Measurement of crack induced damping of cast magnesium alloy AZ91

Strain dependent damping measurements of the widely used commercial cast magnesium alloy AZ91 (Mg + 9 wt.% Al + 1 wt.% Zn) were carried out under controlled fatigue bending loading. Damping was determined at room temperature as the logarithmic decrement of freely decaying vibrations of a bending beam clamped at one side. With increasing number of vibrations a maximum in the amplitude dependent damping curves for strains from 10(-5) Up to 10(-3) Was measured which can be attributed to the presence of cracks contributing to the dissipation of energy by displacement of crack surfaces. This maximum shifts to lower strains with rising number of loading cycles and is correlated with crack growth. A simple theological model on crack damping is discussed. (C) 2004 Elsevier B.V. All rights reserved.