Quantification of damage expansion influence on frequency response function of plate for structural health monitoring with integral differential method

This paper presents a feasibility study on damage size quantification throughout the damage expansion procedure using the integral differential method based on the developed frequency response function (FRF) programme. A designed pattern of piezoelectric Micro Fibre Composite (MFC) transducers was integrated with three composite panels for a real time monitoring testing by swept sine vibration input signals under three varied frequency bandwidths ranged from 10 to 1 kHz, 1k-3 kHz and 3k-5 kHz, respectively. The composite panels under pristine stage without any impact damages were tested and documented as a cross-reference for subsequent quantification estimation. The damages were introduced around transducers array, and its expansion process is equivalently simulated by a repetitive impact test procedure. A modified damage index, difference of response (DoR), was derived through integral differential method to assess the FRF outcome change of damaged composite plate relative to the pristine state. Combined with damage geometrical dimensions measured by thermography imaging technology, a quantification formula is derived reversely through numerical analysis, which showed a segmentation linear relation between the DoR and damage size governed by the power and logarithmic functions. The damages under different severity subjected to an additional composite plate were successfully quantified by the segmentation formula, which validate the feasibility of quantification with DoR.