Localized Response of Damaged Structural Systems

The effects of cracks in a composite beam-mass system on local and global strain caused by external excitation are examined. The natural frequency of the system varied around 8 Hz. Data from strain gage and fiber optics measurements before and after damaging the beam are compared. The results show a general agreement between the different sets of measurements. The level of noise varied between the different gratings and over different locations in individual gratings. From both sets of measurements, the response of the damaged beam has a lower amplitude in comparison with that of the undamaged beam. This indicates that higher damping is associated with the damage. Different ratios of the amplitudes of the response frequency for the undamaged and damaged beams over the regions where cracks were present than in the regions away from the cracks are obtained. This suggests a change in the shape of the excited mode of the beam when damaged.