Complex 3D Geometries Research Articles

Programming mechanoluminescent behaviors of 3D printed cellular structures

Mechanoluminescence (ML) materials enable the transformation of mechanical stimuli into optical signals. However, current ML devices have limited luminescent programmability and mechanical tunability due to the relatively simple geometries as restricted by the conventional fabrication techniques. Here, we develop a strategy that is applicable for various types of zinc sulfide (ZnS)-based phosphors for allowing the fabrication of ML elastomer into complex 2D or 3D geometries with periodic cellular structures. We demonstrate that different cellular structures with tunable mechanical properties enable programmable structure-dependent ML behaviors including anisotropic and isotropic luminescence. We further exploit the quantitative structure-stress-luminescence relationship, which provides fundamental knowledge support for designing next-generation ML-based stress sensors and wearable devices.

Mechanically robust pyrolyzed carbon produced by two photon polymerization

Rapid production of nanoscale carbon-based designs with complex 3D geometry has been recently enabled by nano-3D printing via two-photon polymerization (2PP) combined with post-pyrolysis of the printed polymer. Upon pyrolysis, the design is converted to predominantly carbon, but it remains critical to select the appropriate 2PP printing parameters to produce a high stiffness and strength carbon material. Herein, we evaluate the mechanical performance under both tension and compression of 2PP-derived pyrolyzed carbon designed with modified printing parameters and provide the structural insight toward creating a robust and reliable pyrolyzed carbon material. The 2PP printing parameters are found to influence the Young's modulus of the pyrolyzed carbon by the degree of graphitic sp2 bonding in the carbon while the yield strength is dictated by the degree of porosity which influences crack initiation. These mechanisms are dissimilar to the precursor polymer indicating specific design requirements for the pyrolyzed carbon. Additionally, the surface roughness of the pyrolyzed carbon is uniform and ultra-smooth regardless of the precursor polymer conditions. This article thereby provides a template and structural insight towards the creation of a reliable and robust pyrolyzed carbon material that is suitable for the wide range of nano and microscale designs enabled by this technology.

Use of Superhydrophobic Surfaces for Performance Enhancement of Aerial–Aquatic Vehicles

Aerial–aquatic robotic vehicles show great potential in assisting in disaster response and environmental monitoring. However, to undertake these missions, they need to overcome the challenges of power requirements for takeoff and the difficulty of transitioning reliably between the air and water media. The use of superhydrophobic surfaces offers solutions to these challenges by reducing the wetted surface area of such robotic vehicles. In this article, a range of superhydrophobic surfaces is analyzed for wettability and robustness performance to ascertain their benefits as a design feature for drag reduction in aerial–aquatic robotic vehicles. The silicon dioxide nanoparticle spray coating show the most superhydrophobicity measuring a static water contact angle of 174.8°. The coating's robustness tests yield a similar performance to that of laser‐engraved brass with 200 μm groove separation, displaying a contact angle of 133.0° after ten finger strokes. The silicon dioxide nanoparticle spray is then used for drag reduction testing due to its ease of coating complex 3D geometries among the techniques explored in this study. The spray is applied to the hull of a sailing–flying robot, which resulted in the robot's drag reduction averaging 40% in the hydroplaning regime.

3D ion gyro-orbit heat load predictions for NSTX-U

High power tokamaks operate with divertor heat loads capable of destroying the plasma facing components (PFCs). High fidelity heat load predictions are necessary to ascertain the PFC state for design and during operation. Typical heat flux calculations are 2D, time invariant, and assume that power flows directly along the magnetic field lines (the optical approximation). These assumptions neglect the complex 3D geometries employed to protect the PFCs, the time varying nature of the plasma and PFC thermal state, and the helical trajectories of ions with finite Larmor radii (the gyro-orbit approximation). An integrated software framework, the heat flux engineering analysis toolkit (HEAT), was developed to generate time varying optical heat loads applied to real engineering computer aided design (CAD) (Looby et al 2022 Fusion Sci. Technol. 78 10–27). Recently, an ion-gyro orbit module has been added to HEAT. This module calculates the helical trajectories of ions as they gyrate about the magnetic field lines using kinetic theory macro-particles to accelerate the calculation. First, the new gyro-orbit module will be presented. Next, a comparison to existing research is performed. Finally, an analysis of the gyro-orbit heat loads for NSTX-U is presented for diverted discharges using the engineering CAD models utilized for PFC fabrication. Including these gyro-orbit effects can enhance the PFC performance by ‘smearing’ out the magnetic shadows associated with the castellated fish-scaled geometry. Simultaneously, the helical trajectories can degrade performance when they load narrow regions on edges and corners with high heat fluxes. Analysis of the trade-offs between these competing effects is included, and regions for further investigation are identified.

