An efficient method for solving the Signorini problem in the simulation of free-form surfaces produced by belt grinding

Industrial robots are recently introduced to the belt grinding of free-form surfaces to obtain high productive efficiency and constant surface quality. The simulation of belt grinding process can facilitate planning grinding paths and writing robotic programs before manufacturing. In simulation, it is crucial to get the force distribution in the contact area between the workpiece and the elastic contact wheel because the uneven distributed local forces are the main reason to the unequal local removals on the grated surface. The traditional way is to simplify this contact problem as a Signorini contact problem and use the finite element method (FEM) to calculate the force distribution. However, the FEM model is too computationally expensive to meet the real-time requirement. A new model based on support vector regression (SVR) technique is developed in this paper to calculate the force distribution instead of the FEM model. The new model approximates the FEM model with an error smaller than 5%, but executes much faster (1 s vs 15 min by FEM). With this new model, the real-time simulation and even the on-line robot control of grinding processes can be further conducted.     

Piezoelectric properties and phase transition temperatures of the solid solution of (1 − x)(Bi0.5Na0.5)TiO3–xSrTiO3

The phase diagram of (1 ? x)(Bi_0.5Na_0.5)TiO₃–xSrTiO₃ was completed and investigations on polarization and strain in this system were carried out. (1 ? x)(Bi_0.5Na_0.5)TiO₃–xSrTiO₃-ceramics were prepared by conventional mixed oxide processing. The depolarization temperature (T_d), the temperature of the rhombohedral–tetragonal phase transition (T_r–t) and the Curie temperature (T_m) were determined by measuring the temperature dependence of the relative permittivity. All solid solutions of (1 ? x)(Bi_0.5Na_0.5)TiO₃–xSrTiO₃ show relaxor behavior (A-site relaxor). From XRD-measurements a broad maximum of the lattice parameter can be observed around x = 0.5 but no structural evidence for a morphotropic phase boundary was found. SEM-analysis revealed a decrease of the grain size for increasing SrTiO₃-content. At room temperature a maximum of strain of about 0.29% was found at x = 0.25 which coincides with a transition from a ferroelectric to an antiferroelectric phase. The temperature dependence of the displacement indicates an additional contribution from a structural transition (rhombohedral–tetragonal), which would be of certain relevance for the existence of a morphotropic phase boundary.     

Oxidation of ZrB2–SiC–ZrSi2 ceramics in oxygen

The oxidation of ZrB₂–SiC and ZrB₂–SiC–ZrSi₂ ceramics of different composition has been studied experimentally at 1500 °C in pure oxygen for up to 50 h. ZrB₂–SiC–ZrSi₂ ceramics proved to be the most oxidation-resistant at ZrSi₂ contents of less then 4 wt%. These ceramics were more oxidation-resistant than ZrB₂–SiC ceramics. An analytical model of growth kinetics for a multilayered scale based on an oxidation–diffusion balance was developed and tested.     

Responsive Hybrid Polymeric/Metallic Nanoparticles for Catalytic Applications

The aims of the current study were to synthesize new responsive polymeric microgels with embedded silver nanoparticles and then to employ these particles as catalyst for reduction reactions. To these ends, stimuli‐responsive microgels from PNIPAAm and the chitosan derivative were firstly synthesized by free radical precipitation polymerization. Then, silver nanoparticles were synthesized inside these microgel networks by in situ reduction of AgNO₃. These microgels were temperature/pH sensitive with a phase transition temperature of 32–35 °C in water at pH = 3 and 8, respectively. The catalytic activity of the Ag nanoparticles for the reduction of 4‐nitrophenol can be tuned through the swelling or collapse of the responsive microgel network hosting the active nanoparticles.

     

NanoSIMS: Insights into the Organization of the Proteinaceous Scaffold within Hexactinellid Sponge Spicules

The giant basal spicules (GBS) from Monorhaphis chuni (Porifera [sponges], Hexactinellida) represent the largest biosilica structures on Earth and can reach lengths of 300 cm (diameter of 1.1 cm). The amorphous silica of the inorganic matrix is formed enzymatically by silicatein. During this process, the enzyme remains trapped inside the lamellar‐organized spicules. In order to localize the organic silicatein scaffold, the inside of a lamella has been analyzed by nano‐secondary ion mass spectrometry (NanoSIMS). It is shown that the GBSs are composed of around 245 concentrically arranged individual siliceous lamellae. These surround an internal siliceous axial cylinder. The lamellae adjacent to the cylinder are thicker (10–30 μm) than the more peripheral lamellae (2–10 μm). One lamella of a thickness of 18 μm has been selected for further analysis. This lamella itself is composed of three sublamellae with an individual thickness of 2–6 μm each, which are then further organized into three cylindrical slats (thickness: 1.6–1.8 μm). Other than the main lamellae, the sublamellae are not separated from each other by gaps. The element analysis of the sublamellae by NanoSIMS revealed that the siliceous matrix is embedded in an organic matrix that consists of up to 6–10 wt/% of C. The pattern of C distribution reflects a distinct zonation of the organic material within the solid intralamellar biosiliceous material. A growth model for the lamella starting from nanosized silica particles is proposed: During formation of a lamella nanosized silica particles fuse, through biosintering processes, to slats that build the individual sublamellae, which then finally form the lamellae. In turn, those lamellae may form the higher structural entity, the axial cylinder.     

