Automated Guided Wave System for In-process Cure Monitoring of CFRP Composite Laminates

A guided wave-based in-process cure monitoring technique for carbon fiber reinforced polymer (CFRP) composites was investigated at NASA Langley Research Center. A key cure transition point (vitrification) was identified and the degree of cure was monitored using metrics such as amplitude and time of arrival (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 non-destructive evaluation, which could lead to fabrication process improvements. In the polymer composites industry, cure cycles are typically developed from a trial and error or a more effective processing science approach to reduce the final porosity level in the composite laminate. Using an automated system, high-temperature piezoelectric transducers were utilized to interrogate a twenty-four 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 TOA curve possessed an inverse relationship with degree of cure.