Evolution of Electroplated Cubic Boron Nitride Tool Surface Texture Parameters During Point Grinding

Abstract Point grinding is an abrasive machining process that utilizes small diameter superabrasive single-layer grinding tools for accurate machining of complex 3D geometries. Due to the small nature of these tools, high wear-rates and uneven wear around the tool circumference present a challenge for their successful application for the finish machining of metallic components. It is, therefore, essential to monitor the surface condition of the point grinding tools, to ensure their safe and reliable operation. In this investigation, the 3D topography evolution of single-layer B126 cubic boron nitride (cBN) point grinding tools was characterized using focus-variation imaging. Given the wealth of information obtained using this method, a decision-matrix methodology was used to identify the most important parameters for monitoring the wear condition of the point grinding tools. Grinding trials were also performed with fixed cutting parameters and varied cutting durations up to 520 mm3 of material removed to assess the evolution of the point grinding tool surfaces over time as a result of wear during grinding of hardened D2 tool steel. The best criteria for the characterization of the surface texture of electroplated cBN point grinding tool surfaces were identified to be the average surface height (Sa), skewness (Ssk), root mean square gradient (Sdq), reduced peak height (Spk), peak material volume (Vmp), and developed interfacial area ratio (Sdr). These parameters performed best for direct measurement of point grinding tool surfaces, paving the way for the application of the imaging technique under manufacturing conditions as an on-machine monitoring method for performance assessment.

Computational homogenization of additively manufactured lightweight structures with multiscale topology optimization

Abstract Topology optimization (TO) is an optimal design method to obtain an efficient structure with minimal usage of material by satisfying two conflicting objectives of weight reduction and structural safety. Owing to the recent advances in additive manufacturing technology, TO has been developed in connection with the use of microscale lattices, of which complicated geometries require considerable computational loads to verify their structural performance. This study aims to develop an efficient computational method to analyze a complex TO model. Computational homogenization was then developed for efficient computation of the TO model that contains a number of microscale lattices. The proposed homogenization scheme was then applied to perform three-dimensional (3D) finite element analysis (FEA) on various TO models with three scales (i.e., macroscale, microscale, and multiscale TOs). The homogenized FEAs were conducted to verify the static and dynamic deformation behaviors of three optimized meta-sandwich beams, and their results and computational efficiency were compared with those from full solid FEAs. Experimental verification revealed that the proposed homogenized FEA provided more reliable results and better computational efficiency for the microscale and multiscale TO models, whereas the conventional solid FEA was advantageous for the macroscale TO model. To apply the proposed simulation strategy to a more complex 3D geometry, three TO models were calculated for a 3D block under a compression load. The simulation strategy combining the full solid and homogenized FEAs was then applied to analyze the static and dynamic deformation behaviors of various TO models, which provided reliable predictions of the experimentally observed behaviors within an acceptable computational time.

