Non-Destructive Evaluation of Additive Manufactured Parts by Resonance Spectroscopy

The Phase II research will develop and demonstrate non-destructive techniques/tools for detecting internal voids and defects in additive manufactured (AM) components that can cause premature in-service failures and reduced fatigue life of specific components of interest to MDA. Candidate components under consideration include liquid-cooled rocket nose tips and nozzles, reinforcement structures, and critical items that could be printed in the field where they are put into use. Laser Acoustic Resonance Spectroscopy (LARS) is based on the idea that every object has a unique vibrational spectrum that is sensitive to the material properties of the object, including defects, flaws, material properties, residual stress, and dimensions. Analysis of this information-rich signal measured with a laser Doppler vibrometer can reveal changes in a part, such as defects and any other flaws that modify the vibrational signature and cause it to differ from a known reference signature of a flight-ready component. The research will build on and apply the fundamental knowledge and methods developed in Phase I, which were demonstrated through theory, experiment, and testing-to-failure to be valid for relatively simple components that contained programmed printed defects. These techniques were also shown to be applicable to more complex and MDA-relevant components through computer modeling. The Phase II work will work with a selection of AM components that are planned for actual use in aerospace application by MDA and its prime contractors. In Phase II, we will 1) demonstrate theoretically and experimentally that defects of interest in relevant AM parts are detectable with LARS, 2) develop a practical method for determining useful LARS reference spectra for individual AM components, 3) validate LARS predictions through mechanical tests to failure, 4) develop additional data extraction and interpretation techniques to better characterize defects, and 5) develop a Phase II prototype NDE instrument for use by MDA or one of its prime contractors. We will print AM the parts that include defects that are anticipated to cause problems in the partÆs function. Printing multiple parts in a single run is cost-effective and allows testing for more than one type of defect, provides statistics, and allows comparisons to improve the reliability of results. All selected test components will be analyzed with Finite Element Analysis (FEA) to provide reference spectra and to predict the effect of defects on the LARS signature. FEA will also be employed to determine the detectability of defects by the LARS-based NDE instrument. All printed parts will be fully characterized with LARS measurements, which will be correlated with FEA predictions and mechanical test results to demonstrate the capability of LARS to detect defects that can cause failure for complex and relevant parts. This research will lead to the design and construction of a prototype NDE instrument. Approved for Public Release | 22-MDA-11102 (22 Mar 22)