Complex Three-dimensional Objects Research Articles

Adaptive layer-based computer-generated holograms.

We propose a novel, to the best of our knowledge, and fast adaptive layer-based (ALB) method for generating a computer-generated hologram (CGH) with accurate depth information. A complex three-dimensional (3D) object is adaptively divided into layers along the depth direction according to its own non-uniformly distributed depth coordinates, which reduces the depth error caused by the conventional layer-based method. Each adaptive layer generates a single-layer hologram using the angular spectrum method for diffraction, and the final hologram of a complex three-dimensional object is obtained by superimposing all the adaptive layer holograms. A hologram derived with the proposed method is referred to as an adaptive layer-based hologram (ALBH). Our demonstration shows that the desired reconstruction can be achieved with 52 adaptive layers in 8.7 s, whereas the conventional method requires 397 layers in 74.9 s.

Diagnostics and characterization of a novel multi gas layer RF atmospheric pressure plasma jet for polymer processing

The quest to employ cold plasma sources at atmospheric pressure in polymer processing has emerged as a potent driving force behind their development. Atmospheric pressure operation of plasma jets provides potential cost reductions as well as easier handling and maintenance. In addition, their unique advantage of remote operation allows the substrate to be placed outside the source boundaries. This latter feature makes it easier to process complex three-dimensional objects and to integrate plasma jets into existing production lines. Although conventional atmospheric pressure plasma jet (APPJ) sources have undergone significant advancements in their design and construction, they have reached their technical and technological thresholds in several domains, thereby also impeding further enhancements in material processing applications. To cope with this issue, this work introduces a promising APPJ (named MPPJ3) working in a three co-axial gas layer geometry, incorporating the capability of aerosol and shield gas introduction leading to a configuration rich in reactive plasma species with controllable size and suitable temperature for polymer processing. A parametric study on the novel MPPJ3 device is carried out and plasma characteristics, such as reactive plasma species and temperatures, are determined by means of optical emission spectroscopy (OES), laser scattering, and infrared (IR) camera imaging whereas the fluid dynamics are analyzed using computational fluid dynamics (CFDs) and Schlieren imaging. The obtained promising results clearly show the flexibility and adaptability of the MPPJ3 device for polymer processing applications.

Wave-scattering processes: path-integrals designed for the numerical handling of complex geometries.

Relying on Feynman-Kac path-integral methodology, we present a new statistical perspective on wave single-scattering by complex three-dimensional objects. The approach is implemented on three models-Schiff approximation, Born approximation, and rigorous Born series-and familiar interpretative difficulties such as the analysis of moments over scatterer distributions (size, orientation, shape, etc.) are addressed. In terms of the computational contribution, we show that commonly recognized features of the Monte Carlo method with respect to geometric complexity can now be available when solving electromagnetic scattering.

Biomechanical virtual planning of the stress-strain state of the func-tional masticatory center

A feature of mathematical modeling and study of a complex three-dimensional biomechanical object is the ability to achieve unity of geometric, physical, mechanical and biological indicators with the individual characteristics of the patient. A rather urgent problem of clinical dentistry is the development of recommendations on the distribution of masticatory pressure in patients with balanced occlusal-articulation relationships of the dentition. This paper considers one of the aspects of this problem associated with modeling the stress-strain state of the functional masticatory center, which is localized in the region of the first molars and the premolar groups of the upper and lower jaws during physiological occlusion. To determine the biomechanical parameters of the functional masticatory center, an analysis of the stress-strain state of mathematical models of this fragment of the dentition was carried out using the finite element method. When developing a model of a biomechanical system, the surrounding biological tissues were considered discretely in terms of structure and physical and mechanical properties: dentin, enamel, periodontium, bone, cement. A technique for analyzing models of the functional masticatory center is proposed, which makes it possible to establish the relationship between the magnitudes and directions of functional loads, as well as internal stresses and deformations. As a result of the analysis of the stress-strain state of geometric and finite element models, the distributions of maximum strains and stresses in a given section under the action of specified loads were obtained. It has been established that under the conditions of this mathematical model, the areas of the apical periodontium of the teeth have the maximum shock-absorbing properties, and the functional masticatory center is equated to a static system. The capabilities of modern computer software make it possible to expand the understanding of areas of stress concentration with varying load parameters in the functional masticatory center in order to determine the most “critical” zones in order to predict and prevent the development of long-term complications.

