Complex 3D Shapes Research Articles

Numerical study on the effect of side structure on elastic vibration characteristics of railway vehicle carbodies

Three-dimensional (3D) elastic vibrations that occur in railway vehicle carbodies can have negative impacts on ride quality, and efficient numerical analysis methods are required to study effective counter measure. The authors have proposed a method using a new vibration analysis model in which the railway vehicle carbody is modeled as a box-like structure composed of elastic plates, straight beams, and curved beams. This model can easily express complex 3D vibration shapes observed in actual carbody such as the interaction between the roof, floor, and side structures. This article reports the results of an improvement of this model and a series of studies of the effects of curveture and rigidity changes in the side structures on the natural modal characteristics of the elastic vibrations.

Complex-shaped, finely-featured ZrC/W composites via shape-preserving reactive melt infiltration of porous WC structures fabricated by 3D ink extrusion

Complex-shaped, finely-featured, ultra-high-melting ZrC/W composite structures were produced by coupling, for the first time, three-dimensional (3D) ink-extrusion printing with shape/size-preserving reactive melt infiltration (the Displacive Compensation of Porosity, DCP, process). Inks containing sub-micron WC powders were printed at ambient temperature into either fine-scale structures (sub-millimeter filaments) or into a larger-scale, finely-featured 3D structure (a centimeter-scale nozzle with a sub-millimeter-thick wall). After organic binder removal, the printed structures were sintered at 1650 °C for 1 h to achieve a porosity of 50%. The porous, rigid WC structures then underwent ambient pressure infiltration and reaction with Zr-Cu liquid at up to 1350 °C for 2 h. The reaction of WC to yield more voluminous ZrC and W products filled prior pores (DCP process) to yield shape-preserved, dense ZrC/W structures after Cu dissolution from external surfaces. This new integrated approach opens the door to ultra-high-melting ceramic/metal composite structures with complex 3D shapes and fine (millimeter-scale) features.

Sustainability and recent trends in micro- electric discharge machining (μ-EDM): A state-of-the-art review

In the era of miniature machining, micro Electrical -discharge machining (A thermal energy based materials removal process) is the most recognized non- conventional machining approaches which has the ability to generate complex 2D & 3D shapes on difficult to machine materials in a short time while maintaining high feature quality. Micro-EDM is a noncontact machining process that produces mould cavity and deep holes with less metallurgical losses, stress free and miniaturized features through careful regulation of the electrical and non-electrical process parameters. Input parameters such as current, voltage, and pulse on time, pulse off time and Duty factor play an imperative role to achieve good feature quality. This progressive review of micro–electrical discharge machining studies latest machinable composite materials (conductive), dielectric fluids, issues of surface integrity and various optimization techniques with the perspective of sustainability (i.e. high energy consumption, electrode wear, generation of hazardous dielectric waste, toxic emissions and fire hazard). A brief note on future research trends has been included in the last section. Moreover, recent applications and advantages of micro-EDM machining processes are also presented in this study.

Recyclable, reconfigurable, thermadapt shape memory polythiourethane networks with multiple dynamic bonds for recycling of carbon fiber-reinforced composites

Thermoset polyurethane is an important polymer material due to high strength and adjustable performance. However, the thermoset polyurethane only based on dynamic urethane bond shows poor reprocessing performance. To improve the reprocessability and recyclability, multiple dynamic covalent bonds (ester, urethane, and thiourethane bonds) were introduced into molecular chains to develop a thermoset shape memory polythiourethane (PCTU) with high transparency, excellent mechanical properties, solid state plasticity, reprocessability, and recyclability. The PCTU samples show good mechanical properties and have the highest reprocessing efficiencies with ησ of 144.4% and ηε of 160.1%. Moreover, the samples can realize complex 3D shapes via the combination of solid-state plasticity and shape memory property. Notably, for the prepared PCTU/CFs composites, carbon fibers (CFs) can be easily recycled under mild conditions and can be reused in other polymer composites. Thus, this work provides a new way for developing recyclable, reconfigurable, and thermadapt shape memory polythiourethane fiber composites.

