Comparison of Accelerometer and Laser Modal Tests of a Vertical Stabilizer Assembly

A Vertical Stabilizer Assembly (VSA) prototype of the Space Shuttle Orbiter was modal tested with a Laser Doppler Velocimeter (LDV) and accelerometers in order to compile a data base that can be used to benchmark several damage identification techniques. The VSA was instrumented with 56 accelerometers and one force link attached to a stinger connecting a 500-lb. shaker and the structure. The LDV was used to acquire data from 84 points on one side of the VSA, 35 of which matched with accelerometer locations. Seven controlled damage scenarios were inflicted on the VSA. The test article was modal tested before and after the infliction of the damage. The damage consisted of removing bolts and rivets, disbonding of skin from the aluminum honeycomb, cutting through ribs, and skin removal. The data captured consisted of frequency response functions (FRFs) with accompanying coherence functions and time histories for two scenarios. This paper presents the results and conclusions of the comparison of the laser and accelerometer data on the basis of noise levels and magnitudes of FRFs. In addition, the advantages and disadvantages of the two techniques are discussed with respect to the setup and data acquisition times, as well as the ability to measure data on different points of the structure