Effects of Particle Orientation in Silicon Carbide Particulate Reinforced Aluminum Matrix Composite Extrusions on Ultrasonic Velocity Measurement

In silicon carbide particulate reinforced aluminum matrix composite extrusions, the particles are nonspherical in general and are randomly oriented due to the extrusion process, resulting in sometimes significant anisotropic elastic stiffness. Since the ultrasonic velocity depends upon the elastic stiffness, ultrasonic velocity measurement is employed to characterize the anisotropic elastic stiffness of the composite extrusions. To establish the relationship between the materials' macroscopic response (ultrasonic velocity) and the microstructure, the measured statistical particle orientation distribution has been taken into account in theoretical modeling to predict the velocity of ultrasound that propagates in the composite extrusions, an attempt that has never been made before. The numerically calculated velocity agreed well with the measured velocity. Both numerical calculations and ultrasonic measurements have shown that the randomly oriented particles have led to a higher velocity (stiffness) in the extrusion plane and a lower velocity (stiffness) in the direction perpendicular to the plane, which are just the manifestation of the nonuniform particle orientation. It has also been shown that satisfactory theoretical modeling requires the consideration of the particle orientation distribution in the composite extrusions.