APPLICATION OF SCANNING ACOUSTIC MICROSCOPY TO POLYMERIC MATERIALS

Scanning acoustic microscopy (SAM) is now a viable technique for the nondestructive evaluation of various materials. SAM is capable of distinguishing defects and discontinuities and/or the variations in elastic properties on a scale comparable to optical microscopy. The pulse mode utilizes a single narrow acoustic wave that permits surface and internal studies over a range of frequencies from 5 to 200 MHz with resolution down to approximately 20 mum. This technique was applied to image surface features of an opaque sheet-molding compound and to analyze flow patterns of chopped glass fibers. The pulse mode was also used to image the internal damage sustained from a high-speed projectile in oriented polypropylene and two carbon fiber-reinforced composites, with different matrices. Most importantly, the pulse mode of the acoustic microscope is a nondestructive method and the interior of samples that are entirely opaque can be readily studied with this unique instrument. The burst mode is composed of a group of acoustic waves and is capable of operating at higher frequencies than the pulse mode up to several gigahertz. This mode permits resolution down to the micrometer level and is especially useful for investigating surface and subsurface microstructural features. The burst mode was used to determine the distribution of chopped fibers in a PEEK matrix and carbon black particulates in an adhesive, the orientation of the mineral phase and density variations in a single osteon from a dog femur, and the orientation of collagen fibers in a sheep meniscus. Also, the sensitivity of the burst mode to surface features was used to examine the topographical features in a multilayer composite and a blend of poly (vinyl chloride) (PVC) with poly (ethylene terephthalate) (PET) particulates. (C) 1994 John Wiley & Sons, Inc.