Complex Surface Geometry Research Articles

Toward Bioinspired Wet Adhesives: Lessons from Assessing Surface Structures of the Suction Disc of Intertidal Clingfish

The clingfish attaches to rough surfaces with considerable strength using an intricate suction disc, which displays complex surface geometries from structures called papillae. However, the exact role of these structures in adhesion is poorly understood. To investigate the relationship between papillae geometry and adhesive performance, we developed an image processing tool that analyzed the surface and structural complexity of papillae, which we then used to model hydrodynamic adhesion. Our tool allowed for the automated analysis of thousands of papillae in specimens across a range of body sizes. The results led us to identify spatial trends in papillae across the complex geometry of the suction disc and to establish fundamental structure-function relationships used in hydrodynamic adhesion. We found that the surface area of papillae changed within a suction disc and with fish size, but that the aspect ratios and channel width between papillae did not. Using a mathematical model, we found that the surface structures can adhere considerably when subjected to disturbances of moderate to high velocities. We concluded that a predominant role of the papillae is to leverage hydrodynamic adhesion and wet friction to reinforce the seal of the suction disc. Overall, the trends in papillae characteristics provided insights into bioinspired designs of surface microstructures for future applications in which adhesion is necessary to attach to diverse surfaces (in terrestrial or aquatic environments), even when subjected to disturbance forces of randomized directionality.

A Wind Tunnel Investigation into the Aerodynamics of Lobed Hailstones

The complex surface geometries of hailstones affect their fall behavior, fall speeds, and growth. Systematic experimental investigations on the influence of the number and length of lobes on the fall velocity and the drag coefficient of hailstones were performed in the Mainz vertical wind tunnel to provide relationships for use in numerical models. For this purpose, 3D prints of four artificial lobed hailstone models as well as spheres were used. The derived drag coefficients show no dependency in the Reynolds number in the range between 25,000 and 85,000. Further, the drag coefficients were found to increase with increasing length of lobes. All lobed hailstones show higher or similar drag coefficients than spheres. The terminal velocities of the the hailstones with short lobes are very close to each other and only reduced by about 6% from those of a sphere. The terminal velocities from the long lobed hailstones deviate up to 21% from a sphere. The results indicate that lobes on the surface of hailstones reduce their kinetic energy by a factor of up to 3 compared to a sphere. This has important consequences for the estimation of the destructive potential of hailstones.

Grafting of calcium chelating functionalities onto PLA monofilament fiber surfaces.

Polymer surface grafting is widely used in the field of bone regeneration to increase calcium phosphate (CaP) adhesion, with the intent of improving mechanical properties of CaP-polymer composite cements. Reinforcement can be achieved using multiple combined functional groups and/or complex surface geometries that, however, concurrently influence multiple effects such as wetting, roughness, and interfacial strengthening. This study focused on the influence of a chelating group, namely aspartic acid, on the adsorption of divalent ions such as Ba2+ or Ca2+ onto poly-l-lactic acid (PLA) films. The films were analyzed using contact angle measurements and X-ray photoelectron spectroscopy. The adsorption of CaP and its interfacial mechanical properties were investigated using functionalized PLA monofilaments whose surface roughness was analyzed using white light interferometry. Mechanical analysis was conducted by performing pull-out tests. The surfaces were analyzed using scanning electron microscopy and energy dispersive X-ray spectroscopy. Using aspartic acid as a chelating group resulted in a 50 % increased adsorption of barium, an almost threefold increase in calcium coverage of the fiber compared to the control group and a twofold increase in interfacial stiffness. No significant increase in interfacial strength was determined, most likely due to the weakness of the CaP matrix, which was partially visible as residues on the monofilaments in the postfracture imaging. This study shows the potential of surfaces functionalized with aspartic acid as a simple alternative to complex polypeptide based functional groups for the adsorption of divalent ions such as calcium on poly-lactic acid in bone regenerating applications.

