In the polymer composites industry, cure cycles are typically developed from trial-and-error or a more effective processing science approach to reduce the final porosity level in the composite laminate. Using a guided wave-based in-process cure monitoring technique for carbon fiber reinforced polymer (CFRP) composites, high-temperature piezoelectric transducers were utilized to interrogate a 24-ply unidirectional composite panel fabricated from Hexcel IM7/8552 prepreg during cure. It was shown that the amplitude of the guided wave increased sharply around vitrification, and the time of arrival (TOA) curve possessed an inverse relationship with degree of cure.

The automated guided wave system for in-process cure monitoring. (NASA)

A key cure transition point (vitrification) was identified and the degree of cure was monitored using metrics such as amplitude and TOA of guided waves. Using the technique to perform in-process cure monitoring in an autoclave, defect detection during cure, and a closed-loop process control to maximize composite part quality and consistency enables a significant improvement in nondestructive evaluation, which could lead to fabrication process improvements.

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