Verhalten der Hilbert-Transformation für quasibandbegrenzte Signale

The behaviour of the Hilbert-Transform is investigated in the paper. At first band limited signals are considered. Some well known expressions of the Hilbert-Transform are given in the paper. However, almost all practical signals are not band limited. A new class of quasi band limited signals is proposed in the paper. It is shown that an exact classification of the behaviour is possible with the help of the new class of quasi band limited signals.     

Methoden und Probleme der Schliffherstellung zum Zwecke metallographischer Untersuchungen

Methods and problems of cross section preparation for metallografic investigation . By an analysis of some literature it is tried to demonstrate that – in spite of comprehensive researchs – it is impossible to tell in advance the depth of the disturbed layer of a specimen's polished surface whenever the microstructure has been influenced by mechanical or thermical stresses. Only by chemical methods of preparation it is possible to obtain an unchanged microstructure in a polished metal surface. The approved methods are named and there are given some hints at practical proceeding.     

Untersuchungen zum mechanischen Verhalten von Siliciumnitrid in einem Kugel-Platte-Kontakt

Investigation of the mechanical behaviour of silicon nitride in a sphere-on-plate contact Silicon nitride is recently used as a material for full ceramic roller bearings. The reasons for this are the specific material properties like the high chemical resistance, the low specific weight and the high strength, even at high temperatures. Nevertheless, there is only little experimental and theoretical experience in the field of full ceramic roller bearings with respect to load capacity and lifetime of these components. This lack of information is the motivation for the investigations on the mechanical behaviour of a gas pressured sintered silicon nitride (GPSN) in a sphere-on-plate contact, where fracture or plastic deformation can occur. The load-displacement curves and the load necessary to cause fracture or plastic deformation are determined as a function of sphere radius. The initiation of fracture at natural defects is described by fracture mechanics. The fracture mechanical model is based on independently measurable material constants like young's modulus, poisson's ratio and fracture toughness K_Jc. The plastic deformations are described within a Finite-Element calculation with an elastic-ideal plastic material law according to von Mises. The results form the starting point for further investigations in the field of design and lifetime calculations for ceramic roller bearings.     

Experimentelle und numerische Untersuchungen zum mechanischen Verhalten perforierter Aluminium‐Legierungen unter zyklischer Belastung

Experimental and numerical investigation of the mechanical behaviour of perforated aluminium alloys under cyclic loading The stiffness behaviour of perforated aluminium alloys under cyclic loading is examined in relation to the relative density. Different relative densities between 0.93 and 0.62 could be realized by modification of the hole spacing of the regular square penetration pattern. Unloading experiments were carried out for the determination of the stiffness change. The decrease of the gradient of the un‐ and reloading curves with increasing plastic deformation could be measured. The pore formation was verified exemplarily by using Scanning Electron Microscopy. The quantitative influence of a changing cell structure (size and shape) on the measured stiffness reduction was estimated by means of the Finite Element Method.     

Sonderlagen der Getriebe und ihre Anwendungen

Zusammenfassung Durch Anwenden von Sonderlagen, die sich für alle Getriebeketten gleicher Art in universeller Weise erfassen lassen, gelingt es, die Bestimmung der Winkelgeschwindigkeiten und der Winkelbeschleunigungen der Getriebeglieder sowie der Gelenkkr?fte in allgemein gültiger Form festzulegen. Das Verfahren wurde zun?chst auf viergliedrige Kurbelschwingen angewendet und soll sp?ter auf Getriebe mit mehr als vier Gliedern ausgedehnt werden.     

Sonderlagen der Getriebe und ihre Anwendungen

Ohne Zusammenfassung Schlu? des Aufsatzes aus Heft 3 (1965) S. 77/82.     

Neue Untersuchungen zur Approximierbarkeit und Rekonstruierbarkeit bandbegrenzter Signale

New results on the reconstruction and approximation behaviour of sampling series are reported in the paper. At first we investigate the behaviour of the Shannon sampling series for non bandlimited signals. It is shown in the paper, that the sequence of the Shannon sampling series is divergent for some non bandlimited signals. Some new sampling series with better reconstruction and approximation behaviour are proposed in the paper. We also investigate the problem of non equidistant sampling of bandlimited signals.     

Untersuchungen zum Nachweis der Nutzbarkeit elastischer Wechselwirkungsprozesse zwischen niederenergetischen Elektronen und Gasteilchen zur Druckmessung

In the rough and partly in the medium vacuum range collisions and scattering processes of electrons with gas particles influence the motion of slow electrons in an electric field between anode and cathode significantly. After a sufficient number of elastic collisions the electrons move nearly randomly in the electric field with a mean constant drift velocity to their collecting electrode. Using a suitable electrode configuration these interaction processes between electrons and gas particles can be used for the pressure measurement in the upper vacuum pressure range. A gauge construction using this principle is characterised by of a simple electrode structure and electronic equipment. Experimental investigations and numerical calculations are described in this paper.     

