Assessing the scaling subtraction method for impact damage detection in composite plates

The scaling subtraction method (SSM) is a non-destructive measurement approach used to extract nonlinear features from the elastic response of a structure. As such it can be used for damage detection purposes by identifying nonlinearities that may result from the presence of micro cracks or inclusions in granular and metallic materials. The effectiveness of such a technique to detect the presence of damage modes typical of laminated composite materials has not been yet assessed. With the purpose of filling this gap, in this paper the SSM is applied to inspect two laminated composite plates with different sizes, impact positions and sensor arrangement. Intact and damaged specimens are tested under harmonic excitations of different amplitude and frequency (the latter selected among the ultrasonic natural frequencies of the two plates). For each excitation case the recorded vibration signals are subtracted from the linearly rescaled reference signals and the SSM nonlinear indicators are calculated. The sensitivity of the method to the presence of damage is assessed in different sensor-receiver scenarios as well as for different excitation frequency and amplitude levels. Finite element numerical investigations are also performed to make comparisons with the experimental results.