Mechanically‐Guided 4D Printing of Magnetoresponsive Soft Materials across Different Length Scale

Untethered magnetoresponsive soft materials that can transform between various complex 3D shapes are of growing interests in diverse areas such as soft robotics, flexible electronics, and biomedical engineering. Previous approaches are difficult to precisely encode continuous 3D magnetization profiles in small‐scale 3D structures. Herein, a novel method to produce magnetoresponsive soft materials for shape‐morphing systems across different length scale is reported. The magnetization profiles are programmed by the mechanically‐guided 4D printing with high precision and time‐cost efficiency. A theoretical model and model‐based simulation method are developed to quantitatively predict shape‐morphing of printed structures under applied magnetic fields, and guide the design of complex 3D shapes. A broad set of structures with complex transformations are fabricated to illustrate the capability of the methods. Diverse typical functional applications from centimeter‐ to millimeter‐scale, including soft crawling robots, flexible grippers, bionic butterfly, and multistate magnetic switch, are further demonstrated.

Arbitrarily Reconfigurable and Thermadapt Reversible Two-Way Shape Memory Poly(thiourethane) Accomplished by Multiple Dynamic Covalent Bonds.

The fabrication of a single polymer network that exhibits a good reversible two-way shape memory effect (2W-SME), can be formed into arbitrarily complex three-dimensional (3D) shapes, and is recyclable remains a challenge. Herein, we design and fabricate poly(thiourethane) (PTU) networks with an excellent thermadapt reversible 2W-SME, arbitrary reconfigurability, and good recyclability via the synergistic effects of multiple dynamic covalent bonds (i.e., ester, urethane, and thiourethane bonds). The PTU samples with good mechanical performance simultaneously demonstrate a maximum tensile stress of 29.7 ± 1.1 MPa and a high strain of 474.8 ± 7.5%. In addition, the fraction of reversible strain of the PTU with 20 wt % hard segment reaches 22.4% during the reversible 2W-SME, where the fraction of reversible strain is enhanced by self-nucleated crystallization of the PTU. A sample with arbitrarily complex permanent 3D shapes can be realized via the solid-state plasticity, and that sample also exhibits excellent reversible 2W-SME. A smart light-responsive actuator with a double control switch is fabricated using a reversible two-way shape memory PTU/MXene film. In addition, the PTU networks are de-cross-linked by alcohol solvolysis, enabling the recovery of monomers and the realization of recyclability. Therefore, the present study involving the design and fabrication of a PTU network for potential applications in intelligent actuators and multifunctional shape-shifting devices provides a new strategy for the development of thermadapt reversible two-way shape memory polymers.

Direct-ink-writing (DIW) 3D printing functional composite materials based on supra-molecular interaction

Direct ink writing (DIW) is the most versatile AM technique in terms of materials development, it enables the creation of complex 3D shapes using any material by formulating a paste with controlled rheology. One of the main challenges of DIW is to design and formulate the viscoplastic and self-healing soft inks that easily flow under shear and quickly recover upon deposition. Researchers often look for flexible approaches that can be adapted to formulate printing inks with a wide range of materials. Here we report a supra-molecular interaction system composed of triethanolamine and ammonium oleate for application in DIW technology. Almost any materials (eg. rubber, plastic, ceramic, metal and composites) can be integrated into the ink system, and then can be 3D printing via shear-thinning DIW method. Furthermore, the solid contents of the ink system are higher than 80%, avoiding the formation of porous structure and dimensional changes after shaping. Present DIW method was used to construct sensors based on multi-material for application in real-time monitoring human health. This work may provide an new method to develop 3D printing materials for various practical applications.

