Laser Ultrasonics Toward Remote Detection of Stress Corrosion Cracking

Laser ultrasonic techniques are investigated relative to robotic inspection, with the aim of packaging optics within the cargo bay of a robotic car such that the pulsed laser for generation and the continuous laser for the interferometer are located in a remote command center, and optical fibers deliver the laser beams to and from the optics. The first steps are taken toward showing the feasibility of this type of inspection robot to detect surface cracks using rayleigh waves in the pitch-catch mode. Specifically, the geometry of a slit mask used to create directivity is studied with the aim of generating a rayleigh wave that reflects off a (stress corrosion) crack, and then receiving both the incident wave and the reflection with a laser interferometer. Multiphysics simulations and laboratory experiments agree that a concave (inward arc) line slit functions better than a convex (outward arc) line slit, a straight line slit, or an omnidirectional point source.