Direct Rendering of Three-Dimensional Objects Based on Perturbation Functions Using GPUs

The object of the study is a method of direct rendering of complex three-dimensional objects based on perturbation functions using graphics processors, using a variety of streaming multiprocessors. Direct rendering means that the visualization of functionally defined models takes place without their preliminary conversion to other formats, for example, into triangle grids. The research method is based on analytical geometry in space, differential geometry, interpolation theory and matrix theory, based on mathematical modeling and the theory of computing systems. The main conclusions of the study are: the possibility of direct rendering of functionally specified objects, when rendering it is important that the computing processors are not idle. The first problem that was solved was that different GPUs have different numbers of streaming multiprocessors. Therefore, it was necessary to choose during execution the optimal stage from which the work began. Thus, you can partially get rid of the problem with unused computing resources. The second problem, the balancing problem, was solved by using a large number of computing processors. For implementation, the CUDA parallel programming model was used, which, together with a set of software tools, allows implementing programs in the C language for execution on a GPU. The resulting system visualizes complex functionally defined objects with high resolution interactively. The dependence of performance on the computing power of graphics processors is investigated.

Manufacturing of mesoscale non-assembly mechanism with water-soluble support in projection stereolithography process

Additive manufacturing (AM) excels at building complex three-dimensional objects. With the help of support methods, macroscale non-assembly mechanisms can be built in a single step, eliminating complex and time-consuming assembly process. However, mesoscale non-assembly mechanisms built by AM are scarce for the lack of appropriate support methods. Projection stereolithography (PSL) is most fitted to manufacture mesoscale non-assembly mechanisms for its high resolution and high speed. Clearances in non-assembly mechanisms usually appear with internal overhang characteristic, requiring supports to be built successfully. However, traditional support structure in stereolithography cannot be fitted into these small internal gaps to achieve small clearances, which in turn prevents traditional stereolithography from fabricating mesoscale non-assembly mechanisms. A novel water-soluble support method is presented to overcome this restriction by incorporating water-soluble resin as support via custom-built multi-material PSL process. Internal overhangs and fragile overhangs can be built with fast support removal in mild release conditions. Mesoscale non-assembly mechanism with tight clearances is successfully fabricated. Material design, process parameters and approach to control material cross-contamination of this method are described. This support method may facilitate building functional mesoscale multi-material non-assembly mechanisms for miniaturized robotic applications.

Self-Activating Metal-Polymer Composites for the Selective Electroless Metallization of 3D Printed Parts

Nowadays, polymer based additive manufacturing (AM) is widely recognized as a powerful technology for the fabrication of complex three-dimensional objects of virtually any shape in a time, material, and cost effective way. Thanks to their characteristic advantages over conventional manufacturing strategies, AM technologies are the subject of relevant research efforts. In particular, great attention is placed on developing novel 3D printable materials characterized by improved properties and, among all, by novel functionalities, such as magnetic [1] and conductive properties [2]. In order to do this, the most common strategy relies on doping polymeric matrices with nanoparticles, obtaining thus functional 3D printable polymeric composites.Metal containing composites, in particular, can be exploited for their magnetic properties or for their mechanical behavior but also for their potential capability to trigger electroless deposition. It is well-known that electroless plating requires the presence of a catalytic surface, which can be constituted by the metallic particles embedded in the 3D printed composite. In this way, the need to activate the surface of non-conductive polymeric 3D printed parts can be avoided [3]. In addition, metallization can be carried out selectively by fabricating parts in a multi-material printing process [4] with both metal loaded and non-loaded materials. Since only the layers that contain the particles can metallize, conductive regions can be alternated with insulating zones to create metallic functional patterns on the surface of printed parts. This approach can enable the 3D printing of selectively self-metallizing parts, with possible applicability in the production of flexible and highly tridimensional electronic circuits, radiofrequency devices, microelectromechanical systems or microfluidic setups.The present work focuses on the development of a stereolithography (SLA) printable composite based on an acrylate resin loaded with nickel microparticles and its application as self-catalytic material for electroless metallization. This approach, unprecedented for SLA resins, eliminates the need of noble metal activation of the surface. Moreover, the usage of Ni is of great interest also due to the other properties that it can potentially impart to the printed parts: improved mechanical properties, high thermal conductivity, magnetizability. The SLA printability of the metal-loaded resin is assessed and the morphological properties of the 3D printed composites are investigated. Subsequently, the functional properties of the composites are determined, placing a particular emphasis on their capability to trigger NiP and Cu electroless deposition. Finally, the possibility to selectively metallize only specific areas is successfully demonstrated by metallizing a Ni-loaded pattern printed on a Ni-free base.[1] Huber et al.; Appl. Phys. Lett. 109, 162401 (2016)[2] Postiglione et al.; Compos. Part A Appl. Sci. Manuf. 76, 110-114 (2015)[3] Bernasconi et al.; J. Electrochem. Soc. 164, B3059–B3066 (2017)[4] Choi et al.; J. Mater. Process. Technol. 211, 318–328 (2011)

