Luna Innovations Inc. (Roanoke, Va.) has developed a highly distributed strain sensing system, now available with Luna’s ODiSI (Optical Distributed Sensor Interrogator) instrument. According to tests conducted by the University of California-San Diego and the FAA Airworthiness Assurance Center operated by Sandia National Labs (Albuquerque, N.M.), the ODiSI measures the performance, tolerances and failure mechanisms of structures and vehicles. Luna says researchers fired ice balls approximately 2.5 inches/63.5 mm in diameter into two carbon fiber/epoxy test panels representative of composite surfaces found on a range of modern aircraft such as the Boeing 787 or the Airbus A350 or A380. In one panel, optical sensing fiber was embedded within the composite laminate during layup and co-cured; in the second panel, sensing fiber was surface-bonded to the panel skin. Luna says results showed residual, lasting strain after the impact, offering better insight into how the impact of debris and collisions affects composites. Looking at the residual strain in the fiber as it is mapped to the panel surface, the impact location is identifiable in a single scan of the laser by the strain left in the fiber. ODiSI provides a constant picture of a structure’s load distribution with a sensor mass of only a few grams. It uses low-cost optical fiber for unprecedented sensor density for strain or temperature sensing applications and delivers hundreds of measurement locations per meter of fiber with resolutions of a few microstrains. With sensors suitable for surface bonding or embedding in composites, ODiSI can be used either during manufacturing or later installation. ODiSI applications include composite structure design and model verification, design improvement, manufacturing process verification, structural health monitoring and performance optimization.