A novel all-fiber surface roughness sensor based on laser scattering

Plastic deformation, fretting, and corrosion can induce surface roughening in metallic materials. In-service surface roughness changes can therefore be an excellent indication of early material deterioration. Optical method to characterize material conditions has many advantages, including high speed, great sensitivity, non-contact, and non-destructiveness. The paper discusses the development of a novel optical technique for surface roughness measurement using optical fibers. The all-fiber surface roughness sensor is operated on the principle of laser scattering. The sensor is constructed with two parallel fibers. One fiber serves as the illumination fiber that is coupled to a laser source and delivers light to the component. The other fiber is the receiving fiber that collects the light scattered by the sample surface. Theoretical simulation of the light intensity reflected from a smooth surface is compared with experimental results. The intensity of the light scattered from polished steel samples were measured and correlated with the surface roughness measurements. It was found that the light intensity decreases as the surface roughness increases. Annealed samples and plastically deformed samples are profiled using the all-fiber surface roughness sensor. The experimental results indicated that the surface roughness sensor can detect surface roughness changes induced by thermal exposure and plastic deformation.