Fatigue behaviour and mechanical properties of peak-aged AA6063T6 with ultra-fine grain size, produced by equal channel angular extrusion, were evaluated with special emphasis on the microstructure before and after cyclic loading. The strength significantly increased with grain size reduction and is described by an exponential power-law constitutive relationship. A remarkable enhancement of fatigue life compared to commercial AA6063T6 with coarse grains was found in the high-cycle regime after the first two extrusions. Further extrusions eliminated this improvement. It is shown that the optimum fatigue performance correlates very well with the minimum tensile ductility. Electron backscatter diffraction revealed that the material behaviour can basically be attributed to the grain boundary characteristics. Low grain boundary misorientation angles yield the best fatigue performance in the ultrafine-grained microstructure.

In this work we analyze the strain hardening behaviour of a 42CrMo4 steel. The corresponding experimental data are obtained by a series of torsion tests on thin-walled tubes. In certain experiments the shear strains range up to 160 percent. When the strain path is reversed, the material exhibits a distinct Bauschinger effect. In order to describe this nonlinear effect, we generalize an existing model of finite strain viscoplasticity proposed by Shutov and Kreißig. The generalization consists of the introduction of additional internal variables and of a modification of corresponding evolution equations. A subset of the experimental data is used for the identification of the material parameters. The rest of the data serves the validation of the resulting set of material parameters.

X-ray diffraction line profiles of a ferritic-pearlitic steel at different stages of monotonic and cyclic incremental strain paths were recorded and peak broadening was regarded. Evaluation of integral peak widths shows, that the distortion of structure is strongly dependent on the deformation path. The results for peak broadening at different deformation states correlate with flow stress behaviour and can be explained with certain dislocation arrangements.

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Moderne Verfahren der Warmumformtechnik arbeiten bei sehr hohen Umformgeschwindigkeiten und großen, zumeist inkrementell aufgebrachten Verformungen. Zur Simulation solcher Umformvorgänge werden Werkstoffdaten benötigt, die unter den entsprechenden Umformparametern gewonnen wurden. Dies stellt erhebliche Anforderungen an die Versuchstechnik, da hohe Temperaturen, hohe Umformgeschwindigkeiten und hohe Umformgrade zugleich realisiert werden müssen. Im folgenden Beitrag wird eine solche angepasste Versuchstechnik dargestellt und die Ergebnisse in Form von Warmfließkurven eines unlegierten Stahls angegeben.