Manufacturing of artificial sub-surface cracks to investigate non-linear features of electro-mechanical impedance measurements

The electro-mechanical impedance method is a standard approach for Structural Health Monitoring (SHM). The method evaluates the dynamic frequency response of a structure to harmonic excitation. Both, excitation and measurement are done by a piezoelectric element. This contribution presents a manufacturing process to generate sub-surface cracks in metallic beams with an opening small enough to create non-linear response to harmonic excitation. The generated simple beam with sub-surface crack is analyzed by means of vibration measurements by a piezoelectric element and a Laser-Scanning-Vibrometer, linear and non-linear Finite Element (FE) analysis and microscopic images. Challenges in the measurement of non-linear response signals are revealed and needed further enhancement of the manufacturing process is presented. The non-linear dynamic Response signal calculated by the non-linear FE analysis is presented and discussed regarding the detection and parameter identification of sub-surface cracks typical for composite delamination or sandwich debonding by the electromechanical impedance method.