Drum Tower‐Inspired Kirigami Structures for Rapid Fabrication of Multifunctional Shape‐Memory Smart Devices with Complex and Rigid 3D Geometry in a Two‐Stage Photopolymer

AbstractMechanically robust shape‐morphing materials that can transform from miniaturization into complex structures are highly desirable for real‐world device applications. However, fabricating mechanically robust yet geometrically complex 3D shape‐morphing structures with excellent functionality and high load‐bearing capacity remains a challenge. Inspired by drum tower buildings, a simple, rapid, and universal method is presented for fabricating multifunctional shape‐memory smart devices with complex and rigid 3D kirigami geometry in the two‐stage epoxy‐amine‐acrylate photopolymer systems. In the first‐stage reaction, transparent polymer films with a Tg of 29–49 °C are obtained by the epoxy‐amine chemistry. The shape‐memory programming process allows the first‐stage film with a drum tower‐inspired 2D kirigami pattern to be manipulated into an unsupported 3D structure. In the second‐stage reaction, UV‐induced free‐radical polymerization of methacrylate groups in the first‐stage network is employed to rapidly lock the programmed 3D kirigami structure with a Tg of 66–138 °C. The drum tower‐inspired 3D kirigami structure withstands 1000 times its own weight. The shape memory fluorescent 3D device and shape memory electronic 3D device are engineered by combining the two‐stage photopolymer system and a 3D kirigami structure. This work represents a versatile method to create multifunctional shape‐memory devices with rigid 3D geometry for potential applications.

Deep learning-based surrogate model for three-dimensional patient-specific computational fluid dynamics

Optimization and uncertainty quantification have been playing an increasingly important role in computational hemodynamics. However, existing methods based on principled modeling and classic numerical techniques have faced significant challenges, particularly when it comes to complex three-dimensional (3D) patient-specific shapes in the real world. First, it is notoriously challenging to parameterize the input space of arbitrary complex 3D geometries. Second, the process often involves massive forward simulations, which are extremely computationally demanding or even infeasible. We propose a novel deep learning surrogate modeling solution to address these challenges and enable rapid hemodynamic predictions. Specifically, a statistical generative model for 3D patient-specific shapes is developed based on a small set of baseline patient-specific geometries. An unsupervised shape correspondence solution is used to enable geometric morphing and scalable shape synthesis statistically. Moreover, a simulation routine is developed for automatic data generation by automatic meshing, boundary setting, simulation, and post-processing. An efficient supervised learning solution is proposed to map the geometric inputs to the hemodynamics predictions in latent spaces. Numerical studies on aortic flows are conducted to demonstrate the effectiveness and merit of the proposed techniques.

Microphysiological Modeling of the Structure and Function of Neuromuscular Transmitter Release Sites.

The general mechanism of calcium-triggered chemical transmitter release from neuronal synapses has been intensely studied, is well-known, and highly conserved between species and synapses across the nervous system. However, the structural and functional details within each transmitter release site (or active zone) are difficult to study in living tissue using current experimental approaches owing to the small spatial compartment within the synapse where exocytosis occurs with a very rapid time course. Therefore, computer simulations offer the opportunity to explore these microphysiological environments of the synapse at nanometer spatial scales and on a sub-microsecond timescale. Because biological reactions and physiological processes at synapses occur under conditions where stochastic behavior is dominant, simulation approaches must be driven by such stochastic processes. MCell provides a powerful simulation approach that employs particle-based stochastic simulation tools to study presynaptic processes in realistic and complex (3D) geometries using optimized Monte Carlo algorithms to track finite numbers of molecules as they diffuse and interact in a complex cellular space with other molecules in solution and on surfaces (representing membranes, channels and binding sites). In this review we discuss MCell-based spatially realistic models of the mammalian and frog neuromuscular active zones that were developed to study presynaptic mechanisms that control transmitter release. In particular, these models focus on the role of presynaptic voltage-gated calcium channels, calcium sensors that control the probability of synaptic vesicle fusion, and the effects of action potential waveform shape on presynaptic calcium entry. With the development of these models, they can now be used in the future to predict disease-induced changes to the active zone, and the effects of candidate therapeutic approaches.

