Polar scan technique for material characterization and identification of new operating regimes

The quest for more sophisticated methods imparts a significant challenge in the field of nondestructive testing (NDT) and material characterization. In this paper, we present and discuss experimental polar scans of typical carbon fibre reinforced composite materials recorded with shock wave transducers at frequencies ranging from 1 to 5 MHz. Besides the well-known measurements performed in transmission (T) and double through transmission (2T), we here introduce new investigations based on polar scans of both the backscattered and the double-double through transmission (4T) signals. Amplitude as well as the time of flight diffraction (TOFD) values of the peak amplitude are recorded as a function of the scanned solid angle. One the one hand, it is shown that sharper and more detailed polar scans, especially in TOFD recording, are obtained with the 4T method, which is advantageous for stable polar contour extraction and consequently for inferring the elasticity constants C-ij of the material under consideration. On the other hand, backscatter polar scans are shown to be highly dependent on the acoustic frequency f and relate to the surface state of both the top and the back side of the investigated sample. Results for several kinds of surface roughness, typical for composite materials, are investigated and discussed. As a conclusion of this study, we state that the backscatter polar scan presents a promising tool to map irregularities. Moreover, the TOFD recorded backscatter polar scans even suggest being useful in determining the depth of the irregularities.

ISBN:9789728826253

Jaar van publicatie:2012

BOF-keylabel:ja

IOF-keylabel:ja

Toegankelijkheid:Closed