David Jackson
University of Kent, UK
Title: Multichannel fibre laser Doppler vibrometer studies of hypervelocity impacts
Biography
Biography: David Jackson
Abstract
A multichannel fibre laser Doppler vibrometer was demonstrated with the capability of making simultaneous non contact impacts at 4 different locations. The optical source was a single frequency laser diode at 1500 nm, where the output power was coupled into a single mode fibre and transferred to a specially designed power distribution unit that contained 4 independent heterodyned interferometers with transceiver fibre links with autocollimators. The targets were either aluminium or carbon composites. Two sets of measurements were performed the first using small ball bearings (1-5.5 mm) falling under gravity, the second with small projectiles (micron to 1 mm) fired from an extremely high velocity light gas gun at speeds in the range 1-8 km/s, digital processing was used to recover and process the data. In addition the results of a previous experiment where fibre Bragg gratings strain sensors attached to the target are compared. Determination of impact damage is important for industries such as aerospace, military, auto, where the effect of an impact on the structure can result in a major structural damage. To our knowledge the research reported here demonstrates the first trials of a multichannel fibre laser Doppler vibrometer being used to detect hypervelocity impacts.