Method and means to analyze thermographic data acquired during automated fiber placement
Inventors
JUAREZ, Peter D. • GREGORY, ELIZABETH D. • Cramer, K. Elliott
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-11373264-B2
Publication Date
2022-06-28
Expiration Date
2038-04-16
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Abstract
A method of detecting defects in a composite structure includes applying heat to a surface of a composite structure. Thermographic images or frames captured by a moving camera may be utilized to corm temporally aligned images that include temperature data (pixels) from a plurality of frames, wherein the pixels comprise data captured at a simple (uniform) time delay from the time at which heat was applied. The temporally aligned thermographic data for the surface region may include variations due to differences in thermal transients caused by defects in the composite structure. The variations in the thermographic data may be utilized to detect one or more defects in the composite structure.
Core Innovation
The invention relates to a method for detecting defects in composite structures fabricated by automated fiber placement (AFP) using thermographic data collected in situ or by thermal line scans. The method involves applying heat to a surface of the composite structure, capturing thermographic images with a camera moving together with the heat source relative to the structure, and forming temporally synchronized images by time shifting individual thermal image data to align the heating and cooling curves. These temporally aligned images enable identification of variations in thermal transients caused by defects such as insufficient adhesion, tow peel-up, misalignment, or thickness variations.
The problem addressed is the limitation of existing visual inspection and image processing methods focused primarily on tow tape geometry defects, which may not detect other types of flaws in composite structures. Known thermographic techniques like flash thermography apply heat simultaneously and capture static thermal responses, which are not directly applicable during AFP processes where the heat source and camera move relative to the part. The invention provides a process to temporally align thermographic data collected from moving heat sources and cameras to enable application of advanced thermal signal reconstruction and image processing algorithms, improving detection and localization of defects during composite fabrication.
Claims Coverage
The patent includes one independent claim defining a method of evaluating physical properties of a fiber reinforced composite structure using thermographic imaging data collected with moving heat sources and cameras and synchronized to the heating time.
Temporally synchronized thermographic imaging during AFP
A method comprising heating a composite structure portion with a moving heat source, capturing thermographic data with a moving thermal camera, and time shifting the image data from multiple captured frames to form at least one temporally synchronized image where all surface regions correspond to equal times after heating.
Utilization of thermal variation for defect detection
Using variations in the temporally synchronized thermographic image to identify defects in the composite structure without limiting to specific defect types.
The claims define a method centered on capturing thermographic data during AFP with moving heat sources and cameras, temporal alignment of thermal image data to create synchronized images reflecting equal heating times, and analyzing thermal variations in these images to detect defects in composite structures.
Stated Advantages
Provides in situ nondestructive evaluation for assessing part quality during AFP fabrication processes.
Allows use of known thermal signal reconstruction algorithms traditionally used for flash thermography by temporally aligning thermographic data collected during AFP.
Enables detection of a broader range of defects including tow adhesion issues, delamination, peel-up, misalignment, thickness variations, and foreign object debris.
Facilitates inspection at multiple fabrication stages including during layup, between ply layers, post debulking, and post cure.
Improves speed and objectivity of defect detection compared to visual inspection, allowing early repair and reducing risk of curing defective parts.
Documented Applications
In situ thermal nondestructive evaluation during automated fiber placement layup of composite structures to detect defects immediately after tow application.
Thermal line scan inspections using the AFP robot as a moving heat source and camera platform without layup, performed between ply layers or after curing to assess laminate quality.
Monitoring and tracking laminate quality evolution throughout composite structure fabrication by performing thermal scans at multiple stages including pre- and post-debulking and post multiple ply applications.
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