Efficient and Innovative Polishing Processes for Smoothing Complex Surface Geometries and Internal Contours on Brittle-Hard Components

The material fused silica, as well as other brittle-hard materials such as glass ceramics, have great potential for use in a wide range of applications due to their special material properties. The technical advantages of these materials require sophisticated processing technologies, including polishing steps, in order to be able to use these interesting materials advantageously. In addition, a current trend in modern optical manufacturing is the use of free-form surfaces and monolithic components that combine several optical and mechanical functions in one part. Novel or improved processes are needed in order to meet future requirements for resource-saving and effective production methods at the same time.

Wrinkling prediction, formation and evolution in thin films adhering on polymeric substrata

Wrinkling has recently attracted an increasing interest by suggesting a number of unforeseeable applications in many emerging material science and engineering fields. If guided and somehow designed, wrinkles could be in fact used as an alternative printing way for realizing complex surface geometries and thus employed as an innovative bottom-up process in the fabrication of nano- and micro-devices. For these reasons, the prediction of wrinkles of films adhering on flat as well as on structured substrata is a challenging task, genesis and development of the phenomenon being not yet completely understood both when thin membranes are coupled with soft supports and in cases where the geometry of the surfaces are characterized by complex three-dimensional profiles. Here we investigate the experimental formation of new intriguing and somehow unforeseeable wrinkled patterns achieved on periodic structures, by showing prediction through a new hybrid analytical-numerical strategy capable to overcome some common obstacles encountered in modeling film wrinkling on flat and 3D-shaped substrata. The proposed approach, which drastically reduces the computational effort, furnishes a helpful way for predicting both qualitative and quantitative results in terms of wrinkling patterns, magnitude and wavelength, by also allowing to follow the onset of film instabilities and the progressive evolution of the phenomenon until its final stage.

Understanding of Molecular Contribution of Quinhydrone/Methanol Organic Passivation for Improved Minority Carrier Lifetime on Nanostructured Silicon Surface

In this report, we present a study of the quinhydrone/methanol (QHY/MeOH) organic passivation technique for a silicon (Si) surface. The roles of p-benzoquinone (BQ) and hydroquinone (HQ), which make up QHY, in controlling the uniformity and coverage of the passivation layer as well as the minority carrier lifetime (τeff) of Si were investigated. The uniformity and coverage of the passivation layer after treatment with diverse mixture ratios of BQ and HQ in MeOH were studied with two different atomic force microscope (AFM) techniques, namely tunneling mode (TUNA) and high-resolution tapping mode AFM (HR-AFM). In addition, the τeff and surface potential voltages (SPV) of passivated surfaces were measured to clarify the relationship between the morphologies of the passivation layers and degrees of surface band bending. The molecular interactions between BQ and HQ in MeOH were also analyzed using Fourier-transform infrared spectroscopy (FT-IR). In our study, we successfully demonstrated the role of each molecule for effective Si surface passivation with BQ working as a passivation agent and HQ contributing as a proton (H+) donator to BQ for accelerating the passivation rate. However, our study also clearly revealed that HQ could also hinder the formation of a conformal passivation layer, which raises an issue for passivation over complex surface geometry, especially a nanostructured surface.

Three-Dimensional Microscale Imaging and Measurement of Soft Material Contact Interfaces under Quasi-Static Normal Indentation and Shear.

Understanding the contact and friction between soft materials is vital to a wide variety of engineering applications including soft sealants and medical devices such as catheters and stents. Although the mechanisms of friction between stiff materials have been extensively studied, the mechanisms of friction between soft materials are much less understood. Time-dependent material responses, large deformations, and fluid layers at the contact interface, common in soft materials, pose new challenges toward understanding the friction between soft materials. This article aims to characterize the three-dimensional (3D) contact interfaces in soft materials under large deformations and complex contact conditions. Specifically, we introduce a microindentation and visualization (MIV) system capable of investigating soft material contact interfaces with combined normal and shear loading. When combined with a laser scanning confocal microscope, the MIV system enables the acquisition of 3D image stacks of the deformed substrate and the indenter under fixed normal and shear displacements. The 3D imaging data allows us to quantify the 3D contact profiles and correlate them with the applied normal and shear displacements. Using a spherical indenter and a hydrogel substrate as a model system, we demonstrate that the MIV system and the associated analysis techniques accurately measure the contact area under combined normal and shear loading. Although the limited speed of confocal scanning implies that this method is most suitable for quasi-static loading conditions, potential methods to increase the imaging speed and the corresponding trade-off in image resolution are discussed. The method presented here will be useful for the future investigation of soft material contact and friction involving complex surface geometries.

