Advanced Algorithms to Enhance Signal to Noise Ratio of Peel Ply at the Bondline of Out-of-Autoclave Composite Assemblies

Advanced algorithms were developed to improve the signal to noise ratio between constituents of similar acoustic impedance in bonded out-of-autoclave carbon fiber reinforced polymer assemblies. The assemblies consist of a precured resin infused out-of-autoclave 3D woven fabric preform bonded to a pre-cured out-of-autoclave prepreg fabric substrate. Conventional ultrasonic nondestructive testing techniques and analysis software cannot consistently achieve signal to noise ratios that meet quantifiable rejection thresholds of accurately sized peel ply inserts at the bonded interface To demonstrate the approach, ultrasonic pulse echo with full waveform capture was used to inspect a reference standard with peel ply inserts placed between the film adhesive and the 3D woven fabric preform. The ultrasonic signal was produced by a multi-element array transducer, utilizing a customary shoe and water bubbler. Waveform post-acquisition analysis with post processing software was used to analyze and enhance the signal response between the peel ply and the bondline resulting in the final algorithm. To verify the results, the signal to noise ratio of each insert was calculated for both the raw and processed data. As the measure of detectability, the method relies on principles of statistical measurement to provide an industry standard signal to noise response of3:1.

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