Imagine finding a piece of material while out on a hike with family or friends in a local park. The material is unlike anything you have seen before and appears to be unique in the way it looks and feels. Your curiosity is triggered; what is this? Is it something of value that was lost by a previous hiker? Is it a small piece of a meteorite? Is it something a little more nefarious that requires alerting law enforcement? With a portable probe you are carrying in your pack, you touch the material and immediately a wealth of information becomes available: material type, composition, microstructure, properties, processing, history, and past use. Each value, including uncertainty bounds, provided by the portable instrument enables you to understand what you found. This approach to characterization was the basis for a line of questioning used by Robert Green of John Hopkins University (now retired) during oral qualifying exams for his doctoral students and illustrates the potential of using nondestructive testing-based (NDT) methods for quantitative characterization. When considering the above future scenario, it is important to ponder for a moment what is meant by quantitative characterization. As the topic of a special issue of Materials Evaluation, a number of readers may question if this is new and whether current practice already enables quantitative information to be obtained using NDT methods. Nondestructive testing has a rich history of use across multiple industries. It is commonly used to assure manufac-turing quality and is used extensively in the sustainment of deployed assets, including aerospace, power, oil and gas, and transportation. In addition, inspections testing is common practice and provides a key input in the safe management of assets across all industries. For the US Air Force, nondestructive inspection capability for safety-of-flight critical locations is one of approxi-mately seven inputs required for risk management (safety) of the structural integrity of aircraft managed by damage tolerance (Lindgren, 2007). With the broad-based use of NDT, a reasonable question to ask is why there is the emphasis on characterization in this issue. A direct answer is there is a growing need across multiple industries to move beyond detection, and better support both manufacturing quality assurance and sustainment with quantitative evalua-tion of the material state. Therefore, the scope of this article is to review some definitions of terminology as the same word(s) can often be used to define different things. For example, industrial users of NDT and academic researchers in the same field can infer different meanings from the same words. This will be followed by a summary of some of the main technical chal-lenges to realize quantitative characterization from the author’s perspective. This list may not be comprehen-sive and any feedback on these challenges is always welcomed. The final section of this introductory article will identify possible opportunities for research, devel-opment, and engineering to realize the desired capa-bility. Again, this list is not to be construed as comprehensive, but reflects the opinion of the author and areas that are identified as having significant impact on addressing the identified challenges.
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