INTERNAL-FRICTION IN A MG MATRIX COMPOSITE AFTER THERMAL CYCLING BETWEEN ROOM-TEMPERATURE AND VARIOUS UPPER TEMPERATURES

This paper describes the influence of thermal cycling on the damping b ehaviour of a Mg - 26.0 vol.% Al2O3 composite. The composite was prepa red by squeeze casting. The logarithmic decrement as the characteristi cs of the process responsible for the damping behaviour was measured a fter ten thermal cycles between room temperature and an upper temperat ure. The upper temperature was varied in the interval from 100 to 450 degrees C. The strain dependence of the logarithmic decrement can be d ivided into two regions. A region of strain amplitude independent damp ing at low strains is followed by a region with amplitude dependent da mping at higher strains. The damping level in the strain amplitude ind ependent region depends weakly on the upper temperature of the cycle w hereas the values of the logarithmic decrement in the strain amplitude dependent region depend very sensitively on the upper temperature of the cycles. The observed experiment data can be explained considering creation of new dislocations during thermal cycling.