Geometric control of bacterial surface accumulation.

Controlling and suppressing bacterial accumulation at solid surfaces is essential for preventing biofilm formation and biofouling. Whereas various chemical surface treatments are known to reduce cell accumulation and attachment, the role of complex surface geometries remains less well understood. Here, we report experiments and simulations that explore the effects of locally varying boundary curvature on the scattering and accumulation dynamics of swimming Escherichia coli bacteria in quasi-two-dimensional microfluidic channels. Our experimental and numerical results show that a concave periodic boundary geometry can decrease the average cell concentration at the boundary by more than 50% relative to a flat surface.

PVD‐Schutzschichten für Werkzeuge des Präzisionsblankpressens

SummaryPVD protective coatings for precision molding toolsPrecision glass molding (PGM) is a replicative hot forming process for the production of complex optical components, such as aspherical lenses for digital and mobile phone cameras or optical elements for laser systems. The efficiency and thus also the profitability of the PGM depend on the unit price per pressed component, which correlates primarily with the service lifetime of the pressing tools. To increase tool lifetime, the tool surfaces are coated with protective coatings based on precious metals or carbon using physical vapour deposition (PVD). The PVD coating technology enables the deposition of thin coatings, which also follow more complex surface geometries and achieve a high surface quality. PVD coatings are also commonly used to protect tools from wear and corrosion. This paper presents two chromium‐based nitride hard coatings produced by an industrial PVD unit and investigated for their applicability for PGM. Two different coating architectures were implemented, on the one hand a single coating chromium aluminium nitride (Cr,Al)N coating and on the other hand a nanolaminar CrN/AlN coating with alternating layers of chromium nitride and aluminium nitride. The latter is a coating consisting of hundreds of nano‐layers, only a few nanometers thick. Both coatings, (Cr,Al)N and CrN/AlN, each have a thickness of s ∼ 300 nm in order to follow the tool contour as closely as possible. The properties of the coating systems, which are of particular relevance for PGM, are considered. These include on the one hand the adhesion of glass, the roughness and topography of the surface and the adhesion between the coating and the tool material. In addition, the barrier effect of the coatings against diffusion of oxygen was investigated. In order to reproduce the thermal boundary conditions of the PGM, thermocyclic aging tests are performed and their influence on the different properties is described.

A Highlight-Generation Method for Rendering Translucent Objects.

The acquisition of translucent objects has become a very common task thanks to the progress of 3D scanning technology. Since the characteristic soft appearance of translucent objects is due to subsurface scattering, the details are naturally left out in this appearance. For objects that have complex shapes, this lack of detail is obviously more prominent. In this paper, we propose a method to preserve the details of surface geometry by adding highlight effects. In generating highlight effects, our method employs a local orthonormal frame and combines, in a novel way, the incoming and outgoing light in approximating the subsurface scattering process. When the incident illuminant direction changes from nearly overhead to nearly horizontal, our method effectively preserves complex surface geometry details in the appearance of translucent materials. Through experiments, we show that our method can store surface features as well as maintain the translucency of the original materials and even enhance the perception of translucency. By numerically comparing the generated highlight effects with those generated by the traditional Bidirectional Reflectance Distribution Function (BRDF) models with different bandwidth parameters, we demonstrate the validity of our proposed method.

