Study of thermal stress relaxation in metal matrix composites using mechanical spectroscopy

Mechanical spectroscopy has been performed in magnesium matrix composites by means of an inverted forced torsion pendulum in order to study thermal stress relaxation occurring at the interface of such materials. It is well known that, because of the difference of thermal expansion between matrix and reinforcements, the thermal stresses can be built up at the interface when temperature changes. Composites were submitted to the thermal cycling in the range of 100–400 K and the mechanical loss was measured as a function of temperature for different temperature rates, Ṫ and different excitation circular frequencies, ω. Composites with different reinforcement geometries have been investigated in order to determine the influence of reinforcement orientation in the matrix on the thermal stress relaxation. The main factor influencing the thermal stress relaxation is the coupling between these stresses and the applied stress.