Field tunable three-dimensional magnetic nanotextures in cobalt-nickel nanowires

Cylindrical magnetic nanowires with large transversal magnetocrystalline anisotropy have been shown to sustain non-trivial magnetic configurations resulting from the interplay of spatial confinement, exchange, and anisotropies. Exploiting these peculiar 3D spin configurations and their solitonic inhomogeneities are prospected to improve magnetization switching in future spintronics, such as power-saving magnetic memory and logic applications. Here we employ holographic vector field electron tomography to reconstruct the remanent magnetic states in CoNi nanowires with 10 nm resolution in 3D, with a particular focus on domain walls between remanent states and ubiquitous real-structure effects stemming from irregular morphology and anisotropy variations. By tuning the applied magnetic field direction, both longitudinal and transverse multi-vortex states of different chiralities and peculiar 3D features such as shifted vortex cores are stabilized. The chiral domain wall between the longitudinal vortices of opposite chiralities exhibits a complex 3D shape characterized by a push out of the central vortex line and a gain in exchange and anisotropy energy. A similar complex 3D texture, including bent vortex lines, forms at the domain boundary between transverse-vortex states and longitudinal configurations. Micromagnetic simulations allow an understanding of the origin of the observed complex magnetic states.

SP-GAN

We present SP-GAN, a new unsupervised sphere-guided generative model for direct synthesis of 3D shapes in the form of point clouds. Compared with existing models, SP-GAN is able to synthesize diverse and high-quality shapes with fine details and promote controllability for part-aware shape generation and manipulation, yet trainable without any parts annotations. In SP-GAN, we incorporate a global prior (uniform points on a sphere) to spatially guide the generative process and attach a local prior (a random latent code) to each sphere point to provide local details. The key insight in our design is to disentangle the complex 3D shape generation task into a global shape modeling and a local structure adjustment, to ease the learning process and enhance the shape generation quality. Also, our model forms an implicit dense correspondence between the sphere points and points in every generated shape, enabling various forms of structure-aware shape manipulations such as part editing, part-wise shape interpolation, and multi-shape part composition, etc., beyond the existing generative models. Experimental results, which include both visual and quantitative evaluations, demonstrate that our model is able to synthesize diverse point clouds with fine details and less noise, as compared with the state-of-the-art models.

Diffusion of Anisotropic Colloidal Microparticles Fabricated Using Two‐Photon Lithography

AbstractPolymeric particles with complex shapes are required for biomedical therapies, colloidal self‐assembly, and micro‐robotics. It has been challenging to synthesize particles beyond simple shapes (e.g., spheres, cubes) with high structural accuracy using existing methods. Here, a method for fabricating polymeric microparticles of complex 3D shapes is reported using two‐photon lithography, and dispersing the particles in an aqueous solution on a glass substrate. The fabrication of polyhedrons (e.g., tetrahedron, pyramid), polypods (e.g., tetrapod, hexapod), and other shapes of 5–10 µm in size is demonstrated. Confocal microscopy is used to track the motion of the sphere, tetrahedron, tetrapod, and screw‐shaped particles near the substrate, and determine their translational diffusion coefficients. HYDRO++ is used to simulate the motion of the particles far from the substrate. The influence of particle size and substrate effects on diffusion in the spherical particles is determined and finds that the non‐spherical particles have increased hindrance at the substrate compared to the spherical particles.

Color-difference evaluation for 3D objects.

A psychophysical experiment using 3D printed samples was conducted to investigate the change of perceived color differences caused by two different illuminations and two 3D sample shapes. 150 pairs of 3D printed samples around five CIE color centers [Color Res. Appl. 20, 399-403, 1995], consisting of 75 pairs of spherical samples and 75 pairs of flat samples, with a wide range of color differences covering from small to large magnitude, were printed by an Mcor Iris paper-based 3D color printer. Each pair was assessed twice by a panel of 10 observers using a gray-scale psychophysical method in a spectral tunable LED viewing cabinet with two types of light sources: diffuse lighting with and without an additional overhead spotlight. The experimental results confirmed that the lighting conditions had more effect on the perceived color difference between complex 3D shapes than between 2D objects. The results for 3D and 2D objects were more similar under only diffuse lighting. Current 3D results had good correlations with previous ones [Color Res. Appl. 24, 356-368, 1999; J. Opt. Soc. Am. A 36, 789-799, 2019] using 2D samples with large color differences, meaning that color-difference magnitude had more effect on perceived color differences than sample shape and lighting. Considering ten modern color-difference formulas, the best predictions of the current experimental data were found for CAM02-LCD formula [Color Res. Appl. 31, 320-330, 2006]. For current results, it was also found that predictions of current color-difference formulas were below average inter-observer variability, and remarkable improvements were found by adding power corrections [Opt. Express 23, 597-610, 2015].

