Experimental measurements of vibrations of artificial sub-surface cracks and evaluation of identification potential for the electro-mechanical impedance method

摘要

As standard method for structural health monitoring (SHM) the electro-mechanical impedance method evaluatesthe frequency response of a piezoelectric transducer, which is attached to a mechanical structure of interest. Thepiezoelectric element is excited by a harmonic voltage signal, which causes typically harmonic oscillations on bothelement and structure. The measured impedance of the piezoelectric element reflects thus the structural response.Consequently, changes of the impedance indicate structural changes, i.e., damage. This contribution investigateslinear and possibly non-linear vibrations provoked by contact acoustic non-linearity of a sub-surface crack, adamage typical for composite delamination, in a harmonically excited structure. The considered structure is analuminum beam with a sub-surface crack, which is introduced artificially according to a specific manufacturingprocess developed at the author’s research group and already presented at SPIE Smart Structures+NDE 2018.Numerical studies presented at IWSHM 2017 and SPIE Smart Structures+NDE 2018 showed that the considereddamage causes non-linear response to harmonic excitation. The proposed work continuous this research byexperimental measurements of the vibration response of the considered beam with sub-surface crack to harmonicexcitation by a piezoelectric transducer. Laser-scanning vibrometer measurements along the entire beam and inparticular at the crack location identify linear and non-linear vibrations, allow its mode shape visualization andto assign the structure as most probable source for non-linearity. Furthermore, a piezoelectric transducer thatsimultaneously records the transfer frequency response function passing through the sub-surface crack showshigh potential for vibration-based SHM methods like the electro-mechanical impedance method to assess thenon-linear response of this damage type for identification.