ON THE FEASIBILITY OF DETECTING PRE-CRACKING FATIGUE DAMAGE IN METAL-MATRIX COMPOSITES BY ULTRASONIC TECHNIQUES

The feasibility of using ultrasonic techniques to defect fatigue damag e in metal-matrix composites at an early stage has been investigated t heoretically. The lack of direct independent experimental evidence for such damage required damage mechanisms and levels to be postulated in a somewhat arbitrary fashion. Estimates have been made of the effect of matrix porosity, microcrack formation, particle debonding and dislo cation generation on ultrasonic velocity, attenuation and backscatteri ng. It would seem that velocity measurements provide the best opportun ity for detecting low levels of damage. Initial calculations suggest t hat surface wave velocity measurements and acoustoelastic constant mea surements may also prove useful.