The focused ultrasonic beam technique has been employed for imaging of bulk microstructure of fiber-reinforced composites, for measuring local elastic properties and mapping their distribution over the composite body. Ultrashort probe pulses (operation frequency of 50 MHz) provide resolution of 100 μm. The technique has been employed for nondestructive layer-by-layer imaging of microstructure of CFR laminate composites. Series of acoustic images in planes parallel to the specimen face (C-scans) or perpendicular to it (B-scans) enable to reconstruct of bulk microstructure of compound unidirectional CFR laminates. Different types microdefects, including failures in interply adhesion, buckling of single prepreg plies, internal defoliations and disbonds, have been observed. The method has been applied to measure local values of elastic wave velocities in laminates within area of 100 - 150 μm diameter.
Quality of acoustic images depends on kind and density of fiber packing and on depth of position of the imaging plane. Experience shows that specimens 2-10 mm thick are appropriate for visualization of their bulk microstructure and measuring local values of sonic velocities. The technique is promising for NDE of different composites, not only for carbon-based ones.