UBET analysis of the closed-pass ring rolling of rings having arbitrarily shaped profiles

A simple but effective upper-bound elemental technique (UBET) for prediction of the torque and the deformation pattern during the ring-rolling of rings having arbitrarily shaped profiles is proposed. In order to describe the three-dimensional material flow of profile ring rolling, a new element with a curvilinear side is introduced and the corresponding kinematically admissible velocity field is derived. Upper-bound analysis is carried out for rolling rings with a circular groove or protrusion having a round corner fillet. Comparing with the experimental results, the roll torque and the profile formation are predicted with reasonable accuracy. The effects of some parameters are investigated also. Despite the simplifying assumptions, some aspects of the deformation mechanics in profile ring rolling are shown to be described successfully by the proposed method.     

Mechanical properties of anatase and semi-metallic TiO2 nanotubes

We report for the first time on mechanical properties of anodically formed, self-organized TiO₂ nanotube layers on titanium. We compare their behavior in their virgin state and after conversion to their semi-metallic form by an acetylene treatment. We show that the acetylene treatment leads to significant enhanced hardness, tensile strength and friction behavior.     

Effects of Alkaline-Earth-Metal Addition on the Sinterability and Microwave Characteristics of (Zr,Sn)TiO4 Dielectrics

The sinterability and microwave dielectric properties of (Zr_0.8Sn_0.2)TiO₄ with additions of 1 mol% of magnesium, calcium, strontium, or barium were examined. All the alkaline-earth metals were effective for densification, and the order of effectiveness was as follows: Mg < Ca < Sr < Ba. The dielectric constant and the temperature coefficient of the resonant frequency were not influenced very much by the additives; however, a strong deterioration of the quality factor ( Q ) did occur when magnesium was added. The presence of grain-boundary phases was confirmed via microstructural observation, using transmission electron microscopy. In addition, energy-dispersive X-ray analysis was performed to investigate the cause of the deterioration in the Q value.     

Sintering Behavior of Nanocrystalline Zirconia Doped with Alumina Prepared by Chemical Vapor Synthesis

Powders of nanocrystalline zirconia doped with 3–30 mol% alumina have been synthesized using chemical vapor synthesis (CVS). Dense or mesoporous ceramics of small and narrowly distributed grain and pore sizes in the nanometer range are obtained via pressureless vacuum sintering. The microstructural development of the doped samples is strongly dependent on the alumina content. Sintering of zirconia samples with 3 and 5 mol% alumina at temperatures of 1000°C for 1 h results in fully dense, transparent ceramics with grain sizes of 40–45 nm and homogeneous microstructures.     

Effects of a Conducting LaNiO3 Thick Film as a Buffer Layer of a Pb(Zr,Ti)O3 Film on Titanium Substrates

A conducting 8-μm-thick LaNiO₃ (LNO) film was deposited on a Ti substrate by aerosol deposition for use as a diffusion barrier between a lead zirconate titanate (PZT) and a Ti substrate during postannealing. The deposited 20-μm-thick PZT films were annealed at 800°C. The PZT film deposited without LNO was cracked and partially detached from the substrate after postannealing, presumably due to a severe reaction with the Ti substrate, while no significant reactions were observed when the LNO buffer layer was used. The remnant polarization and relative dielectric constant of the 20-μm-thick annealed PZT films deposited on the LNO-buffered Ti substrate were 43 μC/cm² and 1010, respectively.     

Acoustic emission behavior of epoxies during tensile loading

The acoustic emission behavior during tensile loading of two common epoxy systems of different ductility was investigated at different loading rates. At low threshold voltage, it was possible to register acoustic emissions before the final failure. Only very few emissions were recorded compared with the amount commonly recorded for metals and composite materials. The acoustic emissions detected were of burst-type, revealing a brittle damage accumulation process. They originated from the initiation and incremental growth of microcracks of stochastic nature. The events occurred before gross yielding and during the final “brittle” failure process. Basically no events were detected between gross yielding and the final failure during which large scale yielding, necking, and stable crack growth took place. The occurrence of events at the different loading rates was strongly influenced by the yielding behavior and fracture toughness, characterized by the yield stress σ_y and the plane-strain fracture toughness K_Ic respectively. K_Ic was inversely dependent on the total number of events up to gross yielding. The event distribution normalized with respect to the conditions at gross yielding was hardly affected by the loading rate.     

