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Thermographic Detection of Foreign Object Debris in Cured

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Description

 

Thermographic Detection of Foreign Object Debris in Cured and Uncured Composite Layups

 

Foreign Object Debris (FOD) is typically deposited during the composite layup process in the form of pieces of polymer or paper backing from prepreg or tape, or other stray debris (e.g. dirt, water, coins) that may become embedded between plies.  If detected before cure, it is often possible to remove FOD, reposition the fabric and continue the build.  However, inspection of an uncured layup is challenging to most conventional NDT techniques, as the part must not be contaminated by contact or immersion and the fabric is highly attenuative to ultrasound.  As a result, FOD inspection typically occurs post-cure, which presents a different set of challenges, particularly for ultrasonic detection of polymer or paper backing film.  Active thermography, which is widely used for NDT and characterization of cured composites, also offers a viable solution for FOD detection in uncured laminates, although some limitations must be considered.  Because of the clutter due to the fabric, the minimum detectable flaw size in an uncured composite is significantly larger than that of the cured part.  Also, penetration depth is reduced due to the low density of the material compared to the cured state.  In practice, uncured FOD detection is normally performed during debulk cycles, where fewer than 5 plies have been added.  The inspection may be performed in a stationary or scanning configuration, or from a distance using optical projection to stimulate the part.  Using the projection approach, quarter inch square polymer FOD embedded between layers 3 & 4 of an uncured carbon fiber layup can be detected at a 16 ft. working distance.

 

Authors: Steven M. Shepard and Maria Frendberg Beemer

 

Conference: CAMX 2016 – Anaheim

 

SKU/Code: TP16-0130

 

Pages: 8

 

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