Model-based damage evaluation of layered CFRP structures

Abstract

An ultrasonic evaluation technique for damage identification of layered CFRP structures is presented. This approach relies on a model-based estimation procedure that combines experimental data and simulation of ultrasonic damage-propagation interactions. The CFPR structure, a [0/90]4s lay-up, has been tested in an immersion through transmission experiment, where a scan has been performed on a damaged specimen. Most ultrasonic techniques in industrial practice consider only a few features of the received signals, namely, time of flight, amplitude, attenuation, frequency contents, and so forth. In this case, once signals are captured, an algorithm is used to reconstruct the complete signal waveform and extract the unknown damage parameters by means of modeling procedures. A linear version of the data processing has been performed, where only Young modulus has been monitored and, in a second nonlinear version, the first order nonlinear coefficient was incorporated to test the possibility of detection of early damage. The aforementioned physical simulation models are solved by the Transfer Matrix formalism, which has been extended from linear to nonlinear harmonic generation technique. The damage parameter search strategy is based on minimizing the mismatch between the captured and simulated signals in the time domain in an automated way using Genetic Algorithms. Processing all scanned locations, a C-scan of the parameter of each layer can be reconstructed, obtaining the information describing the state of each layer and each interface. Damage can be located and quantified in terms of changes in the selected parameter with a measurable extension. In the case of the nonlinear coefficient of first order, evidence of higher sensitivity to damage than imaging the linearly estimated Young Modulus is provided.

Tensile and fatigue testing of impacted smart CFRP composites with embedded PZT transducers for nonlinear ultrasonic monitoring of damage evolution

“…Conversely, the friction between the crack surfaces due to slipping ('rubbing') motion changes the local stiffness symmetrically, leading to the generation of odd higher harmonics [54]. Nevertheless, in literature, the detection of second-order frequency harmonics has been broadly associated with the presence of defects [55,56], as it allows direct calculation of the material nonlinearity. Briefly, the equation describing the propagation of one-dimensional elastic waves in the x-direction of the material has a second order approximation of…”

Nonlinear ultrasonic inspection of smart carbon fibre reinforced plastic composites with embedded piezoelectric lead zirconate titanate transducers for space applications

“…This leads to the generation of nonlinear wave effects that can be detected in the form of higher harmonics (even and odd multiples) of the input signal frequency (Ciampa et al, 2017). In particular, second harmonic generation has been reported as the most efficient NEWS feature for damage identification (Landau and Lifshitz, 1986;Munoz et al, 2015). This can be explained by considering the second-order nonlinear stress-strain relationship (from Hooke's law)…”