Laser Vibrometry for Aircraft Defect Detection

Cornerstone Research Group Inc. (CRG) proposes to demonstrate the use of Laser Doppler Vibrometry as an effective method for detecting corrosion faults curved surfaces and fasteners. Corrosion of airframe structures is a very prevalent issue for the Navy, leading to significant cost and aircraft down time, thus impacting mission readiness. The Navy has had to spend over $2 billion for the F/A-18C-G fleet alone from 2017-2020. Corrosion of aluminum alloy structures results in material pitting, thinning, and cracking, which weakens the structure performance. Corrosion occurring in fasteners can result in weakened connections between components, providing a weak point for failures. When left untreated and unrepaired, corrosive defects can lead to destructive part failures, putting the safety of the operator at risk. Unfortunately, it can be very difficult to detect corrosion of structures such as landing gear because these parts are coated in polymer coatings, paints, or composite skins, which obscure the surface for effective visual inspection. In order to get an evaluation of these parts, the paints and coatings are removed in a costly, labor intensive operation that leads to significant aircraft downtime. The Navy would find a lot of benefit from an easy-to-use, portable, non-destructive evaluation (NDE) technology that is able to perform early detection of corrosion without needing to remove the structural coatings. An ideal system would be able to detect faults very quickly, require minimal amount of training to utilize, and could detect defects as small as 0.005 inches on a curved surface. Laser Doppler vibrometry is a non-contact measurement technique used to quantify and analyze vibrations in various objects and structures. It involves the use of a laser beam to measure the displacement or velocity of a target's surface by detecting the Doppler shift caused by the movement. Given a standard armor configuration, fasteners will vibrate with an expected vibration profile. Cracks and delaminations will cause the vibration profile to change, and therefore will be detectable. In the Phase I Base effort, CRG will demonstrate the feasibility of Corrosion Detection on Curved Surfaces using Laser Vibrometry. CRG will generate an expected range of vibration profiles. Based on the results from testing, CRG will develop an algorithm that will detect deviations from the undamaged armor profile. CRG will then fabricate a prototype test system that will securely hold the armor plates in a known position and measure them. A scanning laser doppler vibrometer (SLDV) will measure the frequency and amplitude response across the face of the armor and provide a pass / fail criterion for the armor defect detection. CRG plans to capstone the Phase I with a demonstration of the prototype testing system.