Purification,surface modification of coal ash silica and its potential application in rubber composites

This article reports the purification and surface modification of coal ash silica and afterwards its utilization as reinforcing filler in solution‐styrene‐butadiene rubber/butadiene rubber (S‐SBR/BR). The coal ash silica free of unwanted metal ions/mineral oxides was obtained using phosphoric acid. The chemical composition of the purified coal ash silica in comparison to impure coal ash indicates the presence of characteristic hydroxyl functional group at 3440 cm^?1 and an increase in the oxygen content as determined with the help of Fourier Transform Infrared and x‐ray photoelectron spectroscopy, respectively. The contact angle analysis shows that after purification the polar part of the surface energy increased to 17.5 from 12 m Jm^?2. While the surface area increased to an order of magnitude, i.e., 11.6 to 110.5 m² g^?1. The modification of purified silica particles with bis(3‐triethoxysilylpropyl) tetrasulfane reveal the functionalization of hydroxyl to ‐Si‐O‐R groups as detected at 1560 cm^?1. As a consequence, the modified silica based S‐SBR/BR composite resulted in improved mechanical properties due to enhanced silica‐rubber interaction. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Absorbable polymer stent technologies for vascular regeneration

Stents are structural implants with widespread clinical use in vascular intervention to re‐open stenotic vessels for the treatment of coronary artery disease and peripheral arterial occlusive disease. Apart from their mechanical function, current drug‐eluting stents (DES) utilize local drug delivery from a drug‐incorporated permanent polymer coating to prevent in‐stent restenosis. This delayed closure of the stented vessel is considered one of the major limitations of conventional bare metal stents (BMS). The long‐term safety of DES, however, is still under debate, with reported cases of delayed healing, late thrombosis and hypersensitivity demanding further evolution in this field. A promising approach to circumvent the limitations of first generation DES is the application of degradable polymer coatings in second generation DES, and fully absorbable polymer stents. From a materials and engineering perspective, this paper provides a mini‐review of current clinically relevant DES technology and recent advancements in the development of stents from degradable polymeric materials as an alternative to permanent BMS and DES. This review, includes work on degradable stents and coatings based on blends of polylactic acid and the microbially‐produced poly(4‐hydroxybutyrate). Copyright © 2009 Society of Chemical Industry     

Optical spectroscopic and electrochemical characterization of oxide films on a ferritic stainless steel

Colored oxide films that form on ferritic stainless steel in a high-temperature, oxidizing environment and correspond to different chemical compositions can cause a deterioration of pitting resistance and corrosion performance. Herein, optical spectroscopic and electrochemical techniques have been used to reveal the relationship between color, chemical composition, and corrosion resistance of oxide films formed in the temperature range from 400°C to 800°C for 30 min and at 800°C for 10, 20, 30, and 60 min. The substrate with a thin and dense passivation film leads to a low pitting potential but high corrosion resistance. Oxide films of yellowish or brownish color formed below 600°C are mainly iron oxides, which correspond to low corrosion resistance. No passivation characteristics can be observed for polarization curves of oxide films formed at 500°C and 600°C. The color of oxide films varies from blue to dark gray with the increase of oxidation time at 800°C. Corrosion resistance changes with different proportions of Fe₃O₄, Cr₂O₃, and FeCr₂O₄. The gray oxide films formed at 800°C for 30 min exhibit the lowest pitting susceptibility and the highest corrosion resistance.     

Particle In-Flight and Coating Properties of Fe-Based Feedstock Materials Sprayed with Modern Thermal Spray Systems

New developments in the field of thermal spraying systems (increased particle velocities, enhanced process stability) are leading to improved coatings. Innovations in the field of feedstock materials are supporting this trend. The combination of both has led to a renaissance of Fe-based feedstocks. Using modern APS or HVOF systems, it is now possible to compete with classical materials for wear and corrosion applications like Ni-basis or metal-matrix composites. This study intends to give an analysis of the in-flight particle and spray jet properties achievable with two different modern thermal spraying systems using Fe-based powders. The velocity fields are measured with the Laser Doppler Anemometry. Resulting coatings are analyzed and a correlation with the particle in-flight properties is given. The experiments are accompanied by computational fluid dynamics simulations of spray jet and particle velocities, leading to a comprehensive analysis of the achievable particle properties with state-of-the-art HVOF and APS systems.