In-situ diffraction investigations of superelastic NiTi shape memory alloys with neutron and synchrotron x-ray radiation were used to examine the evolution of the phase state of the material as a function of stress and strain, respectively. The results suggest that the transition from austenite to martensite is not complete even at the end of the superelastic plateau, and that significant load transfer to residual austenite takes place.Keywords: Neutron diffraction, x-ray diffraction, evolution of phase state, residual austenite Der Phasenanteil in superelastischen NiTi Formgedächtnislegie-rungen als Funktion von Spannung und Dehnung wurde mittels Neutronen-und Röntgen-Diffraktometrie in-situ untersucht. Die Ergebnisse deuten darauf hin, dass die Umwandlung von Austenit zu Martensit selbst am Ende des superelastischen Plateaus nicht vollständig abgeschlossen ist, und dass ein deutlicher Lasttransfer auf den residuellen Austenit stattfindet.
This paper presents an experimental and numerical study of residual stress states and deformation in fillet welded AA2024-T3 T-joints produced using a high-power fibre laser. Welded sheets with one and three stiffeners were prepared, respectively, to determine changes in microstructure, residual stress, distortion and micro-hardness. 3D sequentially coupled thermo-mechanical finite element models were developed to analyse welding temperature fields, and accurately simulate welding residual stresses and deformation. The simulated results were calibrated using the experimental database on weld pool geometry obtained from optical metallography and temperature fields measured using thermocouples. Residual stress measurements were made using neutron diffraction techniques and sheet distortions were measured using a coordinate measuring machine. The influence of various mechanical boundary conditions on angular and cambering sheet distortions was examined to optimise the restraint parameters. The application of element death and rebirth and dummy element techniques were studied and compared to incorporate the effect of filler metal deposition during welding. The level of residual microstrain was evaluated by diffraction peak width analysis, which indicated the maximal values in the weld metal. The effect of grain growth with respect to strength was of minor importance, whereas, considerable softening in the weld metal was observed
a b s t r a c tAs-cast stresses in the foot of the ingot corresponding to the transient start-up phase of the direct chill casting have been determined in aluminum alloy AA7050 rectangular ingots. This high strength alloy is usually cast with a wiper that is placed below the mold and ejects the falling water from its surface thus reducing the cooling intensity. The ingot being hotter, internal stresses are relaxed. The efficiency of a wiper has been evaluated using both neutron diffraction measurements on ingots cast with and without a wiper and a 3D numerical model simulating the stress generation during casting. The stress level is reduced by 33% when a wiper is used during casting and the stored elastic energy by 50%.
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