Encoding of direct 4D printing of isotropic single-material system for double-curvature and multimodal morphing

The ability to morph flat sheets into complex 3D shapes is extremely useful for fast manufacturing and saving materials while also allowing volumetrically efficient storage and shipment and a functional use. Direct 4D printing is a compelling method to morph complex 3D shapes out of as-printed 2D plates. However, most direct 4D printing methods require multi-material systems involving costly machines. Moreover, most works have used an open-cell design for shape shifting by encoding a collection of 1D rib deformations, which cannot remain structurally stable. Here, we demonstrate the direct 4D printing of an isotropic single-material system to morph 2D continuous bilayer plates into doubly curved and multimodal 3D complex shapes whose geometry can also be locked after deployment. We develop an inverse-design algorithm that integrates extrusion-based 3D printing of a single-material system to directly morph a raw printed sheet into complex 3D geometries such as a doubly curved surface with shape locking. Furthermore, our inverse-design tool encodes the localized shape-memory anisotropy during the process, providing the processing conditions for a target 3D morphed geometry. Our approach could be used for conventional extrusion-based 3D printing for various applications including biomedical devices, deployable structures, smart textiles, and pop-up Kirigami structures.

Direct visualization of floppy two-dimensional DNA origami using cryogenic electron microscopy

SummaryTwo-dimensional (2D) DNA origami that is capable of self-assembling into complex 2D and 3D geometries pave the way for a bottom-up synthesis for various applications in nano/biotechnology. Here, we directly visualized the aqueous structure of 2D DNA origami cross-tiles and their assemblies using cryogenic electron microscopy. We uncovered flexible arms in cross-tile monomers and designated inter-tile folding. In addition, we observed the formation of clusters and stacks of DNA cross-tiles in solution, which could potentially affect the interaction and assembly of DNA origami. Finally, we quantitatively evaluated the flexibility of DNA origami in solution using finite element analysis. Our discovery has laid the foundation for investigating the dynamic structures of 2D DNA origami assemblies in solution, providing insights regarding the self-assembly and self-replication mechanisms of 2D DNA origami.

Process development and mechanical properties of Ti-6Al-4V samples generated by laser material deposition with coaxial wire feed

The use of wire in laser material deposition (LMD) eliminates major disadvantages of powder-based LMD processes, namely, contamination of the process cell with metal powder, significant material losses during the process, health and safety issues, as well as the impact of insufficient powder quality. A processing head with coaxial wire feed is used with a closed annularly shaped laser beam surrounding the wire, which is one of the distinguishing features. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of an annularly shaped laser beam without any shadowing. In contrast to lateral wire feeding, two substantial technological advantages can be identified: the process is independent of the feed direction and can manufacture complex 3D geometries. In this paper, a novel approach to deposit Ti-6Al-4V with wire-based LMD to increase the deposition rate to 500 g/h and develop process strategies to build up 3D volumes is described. In addition, stability criteria for the LMD process are determined and used for process development. The paper also presents characterization of the deposited layers and the procedure for generating tensile test samples from Ti-6Al-4V. Finally, the results of the built-up, heat-treated, mechanically processed, and tested samples are discussed, and the results are compared with those from the literature on powder-based LMD. Finally, an outlook toward future research and possible applications is given.

Comparison of defect detectability between Computed Tomography inspection and CT simulation using a calibrated defect phantom

The usage of metal Additive Manufactured (AM) components is growing in aerospace industry since the establishment of quality standards and due to the current maturity of the manufacturing systems, processing route, and inspection methodology. Moreover, possibilities of designing complex shapes by using 3D-printers enables design engineers to build lightweight structures and/or increase part functionality. However, the freedom in design is often a challenge for non-destructive testing (NDT), especially in parts with limited access, non-flat surfaces, etc. Therefore, there are few NDT methods which can be applied on such complex 3D geometries and capable of inspecting the whole part volume. Computed Tomography (CT) and Digital Xray methods are the most relevant ones offering rich information of inner defectology and the outer geometrical metrology. Simulation tools regarding manufacturing process and mechanical behavior are already considered as part of the definition phase of AM components and utilized as inputs in the design loop. However, inspectionability issues are mainly considered during the quality assurance phase. Therefore, inspection problems related with the detectability of defects above the part allowable can appear once the part have been designed, validated, and manufactured. On the other hand, tools that perform numerical simulations of X-ray imaging like SimCT could be a valuable source of additional information [1]. Firstly, for the users of XRay imaging devices in order to set up best inspection parameters and system configuration [2, 3]. Secondly, for producing CT simulations which can evaluate the inspectionability of a part, avoiding non-inspectionable regions limited by the inspection method. In this way, this information can be introduced for validating the part design for instance at PDR (Preliminary Design Review) and later at CDR (Critical Design Review) levels. In this work, an aluminum Image Quality Indicator (IQI) with calibrated defects has been analyzed with both real and simulated CT scans using different physical resolutions. In this way, a comprensive analysis for determining the limits of defect detectability by comparing both simultaion and test results has been developed. Defects of 100, 200 and 500µm diameter have been evaluated, corresponding to aerospace allowable for pores in AM hardware, depending on part criticality.