Neue Untersuchungen zur Approximierbarkeit und Rekonstruierbarkeit bandbegrenzter Signale

Forschung im Ingenieurwesen - In der Arbeit werden neue Resultate über das Rekonstruktions- und Approximationsverhalten von Abtastreihen vorgestellt. Es wird als erstes das Verhalten der...     

Numerische und experimentelle Untersuchungen zum Pulverpressen von Aluminium

Numerical and Experimental Investigations of Aluminium Powder Compaction The FEM simulation is a powerful means which can drastically reduce the time to production and costs in the optimization of powder forming processes. The current paper investigates experimentally and numerically die compaction of aluminium powder. The plastic deformation is formulated by using the Drucker‐Prager‐Cap‐model. This yield criterion describes the compressibility of porous bodies and allows the prediction of crack formation in the green compact. Axial compaction tests have been performed to determine material parameters for hardening. Simulation examples are presented to demonstrate the ability of the model to compute the distribution of the relative density. Furthermore, the compaction of an axisymmetric workpiece was simulated in order to determine optimal tools kinematics and to avoid crack formation.     

Meßmethoden und technische Anwendungen der Bruchmechanik

Measuring methods and technical application of fracture mechanics. A method of measuring the plane-strain fracture toughness K_lc using compact-tension-specimens according to American (ASTM) and British (BISRA) standards is described. There exist conditions for the minimum thickness and minimum crack length necessary for the determination of valid K_lc-values. The K_lc-values decrease with decreasing temperature. Own results and pictures of the fracture surfaces of the tempering steel 30 Cr Ni Mo 8 are shown as examples. With low strength steels linear elastic fracture mechanics characterized by K_lc is normally not valid at room temperature. Therefore it is supplemented by the crack-opening-displacement concept (COD-concept) applicable up to macroscopic yielding. — After a survey of three failure categories for cylindrical pressure vessels with axial through the wall cracks and the controlling material properties two examples are given for the application of fracture mechanics to test pressure vessels containing longitudinal slits.     

Numerische und experimentelle Untersuchungen zum Matrizenpressen und Sintern von Aluminiumpulver

Formation of density gradients in green bodies during powder compaction and the resulting sintering distortion still poses a problem in the powder metal industry. Consequently, the design and optimization of powder metallurgical production processes is of paramount relevance to avoid these part defects in the green bodies. However, this technology is currently based to a large extent on expert knowledge. The numerical simulation based on the Finite Element Method (FEM), represents a cost and time‐saving alternative in comparison to the “trial and error” method. With the help of FE calculations, powder compaction processes can be optimized in terms of reducing the density gradients and the resulting sintering distortion already in their development and design phase.     

Untersuchungen zum Sorptions-, Desorptions- und Quellungsverhalten von Klebstoffen

Investigation of the Sorption, Desorption and Swelling Behaviour of Adhesive Substances Bonded metal joints, when in use, are subject to numerous effects which can alter or impair the mechanical structural properties of the adhesive. Amongst the most important of these effects is, apart from the mechanical, the hygrothermic demand. For this reason the sorption, desorption and swelling behaviour of adhesive bond line under hygrothermic strain is determined within the framework of this investigation. It was found out that the tests allowed differentiated statements to be made concerning the structural composition and the proporties of the adhesive. The investigation showed that the material behaviour and the development of damage around the edges and in the central area of the bonded metal joint differ under hygrothermic strains. The structural composition and the morphology have a superior effect on the ageing behaviour.     

Untersuchungen zum Einfluß der Probendicke auf das Verformungs- und Bruchverhalten bauteilähnlicher Großzugproben

Influence of specimen thickness on the deformation and fracture behaviour of wide plates The influence of specimen thickness on the deformation behaviour and the load bearing capacity has been investigated with large scale double-edge-notched-tension-specimens (DENT). The difference of the state of stress can be modelled by simplifications (plain strain, plain stress). Equations for the calculation of plastic limit loads taking into account the defect ratio a/W have been derived based on analytical, numerical and experimental investigations. Already existing equations may lead to unsafe prediction in special situations. The difference between plastic limit and maximum load is smaller for the thicker specimens due to higher toughness requirements. The toughness requirements have been quantified for the DENT-specimens using the J-integral analysis. The requirements mainly depend on the overall dimensions (W, B), the thickness ratio (B/W) and the defect ratio (a/W).     

Experimentelle und theoretische Untersuchungen zum Dämpfungsverhalten von Stahlbetonkonstruktionen

Zusammenfassung Zur Messung der D?mpfungseigenschaften des Werkstoffs Stahlbeton, dessen Materialeigenschaften besonders schwer zu erfassen sind, wurden Identifikationsverfahren herangezogen. Die Materialeigenschaften werden mit sog. Masing-Elementen modelliert, die aus Federn und Reibelementen bestehen, und somit auf nichtlineare Gesetze führen. Die Masing-Elemente wurden für die Rechnersimulation aufbereitet. Damit wird es m?glich, die D?mpfung von Stahlbeton genauer zu erfassen und für Vorausberechnungen zu benutzen. Schwingungsgef?hrdete Strukturen sind dann genauer zu berechnen.