A Non-Linear Ultrasonic Approach Using a Fine-Tuned Experimentally Defined Frequency for Structural Health Monitoring of Composite Plates

Abstract

The Sideband Peak Count – Index (SPC-I) technique, which is a newly developed non-linear ultrasonic (NLU) technique has been established as a reliable technique for detecting and monitoring non-linear detects in various materials such as metals, composites, and concrete. In prior investigations the SPC-I technique is performed by exciting a wideband sweep signal through the material. Although this is a good general approach, the SPC-I technique can be fine-tuned for specific specimens under investigation. In this investigation, a single frequency is selected as an excitation signal that is propagated through the composite plate specimens. This single frequency is experimentally defined using a pristine composite plate as a control specimen. Multiple signals are propagated through the pristine specimen at a range of frequencies in order to find the sensitive frequency. By applying the SPC-I technique on the range of signals obtained for the pristine specimen, a single fine-tuned frequency can be identified that can be used to detect and monitor impact damage in composite plates. In this investigation glass fiber composite plates that are impacted with increasing impact energy (0J, 5J, 10J, 20J, 30J, 40J and 50J) are examined using the fine-tuned excitation frequency coupled with the NLU SPC-I technique. The SPC-I technique is capable of detecting and monitoring the impact induced damage in the composite plate specimens.