Abstract
This research presents a new technique using pulse echo ultrasound for sizing foreign objects within carbon fiber laminates. Carbon fiber laminates are becoming increasingly popular in a wide variety of industries for their desirable properties. It is not uncommon for manufacturing defects to occur within a carbon fiber laminates, causing waste, either in the discarding of failed parts or the overdesign of the initial part to account for these anticipated and undetected errors. One such manufacturing defect is the occurrence of a foreign object within the laminate. This defect will lead to a localized weakness within the laminate including, but not limited to, stress risers, delamination, and catastrophic failure. This paper presents a method to analyze high-resolution c-scan full waveform captured data to automatically capture the geometry of the foreign object with minimal user inputs without a-priori knowledge of the shape of the defect. This paper analyzes twelve samples, each a twelve-lamina carbon fiber laminate. Foreign objects are made from polytetrafluoroethylene (PTFE) measuring 0.05 mm (0.002 in.) thick and ranging in diameter from 12.7 mm (0.5 in) to 1.588 mm (0.0625 in), are placed within the laminates during fabrication at varying depths. The samples are analyzed with a custom high-resolution c-scan system and smoothing, and edge detection methods are applied to the collected c-scan data. Results are presented on the sizing of the foreign objects with an average error of 6% of the true area, and an average absolute difference in the estimation of the diameter of 0.1 mm (0.004 in), an improvement over recently presented ultrasonic methods by a factor of three.
Highlights
Published: 28 May 2021Carbon fiber composites are highly desirable due to their high strength to weight ratio and their anisotropy, which allows for parts to be designed with a directionally biased strength
Poudel et al [10] compare the abilities of through-transmission acoustography with through-transmission ultrasound and infrared thermography to detect inclusions within a carbon fiber laminate
The research described in this present paper uses a custom ultrasonic c-scan immersion system to inspect carbon fiber laminates for the identification and quantification of foreign object defects from the manufacturing process
Summary
Carbon fiber composites are highly desirable due to their high strength to weight ratio and their anisotropy, which allows for parts to be designed with a directionally biased strength. Poudel et al [10] compare the abilities of through-transmission acoustography with through-transmission ultrasound and infrared thermography to detect inclusions within a carbon fiber laminate They fabricated three panels with Teflon inserts of differing shapes and sizes, and placed at different thicknesses throughout the part. They prefer the better axial resolution that is promised by the 10 MHz phased array elements and address some of the challenges that are inherit in scanning a carbon fiber laminate with higher frequency transducers They present the results of their algorithm on a twelve-lamina unidirectional carbon fiber panel made in an autoclave with 5 different types of inclusions; Teflon, paper, release tape bag tape, and peel ply; placed between the 8th and 9th lamina and all 6 mm × 6 mm squares. The research described in this present paper uses a custom ultrasonic c-scan immersion system to inspect carbon fiber laminates for the identification and quantification of foreign object defects from the manufacturing process. Future research is planned to automate the analysis technique presented, as well as study new types of manufactured defects including irregularly shaped defects
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