Rohrfertigung für den Reparaturbereich

Pipe fabrication for the repair sector. The paper discusses the changes in pipe fabrication that have taken place in recent years. These enable repair work to be carried out more efficiently, without thereby impairing the flexibility and speed of operation that are essential to maintenance work. A prerequisite for this is that work on the pipes be transferred to workshops. Only here is it possible for manual operations, such as manual welding, to be reduced to a minimum and be replaced by mechanized or semi-mechanized welding methods. The use of modern machines for bending the pipes is more economic than the welding in of pipe bends. Necking out of the pipes by mechanical means or the use of mechanically pre-fabricated connections permit optimum preparation of the weld seam for branch fittings. Any additional work on the pipes, where this is necessary, is carried out at workplaces specially designed for the purpose.     

Einfluß von Wasserdampf im Sintergas auf das Verhalten von Metallpulvern mit unter Sinterbedingungen reduzierbaren Oxydschichten

An aus Elektrolyteisen-, Karbonylnickel- und Kupferpulver hergestellten Preßkörpern Untersuchung ihres Sinterverhaltens unter Wasserstoffgas mit Zusätzen von 0,1 und 10 Vol.-% Wasserdampf bei Sintertemperaturen von 870 bis 1200 °C und Sinterdauern von 0 bis 8 h. Messung von Dichte, 0,2-Orenze, Zugfestigkeit und Bruchdehnung der Proben in Abhängigkeit vom Wasserdampfgehalt im Sintergas und dementsprechende thermochemische Deutung der Versuchsergebnisse.     

Analysis of the temperature dependence of the fracture stress of sharp notched bending specimens of a structural steel with respect to intermediate transitions

The flow and fracture stresses, σ_y^g and σ_f^g (δ = crack tip displacement), of sharply notched bending specimens of a structural steel U St 37-1 are measured in the temperature range from full scale to small scale yielding. The best adaption of the experimental results for σ_f^g is obtained by a curve which exhibits an intermediate transition, i.e. which follows in a temperature range between an upper, T_tM¹ and a lower, T_tl¹, transition temperature to the curve σ_y^g(T) for the flow stress with a constant δ = δ₁. This transition corresponds to that of the slip to the twin nucleated fracture. Two analyses [3,5] according to the local fracture stress, σ_f^*, concept show that the amount and the temperature dependence of σ_f^* are somewhat different for both methods, but that both exhibit an increase of σ_f^* in the transition range. It is concluded that each transition in the nucleation mode of the fracture is connected with such a transition in the fracture stress. It may, however, become indistinct or even be covered by the scatter of the experimental points.     

Electrical conductivity in thin and very thin platinum films

The two-photon transition probability between electron energy bands in a semiconductor film is discussed, taking quantum size effects into account. An expression for the absorption rate of one of the two photons is given as a function of the frequency corresponding to all the types of critical points. The anisotropy of non-cubic materials is taken into account. The numerical calculation of the absorption coefficient is performed for the case of ZnS near the extremal point.     

Crack formation,crack healing and porosity redistribution during irradiation of UO2 and (U,Pu) O2

The irradiation-induced void volume redistribution in the fuel was analysed. The radial crack volume and porosity distributions, the central radii and the radial gap width were measured after irradiation and compared with the calculated values. Short-time (He-loop experiments in the FR2 reactor), medium-time (bundle irradiation in the BR2 reactor) and long-time (trefoil-irradiation in the DFR reactor) irradiated fuel pins were examined. The model of pore migration, used in the computer code SATURN-la, is based on the evaporation-condensation mechanism. Measured swelling rates were extrapolated to higher temperatures and used. The crack volume distribution was calculated on the basis of a multifractured fuel model. One can conclude from the comparison between calculated and measured void volume distributions that several mechanisms redistribute void volume. These are crack formation, crack healing, migration of sinter pores and fission gas bubbles, gas swelling, evaporation-condensation phenomena in the region of the central void, irradiation-induced sintering and increase in diameter of the cladding.     

Electrochemical curing of epoxy resins

An electrochemical method has been developed for bonding electrically-conductive adherends. The procedure is based on the electrochemical generation of a curing agent from an otherwise chemically-unreactive precursor mixed with an epoxy resin sandwiched between the bonding members. The one-part epoxy resin is storage stable and cured rapidly on passage of current.