A critical note on the sideband peak count-index technique: failure for nonlinear damage characterization of impacted CFRP plates

TL;DR

This study critically evaluates the sideband peak count index (SPC-I) method for nonlinear damage detection in CFRP plates, revealing its unreliability due to procedural variability and inconsistent responses to material nonlinearities.

Contribution

The paper demonstrates that SPC-I is unreliable for nonlinear damage characterization, highlighting the need for standardized procedures and independent validation.

Findings

SPC-I values vary with undocumented calculation procedures

SPC-I response contradicts expected behavior with material nonlinearity

Re-evaluation of previous studies is recommended

Abstract

It is widely accepted, that nonlinear elastodynamic methods are superior to linear methods in detecting early stages of material deterioration. A number of recently developed methods are reported to be particularly sensitive to nonlinearities and thus appropriate to indicate early damage. We applied systematically one of the methods, the sideband peak count index (SPC-I), to a series of increasingly damaged carbon fiber reinforced plastic (CFRP) plates. Our data leads to different conclusions. The SPC-I values are influenced by (usually undocumented) variations in the index calculation procedure, which is not acceptable for a robust method. Moreover, the behavior of the index when the ultrasound amplitude is varied contradicts material nonlinearity as a direct and significant contributor to the index value. To clarify the apparent contradiction of our results with the previously published statements, it is recommended that (a) our data are re-evaluated by independent researchers and (b) the experiments already published are repeated or (if sufficient data is availThe paper has been updated for submission to NDT&E.able) also re-evaluated.