✍ Scribed by Peter Palček; Jakub Porubčan; Dalibor Blažek; Zuzanka Trojanová
No coin nor oath required. For personal study only.
The aim of this work is to state internal friction on stress amplitude dependence in an experimental aluminium alloy AW -2007. Dependence was examined on sample made of extruded material after annealing at the temperatures of 200 °C and 250 °C. Annealing at the increased temperature has significant effect on dislocation structure. All slip systems are activated in material and thermally activated dislocation transport also occurs. At the same time the annihilation of dislocations with opposite direction occurs. The Frank-Read sources are removed. After quenching at the room temperature the relatively immobile dislocation forest is present in the material that does not contribute to the internal friction and does not generate new dislocations. The amplitude dependence of internal friction can be described by Granato and Lücke model, which presumes the existence of weak attached barriers in slip plane of dislocation. This model involves average dislocation length, Young's elasticity modulus, interaction energy between dislocations and pinning points, magnitude of Burgers vector. The method of quality of resonant system was used to measure the internal damping. All experiments were carried out at the frequency range of 20 kHz at the room temperature.
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