A Coupled Model for the Prediction of Surface Variation in Face Milling Large-Scale Workpiece With Complex Geometry

Face milling commonly generates surface quality of variation, is especially severe for milling of large-scale components with complex surface geometry such as cylinder block, engine head, and valve body. Thus surface variation serves as an important indicator both for machining parameter selection and components' service performance such as sealing, energy consumption, and emission. An efficient and comprehensive numerical model is highly desired for the prediction of surface variation of entire surface. This study proposes a coupled numerical simulation method, updating finite element (FE) model iteratively based on integration of data from abaqus and matlab, to predict surface variation induced by face milling of large-scale components with complex surfaces. Using the coupled model, three-dimensional (3D) variation of large-scale surface can be successfully simulated by considering face milling process including dynamic milling force, spiral curve of milling trajectory, and intermittently rotating contact characteristics. Surface variation is finally represented with point cloud from iterative FE analysis and verified by face milling experiment. Comparison between measured and predicted results shows that the new prediction method can simulate surface variation of complex components well. Based on the verified model, a set of analyses are conducted to evaluate the effects of local stiffness nonhomogenization and milling force variation on machined surface variation. It demonstrates that surface variation with surface peaks and concaves is strongly correlated with local stiffness nonhomogenization especially in feed direction. And thus the coupled prediction method provides a theoretical and efficient way to study surface variation induced by face milling of large-scale complex components.

Robotic concrete surface finishing: a moldless approach to creating thermally tuned surface geometry for architectural building components using Profile-3D-Printing

This paper focuses on describing a novel hybrid concrete printing/casting process we term Profile-3D-Printing. Profile-3D-Printing is an additive/subtractive manufacturing process that combines deposition of concrete for rough layup with precision tooling for surface finishing of architectural building components commonly found in the architectural precast industry. Our research team from Architecture, the Robotics Institute, and Material Science invented this novel hybrid manufacturing process for robotically printing architectural facade panels with complex surface geometries. This effort was motivated by previously validated research focused on calibrating the thermal exchange rate of vertical surface geometries for the purpose of improving both the esthetic and thermodynamic performance of passive heating and cooling systems in buildings. Our hybrid approach to concrete 3D printing is unique because it combines high-volume material deposition, multi-resolution surface finishing, and the ability for high customization without significant increases in production time. Our project will significantly advance systems integration between energy-based building performance design and advance additive manufacturing, enabling precast concrete suppliers to design and manufacture innovative architectural products with added value for end users in energy savings. This project serves as a template for other industries to adopt hybrid additive manufacturing systems to transform traditionally mold-based approaches. The goal of our project is to develop and test robotic 3D-printing systems that enable customization for high-resolution parts. Hybrid additive manufacturing (Hybrid-AM) enables automated tooling of soft and phase-changing materials to achieve fine feature resolution and finish quality independent of print nozzle size. Currently, speed of printing, control of finish quality, and flexibility of application are three of the most significant barriers for industries seeking to adopt additive manufacturing for part production. This project highlights how Hybrid-AM techniques, built on robotic work cells, address these challenges to enable customization of value-added products.

2D Transition Metal Dichalcogenide Thin Films Obtained by Chemical Gas Phase Deposition Techniques

AbstractUltrathin 2D transition metal dichalcogenide (TMD) thin films have attracted much attention due to their very good electrical, optical, and electrochemical properties. Chemical vapor deposition (CVD) and atomic layer deposition (ALD), which is in some regards an enhanced version of CVD, are techniques that can provide exceptionally conformal large‐area coatings, even for complex surface geometries. Besides, these techniques include the transport of one or more precursor chemicals in the gas phase onto a substrate. Subsequently, a chemical reaction occurs, resulting in the deposition of a film of a solid material on the substrate. One of the advantageous aspects of chemical deposition methods, such as CVD and ALD, is the growth of thin films onto a variety of substrates as well as 3D structures. Because of their chemical approach, these techniques are well suited to synthesizing 2D materials (2DMs) with a low defect concentration. Furthermore, the scalability would allow industrial application, as opposed to, e.g., micromechanical cleavage. Here, the recent progress in 2D TMD thin films is reviewed and the current applications of these materials fabricated by CVD and ALD are surveyed.

