Plane longitudinal waves of small amplitude in a nonlinear viscoelastic material

Summary A study of small amplitude, plane, longitudinal waves in a nonlinear, viscoelastic material is presented. The mechanical behavior of the material is described by the use of state variables and the associated differential equations. In particular, we examine the response of a half-space of viscoelastic material which is subjected to a small constant velocityu(0,t)=, 1 at the surface of the halfspace for timet>0. This behavior is analyzed by the use of matched asymptotic expansions in the plane of characteristic coordinates. With the use of these matched asymptotic expansions, the nature of the waves in the near and far fields are discussed. A particular advantage of this method is that wave velocities in the far field can be corrected to second and higher orders. We show that the far field wave is a steady state wave to first order, but that its higher order behavior is transient.

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Ebene Longitudinalwellen kleiner Amplitude in einem nichtlinearen viskoelastischen Werkstoff

Zusammenfassung Eine Untersuchung der im Titel genannten Wellen wird angegeben. Das mechanische Verhalten des Werkstoffes wird unter Verwendung innerer Zustandsvariablen durch Differentialgleichungen beschrieben. Insbesondere untersucht wird das Verhalten eines Halbraumes aus viskoelastischem Material, dessen Oberfläche sich für Zeitent>0 mit einer kleinen konstanten Geschwindigkeitu(0,t)=, 1, bewegt. Das Verhalten wird untersucht unter Verwendung von asymptotischen Entwicklungen in der Ebene der charakteristischen Koordinaten. Dadurch wird die Art der Wellen im Nah- und Fernfeld erläutert. Eine besonderer Vorteil dieser Methode ist die Möglichkeit von Korrekturen zweiter und höherer Ordnung beim Fernfeld. Gezeigt wird, daß die Fernfeldwelle erster Ordnung stationär ist, nicht jedoch die höherer Ordnung.

     

Widely tunable narrow linewidth erbium doped fibre ring laser

An erbium doped fibre ring laser enabling singlemode operation over a continuous wavelength tuning range of 44 nm (1528 nm-1572 nm) with laser linewidths of less than 10 kHz is reported.<>     

Oxidation effects during laser cladding of aluminium with SiC/Al powders

Aluminium substrates were covered with a layer of an Al-SiC powder mixture. The surface was scanned with a laser beam during which the surface was melted. The top layer of the laser tracks contained oxide plates apart from some large SiC particles. In the bottom layer a cellular network was found with aluminium cells and silicon-rich cell walls.     

Knowledge-Based configuration of image segmentation processes

The solution of an image interpretation problem using digital image analysis methods requires the configuration of an image analysis system to meet the requirements of this specific task the specific data material. This process includes the selection of the appropriate sequence of operators and the adaptation of the free parameters. A system has been developed and is described, which performs this configuration process automatically on the basis of a user-specified task definition, and general knowledge of an image analysis expert. The latter knowledge has been assessed, stored, and used by employing different paradigms of knowledge representation similar to expert systems.     

Korrosionsinspektion im Flugzeugbau

Corrosion inspection in aircraft construction The inspections required on an aircraft during its operational phase are determined largely by the materials and constructions used. Practical experience has shown that corrosion can generally not be prevented on metallic aircraft structures, even if the surface protection systems have been chosen with great care. Constructions and materials used on aircraft and the result types of corrosion are described and the inspection concept is explained on the basis of this. Finally, typical inspection tasks are presented and the measurement results obtained with different NDT methods are presented and discussed.     

Thermogravimetrische Methode zur Untersuchung der Gleichgewichte Festkörper/Gas und Schmelze/Gas in korrosionschemisch wichtigen Sulfatsystemen

Thermogravimetric method for investigating the solid/gas and melt/gas equilibria in sulphate systems of corrosion-chemical importance The authors describe a micro-thermogravimetric method which permits the determination of the phase zones of sulphate systems as a function of temperature and of the SO₃-partial pressure. At the Me₂SO₄ SO₃ (Me = Na, K) system, the existence limits of the bi-variant melt and the mono-variant equilibria Me₂SO₄(solid)-melt and Me₂SO₄(solid)-Me₂S₂O₇(solid) are determined. Water vapour is dissolved in the melt phases investigated because the existence limits of the latter are modified by the vapour.     

The alimentary ingestion, analysis and biological significance of thiocyanate

A survey is given of the alimentary ingestion, metabolization and elimination as well as of the biological significance of thiocyanate (SCN-) in the mammalian organism. SCN- is an important nutritional factor since it influences essential bodily functions, e.g. immune response. Its analytical determination in vegetable and animal foodstuffs may be considerably affected by the reversible binding of SCN- to protein molecules and by natural products, e.g. amino acids and cyanide, from glycosidic precursors, which interfere with the reaction with bromine. This will be combining paper chromatography with gas chromatography. Except Brassica species which are relatively high in SCN- in glycosidic combination, vegetable foodstuffs contain nearly 0.1-1.3 mg SCN-/kg fresh material; animal foodstuffs, e.g. beef, contains 0.5-0.7 mg SCN-/kg. Balances calculations have shown that in non-smokers the average alimentary ingestion ranges from 1.8 to 5.2 mg SCN-/d.     

Bücherschau

Ohne Zusammenfassung     

Development of stresses in concrete structures with alkali-silica reactions

The present paper, deals with the development in time of stresses and strains in concrete structures suffering from alkali-silica reaction (ASR). The properties of the concrete are combined with the dimensions of the structure in which the concrete is placed. A geometrical model that permits the determination of stresses and strains is established for concrete. This model is combined with a computer program which is able to calculate the moisture flow into a given structure, and this moisture flow is connected with the development of ASR. The resulting calculation takes into account the dimensions of the structure, the concrete quality, the content of reactive silica and the climate around the structure, as it predicts the strains and stresses developed in concrete structures suffering from ASR. It is shown that, cracks are developed locally around the reacting particles, and it is proposed that most of the cracks that become visible on the surface of a structure originate from the period of construction.

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Resume Cet article traite de la croissance des contraintes et des déformations dansle béton de structure où se développent des réactions silico-alcalines (ASR). Les propriétés du béton sont associées aux dimensions de la construction dans laquelle la béton est mis en place. On a établi un modèle géométrique du béton permettant de déterminer les contraintes et les déformations, combiné avec un programme informatique qui, pour une construction donnée, peut calculer la migration d’eau qui est liée au développement de réactions silico-alcalines. L’ensemble des calculs pour la prédiction, des contraintes et déformations dans les constructions en béton où se développent, ces réactions prend en compte la dimension de la structure, la qualité du béton, la teneur en silice réactive et les conditions ambiantes. On montre que des fissures se produisent localement autour des particules réactives, et on présume que la plupart de celles qui aparaissent à la surface d’une structure remontent à l’époque de la construction.