Günter Gottstein

On the correlation of microstructure and electromagnetic properties of heavily cold worked Cu-20 wt% Nb wires

Abstract Fibre or ribbon reinforcedin situ metal matrix composites (MMCs) consisting of Cu and 20 wt% Nb were produced by large strain wire drawing. The microstructure of the composites was investigated by means of optical and electron microscopy. The normal and superconducting properties of the MMC wires in the presence of external magnetic fields were examined and compared to the electromagnetic properties of pure Cu wires. The findings are discussed on the basis of the microstructural changes during deformation. The current results substantiate that the amount of internal boundaries and the filament spacing have considerable influence on the normal and superconducting properties of Cu-20% Nb.

Calculation of stress—strain curves by using 2 dimensional dislocation dynamics

Abstract A method is presented to derive stress-strain curves by using 2 dimensional dislocation dynamics. The simulation treats plastic deformation of single grains, in which one or more slip systems are active. The involved dislocations are regarded as infinite straight line defects which are embedded in an otherwise isotropic linear elastic medium. As the model is two dimensional only edge dislocations are incorporated. The calculation of the local stressfield considers the long range elastic stress contribution of all dislocations within the grain, of the externally imposed stressfields and of the short range stressfield imposed by large angle grain boundaries. Due to the net local value of the stressfield the dislocations may either glide or climb. Dislocation multiplication, annihilation and reactions are taken into account. Thermal activation is considered. The simulations allow to compute the evolution of the dislocation distribution, the stressfield and the plastic strain during a simulated deformation experiment. The latter quantities are used for the calculation of stress-strain curves.

Integral modeling of metallic materials

Abstract One of the most dynamic domains of materials science is the integral modeling and simulation of metallic materials. Integral approaches consist of the coupling of computer codes to bridge scale discrepancies among different microstructure levels. Two approaches deserve particular attention in this context, namely, simultaneous (synchronous, direct) integration methods, where interacting simulation levels are simultaneously considered in one computer experiment, and sequential (non-synchronous, indirect) integration methods, which consist of an appropriate transfer of parameters among calculations that are used sequentially. Another way to classify the recent developments in the field of integral modeling and simulation is the distinction between the methods which are discrete both at the macro- and at the micro-level and methods which are discrete at the macrolevel but statistical at the microlevel.