System for In-situ Defect Detection in Composites During Cure

NASA's System for In-situ Defect (e.g., porosity, fiber waviness) Detection in Composites During Cure consists of an ultrasonic portable automated C-Scan system with an attached ultrasonic contact probe. This scanner is placed inside of an insulated vessel that protects the temperature-sensitive components of the scanner. A liquid nitrogen cooling systems keeps the interior of the vessel below 38°C. A motorized X-Y raster scanner is mounted inside an unsealed cooling container made of porous insulation boards with a cantilever scanning arm protruding out of the cooling container through a slot. The cooling container that houses the X-Y raster scanner is periodically cooled using a liquid nitrogen (LN2) delivery system. Flexible bellows in the slot opening of the box minimize heat transfer between the box and the external autoclave environment. The box and scanning arm are located on a precision cast tool plate. A thin layer of ultrasonic couplant is placed between the transducer and the tool plate. The composite parts are vacuum bagged on the other side of the tool plate and inspected. The scanning system inside of the vessel is connected to the controller outside of the autoclave. The system can provide A-scan, B-scan, and C-scan images of the composite panel at multiple times during the cure process. The in-situ system provides higher resolution data to find, characterize, and track defects during cure better than other cure monitoring techniques. In addition, this system also shows the through-thickness location of any composite manufacturing defects during cure with real-time localization and tracking. This has been demonstrated for both intentionally introduced porosity (i.e., trapped during layup) as well processing induced porosity (e.g., resulting from uneven pressure distribution on a part). The technology can be used as a non-destructive evaluation system when making composite parts in in an oven or an autoclave, including thermosets, thermoplastics, composite laminates, high-temperature resins, and ceramics. Innovators at the NASA Langley Research Center, in collaboration with Analytical Mechanics Associates, have developed an automated ultrasonic scanning system for in-situ cure monitoring and defect detection of composites in an autoclave or an oven. This non-destructive evaluation system is based on an ultrasonic contact scanner enclosed in an insulated vessel placed inside of the autoclave. The system actively scans for any defects that may form in composites during the cure process and tracks movement of defects originating during layup or cure. Typically, non-destructive evaluation of composites, by ultrasound or other means, is conducted either before or after the cure process, but many defects vanish and form during cure. NASA's in-situ cure monitoring system, by contrast, provides real-time monitoring of defect formation and movement during cure. This not only offers a better understanding of defect sources and sinks, but also the ability to more accurately validate process models for the prediction of cure process defects.