Robust Detection of Damage in Composite Plates Using the Nonlinear SPC-I Ultrasonic Technique

The newly developed non-linear ultrasonic (NLU) technique known as the Sideband Peak Count - Index (SPC-I) has demonstrated that it can detect and monitor the non-linearity generated by defects in a wide range of materials such as metals, composites, and concrete. The general approach of applying the SPC-I technique is by using a single sweep wideband excitation signal that is propagated through the specimen and a single signal is received which is then analyzed. This general approach has proven to be effective in giving a big picture measure of the non-linearity of the material. However, it can be further tuned and improved by exciting a sweep signal using multiple excitation signals. As a result, multiple signals are received and analyzed. These multiple sweep signals have the benefit of not being contaminated (dispersion effects) by multiple wave modes propagating at the same time compared to exciting a wide band single sweep signal. Additionally, by using these multiple sweep signals the effects of frequency modulation of wave modes and higher harmonics are easier to detect. By analyzing the received signals multiple frequency ranges can be discovered that are sensitive to different failure modes or types of defects. These frequency ranges of interest are then used to detect damage initiation and progression in the composite plate specimens. Two sets of composite plate specimens with two types of fiber reinforcements (Glass and Basalt) are investigated in this study. The specimens are impacted with a dart impact machine at increasing impact energies. By focusing on a frequency range that is sensitive to the damage in the composite plate specimens. The NLU SPC-I technique can robustly detect and monitor the impact induced damages in composite plates.