A versatile thermally initiated crosslinking binder for additive manufacturing of strong structures

Binder jetting additive manufacturing (BJAM) is one of the most promising additive manufacturing (AM) techniques for industrial manufacturing due to its high productivity, wide material compatibility, and the possibility to achieve large-scale production. BJAM utilizes binder jetting to selectively bind powdered materials into complex three-dimensional (3D) objects. However, the inability of conventional binders to create high-strength green parts has become a major limitation for BJAM. Here, we report on a versatile thermally initiated crosslinking (TIC) binder to overcome the low green strength issue; the binder is composed of an initiator ink and an in-bed monomer/crosslinker mixture. The TIC binder can form a continuous, uniform, and strong crosslinked network to pack the printed powder. A flexural strength of 10.1–13.9 MPa of green parts is achieved for several powders, including SiC, Al2O3, and 316 L stainless steel, using the developed TIC binder. The TIC binder also shows a high print reliability and a good robustness for complex and fine geometric structures. These features combined with the advantages of a low cost, ultrahigh curing speed, and reasonable burnout performance indicate that the TIC binder solution has the potential to make a large impact on the BJAM progress.

Effect of stress relief and inherent strain-based pre-deformation on the geometric accuracy of stator vanes additively manufactured from inconel 718 using laser powder bed fusion

Laser powder bed fusion (LPBF) enables additive manufacturing (AM) of complex three-dimensional objects. Inconel 718 is a widely used aerospace material and a material that has been well adopted for the LPBF process. However, when manufacturing geometrically complex Inconel 718 parts in the aerospace industry, some aspects of the LPBF processes still require optimisation. This is because high residual stresses arise during the LPBF process, which remain within the part, in turn affecting its geometric accuracy. Therefore, the paper presents the results of a multicriteria evaluation of the geometric accuracy of LPBF-made stator vanes from Inconel 718. The part represents a group of thin-walled, axisymmetric parts. The results are based on measurements made with the use of X-ray computed tomography (XCT). XCT was used as a coordinate measurements system. Measurement data was collected both before and after build plate cut-off. The parts were prepared in variants, and considered: the build plate cut-off (before and after cutting), two types of stress relief annealing (standard – 1065 °C/1 h and high-temperature – 1150 °C/6 h), and a pre-deformation simulated by the inherent strain method. Stress relief annealing, particularly high-temperature variants, ensures the relaxation of macro- and micro-stresses, thus minimising part distortion during the build plate cut-off. This results in a very high symmetry of the stator vanes (angular pitch deviation of ±0.01° and the chord angle deviation of ±0.1°). Stress relief before the cut-off allows a twofold reduction of the cut-off caused distortion. The LPBF process residual stresses simulation allows for developing a pre-deformed model and a threefold reduction of the global distortion of the parts and a total cumulative deviation of 98% of the part's surface below 0.169 mm. A critical aspect to the geometric accuracy of LPBF-made stator vanes is the trailing edge of the vanes. The presented study shows that a careful LPBF process design combined with pre- and post-process operations allows precise manufacturing of thin-walled, axisymmetric parts within the aerospace specified tolerances.

