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81.
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83.
Hartmut Pawelski 《国际钢铁研究》1998,69(4-5):161-164
The friction measuring apparatus according to O. Pawelski, which is based on the strip drawing experiment, is used to determine friction coefficients in plastic shaping of metals. By implementing elastomer inlays into the drawing cheeks the same principle has been applied to the contact between metals and elastomeric media. The plastification of metal by the extremely shear-weak elastomer is possible, because it is completely constrained with metal, so that a sufficiently high hydrostatic pressure in the inlay is generated. Elementary theory in combination with FEM showed that the friction coefficient, calculated using only the global static equilibrium of forces, is in very good approximation with simply the mixture of the friction coefficient between metal strip and elastomer and the friction coefficient between metal strip and drawing cheek weighted with the corresponding contact areas. Drawing experiments with aluminium 99.5 or steel St 37 and polyurethane or soft rubber were carried out. The important influence of lubrication and roughness of the metal strip on the friction coefficient was investigated. 相似文献
84.
85.
Experimentelle Untersuchung des Kriech- und Wechseldehnverhaltens des austenitischen Stahles X 6 CrNi 18 11 (Werkstoffnummer 1.4948) bei Beanspruchung durch Kriechen und Ermüden. Auswertung der Ergebnisse unter Anwendung der linearen Schadensregel. Vergleich mit Auslegungskriterien nach dem ASME BPVC. 相似文献
86.
An accurate method for the quantitative determination of hydroperoxy and hydroxy fatty acids in liver microsomes is presented
which involves the use of18O-labeled internal standards. The method is employed for the determination of hydroperoxides in rat liver microsomes after
aerobic incubation with Fe2+/ADP and in microsomes from animals exposed to 75 mg tetrachloromethane/kg body weight. The amounts found after artificial
microsomal “lipid peroxidation” are almost two orders of magnitude larger than those in microsomes from tetrachloromethaneexposed
animals. 相似文献
87.
Hartmut Widdecke 《Polymer International》1984,16(4):188-192
The present state of polymer-supported acid catalysis is considered. Models describing the catalytic action of gel-like and macroporous resin catalysts are presented. By chemical modification of poly (styrene-co-divinylbenzene) matrices, e.g. different ways of sulphonation, nitration, chlorination, fluorination and sulphoalkylation, the activity/selectivity and thermal stability of sulphonic acid resin catalysts can be improved. The synthesis of polymer-supported Lewis acids is described. By comparison to AlCl3 higher catalytic activities are obtained with the use of AlBr3. 相似文献
88.
Electron paramagnetic studies showed that Ti3+ and Fe2+ occur in mullites taken from a refractory material which was fused-cast under a reducing atmosphere. Exposure of the mullite samples to temperatures >1600°C caused oxidation of Ti3+ and Fe2+ to Ti4+ and Fe3+ , respectively. 相似文献
89.
In six different ordinary vegetables, namely kohlrabi, Chinese cabbage, chard, leek, spinach and Jerusalem artichoke, zinc was mainly found as low molecular weight species. In the present study, these important zinc compounds are further investigated. The determinations of the metal are performed by ET-AAS. The zinc complexes of all vegetables are anionic at pH 8.0 and show similar elution behaviour in gel permeation and anion exchange chromatography. Consequently, a great resemblance in structure between the low molecular weight zinc species from the different vegetables can be supposed. Exemplary, the zinc complexes of kohlrabi and Chinese cabbage are further examined. In more purified samples of these vegetables compared to zinc neither stoichiometric amounts of free protein amino acids nor nicotianamine, free malic acid, citric acid or phytic acid have been detected. Mainly glutamic acid is found in molar excess to zinc after acid hydrolysis in both cases. The cysteine contents of both zinc-binding fractions are very low. Conclusively, the wellknown γ-glutamylcysteinyl-glycines (phytochelatines) can not be responsible for the bonding of zinc in both ordinary vegetables. We suppose that zinc in kohlrabi and Chinese cabbage is bound to a glutamic acid derivative unknown as yet, possibly a malic acid ester. 相似文献
90.
Summary In the present study three different techniques have been employed to observe the lamellar texture of isotactic polypropylene (iPP) crystallized from the melt under the influence of shearing: (a) Transmission electron microscopy (TEM) of surface replicas of permanganically etched samples (b) TEM of thin sections of Ruthenium-oxide stained samples and (c) Scanning force microscopy (SFM) in contact mode of permanganically etched samples. The aim was to assess their relative merits in terms of practicability, resolution and type of information. 相似文献