SBIR-STTR Award

Additive manufacturing technology enables field production of spare parts, building non-traditional shapes and sizes, a reduction in the required number of individual parts, and expedited production, all offering great potential to the DOD. However, such parts can suffer from a combination of defect types and inherent problems, specific to AM that are difficult to detect in the finished part with conventional inspection methods. Such defects change the mechanical properties of the material and affect performance of a part. This SBIR Phase I proposal is to develop and demonstrate a method to evaluate printed parts and to enable certification of subsequent similar printed parts without employing current destructive, expensive, and time-consuming methods. Every object is a unique vibrational system that can be categorized by its vibrational spectrum. It is virtually impossible for two objects that are not identical to have the same vibrational spectrum; therefore, this spectrum provides a unique signature that matches and identifies specific components free of many types of defects. Vibrational properties of components, such as resonant modes, damping, and spectral frequency depend strongly upon the mechanical properties of the material, including its internal hardness, tensile strength, alloy/composite compositions, flaws, defects, and other internal material properties, and they respond differently to various forcing functions. In previous research we have demonstrated how such defects and printing errors affect the vibrational spectrum of AM parts, how the spectrum can be employed as a signature that is altered in a detectable manner, and how to measure and correlate such signatures with AM anomalies. The concept leads to a non- destructive testing method that can detect relevant defects in 3D printed metal parts and provide information for an assortment of representative part designs that can be correlated statistically with tests-to-failure. In this research we will print a large number of metal test coupons with and without known defects, measure their acoustical signatures with laser Doppler vibrometry, and determine if deviations from the predicted signature and parts known to be without defects can be correlated with the known defects and correlate these with tests to failure. The proposal includes a plan to develop and demonstrate methods of both predicting and measuring the effects of typical manufacturing defects on the acoustical signatures of AM parts This can lead to a relatively simple procedure to anticipate critical problems in AM parts without employing complex and expensive NDE or destructive testing methods. Approved for Public Release | 20-MDA-10643 (3 Dec 20)

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 part’s 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