Inspection of the machined features created at the embedded sensor aluminum plates

Manufacturing the raw materials for aerospace structures with embedded sensors to be connected them to the central monitoring station of the structural health monitoring (SHM) systems has been considered by many researchers and industries. These structures can be inspected in very short time by connecting the sensors to a monitoring system. The quality of the part may be evaluated while geometric features such as holes and slots are created during the machining process. Surface response to excitation (SuRE) method is a low-cost alternative to the electromechanical impedance (EMI) method. The SuRE method uses one piezoelectric transducer to excite the surface of a structure with a sweep sine wave, and one or more piezoelectric sensors or scanning laser vibrometer monitor the dynamic response of the system. Once a change which may lead to a structural failure is introduced to the structure, some mechanical properties are altered. The frequency spectrum of the signal received by the sensors will change after the dimensions of the geometric features are modified. In this study, feasibility of the SuRE method was evaluated for inspection of the quality of the machined features on aluminum plates. The SuRE method was used to characterize different geometric features created by the milling operation on identical aluminum plates. One piezoelectric transducer was used as an exciter and propagation of the surface waves were monitored by a scanning laser vibrometer. The Fast Fourier Transformation (FFT) was used for the analysis of the sensory data after each data collection. By increasing the size of milling in two different dimensions, the sum of the squares of the differences (SSD) of the spectrums drastically changed. Also in order to get rid of the need for baseline (reference) data collected at the initial conditions, some advanced techniques such as Geometric mean, Harmonic mean and 5th momentum were introduced.