Electronic Properties of the Weyl Semimetals Co2MnX (X=Si, Ge, Sn)

Using first‐principles electronic structure calculations, it is shown that ferromagnetic Heusler compounds Co2MnX (X = Si, Ge, Sn) present nontrivial topological characteristics and belong to the category of Weyl semimetals. These materials exhibit two topologically interesting band crossings near the Fermi level. These band crossings have complex 3D geometries in the Brillouin zone and are characterized by nontrivial topology as Hopf links and chain‐like nodal lines that are protected by the perpendicular mirror planes. The spin–orbit interaction split these nodal lines into several 0D Weyl band crossings. Unlike previously known topologically nontrivial Heusler materials, these majority spin band crossings lie in or very near to the bandgap of minority spin bands, potentially facilitating experimental observation.

GEOMETRIC PRIMITIVE EXTRACTION FROM SEMANTICALLY ENRICHED POINT CLOUDS

Abstract. 3D point clouds are robust representations of real-world objects and usually contain information about the shape, size, position and radiometry of the scene. However, unstructured point clouds do not directly exploit the full potential of such information and thus, further analysis is commonly required. Especially when dealing with cultural heritage objects which are, typically, described by complex 3D geometries, semantic segmentation is a fundamental step for the automatic identification of shapes, erosions, etc. This paper focuses on the efficient extraction of semantic classes that would support the generation of geometric primitives such as planes, spheres, cylinders, etc. Our semantic segmentation approach relies on supervised learning using a Random Forest algorithm, while the geometric shapes are identified and extracted with the RANSAC model fitting algorithm. In this way the parametric modelling procedure in a HBIM environment is easily enabled. Our experiments show the efficient label transferability of our 3D semantic segmentation approach across different Doric Greek temples, with qualitatively and quantitatively evaluations.

Coseismic surface ruptures, slip distribution, and 3D seismogenic fault for the 2021 Mw 7.3 Maduo earthquake, central Tibetan Plateau, and its tectonic implications

The 2021 Mw 7.3 Maduo earthquake, which hit the high mountain area of the internal Bayan Har Block in the central Tibetan Plateau, generated a ~ 154 km-long, nearly E-W-striking surface rupture zone. Field observations indicate prominent surface breaks characterized by discontinuous shear faults, en echelon tensional fissures, and mole track structures, revealing a dominantly left-lateral strike-slip motion with a maximum sinistral offset of ~2.7–2.8 m and general offset of ~1.0–1.5 m. The west part of the Maduo surface rupture zone occurred along the pre-existing Jiangcuo fault. Its east portion cut through some WNW-trending tectonics, indicating a previously unknown fault. The epicenter and slip distribution show a bilateral rupture for the Maduo quake. The complex 3D geometry of the Maduo seismogenic fault has controlled the occurrence of aftershocks and the multimodal distribution of coseismic displacements. The abnormally long Maduo surface rupture zone suggests that the rupture area-magnitude relationship might be more applicable than the rupture length-magnitude relationship for the magnitude estimation of a paleo-event. The occurrence of the Maduo earthquake challenges the active block model which used to predict little or no slip partitioning and large earthquakes in the block interior. A reappraisal of seismic hazard along intra-block faults with low strain rates is needed, especially across densely populated regions.