Reaction of Aroylpyrrolobenzothiazinetriones with Electron‐Rich Dienophiles

AbstractThe development of synthetic protocols to small molecules with a complex 3D shape is a relevant problem for modern chemists because such molecules are required by drug discovery. The Diels‐Alder reaction is a good synthetic approach to complex three‐dimensional structures. In the present paper, a reaction of aroylpyrrolobenzothiazinetriones (oxa‐dienes) with electron‐rich dienophiles is investigated in order to reach novel alkaloid‐like pyrano[4,3‐b]pyrroles fused to a 1,4‐benzothiazine‐2‐one moiety. The studied reaction was found to proceed highly regioselectively. Its stereoselectivity was dramatically dependent on the reaction solvent. The experimental results are supplemented with computational studies, which demonstrate that the studied reaction proceeds via a one‐step polar mechanism. In addition, an improved synthesis of alkaloid‐like pentacyclic 6/6/5/6/5‐ and 6/6/5/6/6‐angularly fused pyrano[4,3‐b]pyrroles via an acid‐catalyzed intramolecular cyclization of Michael adducts to hetero‐Diels‐Alder cycloadducts was discovered. The synthesized alkaloid‐like heterocycles represent an interest to pharmaceutics, since their close analogs show significant antiviral activity.

A novel approach of random packing generation of complex-shaped 3D particles with controllable sizes and shapes

A novel approach of random packing generation of complex-shaped 3D particles with controllable sizes and shapes

On the Left Ventricular Remodeling of Patients with Stenotic Aortic Valve: A Statistical Shape Analysis.

The left ventricle (LV) constantly changes its shape and function as a response to pathological conditions, and this process is known as remodeling. In the presence of aortic stenosis (AS), the degenerative process is not limited to the aortic valve but also involves the remodeling of LV. Statistical shape analysis (SSA) offers a powerful tool for the visualization and quantification of the geometrical and functional patterns of any anatomic changes. In this paper, a SSA method was developed to determine shape descriptors of the LV under different degrees of AS and thus to shed light on the mechanistic link between shape and function. A total of patients underwent computed tomography (CT) for the evaluation of valvulopathy were segmented to obtain the LV surface and then were automatically aligned to a reference template by rigid registrations and transformations. Shape modes of the anatomical LV variation induced by the degree of AS were assessed by principal component analysis (PCA). The first shape mode represented nearly 50% of the total variance of LV shape in our patient population and was mainly associated to a spherical LV geometry. At Pearson’s analysis, the first shape mode was positively correlated to both the end-diastolic volume (, ) and end-systolic volume (, and ), suggesting LV impairment in patients with severe AS. A predictive model built with PCA-related shape modes achieved better performance in stratifying the occurrence of adverse events with respect to a baseline model using clinical demographic data as risk predictors. This study demonstrated the potential of SSA approaches to detect the association of complex 3D shape features with functional LV parameters.

Impact of COMPASS-U vacuum vessel and the first wall structures on signals of in-vessel magnetic diagnostic coils

The paper evaluates the impact of metallic structures of the COMPASS-U tokamak design on signals measured by in-vessel magnetic diagnostic coils. The eddy current shielding caused by the tokamak conductive structures of the vacuum vessel and plasma facing components is evaluated using finite element analysis performed by ANSYS Maxwell software. The simulation of the sudden shifts in the radial or vertical position of the plasma column returns 33–45% amplification of the tangential field component that from the most part would be analogous to a simple lumped circuit model approximation, despite the complex 3D shape of the nearby plasma facing components. The simulation of a rotating helical filament close to plasma edge (approximating a rotating magnetic island magnetohydrodynamic (MHD) structure) reveals an unexpected spatial modulation of the magnitude attenuation coefficient of up to 45% for the tangential field component across different positions relative to the PFC holders. Both results have led to the described conclusions for the sensor positioning design, specifically to the decision to install plasma position feedback sensors in between the robust holders of the PFC tiles, and the plasma MHD activity sensors strictly symmetrically with respect to these PFC structures.