Deployment of SMP Miura-ori sheet and its application: Aerodynamic drag and RCS reduction

Origami, such as Miura-ori, is the art of folding two-dimensional materials into complex, elaborate, and multifunctional three-dimensional objects. In this paper, SMP MO sheet are prepared, and the accuracy of deployable process is verified by experiments. The folding and deployable process of SMP MO sheet is divided into 4 stages, and each stage is described in detail. The stiffness of smart deployable stage is characterized by an exponential decline at the beginning and a gradual decrease to 0, and this is similar to the theoretical shear equivalent modulus in the Y direction. The effects of various parameters on strain and stress are also explored. The purpose of studying these mechanical characteristics is to provide driving force reference in application; In terms of application, the flow field and electromagnetic characteristics of MO sheet in different directions are studied. The aerodynamic drag and RCS reduction of MO unit cell and graded MO sheet during the deployable process are evaluated. When the dihedral fold angle is about 45°, the RCS reduction and drag reduction characteristics of MO sheet are relatively optimal, which is most beneficial to morphing aircraft.

Properties and structure of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) filaments for fused deposition modelling

Fused deposition modelling (FDM) is a process of additive manufacturing allowing creating of highly precise complex three-dimensional objects for a large range of applications. The principle of FDM is an extrusion of the molten filament and gradual deposition of layers and their solidification. Potential applications in pharmaceutical and medical fields require the development of biodegradable and biocompatible thermoplastics for the processing of filaments. In this work, the potential of production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) filaments for FDM was investigated in respect to its thermal stability. Copolymer P(3HB-co-4HB) was biosynthesised by Cupriavidus malaysiensis. Rheological and mechanical properties of the copolymer were modified by the addition of plasticizers or blending with poly(lactic acid). Thermal stability of mixtures was studied employing thermogravimetric analysis and rheological analyses by monitoring the time-dependent changes in the complex viscosity of melt samples. The plasticization of P(3HB-co-4HB) slightly hindered its thermal degradation but the best stabilization effect was found in case of the copolymer blended with poly(lactic acid). Overall, rheological, thermal and mechanical properties demonstrated that the plasticized P(3HB-co-4HB) is a potential candidate of biodegradable polymer for FDM processes.

Spatial integration during active tactile sensation drives orientation perception

Active haptic sensation is critical for object identification, but its neural circuit basis is poorly understood. We combined optogenetics, two-photon imaging, and high-speed behavioral tracking in mice solving a whisker-based object orientation discrimination task. We found that orientation discrimination required animals to summate input from multiple whiskers specifically along the whisker arc. Animals discriminated the orientation of the stimulus per se as their performance was invariant to the location of the presented stimulus. Populations of barrel cortex neurons summated across whiskers to encode each orientation. Finally, acute optogenetic inactivation of the barrel cortex and cell-type-specific optogenetic suppression of layer 4 excitatory neurons degraded performance, implying that infragranular layers alone are not sufficient to solve the task. These data suggest that spatial summation over an active haptic array generates representations of an object's orientation, which may facilitate encoding of complex three-dimensional objects during active exploration.

Magnetically switchable soft suction grippers

Grasping is one of the key tasks for robots. Gripping fragile and complex three-dimensional (3D) objects without applying excessive contact forces has been a challenge for traditional rigid robot grippers. To solve this challenge, soft robotic grippers have been recently proposed for applying small forces and for conforming to complex 3D object shapes passively and easily. However, rigid grippers are still able to exert larger forces, necessary for picking heavy objects. Therefore, in this study, we propose a magnetically switchable soft suction gripper (diameter: 20 mm) to be able to apply both small and large forces. The suction gripper is in its soft state during approach and attachment while it is switched to its rigid state during picking. Such stiffness switching is enabled by filling the soft suction cup with a magnetorheological fluid (MR fluid), which is switched between low-viscosity (soft) and high-viscosity (rigid) states using a strong magnetic field. We characterized the gripper by measuring the force required to pull the gripper from a smooth glass surface. The force was up to 90% larger when the magnetic field was applied (7.1 N vs. 3.8 N). We also demonstrated picking of curved, rough, and wet 3D objects, and thin and delicate films. The proposed stiffness-switchable gripper can also carry heavy objects and still be delicate while handling fragile objects, which is very beneficial for future potential industrial part pick-and-place applications.

