation of existing buildings into line with the modern digital planning methodology called building information modelling (BIM). This article describes how scan-to-BIM uses 3D laser scanning to capture digitally an existing building as a point cloud, for the creation and updating of a BIM model. Renovation of an existing old lattice grid structure, out of service for more than ten years, was a real challenge for investigation, capturing geometry and determining the rest load-carrying capacity. The original structure was calculated and produced in Italy and assembled at Bulgaria during the 80s of 20th century and was covered with a single layer membrane. It was used for 30 years before it was left without service and maintenance for more than 10 years. Strong corrosion processes was investigated for some of the members and almost all applied bolts which reduce seriously the rest load-carrying capacity. Laser scanning technology was chosen for getting the complex 3D geometry of the lattice grid structure. It was a real challenge to find a software for processing the scanned data and extracting the axial geometry of structure. Investigations for determining of the applied steel class and class of bolts was done on the site and at laboratory. Different concepts for rehabilitation was discussed before choosing the double layered stressed textile membrane. Numerical FEM models was used for proofing the adequacy of chosen structural solution. Modelling is a necessary process for converting the point cloud to a useful CAD representation. It provides a complete picture of the as-built situation by filling the gaps coming from occlusions, by averaging the effects of noise and by providing the quality measures about the final results.

Multimaterial direct 4D printing of high stiffness structures with large bending curvature

The emerging direct four dimensional (4D) printing approach is considered as an easy, fast and economical manufacturing strategy that fabricates complex 3D geometries evolving from printed flat patterns in response to external stimuli. However, its implementation to practical engineering applications is impeded by the fact that the existing direct 4D printing methods could not render both the large bending curvature and high loading capacity at the same time. Herein, we report a multimaterial direct 4D printing method to fabricate patterned laminate that consists of covalently bonded elastomer and high-water-content hydrogel. The dehydration induced large volumetric shrinkage (up to 60%) and great modulus escalation (from 100 kPa to 4 GPa) allow the printed flat patterns to evolve into complex 3D structures with large bending curvature (up to 0.7 mm−1) and high bending stiffness (up to 104 MPa m3). To facilitate the structural design, we develop a phenomenological model to describe the dehydration induced shrinkage and stiffening, and implement this model into Euler–Bernoulli beam theory and finite element simulations. Compared with other 3D printing technologies, the proposed multimaterial direct 4D printing approach demonstrates the merits in terms of less building time and high load capacity at both room temperature and high temperature.

Near-Net-Shape Trimming Process by Abrasive Water Jet Cutting of High-Performance Workpieces for the Aerospace Industry

High-performance materials offer enormous potential for increasing the efficiency of many complex and highly stressed systems in the aerospace industry. However, due to their special material properties, most of these materials are very difficult to machine using conventional machining processes such as turning, milling and drilling. In comparison, water jet cutting technology offers all the prerequisites to bring high-performance materials to their final contour and to efficiently realize a large portion of the material removal. Because of the complex geometry of 3D components used in the aerospace industry, a further development of existing system technology as well as the generation of cutting paths, which are usually designed for pure 2D machining, is required. The aim of the study is the implementation of an automated pre-contouring for difficult to machine materials using abrasive water jet cutting for industrial 3D applications. This is achieved by using an innovative workpiece clamping as well as a new cutting technology, the trimming, in order to reduce the costs of the pre-contouring process as well as the time and resource consumption of the entire process chain. During trimming, a continuous cut takes place and the semi-finished product is brought closer and closer to the required component geometry by cutting off the outer material areas. For this purpose, tests were carried out on workpieces made of stainless steel X5CrNi18 (EN 1.4301) with cutting conditions that are demanding for the abrasive water jet cutting process, such as high cutting depths with simultaneously low cutting angles. It was possible to use these findings to extend existing material models and thus ensure an error-free path generation for cutting processes. The investigations are the basis for the future use of waterjet cutting for near-net-shape machining of workpieces with complex 3D geometry. The experiments showed promising results in terms of the economic efficiency of the trimming process and provide a basis for subsequent investigations with difficult-to-machine workpieces for the aerospace industry.

Enhancement of accuracy in double sided incremental forming by compensating tool path for machine tool errors

Incremental Sheet Forming (ISF) is a dieless forming process and has capability to form complex 3D geometries. Double Sided Incremental Forming (DSIF) is the most flexible variant of ISF as it uses two tools, one on either side of the sheet (one tool forms the sheet and other acts as support). However, forming the components with acceptable accuracy is one of the challenges as it depends on many factors such as sheet and tool(s) deflections as well as machine tool errors. If these deflections/deviations are not compensated in tool path, accuracy of the component gets affected and support tool may lose contact or squeeze the sheet while forming components. In the present work, grid-based method is used to measure the machine tool error at discrete points of the work envelope. To enhance the accuracy and support tool contact condition, machine tool errors are compensated in tool path along with tool and sheet deflection compensations developed earlier. To demonstrate the effectiveness of developed methodology on the accuracy, components having different geometric characteristics as well as opening sizes are formed with and without compensating for machine tool errors in tool path. Results indicate that deviation in symmetry within the same contour reduced from 850 μm to less than 40 μm. In addition, support tool has maintained contact throughout support surface with maximum force of 50 N when machine tool errors are compensated.

Realizing CsPbBr3 Light-Emitting Diode Arrays Based on PDMS Template Confined Solution Growth of Single-Crystalline Perovskite.

Metal-halide perovskites have shown excellent optoelectronic properties, among which the array-type architecture is highly desirable. However, both the susceptibility of perovskites to polar solvents and the complex 3D geometry of array structure have led to great challenges for device fabrication and performance, which hinders their further applications. Here, we report a simple but efficient approach highly compatible with the state-of-the-art microelectronics processes to construct single-crystalline array light-emitting diodes (LEDs) of perovskite. The well-aligned single-crystalline array was sandwiched as the emission layer, among the carefully designed multilayer ITO/NiO/CsPbBr3/PMMA/ZnO/Ag structure. Through systematically altering the size of CsPbBr3 single crystal and the thickness of insulation layer, the device performance has been optimized and eventually achieved a 99% working ratio in a 62 × 47 array. Moreover, a prototype device of LED display was also fabricated. These results clearly demonstrate that our strategy is efficient, reliable, and versatile, which can be easily extended to other perovskites.