Anisotropy Measurements and Indication of Ply Orientation in Composite Materials Using Holographic Mapping of Large Amplitude Acoustic Waves

Summary

Examination of graphite reinforced polymer matrix composite materials was performed using high speed, pulsed holographic interferometry. Holographic recordings of one face of a composite sheet were made before and immediately following mechanical excitation of the opposite side. Excitation was provided through a length of 6mm diameter aluminum rod affixed at one end to the back surface of the specimen. A pulsed laser beam was focused at the other end of the rod, launching an acoustic wave toward the specimen.

Surface displacements from the acoustic plate waves traveling along the sheet result in interference fringes superimposed on the holographic reconstruction of the specimen image. Thus variations in wavefront velocity are directly observable in the holographic fringe patterns. From the results of these experiments the effects of mechanical anisotropy of the composite material are clearly visible providing a positive indication of ply orientation.