Flow Check and Adiabatic Effectiveness Measurements on Traditionally Versus Additively Manufactured Film-Cooling Holes

Abstract In the recent years Additive Manufacturing (AM) methods, such as the Direct Metal Laser Melting (DMLM) technology, are getting more and more attractive and feasible for the realization of components and subcomponents of gas turbines. In particular, they are receiving much attention since, on the one hand, the manufacturing of complex 3D geometries is allowed and, on the other, manufacturing and delivery times can be cut down. Lately, Baker Hughes is studying the possibility to manufacture film-cooling holes via the DMLM technology in order to exploit the flexibility of such innovative manufacturing method and hence eliminate additional processes and lead time. From the open literature, it is known that additively manufactured holes can have a more irregular shape and higher roughness than traditional ones, which may lead not only to a reduction in coolant flow but more importantly to decay of the film-cooling adiabatic effectiveness. For this reason, a test campaign has been conducted in collaboration with the University of Florence (Italy) with the objective of characterizing the performance (minimum passage diameter, flow check, and adiabatic effectiveness) of AM versus traditional cylindrical holes on simple-geometry coupons built upon different construction angles. Ultimately, the dependency of AM holes performance on print angles is sought with the purpose of characterizing the impact of such manufacturing technology on film-cooling holes design.

Selective laser melting of a Fe-Si-Cr-B-C-based complex-shaped amorphous soft-magnetic electric motor rotor with record dimensions

A record large amorphous rotor bearing an intricate 3D-geometry is produced through additive manufacturing via selecting laser melting using a powder of a bulk metallic glass-forming composition of the Fe-Si-Cr-B-C system. Not only does this technique overcome the technical limitations characteristic of casting processes for amorphous alloys, but also the possibility to print complex 3D geometries is expected to greatly facilitate the channelling of the magnetic flux, when such component is used as a rotor in an electric machine. The rotor is characterized in comparison to the powder material as well as the as-spun ribbon using complementary techniques, including synchrotron x-ray diffraction, calorimetry, scanning and transmission electron microscopy as well as room temperature ferromagnetic and hardness testing. The rotor has extraordinarily high values of hardness (877 HV), high electrical resistivity (178.2 µΩ cm) and remarkable high magnetic susceptibility (9.17). This latter feature leads to a better magnetic response in the presence of an external magnetic field evidenced by a faster approach to saturation. The coercivity is relatively small (0.51 kA/m) and the magnetic saturation relatively high (1.29 T). In addition, a large anisotropic effect on the magnetization response in connection with partial crystallization in the melt pool areas is assessed experimentally.

Mechanically Guided Hierarchical Assembly of 3D Mesostructures.

3D, hierarchical micro/nanostructures formed with advanced functional materials are of growing interest due to their broad potential utility in electronics, robotics, battery technology, and biomedical engineering. Among various strategies in 3D micro/nanofabrication, a set of methods based on compressive buckling offers wide-ranging material compatibility, fabrication scalability, and precise process control. Previously reports on this type of approach rely on a single, planar prestretched elastomeric platform to transform thin-film precursors with 2D layouts into 3D architectures. The simple planar configuration of bonding sites between these precursors and their assembly substrates prevents the realization of certain types of complex 3D geometries. In this paper, a set of hierarchical assembly concepts is reported that leverage multiple layers of prestretched elastomeric substrates to induce not only compressive buckling of 2D precursors bonded to them but also of themselves, thereby creating 3D mesostructures mounted at multiple levels of 3D frameworks with complex, elaborate configurations. Control over strains used in these processes provides reversible access to multiple different 3D layouts in a given structure. Examples to demonstrate these ideas through both experimental and computational results span vertically aligned helices to closed 3D cages, selected for their relevance to 3D conformal bio-interfaces and multifunctional microsystems.

Temperature‐Responsive 4D Liquid Crystal Microactuators Fabricated by Direct Laser Writing by Two‐Photon Polymerization

Untethered Microactuators In article number 2100158, Marc del Pozo, Larisa Florea, Albert P. H. J. Schenning, and co-workers present a new liquid crystalline photoresist for the creation of untethered microactuators using direct laser writing by two-photon polymerization. The presented responsive microstructures have a high crosslink density that facilitates the creation of complex 3D geometries which exhibit temperature induced anisotropic shape changes. Such untethered microactuators are attractive to fields including microfluidics or medicine.