Material characterization of composites by acoustic microscopy

In recent years, acoustic microscopy has been found to be very useful for characterizing engineering as well as biologic materials. With the present state of knowledge on acoustic microscopy, one can obtain the surface wave velocity of a homogeneous specimen or coating thickness of a coated material and produce images of near surface internal defects and inhomogeneities in a specimen. Applications of acoustic microscopy for obtaining material properties of anisotropic specimens and detecting material defects at a greater depth are meager because commercially available acoustic microscopes are insensitive to direction dependent material properties and they, in general, have poor penetration properties because they operate at high frequencies. Recently at the University of Arizona an unconventional low frequency (0.5-2.5 MHz) acoustic microscope has been fabricated where the microscope lens has been replaced by two ultrasonic transducers with cylindrical concave faces; one works as a transmitter and the other one works as a receiver. Using this arrangement it has been found that it is possible to detect internal damages in a material and identify material anisotropy in fiber reinforced composite plates. These capabilities of the microscope are demonstrated in this paper by presenting some experimental results. It can also generate AMS or V(z) curves of any specimen. V(z) curves of isotropic and orthotropic plates are analytically synthesized in this paper and experimental results are compared with analytically synthesized curves.