Singular energy component for identification of initial delamination in CFRP laminates through piezoelectric actuation and non-contact measurement

Delamination is typically barely visible impact damage in carbon fiber reinforced polymer (CFRP) laminates. It is important to identify initial delamination in the early stage. The concept of 2D multi-resolution modal Teager-Kaiser energy (MRM-TKE^2D) was recently proposed to reveal delamination-caused singularity in a mode shape for delamination identification with high robustness against environmental noise. However, inadequate sensitivity impairs its capability to identify initial delamination. A damage indicator needs to be further formulated to characterize the presence and location of initial delamination. To address this problem, a scheme of decomposing the MRM-TKE^2D into components is proposed for identification of initial delamination. Among the energy components of the MRM-TKE^2D for a CFRP laminate with an initial delamination, a singular energy component is dominated by the delamination and can be determined by its spectral entropy. In the singular energy component, energy converges into the delamination region to form a singular peak and almost vanishes in other places, from which the presence and location of the initial delamination can be characterized by the singular peak. This method is numerically verified on CFRP laminates with initial delamination. Its applicability is experimentally validated by identifying an initial delamination in a CFRP laminate, the mode shapes of which are acquired by piezoelectric actuation using a lead-zirconate-titanate actuator and non-contact measurement using a scanning laser vibrometer. Numerical and experimental results show that singular energy components are capable of identifying initial delamination under noisy environments.