Acoustic plane wave reflection from a composite laminate: normal incidence

In using ultrasonic non-destructive evaluation methods for composite laminates, some features appear which are essentially due to the heterogeneity of the material. In performing backscattering phenomena, one such feature is the seemingly random backscattered amplitude with change of position in a c -scan. This is attributed to the local heterogeneity due to slight changes in position, orientation and bonding characteristics of the fibers. In the case of incidence normal to the laminate, the average reflection coefficient, containing the backscattered waves from the fibers, is determined in terms of the fiber concentration and the properties of the fiber and matrix phases. The case of thin fibers, such as those of glass and carbon, in a polymeric matrix is also an assumption in the theory. Next, attention is paid to the actual random backscattered reflection coefficient, to estimate it at any location from experimental data at a given grid of locations of the lamina. The method used is called "kriging" in mining geostatistics.