ULTRASONIC C-SCAN STANDARDIZATION FOR FIBER-REINFORCED POLYMER COMPOSITES-MINIMIZING THE UNCERTAINTIES IN ATTENUATION MEASUREMENTS

The need for an internationally-accepted standard addressing C-scannin g of composite materials has resulted in a DTI-funded collaborative pr ogramme involving the National Physical Laboratory, the Defence Evalua tion and Research Agency, and many manufacturing and industrial partne rs, As a result a draft standard has been produced and is being evalua ted in a round-robin exercise. One of the main difficulties encountere d in drafting the standard was in isolating the various sources of sys tematic uncertainty in C-scan attenuation measurements. Three main sou rces were found: diffraction and refraction effects, peak-frequency do wnshift, and nonlinear propagation in water. Although it may be possib le to produce corrections for these effects, the principal purpose of the draft standard is to provide a measurement method which minimises them and to describe how to estimate the remaining uncertainties. This paper represents an experimental validation of the conclusions embodi ed in the draft standard, including the methods for reducing measureme nt uncertainties.