Laser polishing of additive manufactured CoCr alloy components with complex surface geometry

Laser polishing, capable of polishing selective nonplanar areas, is exploited to improve the surface roughness of additive manufactured metal components. It offers a highly repeatable, higher speed polishing process as well as low labor costs compared with traditional mechanical abrasive polishing. In spite of the fact that many studies can be found on laser polishing processes, few have reported that focus on metal components, manufactured additively by selective laser melting (SLM) technology, with geometrically different complex surfaces. This paper presents a novel method to reduce the surface roughness of Cobalt Chromium (CoCr) components with complex surface geometry by using a layered polishing method which can constantly adjust the defocusing distance of the laser along with the surface shape of the components. The optimized laser polishing parameters used were firstly obtained from the test results on planar surfaces of CoCr alloy samples and samples with complex surface geometry were then polished based on the laser parameters. Characterizations for the laser polished samples were conducted using optical profiling and scanning electron microscopy, showing that the surface roughness was reduced significantly in comparison with the as-received samples. A reduction of up to 93% in surface roughness was achieved. The mechanical hardness was also characterized by testing for Vickers hardness, which indicated the surface hardness of the laser polished samples was enhanced by 8%. Moreover, a simple and effective model was developed to illustrate the method of laser polishing on the complex surface geometry of additive manufactured CoCr alloy components. The analytical model is helpful in understanding and evaluating the underlying mechanisms of laser polishing.

Multi-scale characterization of topographic modifications on metallic biomaterials induced by nanosecond Nd:YVO4 laser structuring

Laser surface structuring of biometals allows to achieve complex surface geometries at several scales since a rough surface is preferred to induce an optimal cellular response. A lack of standard measurement techniques to characterize implant surfaces was detected. This paper presents a comprehensive, multi-scale characterization of the topography of laser textured biometals with the ISO standard profile method; which allows to separate the contribution of the superimposed textures of the profile, the low frequency component (waviness) and the high frequency component (roughness), and to calculate the respective height parameters according to the standard definitions. Furthermore, the characterization was completed by the calculation of the spatial parameters obtained by FFT calculation in order to assess the horizontal characteristics of the surface. We focused on two common biometals, stainless steel 316L and titanium alloy Ti6Al4V, structured with an array of parallel grooves obtained by using a nanosecond Nd:YVO4 laser. Regarding waviness, some differences in symmetry and sharpness were found according to the metal. Conversely, the roughness of the topography revealed that the average height of the micro-structures developed inside the grooves is similar in both metals. The spatial periodicity of the micro-structures showed that the aspect ratio resulted higher in AISI 316L than in Ti6Al4V. The analytical approach presented in this paper allows to establish an elementary comparison of the results obtained in the scientific community, contributing to a better understanding of in vitro/vivo cellular growing on textured surfaces.

Abnormality detection strategies for surface inspection using robot mounted laser scanners

The detection of small surface abnormalities on large complex free-form surfaces represents a significant challenge. Often surfaces abnormalities are less than a millimeter square in area but, must be located on surfaces of multiple meters square. To achieve consistent, cost effective and fast inspection, robotic or automated inspection systems are highly desirable. The challenge with automated inspection systems is to create a robust and accurate system that is not adversely affected by environmental variation. Robot-mounted laser line scanner systems can be used to acquire surface measurements, in the form of a point cloud11PC: point cloud, PCA: principal component analysis, CAD: computer-aided design, ROC: receiving operating characteristic, TP: true positives, FP: false positive, FN: false negative, TPR: true positive rate, TNR: true negative rate, SVM: support vector machine, CV: cross validation. (PC), from large complex geometries. This paper addresses the challenge of how surface abnormalities can be detected based on PC data by considering two different analysis strategies. First, an unsupervised thresholding strategy is considered, and through an experimental study the factors that affect abnormality detection performance are considered. Second, a robust supervised abnormality detection strategy is proposed. The performance of the proposed robust detection algorithm is evaluated experimentally using a realistic test scenario including a complex surface geometry, inconsistent PC quality and variable PC noise. Test results of the unsupervised analysis strategy shows that besides the abnormality size, the laser projection angle and laser lines spacing play an important role on the performance of the unsupervised detection strategy. In addition, a compromise should be made between the threshold value and the sensitivity and specificity of the results.

Selectively Electron-Transparent Microstamping Toward Concurrent Digital Image Correlation and High-Angular Resolution Electron Backscatter Diffraction (EBSD) Analysis.

