DELAMINATION SIZING IN COMPOSITE-MATERIALS USING A GAUSS-HERMITE BEAMMODEL

Non-destructive flaw sizing is an important part of the quality contro l of materials. In composites, problems such as delaminations can cons iderably reduce the effectiveness of such materials. Ultrasound is an effective method for inspection of composites. However, owing to the h igh degree of anisotropy in composites, ultrasonic inspection may prod uce false or distorted information about the delamination. In this stu dy, an iterative sizing technique has been developed that utilizes the Gauss-Hermite beam model and Auld's reciprocity relation. The beam mo del compensates for excessive beam spread in certain directions in com posites. In this sizing method, a line scan of a circular delamination is first obtained using the pulse-echo technique, and the resulting a mplitude versus position data for a chosen frequency are fed to a comp uter program. The computer program computes the size for a delaminatio n that best fits the line scan result of the experiment. The sizing te chnique was tested on a simulated delamination inside a unidirectional graphite/epoxy composite. The results showed significant improvement in sizing over the apparent size measurement based on the full width a t the half maximum amplitude of the experimental line scan.