Effect of the fiber orientation on the transient damping in metal matrix composites

Mechanical spectroscopy has been used in order to investigate thermal stress relaxation in metal matrix composites. Mg- and Al-based composites reinforced with SiC long fibers have been processed by a gas-pressure infiltration technique. Fiber orientations either parallel or perpendicular to the composite axis have been obtained. Specimens have undergone thermal cycling between 150 and 450 K with different temperature rate Ṫ and excitation frequency ω. A model where thermal stresses are relaxed by dislocation motion controlled by a solid friction mechanism has been used to interpret the experimental results. The model is in good agreement with experimental data and two fitting parameters can be calculated. The first parameter is sensitive to the mobile dislocation density during thermal cycling. The second one is sensitive to the interface strength.