Effect of thermal cycling on the damping behaviour of Mg matrix composites

This paper describes the influence of thermal cycling on the damping behaviour of a short fibre reinforced magnesium matrix composite. A Mg-26.5vol.% delta-Al2O3 short fibre composite was prepared by squeeze casting. The damping behaviour of the material is characterised by the logarithmic decrement after the thermal treatment Two types of thermal treatments were applied to the composite specimens prepared for damping experiments: a) Thermal cycling between room temperature and 300 degrees C was performed. Up to 100 cycles were realised. b) Ten thermal cycles between room temperature and an upper temperature were performed. The upper temperature was varied in the interval from 100 degrees C to 450 degrees C. The strain dependence of the logarithmic decrement can be divided in two regions. A region of strain amplitude independent damping at low strains is followed by a region with amplitude dependent damping at higher strains. The damping level in the strain amplitude independent region depends weakly on the number of cycles whereas the values of the logarithmic decrement in the strain amplitude dependent region increase very strongly with increasing strain amplitude and depend also very sensitively on the number of cycles. The observed experiment data can be explained if one considers that during thermal cycling new dislocations are created.