Frequency Response Modeling of Additive Friction Stir Deposition Parts with Print Defects

A change in a part's response to vibrations can be measured and utilized as a non-destructive testing method to detect deviations in the part's materials or geometry through processes such as laser acoustic resonance spectroscopy. This work focuses on leveraging vibration resonance to detect flaws in prints produced through additive friction stir deposition that arise through environmental contamination. More specifically, the use case considered is the printing of AA7075 in an iron oxide rich environment, where iron oxide dust or powder could accidentally be stirred into the printed material creating a print flaw. The modeling of printed parts contaminated with iron oxide to predict their natural frequencies is examined. Two different finite element models are discussed, which were created to represent contamination flaws with and without voids. The first model considers the case where a part is void-free. In this case, the model assumes a solid, homogeneous material condition in the stir region. The second model considers the case where voids are present in the part. This model leverages x-ray computed tomography data to build a representative mesh. These models show that with a well-understood part and corresponding flaw, it is possible to predict the natural frequencies of a flawed part. By leveraging the part vibration measurements and model predictions of known defects, it may be possible to gain insights into and characterize unknown print flaws.