J A N U A R Y 2 0 2 0 • M A T E R I A L S E V A L U A T I O N 11 NDE Modeling & Simulation Welcome to the Technical Focus Issue on nondestructive evaluation (NDE) modeling and simulation. In recent years, the availability of inexpensive multicore and manycore computer hardware has enabled the increased use of—and reliance on—modeling and simulation across numerous scientific fields and engineering industries. In the context of this special issue, an NDE model is defined as a mathematical and/or physical representation of the NDE system (where the system includes the specimen under inspection and the inspection method/setup). NDE models are useful tools for investigating and assessing new or existing inspection approaches and are the basis for physics-based NDE simulation (the computa- tional implementation of the model). NDE modeling and simulation tools can be used for forward modeling, which entails direct modeling/simulation of an inspection setup to yield simulated NDE signals, or for model-based inversion, where one starts with measured signals and uses modeling/simulation to determine what parameters led to the measured signal. Combined with modern computer hardware, NDE modeling and simulation can enable a rapid, cost-effective route for optimizing inspection methods, investigating and developing new inspection and data analysis techniques, and assessing inspection limitations. NDE simulation can also provide an understanding of features in measured data and aid in the improvement of defect char- acterization methods. Further, validated modeling and simulation tools allow for a more thorough exploration of a problem space than is often feasible through experimental methods alone. In this realm, validation is key. While not the primary focus of the papers in this issue, whenever modeling and simulation tools are used, validation should come to mind, and deserves a mention in this letter. Whether you are using custom code or commercial off-the-shelf packages, the model should be validated for relevant scenarios prior to use in guiding real-world inspection decisions. This issue highlights the usefulness of NDE modeling and simulation. The feature paper describes a novel approach for using real-time simulation of NDE signals to train inspectors and assess the impact of human factors. The technical papers give a variety of examples of NDE modeling and simulation to inform NDE inspection and signal interpretation. The first paper by Sabbagh et al. describes the use of an eddy current modeling tool to study a specific probe design intended for the inspection of carbon fiber composites. The paper also details a case of model- based inversion for a composite specimen with cracking. The second paper from the Air Force Research Laboratory focuses on ultrasound modeling in composites in order to aid signal interpre- tation for cases with complex scattering from defects and to investigate approaches for improved delamination characterization. The paper from Holland et al. describes the use of 3D CAD models of inspection specimens to improve NDE modeling and data analysis. Specifically, the paper discusses the use of the 3D part geometry to aid model-based inversion for thermographic inspec- tion. The final paper from Shrestha et al. describes the use of custom ultrasound models to investi- gate the impact of microscale defects on ultrasonic inspection. With the increased use of advanced materials and complex structures (for example, tailored composites, additively manufactured parts, and so on) across numerous industries, it is expected that NDE can greatly benefit from an increased use of modeling and simulation. While several of the papers in this issue give examples for aerospace applications, the fundamental approaches on how to use modeling and simulation for improved inspection results are relevant across industries that require NDE (such as shipbuilding, automotive, power, and more). We hope that the papers provide insight into some of the benefits of NDE modeling and simulation. CARA A .C. LECKEY, PH.D. Technical Focus Issue Editor FOCUS letter NDE models are useful tools for investigating and assessing new or existing inspection approaches …