Augmented and Facilitated Nondestructive Inspection (NDI) for Large Area Assessments

TECHNOLOGY AREA(S): Materials OBJECTIVE: Develop new method(s) to augment and facilitate the NDI of upper wing skins that minimize inspector workload, especially after initial set-up, and accelerates inspection process to detect corrosion in wing skins that are attached to aircraft. DESCRIPTION: Pervasive hidden corrosion issues on upper wing surfaces of select larger US Air Force aircraft generates the need to nondestructively inspect large areas while the wing skin is in place. The areas of greatest interest include fastener rows and faying surfaces of the wing skins when there is a second layer underneath the skin, such as a stringer flange. The corrosion types of predominant interest are exfoliation and general thinning, though other corrosion types, such as intergranular, are also present. Current inspection capability is based on a using portable scanning systems that require a sequential process of scanning the areas of interest, typically with multiple set-ups and placements of the portable scanning system, followed by integration of the images from the scans, evaluation of the scans, and reporting of the inspection results. Current inspection time is approximately 400 square inches per hour. Current inspection criteria is commonly to detect 10% thickness loss of skin thickness values that range from 0.125 to 0.625 . The skin material is commonly aerospace aluminum alloys. The desired capability for a new inspection process is to decrease the current inspection time as much as possible, with desired metrics being by a reduction by a factor of 10 as a threshold and a factor of 20 as an objective. Innovative solutions are sought to enable accelerated scanning time, image integration, evaluation, and/or reporting, including parallelization these processes. Decreased human interaction with the inspection process by increased autonomy must consider both the variability of the structural areas of interest in terms of thickness, fastener location, and/or configuration of any structure underneath the wing skin that is attached to the skin. This includes addressing any possible variations in the detection capability due to irregular geometric features and changing in the boundary condition at the faying surfaces, e.g. intimate contact to enable coupling between the layers to no contact between the layers. Variations in fastener fit-up stresses need to be considered. In addition, these methods must include requisite safety measures to protect mechanics and not create additional safety hazards. Another consideration is that these methods should not induce damage to the aircraft. The threshold for corrosion detection is 10% of the total skin thickness loss for general thinning and exfoliation for the current typical wing skin thickness values which range from 0.125 to 0.625 . The objective for the detection is thickness loss of 5%. The approach should show a path to adapt it to other aircraft structure, such as fuselage skis and lap joints, where the thickness of the pristine skin ranges from 0.04 to 0.2 . In addition, the approach should show a path to detect other types of corrosion, such as intergranular, pitting, and fretting corrosion. PHASE I: Develop accelerated nondestructive inspection method to detect the corrosion types of interest that meets the performance specifications provided in the topic description. Show feasibility of the capability in a laboratory environment for representative corrosion and not for flat bottom holes or similar machined material loss with regular geometry features. PHASE II: Demonstrate accelerated NDI method to meet the performance specifications provided in the description in a representative operational environment, such as an Air Force Depot. Ensure demonstration includes safety parameters that need to be addressed when in the operational environment. Demonstrate sensitivity meets desired detection metrics for representative corrosion, not machined test samples. Illustrate potential to extend capability to fuselage structures and other corrosion types. PHASE III: Validate capability by a statistically significant testing process. Establish all design and testing criteria for implementation in an US Air Force Depot environment. Define all support infrastructure and training materials required for implementation of the new capability, including anticipated life cycle costs to sustain the inspection capability. REFERENCES: 1. Corrosion in the Aerospace Industry, Samuel Benavides, ed., CRC Press, Washington, DC 2009, ISBN: 978-1-4200-7965-4; Corrosion Detection Technologies, Sector Study Final Report, Prepared by BDM Federal, Inc., Prepared for: North American Technology and Industrial Base Organization, Available at: www.acq.osd.mil/mibp/natibo/docs/cdt_ss.pdf; 3. Review of Progress in Quantitative Nondestructive Evaluation, Proceedings Vol. 1 through 38, inclusive (1981 - 2017), D.O. Thompson and D.E. Chementi, eds., or L.J. Bond and D.E. Chementi, eds. Plenum Press or AIP