ON THE ESTIMATION OF POROSITY IN COMPOSITES BY OBLIQUE ANGLE ILLUMINATION AND NORMAL RECEPTION.

Abstract

Computer simulation programs that substantiate the use of oblique ultrasonic illumination for the detection and estimation of porosity in composites are recalled. These initial computer programs were based on Born approximation, which is not truly applicable to composites. A major correction has now been incorporated that allows one to compensate for both the refraction effects and the energy loss due to mode conversion suffered by the illuminating field as it propagates from the transducer to the porosity sites. The new computer simulations assume that at low frequencies when the wavelength is much longer than the fiber diameter, each ply of a graphite-epoxy composite may be approximated by a homogeneous and anisotropic plate. Using these new computer simulations, the interesting conclusion is reached that the optimum way to detect porosity is by oblique illumination and normal reception.