MEASUREMENTS OF GROUP WAVESPEEDS OBTAINED BY LASER GENERATION OF ELASTIC-WAVES IN COMPOSITE-MATERIALS

The present Note describes some measurements of elastic wavespeeds obt ained in several composite materials by using laser generation of ultr asound The three bulk modes are generally identified at the epicentre configuration. The quasi-longitudinal mode is tracked by using a corre lation algorithm, during scanning experiments along principal acoustic axes, up to a large observation angle (typically in the range of 80-d egrees). The two transverse modes are more difficult, for several reas ons, to obtain with precision. The wavespeeds obtained by using the la ser technique are compared with traditional ultrasonic data for two di fferent composite materials. The agreement is generally satisfactory, tending to indicate the fact that the characterization of elastic prop erties of composite materials by laser generation of ultrasound is pos sible along arbitrary directions.