Publications

The Design for Tractable Analysis (DTA) framework was developed to address the analysis of complex systems and so-called “wicked problems.” DTA is distinctive because it treats analytic processes as key artifacts that can be created and improved through formal design processes. Systems (or enterprises) are analyzed as a whole, in conjunction with decomposing them into constituent elements for domain-specific analyses that are informed by the whole. After using the Systems Modeling Language (SysML) to frame the problem in the context of stakeholder needs, DTA harnesses the Design Structure Matrix (DSM) to structure the analysis of the system and address questions about the emergent properties of the system. The novel use of DSM to “design the analysis” makes DTA particularly suitable for addressing the interdependent nature of complex systems. The use of DTA is demonstrated by a case study of sensor grid placement decisions to secure assets at a fixed site. © 2009, IGI Global. All rights reserved.

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Sandia National Laboratories Airworthiness Assurance Nondestructive Inspection Validation Center (AANC) implemented two crack probability of detection (POD) experiments to compare in a quantitative manner the ability of Sonic Infrared (IR) Imaging and fluorescent penetrant inspection (FPI) to reliably detect cracks. Blind Sonic IR and FPI inspections were performed on titanium and Inconel® specimens having statistically relevant flaw profiles. Inspector hit/miss data was collected and POD curves for each technique were generated and compared. In addition, the crack lengths for a number of titanium and Inconel® reference standards were measured before and after repeated Sonic IR inspections to determine if crack growth occurred. © 2007 American Institute of Physics.

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The purposes of a POD study often go beyond the estimation of a single curve based on discontinuity size. The larger goals of a particular POD study will dictate the need for additional planning beyond just deciding on the number of discontinuities and discontinuity-free areas to be included in a test specimen set. The bigger concerns lead to implementation issues that need to be planned for and fully specified prior to the collection of data. These bigger issues have been discussed under the general program areas of experimental design, protocol development and logistic and dress rehearsal. Two different programs were also summarized. Each program led to very different experimental plans. However, the common element in these programs was the use of the POD study as the basic metric for establishing capabilities and important influencing factors. Both programs were developed under the guidelines noted and referenced. Results from these studies are discussed in more detail in Spencer (2007).

The purpose of this study was to investigate the impact of instructions on aircraft visual inspection performance and strategy. Forty-two inspectors from industry were asked to perform inspections of six areas of a Boeing 737. Six different instruction versions were developed for each inspection task, varying in the number and type of directed inspections. The amount of time spent inspecting, the number of calls made, and the number of the feedback calls detected all varied widely across the inspectors. However, inspectors who used instructions with a higher number of directed inspections referred to the instructions more often during and after the task, and found a higher percentage of a selected set of feedback cracks than inspectors using other instruction versions. This suggests that specific instructions can help overall inspection performance, not just performance on the defects specified. Further, instructions were shown to change the way an inspector approaches a task.

It has been recognized that nondestructive inspection (NDI) techniques and instruments that have proven themselves in the laboratory do not always perform as well under field conditions. In this paper the authors explore combinations of formal laboratory and field experimentation to characterize NDI processes as they may be implemented in field conditions. They also discuss appropriate modeling for probability of detection (POD) curves as applied to data gathered under field conditions. A case is made for expanding the more traditional two-parameter models to models using either three or four parameters. They use NDI data gathered from various airframe inspection programs to illustrate the points.

This report presents the results of an inspection around fastener holes in simulated lap splice specimens using a Nortec-30 Eddyscan inspection system. The inspector performing the tests had no prior knowledge of the extent or location of cracks in the specimens examined. The results of the inspection are presented in terms of various probability of detection curve models and are compared to various other eddy current inspections performed on the same set of test specimens. Results indicate that the system is capable, with high confidence, of detecting 60 to 70 mil cracks from under countersink fasteners.

Multiple sources of variation will often affect the stability of a manufacturing process. Items from different batches may vary because of variation both within a batch and among different batches. Potential sources of variation include within run, run-to-run and week-to-week differences in a manufacturing process. If multiple sources of variation are present, traditional control chart methods may not be appropriate. In this report we develop control charts for monitoring these sources of variation as well as the process average. An example of how to use the control charts is given, using Field 89 data from functional testing of the MC3854 neutron tube.