Ultrasonic inspection of composite materials

Abstract

A method of ultrasonically inspecting the internal structure of a multi-ply composite material using ultrasonic transducers includes the steps of positioning an ultrasonic transmitter in acoustical contact with one surface of the material, directing a beam of acoustic energy into the material with the angle of incidence of the beam with respect to the surface being less than the second critical angle for the material but greater than normal to the surface, and receiving the reflected energy. In one embodiment, the transmitting and receiving transducers are positioned with their axis perpendicular to the orientation of the reinforcing fibers within the ply being inspected. In another embodiment, the transmitter and receiver are aligned at equal angles on either side of a line which is perpendicular to the orientation of the fibers. The receiver may be located on the same or the opposite side of the material from the transmitter. Internal cracks within each layer of the composite material can be detected along with information regarding their length and number. Further, by precessing the transducers, the orientation of the fibers within each ply will be revealed and this information may be used to confirm proper construction of the composite. Also, information regarding fiber overlap, wavyness and other characteristics of the composite with each ply can be ascertained.