Zur charakterisierung von polymerfilmen und lichtleitfaserummantelungen aus additionsvernetzendem siliconkautschuk

The crosslinking behaviour of addition-crosslinking Wacker SilGel 600 silicone was investigated in the temperature range of 50 to 90°C with respect to its dependence on heating time. Measurements of the swelling of thin polymer films on special paper (Pecozet Z10) allow the observation of the swelling process which reaches the swelling equilibrium within a few minutes, the selection of a suitable swelling agent, and the rapid determination of the temperature dependence of the degree of swelling Q. Aside from Q, the ?solubility parameter”? of the polymer network, the rate constants, and the activation energy of the crosslinking process can be obtained. Measurements of the swelling combined with determination of Huggins' interaction parameter additionally provide the possibility of determining the density of crosslinking of the polymer films. On the basis of these investigations, a rapid method for characterizing the sheathing of optical fibres could be developed. The cylindrical polymer films detach from the glass core during swelling in toluene (25°C). After 5 min the degree of swelling of the sheathing can be measured.     

Meteorological advice as an aid to productivity

The increasing sophistication of construction processes has done much to make the building industry more independent of the severities of the weather. But bad weather still remains a considerable hazard to production programmes. In the German Democratic Republic, where the weather can be exceptionally severe, a system of meteorological advice has been introduced especially for the benefit of construction firms, and the authors discuss the way in which it operates and how the best advantage can be taken of such a service.     

Nickel ion release from orthodontic NiTi wires under simulation of realistic <Emphasis Type="Italic">in-situ</Emphasis> conditions

The increasing use of nickel containing devices in orthodontics and the growing prevalence of nickel allergy in the population significantly increases the interest in biocompatibility studies of these devices. The decisive factor determining the biocompatibility of orthodontic wires is their corrosion behaviour. Therefore seven nickel titanium levelling arches, one titanium molybdenum, a cobalt chromium and three stainless steel wires were analysed with respect to their corrosion behaviour under realistic conditions. Potentiostatic tests to determine rupture potentials in artificial saliva and static immersion tests in artificial saliva (AS) or lactic acid (LA), as well as immersion tests with mechanical, thermal and combined mechanical and thermal stresses were performed. Subsequently, the surfaces of the wires were investigated employing scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and the nickel release into the corrosion media of the specimens was measured with inductively coupled plasma mass spectrometry (ICP-MS). The results yield information not only about the relative corrosion tendency of the wires under in vitro conditions but also give a quantitative estimation about the nickel ion release of the orthodontic wires during in vivo treatment. Generally, the maximum release of nickel ions was two orders of magnitude below the daily dietary intake level. Mechanical and thermal loading increases nickel release in the immersion tests by a factor of 10 to 30. Two NiTi wires (Dentaurum Tensic, Forestadent Titanol Low Force) examined showed lower rupture potentials and a higher tendency towards corrosion in the immersion tests than the others due to their surface composition. However these differences are levelled off by long-term mechanical and thermal loading.     

Aus der rechtsprechung des bundesgerichtshofs

Ohne Zusammenfassung     

Mechanisms in fatigue strength improvement of thermomechanically manufactured automotive suspension springs

In a previous work, application of thermomechanical treatment (TMT) to suspension spring samples led to high increases in fatigue strength (up to 40 %). For the purpose of a better comprehension of these results, further investigations were carried out with major attention to the mechanical properties of quenched and tempered steel 50CrV4 and a Nb-microalloyed variant of this steel, respectively. First, the samples were ground prior to presetting, stress peening and subsequent dynamic testing. This was done to work out the influence of the surface state on the benefits of TMT. An extended program of materials testing was carried out with particular attention on the crack initiation and growth features of thermomechanically treated steel compared to conventional heat treatment (CHT). One of the results was that grinding of the spring surface causes further improvement of fatigue strength. On the other hand, the advantages of TMT compared to CHT are reduced as a result of surface grinding. The reason for this result is an overproportional increase in fatigue strength of CHT specimens due to grinding. An explanation imaginable for both the improvements caused by TMT and the reduction of these improvements after grinding could be the change in fracture mechanical properties. In particular TMT causes a significantly retarded crack initiation in the finite life range and an increased permissible stress intensity without crack formation.