Grundlegende Betrachtungen zur Eigenspannungsanalyse an Keramik-Metall-Verbunden mittels FEM

Fundamental Investigations of Residual Stresses in Metal-Ceramic-Joints by FEM The reduction of damages in metal-ceramic-joints caused by residual stresses is of essential significance. Therefore, a model was created to simulate the behaviour of metal-ceramic-joints under thermal stress. In this paper, results of fundamental investigations are presented.     

Tensile behavior and cyclic creep of continuous fiber-reinforced glass matrix composites at room and elevated temperatures

In this study we investigated the stress-strain behavior at room and elevated temperatures and the tensile creep and cyclic creep response of a unidirectional SiC fiber-reinforced aluminosilicate glass matrix composite. The interfacial condition of the as-received material was measured by a push-out indentation technique. The stress-strain behavior was that expected for this kind of composite, i.e. “pseudoductile” behavior with extensive fiber “pull-out” at room temperature and brittle failure at intermediate temperatures (750 °C) due to oxidation embrittlement. The stiffness of the composite at 750°C was analyzed for different loading rates, highlighing the influence of the loading rate on apparent composite stiffness, due to matrix softening. The creep studies were conducted at temperatures above and below the softening temperature of the glass (T _g, 745 °C) in air. The cyclic creep experiments showed the existence of extensive viscous strain recovery during the unloading period. The creep strain recovery was quantified using strain recovery ratios. These ratios showed a slight dependence on the temperatures investigated (700 and 750 °C). The crept composites retained their “graceful” fracture behavior only partially after testing, indicating that oxidation of the fiber/matrix interface due to oxygen diffusion through the matrix occurred in the peripheral area of the samples. Dr. Boccaccini is presently at the Institute for Mechanics and Materials, University of California, San Diego, CA 92093, USA.     

Early cellular and humoral response after vascular prosthesis implantation in the arterial system]

The aim of the study was to determine the level of leukocytes activation after the implantation of vascular graft. As an experimental model we used 20 dogs. The aorto-iliac unilateral graft (dacron 6 mm) was implanted to all animals. The adhesion and migration of the leukocytes was estimated postoperatively by scintigraphy using Tc99 labeled leukocytes. The increased migration and adhesion was found in both proximal and distal anastomoses till the 30th postoperative day and it was more intensive in the distal anastomosis.     

A simple, novel method for the preparation of metallophthalocyanines

New metallophthalocyanines (Me---Pc) in the crystalline form were synthesized by the direct reaction between the 1,2-dicyanobenzene and filings of the metallic elements or intermetallic alloys. The reaction took place at about 480 K in vacuum over a few days. Some remarks on the reaction mechanism of the Me---Pc formation are made. It is assumed that under the experimental conditions used the 1,2-dicyanobenzene liquid undergoes a catalytic tetramerization. The catalytic atom of the metal is simultaneously coordinated by the forming tetramer.     

Comparison of four gradient-learning algorithms for neural network Wiener models

A gradient-based approach to training neural network Wiener models is presented. Calculation of the gradient or approximate gradient for the series-parallel and parallel Wiener models by the backpropagation, the sensitivity method (SM) and the backpropagation through time (BPTT) is considered in a unified framework. Four different recursive learning algorithms are derived, analysed and compared. For the truncated BPTT, it is shown that the determination of the number of unfolding time steps can be made on the basis of an impulse response function of sensitivity models. Analysis of the computational complexity of these algorithms shows that, contrary to the other recurrent neural network models, computation of the gradient in parallel Wiener models with the sensitivity method or backpropagation through time requires only a little more computational burden than the backpropagation. A simulated data example and a real data example of a laboratory two-tank system are also included to make comparison of different methods and their effectiveness and practical feasibility are shown.     

Silver/dendrimer nanocomposites as biomarkers: fabrication, characterization, in vitro toxicity, and intracellular detection