Digital image correlation (DIC) in a scanning electron microscope and high-angular resolution electron backscatter diffraction (HREBSD) provide valuable and complementary data concerning local deformation at the microscale. However, standard surface preparation techniques are mutually exclusive, which makes combining these techniques in situ impossible. This paper introduces a new method of applying surface patterning for DIC, namely a urethane microstamp, that provides a pattern with enough contrast for DIC at low accelerating voltages, but is virtually transparent at the higher voltages necessary for HREBSD and conventional EBSD analysis. Furthermore, microstamping is inexpensive and repeatable, and is more suitable to the analysis of patterns from complex surface geometries and larger surface areas than other patterning techniques.

A fast mass spring model solver for high-resolution elastic objects

Real-time simulation of elastic objects is of great importance for computer graphics and virtual reality applications. The fast mass spring model solver can achieve visually realistic simulation in an efficient way. Unfortunately, this method suffers from resolution limitations and lack of mechanical realism for a surface geometry model, which greatly restricts its application. To tackle these problems, in this paper we propose a fast mass spring model solver for high-resolution elastic objects. First, we project the complex surface geometry model into a set of uniform grid cells as cages through *cages mean value coordinate method to reflect its internal structure and mechanics properties. Then, we replace the original Cholesky decomposition method in the fast mass spring model solver with a conjugate gradient method, which can make the fast mass spring model solver more efficient for detailed surface geometry models. Finally, we propose a graphics processing unit accelerated parallel algorithm for the conjugate gradient method. Experimental results show that our method can realize efficient deformation simulation of 3D elastic objects with visual reality and physical fidelity, which has a great potential for applications in computer animation.

Using computed tomography and 3D printing to construct custom prosthetics attachments and devices

BackgroundThe prosthetic devices the military uses to restore function and mobility to our wounded warriors are highly advanced, and in many instances not publically available. There is considerable research aimed at this population of young patients who are extremely active and desire to take part in numerous complex activities. While prosthetists design and manufacture numerous devices with standard materials and limb assemblies, patients often require individualized prosthetic design and/or modifications to enable them to participate fully in complex activities.MethodsProsthetists and engineers perform research and implement digitally designs in collaboration to generate equipment for their patient’s rehabilitation needs. 3D printing allows for these devices to be manufactured from an array of materials ranging from plastic to titanium alloy. Many designs require form fitting to a prosthetic socket or a complex surface geometry. Specialty items can be scanned using computed tomography and digitally reconstructed to produce a virtual 3D model the engineer can use to design the necessary features of the desired prosthetic, device, or attachment. Completed devices are tested for fit and function.ResultsNumerous custom prostheses and attachments have been successfully translated from the research domain to clinical reality, in particular, those that feature the use of computed tomography (CT) reconstructions. The purpose of this project is to describe the research pathways to implementation for the following clinical designs: sets of bilateral hockey skates; custom weightlifting prosthetic hands; and a wine glass holder.ConclusionThis article will demonstrate how to incorporate CT imaging and 3D printing in the design and manufacturing process of custom attachments and assistive technology devices. Even though some of these prosthesis attachments may be relatively simple in design to an engineer, they have an enormous impact on the lives of our wounded warriors.

A Novel Surface Remeshing Scheme via Radial Basis Functions and Higher-Dimensional Embedding

Many applications heavily rely on piecewise triangular meshes to describe complex surface geometries. The quality of the meshes directly impacts numerical simulations. In practice, however, one often has to deal with several challenges to construct suitable meshes. Some regions in a naively built mesh may be overrefined, others too coarse. Additionally, the triangles may be too thin or not properly oriented. We present a novel surface remeshing procedure which greatly improves a problematic input mesh and overcomes all of these drawbacks. By coupling surface reconstruction via radial basis functions with the higher-dimensional embedding surface remeshing technique, we can automatically generate a new anisotropic surface mesh with improved mesh quality. Moreover, we are not only able to refine or coarsen certain mesh regions but also align the triangles according to the curvature of the reconstructed surface. This yields an acceptable trade-off between computational complexity and accuracy.