Biomimetic 4D printed materials: A state-of-the-art review on concepts, opportunities, and challenges

The additive manufacturing is a transformative technique which improves the mechanical properties, e.g., the strength of the fabricated light weight industrial products. CAD softwares are integrated in the rapid prototyping setup and fabrication of the product is done through bottom-to-top approach via layer-wise deposition using stereo lithography file format as input. The 4D printed biomimetic materials are having shape changing capabilities, i.e., stimuli responsive features such as heat and thermal sensitivity, electromagnetic sensitivity, so, and so forth, as that comes under the fourth dimension. 4D printing is not just the extended technique of 3D printing but also the manufacturing technique of fabricating complex three-dimensional objects which can change the shape and forms when they are exposed to external environmental stimuli. 4D printing is appending one more dimension in the 3D printing, i.e., time. The review paper covers all aspects related to shape changing mechanisms from conceptual to actual design and emphasize has been given to the modern advancements in biomimetic 4D printing and sustainable biomedical and environmental applications.

Novel laser micro-texturing on silicon with liquid lenses by breath figure method

Surface texturing is a way of managing the surface properties of a material. This paper adopts a novel approach to laser texturing by using it in conjunction with liquid glycerin lenses and a polymer template. Such a process can effectively be used to produce micro- or even nano-scale textures on complex three-dimensional surfaces. A polymer film with an array of glycerin–water-mixed droplets proved economical and easy to produce. The resulting liquid lenses were penetrated by a nanosecond pulsed Nd:YAG laser. As the laser beam passed through the liquid lens array, it was refocused and converted to multiple beams that all engineered the substrate surface. The surface was thus successfully textured. The adaptation laser texturing technology shows potential for the application of textures to complex three-dimensional objects. In this study, a large area of microscale surface texturing on a silicon substrate was demonstrated; the texturing size lay between 1 and 3 μm, and the depth of the texturing was around 20 nm.

Self-Limiting Electrospray Deposition for the Surface Modification of Additively Manufactured Parts.

Electrospray deposition (ESD) is a spray coating process that utilizes a high voltage to atomize a flowing solution into charged microdroplets. These self-repulsive droplets evaporate as they travel to a target substrate, depositing the solution solids. Our previous research investigated the conditions necessary to minimize charge dissipation and deposit a thickness-limited film that grows in area over time through self-limiting electrospray deposition. Such sprays possess the ability to conformally coat complex three-dimensional (3D) objects without changing the location of the spray needle or orientation of the object. This makes them ideally suited for the postprocessing of materials fabricated through additive manufacturing (AM), opening a paradigm of independent bulk and surface functionality. Having demonstrated 3D coating with film thickness in the range of 1-50 μm on a variety of conductive objects, in this study, we employed model substrates to quantitatively study the technique's limits with regard to geometry and scale. Specifically, we examined the effectiveness of thickness-limited ESD for coating recessed features with gaps ranging from 50 μm to 1 cm, as well as the ability to coat surfaces hidden from the line-of-sight of the spray needle. This was then extended to the coating of hydrogel structures printed by AM, demonstrating that coating could be conducted even into the body of the structures as a means to create hydrophobic surfaces without affecting the absorption-driven humidity response. Further, these coatings were robust enough to create superhydrophobicity in the entire structure, causing it to resist immersion in water.

Additive Manufacturing of Bovine Serum Albumin-Based Hydrogels and Bioplastics.

Biosourced and biodegradable polymers for additive manufacturing could enable the rapid fabrication of parts for a broad spectrum of applications ranging from healthcare to aerospace. However, a limited number of these materials are suitable for vat photopolymerization processes. Herein, we report a two-step additive manufacturing process to fabricate robust protein-based constructs using a commercially available laser-based stereolithography printer. Methacrylated bovine serum albumin (MA-BSA) was synthesized and formulated into aqueous resins that were used to print complex three-dimensional (3D) objects with a resolution comparable to a commercially available resin. The MA-BSA resins were characterized by rheometry to determine the viscosity and the cure rate, as both parameters can ultimately be used to predict the printability of the resin. In the first step of patterning these materials, the MA-BSA resin was 3D printed, and in the second step, the printed construct was thermally cured to denature the globular protein and increase the intermolecular noncovalent interactions. Thus, the final 3D printed part was comprised of both chemical and physical cross-links. Compression studies of hydrated and dehydrated constructs demonstrated a broad range of compressive strengths and Young's moduli that could be further modulated by adjusting the type and amount of co-monomer. The printed hydrogel constructs demonstrated good cell viability (>95%) after a 21 day culture period. These MA-BSA resins are expected to be compatible with other vat photopolymerization techniques including digital light projection and continuous liquid interface production.

