Perspective on Nondestructive Evaluation of Additive Manufactured Components

Nondestructive evaluation (NDE) has been used for materials and component manufacturing, typically for process quality control or at multiple steps in manufacturing processes. In addition, NDE is used in sustainment of aircraft components to detect defects with a validated capability quantified by probability of detection. U.S. Air Force (USAF) Structures Bulletin EZ-SB-19-01, “Durability and Damage Tolerance Certification for Additive Manufacturing of Aircraft Structural Metallic Parts,” emphasizes the use of NDE in manufacturing by defining five factors to be evaluated to specify a new material, process, joining method, and/or structural concepts. The factors include stability, producibility, characterization of mechanical or physical properties, predictability of structural performance, and supportability. Included is Section 3.4, “Nondestructive Inspection Development, Validation, Verification, and Implementation,” which provides instructions to determine the validated capability for all damage types, orientations, and locations for specific regions of interest. Factors that affect NDE capability include where in the manufacturing process the assessment occurs, the nature of the raw feedstock, and the diagnostic information required to ensure the quality of the produced part. Once manufactured, additional factors must be considered, including the nature/orientation of defects, access, surface condition, geometric complexity, internal microstructural characteristics, and potential residual stresses. Representative defects within additive manufactured (AM) parts/materials include micro-cracks, voids, delaminations, lack of fusion, porosity, and inclusions. Systematic approaches are needed that leverage existing methods for other manufacturing processes. Methods to assist in determining which NDE method(s) have the highest potential of success are discussed. However, the intent is not to provide an overview of all NDE methods and their applicability to assessing AM components. In addition, methods to simplify or accelerate the assessment of the probability of detection of the defect of interest are addressed. These items should provide insight into how to ensure AM parts can be qualified and sustained for aerospace applications.