We have synthesized water-soluble, biocompatible, fluorescent, and stable silver/dendrimer nanocomposites that exhibit a potential for in vitro cell labeling. Amino-, hydroxyl-, and carboxyl-terminated ethylenediamine core generation 5 poly(amidoamine) dendrimers were utilized to prepare aqueous silver(I)-dendrimer complexes (with the molar ratio of 25 Ag+ per dendrimer) at the biologic pH of 7.4. Conversion of silver(I)-dendrimer complexes into dendrimer nanocomposites was achieved by irradiating the solutions with UV light to reduce the bound Ag+ cations to zerovalent Ag0 atoms, which were simultaneously trapped in the dendrimer network, resulting in the formation of {(Ag0)25-PAMAM_E5.NH2}, {(Ag0)25-PAMAM_E5.NGly}, and {(Ag0)25-PAMAM_E5.NSAH} dendrimer nanocomposites (DNC), respectively. The silver-DNCs were characterized by means of UV-vis, fluorescence spectroscopy, dynamic light-scattering, zeta potential measurements, high-resolution transmission electron microscopy, X-ray energy dispersive spectroscopy, and selected area electron diffraction. The cytotoxicity of dendrimers and related silver nanocomposites was evaluated using an XTT colorimetric assay of cellular viability. The cellular uptake of nanoparticles was examined by transmission electron and confocal microscopy. Results indicate that {(Ag0)25-PAMAM_E5.NH2}, {(Ag0-)25-PAMAM_E5.NGly}, and {(Ag0)25-PAMAM_E5.NSAH} form primarily single particles with diameters between 3 and 7 nm. The dendrimer nanocomposites are fluorescent, and their surface charge, cellular internalization, toxicity, and cell labeling capabilities are determined by the surface functionalities of dendrimer templates. The {(Ag0)25-PAMAM_E5.NH2} and {(Ag0)25-PAMAM_E5.NSAH} nanocomposites exhibit potential application as cell biomarkers.     

Influence of Specific Processing Conditions and Aliphatic-Aromatic Copolyester on Polylactide Properties

This study reports the influence of aliphatic-aromatic copolyesters (AAC) on selected polylactide (PLA) properties. Processing, mechanical, and thermal properties were determined. In addition, we examined changes occurring in the surface geometrical structure of sample fractures. It was found that PLA as modified with AAC exhibited enhanced impact strength and melt flow rate, unaffected elongation at break, and reduced tensile strength and elasticity modulus. The results also demonstrate the plasticizing properties of AAC, which improved PLA processing and its thermal stability. We also observed insufficient adhesion at the interface between the two components, as well as heterogeneity of the obtained material.     

Experimentelle Verifizierung einer neuer Modellgleichung für die voraussage des Elastizitätsmoduls eines Verbundwerkstoffes

Experimental Verification of a New Enquation for the Youngs Modulus of Composite Materials A recently proposed model equation for the prediction of Youngs modulus of elasticity of composite materials has been compared with extensive experimental data from the literature. As the derivation of the equation assumes a definite matrix-type microstructure with spheroidal inclusions, only composites containing particulate inclusions of different geometries were considered, including data on ceramic, glass and polymer matrix composites. A quantitative good agreement between theory and experiment was found, specially when the inclusion shape and orientation, being the microstructural parameters entering in the equation, were accurately known. The microstructural parameters involved in the equation can be obtained from real microstructural data via quantitative microstructural analysis and sterology, no fitting is involved. This fact makes the proposed equation substantial also for practical applications.     

Mechanical behavior of SiC joints brazed using an active Ag‐Cu‐In‐Ti braze at elevated temperatures

The behavior of SiC ceramic joints brazed with commercially available Incusil ABA (Ag‐32.25Cu‐12.5In‐1.25Ti, in wt.%) was characterized especially with respect to the mechanical performance at temperatures up to 550°C using four‐point bending and torsional shear tests. The failure mechanisms with changing temperature were investigated with the aid of fractography. Additionally, the microstructure of brazed specimens was characterized in detail by high resolution scanning electron microscopy. The test geometry and setup for the high temperature torsional shear test is presented. The change in mechanical behavior of the joints as a function of temperature is shown and discussed. The brazed joints interestingly showed that flexural bending strength was maintained with only a small decrease up to 300°C. Above 300°C, the bending strength decreased much faster. For the first time, this joint system was characterized in torsional shear test at temperatures up to 550°C to achieve the intrinsic shear strength values. Very strong joints were achieved, resulting in failure through the ceramic base materials up to (torsional shear) testing temperatures of 400°C. The results indicate that SiC joints brazed with Incusil ABA exhibit excellent mechanical performance for applications up to 300°C.     

Data fusion for ballistic targets tracking using least squares

The paper deals with the problem of state estimation of continuous-time nonlinear system using discrete-time measurements from multiple sensors. In particular, the problem of multi-radar tracking of artillery ballistic objects is considered. A batch estimator based on the iterative least squares approach is developed using simplified and accurate models of ballistic flight. The estimator is applied to process the sequences of measurements from radars tracking the same ballistic target. Estimates of the target state over time are computed and their accuracy is compared to the estimates yielded by the extended Kalman filter. Partial estimates from multiple radars are combined using track fusion approach and propagated using the 3 degree of freedom model of ballistic flight. Accuracy of target's firing point estimation is also analysed with respect to the data rates and locations of the radars with respect to the target. Practical aspects of the proposed method are also discussed.