This paper demonstrates how contact angle is an extremely sensitive and rapid method to check for surface cleanliness and consistency for aircraft repair.

A major concern with any bonded repair are disbonds that can occur at installation of the doubler or at anytime during the service life of the aircraft.
Measurement of the geometry of a liquid drop deposited onto the surface can be done extremely rapidly and form the basis of a sensitive check of surface cleanliness and consistency in a repair depot or in challenging field situations. This paper discusses the use of these rapid wetting measurements for quality assurance of surface treatments for adhesively bonded repairs.
Download the paper: Qualification of Surface Preparation Processes for Bonded Aircraft Repair