The electro-mechanical impedance method is a standard SHM approach. 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 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 electro-mechanical impedance method.
Christoph Kralovec, Thomas Erlinger, Sandra Gschossmann, and Martin Schagerl, "Manufacturing of artificial sub-surface cracks to investigate non-linear features of electro-mechanical impedance measurements," Proc. SPIE 10599, Nondestructive Characterization and Monitoring of Advanced Materials, Aerospace, Civil Infrastructure, and Transportation XII, 105990S (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 07, 2018; Published: 27 March 2018); https://doi.org/10.1117/12.2296598.
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