Scaling Subtraction Method for Damage Detection in Composite Beams

Composite materials have been widely used in many advanced engineering structures, because of their high strength and good resistance to fatigue and corrosion. Nevertheless, their susceptibility to impact damage is one of the biggest concerns for use in critical load-bearing structures. Over the last few decades, many non-destructive techniques based on the analysis of nonlinear vibrations and other acoustic phenomena have been developed. Among them, the Scaling Subtraction Method (SSM) is an approach used to extract nonlinear features of an acquired signal generated by the response of a system to an impinging wave, in order to reveal effects that can be associated to internal damage. In this paper, the SSM is applied to examine the response of laminated composite beams to the presence of damage induced by low-velocity impact. The composite beams are tested, both before and after impact, under either impulsive or harmonic excitation of different frequencies, selected among the natural frequencies of the beams. Piezoceramics transducers bonded to the surface of the beam are used for both excitation and sensing. For each harmonic excitation case, the linearly scaled reference signal is compared to the response at large amplitude excitation. An extension of the SSM in the frequency domain is proposed in this paper to detect damage under an impulsive excitation, which typically covers a wide range of frequencies. The results show that this pulse-based extension of the method may be a promising option for detection of nonlinearities associated to damage occurring in composite structures.