Three-dimensional maps of human skin properties on full face with shadows using 3-D hyperspectral imaging.

.Hyperspectral imaging has shown great potential for optical skin analysis by providing noninvasive, pixel-by-pixel surface measurements from which, applying an optical model, information such as melanin concentration and total blood volume fraction can be mapped. Such applications have been successfully performed on small flat skin areas, but existing methods are not suited to large areas such as an organ or a face, due to the difficulty of ensuring homogeneous illumination on complex three-dimensional (3-D) objects, which leads to errors in the maps. We investigate two methods to account for these irradiance variations on a face. The first one relies on a radiometric correction of the irradiance, using 3-D information on the face’s shape acquired by combining the hyperspectral camera with a 3-D scanner; the second relies on an optimization metric used in the map computation, which is invariant to irradiance. We discuss the advantages and drawbacks of the two methods, after having presented in detail the whole acquisition setup, which has been designed to provide high-resolution images with a short acquisition time, as required for live surface measurements of complex 3-D objects such as the face.

High mass loading ultrathick porous Li4Ti5O12 electrodes with improved areal capacity fabricated via low temperature direct writing

3D printing has the capability of fabricating highly complex three-dimensional (3D) objects with tailored shapes and geometries, thereby offering an unparalleled tool for the creation of unconventional electrodes for lithium-ion batteries. In this study, high mass loading ultrathick porous Li4Ti5O12 (LTO) electrodes were fabricated via low temperature direct writing for the first time. A LTO ink that was capable of freezing at low temperature was developed and the 3D printing process was optimized to obtain the optimal printing parameters. LTO electrodes with the thickness of ∼200 μm, ∼450 μm and ∼820 μm and the corresponding mass loading of ∼13.3 mg cm−2, 24.1 mg cm−2 and 32.3 mg cm−2 were fabricated. These thick LTO electrodes displayed impressive areal capacities up to ∼4.8 mAh cm−2 @ 0.2 C and ∼3.6 mAh cm−2 @ 2.0 C with the electrode thickness of 820 μm. All the thick electrodes showed excellent rate capacities below the charge/discharge rate of 2.0 C and excellent cycling performance with no deterioration in specific capacities after 100 cycles at 0.5 C. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) revealed that the thick LTO electrodes had excellent reversibility and good kinetics of electrochemical reactions. The major defect of the thick LTO electrodes is the degradation of rate capacities at high charge/discharge rate up to 5.0 C due to the slow kinetics resulted from large thickness.

МОДЕЛІ ПОТОЧНИХ ЗОБРАЖЕНЬ, ЩО ФОРМУЮТЬСЯ КАНАЛАМИ КОМБІНОВАНОЇ КОРЕЛЯЦІЙНО-ЕКСТРЕМАЛЬНОЇ СИСТЕМИ НАВІГАЦІЇ БЕЗПІЛОТНОГО ЛІТАЛЬНОГО АПАРАТУ

A refinement of the current image model has been accomplished, which are formed by separate channels of the combined correlation-extreme navigation system depending on the spatial position of the unmanned aerial vehicle and its changes. The model takes into account the influence of the three-dimensional shape of complex objects of the sighting surface on the effective antenna temperature of the radiometric channel, which made it possible to refine the moles of the description of the radiometric and television current image of the sighting surface, depending on the informative features. It is determined that at small viewing altitudes the change in the spatial position of the unmanned aerial vehicle leads to significant differences in the radio brightness temperature within a single sighting object, which causes the blurring and appearance of new interfaces on the current image of the viewing surface. It is established that the discrepancy between the current image and the reference image, which arises from the appearance of new interfaces at the sight of complex three-dimensional objects from low altitudes and with a change in the spatial position and orientation of the unmanned aerial vehicle, leads to the formation of a multi-extremal decision function and a decrease in the accuracy of the location of the correlation-extreme navigation system.