Electrochemical synthesis and characterization of mixed molybdenum-rhenium oxides

The electrodeposition of Mo_xRe_1−xO_y films (0.6 ≤ x ≤ 1) on indium-tin oxide (ITO) coated glass substrates from acidic peroxo-polymolybdo-perrhenate solutions is described. Trends in film growth were established as a function of potential from +0.4 V to −0.7 V vs Ag/AgCl by analyzing the composition and stoichiometry of the deposit using inductively coupled plasma mass spectrometry (ICPMS) and X-ray photoelectron spectroscopy (XPS). These experiments show that the concentration of rhenium increases linearly with the deposition potential and that the deposits are mixed-valent containing up to five different metal oxidation states (i.e., Mo^IV, Mo^V, Mo^VI, Re⁰, Re^IV). Electroanalytical techniques were used to explore the deposition mechanism, including chronocoulometry, cyclic voltammetry, spectroelectrochemistry, and electrochemical quartz crystal nanogravimetry (EQCN). At potentials positive to −0.26 V, perrhenate (Re^VIIO₄⁻) behaves as a redox mediator to accelerate the deposition of a mixed-valent molybdenum oxide, but at more negative potentials mixed molybdenum-rhenium oxides are produced.     

In Vivo Analysis of the Biocompatibility and Bone Healing Capacity of a Novel Bone Grafting Material Combined with Hyaluronic Acid

The present in vivo study analyses both the inflammatory tissue reactions and the bone healing capacity of a newly developed bone substitute material (BSM) based on xenogeneic bone substitute granules combined with hyaluronate (HY) as a water-binding molecule. The results of the hyaluronate containing bone substitute material (BSM) were compared to a control xenogeneic BSM of the same chemical composition and a sham operation group up to 16 weeks post implantationem. A major focus of the study was to analyze the residual hyaluronate and its effects on the material-dependent healing behavior and the inflammatory tissue responses. The study included 63 male Wistar rats using the calvaria implantation model for 2, 8, and 16 weeks post implantationem. Established and Good Laboratory Practice (GLP)-conforming histological, histopathological, and histomorphometrical analysis methods were conducted. The results showed that the new hyaluronate containing BSM was gradually integrated within newly formed bone up to the end of the study that ended in a condition of complete bone defect healing. Thereby, no differences to the healing capacity of the control BSM were found. However, the bone formation in both groups was continuously significantly higher compared to the sham operation group. Additionally, no differences in the (inflammatory) tissue response that was analyzed via qualitative and (semi-) quantitative methods were found. Interestingly, no differences were found between the numbers of pro- and anti-inflammatory macrophages between the three study groups over the entire course of the study. No signs of the HY as a water-binding part of the BSM were histologically detectable at any of the study time points, altogether the results of the present study show that HY allows for an optimal material-associated bone tissue healing comparable to the control xenogeneic BSM. The added HY seems to be degraded within a very short time period of less than 2 weeks so that the remaining BSM granules allow for a gradual osteoconductive bone regeneration. Additionally, no differences between the inflammatory tissue reactions in both material groups and the sham operation group were found. Thus, the new hyaluronate containing xenogeneic BSM and also the control BSM have been shown to be fully biocompatible without any differences regarding bone regeneration.     

Effect of ductility on the fatigue behavior of epoxy resins

The effect of ductility on fatigue behavior was studied using two DGEBA-based (diglycidyl ether of bisphenol A) epoxies: a ductile Epon 815/Versamid 140 and a brittle Epon 828/Epon Z. Failure modes were different although normalized stress-life relations were similar for both resins. Two competing failure mechanisms were identified: viscoelastic creep, and nucleation and coalescence into a main crack of microcracks. No signs of crazing or fibrillation were detected. The plastic elongation during fatigue was larger in Epon 815/Versamid 140. Fracture sources showed cracked material surrounded by a region of stable growth of the main crack. In the brittle Epon 828/Epon Z cracked material was scarce and the crack initiation region was clean, especially at high stress levels. Discontinuous crack growth bands and striations were seen in the stable crack growth regions. During unstable propagation the crack advanced at different levels joined by deep cleavage steps. Branching of the main crack occurred only in the brittle resin at the final stage of propagation.