Material Design for 3D Multifunctional Hydrogel Structure Preparation

AbstractHydrogels are recognized as one of the most promising materials for e‐skin devices because of their unique applicable functionalities such as flexibility, stretchability, biocompatibility, and conductivity. Beyond the excellent sensing functionalities, the e‐skin devices further need to secure a target‐oriented 3D structure to be applied onto various body parts having complex 3D shapes. However, most e‐skin devices are still fabricated in simple 2D film‐type devices, and it is an intriguing issue to fabricate complex 3D e‐skin devices resembling target body parts via 3D printing. Here, a material design guideline is provided to prepare multifunctional hydrogels and their target‐oriented 3D structures based on extrusion‐based 3D printing. The material design parameters to realize target‐oriented 3D structures via 3D printing are systematically derived from the correlation between material design of hydrogels and their gelation characteristics, rheological properties, and 3D printing processability for extrusion‐based 3D printing. Based on the suggested material design window, ion conductive self‐healable hydrogels are designed and successfully applied to extrusion‐based 3D printing to realize various 3D shapes.

Shape‐Memory Balloon Structures by Pneumatic Multi‐material 4D Printing

Abstract4D printing is an attractive approach for manufacturing structures that can adopt new shapes or functionalities after printing. However, 4D printing methods and materials that can be used to achieve structures with complex shapes and excellent mechanical properties simultaneously are still lacking. Here, a novel 4D printing is developed where multi‐material digital light process 3D printing of shape memory polymers (SMPs) fabricates a structure that is later transformed into a complex 3D shape with robust mechanical properties by pneumatic manipulation. In this method, the shape change is controlled by the spatial distributions of SMPs, which is designed by finite element analysis. Experimental investigations are carried out to print various structured balloons with predefined intricate shapes, including a structure in dog‐like shape and a surface with the human face contour. These structures are also endowed with robust mechanical stiffness and lightweight features, which allow this new 4D printing approach for potential applications in biomedical devices, reconfigurable structures, and metamaterials.

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.

Actuation of Three‐Dimensional‐Printed Nanocolloidal Hydrogel with Structural Anisotropy

AbstractPolymer hydrogels exhibit actuation properties that result in reversible shape transformations and have promising applications in soft robotics, drug delivery systems, sensors, and microfluidic devices. Actuation occurs due to differential hydrogel swelling and is generally achieved by modulating hydrogel composition. Here a different approach to hydrogel actuation that originates solely from its structural anisotropy is reported. For 3D‐printed single‐layer hydrogels formed by cellulose nanocrystals (CNCs) and gelatin methacryloyl it is shown that shear‐induced orientation of CNCs results in anisotropic mechanical and swelling properties of the hydrogel. Upon swelling in water, planar hydrogels acquire multiple complex 3D shapes that are achieved by i) varying CNC orientation with respect to the shape on the hydrogel sheet and ii) patterning the hydrogel with the regions of shear‐mediated and random CNC orientation. This study shows the capability to generate multiple shapes from the same hydrogel actuator based on the degree of its structural anisotropy. In addition, it introduces a biocompatible nanocolloidal ink with shear‐thinning and self‐healing properties for additive manufacturing of hydrogel actuators.

Bayesian inversion algorithm for estimating local variations in permeability and porosity of reinforcements using experimental data

A novel Regularising Ensemble Kalman filter Algorithm based on the Bayesian paradigm was applied to RTM processes to estimate local porosity and permeability of fibrous reinforcements using measured values of local resin pressure and flow front positions during resin injection. The algorithm allows to detect locations of defects in the preform. It was tested in virtual experiments with two geometries, a two-dimensional rectangular preform and a more complex 3D shape, as well as in laboratory experiments. In both the virtual and laboratory experiments, it was demonstrated that the proposed methodology is able to successfully discover defects and estimate local porosity and permeability with good accuracy. The algorithm also provides confidence intervals for the predictions and estimations of defect probabilities, which are valuable for analysis of the process.