Towards in-plane local defect resonance for non-destructive testing of polymers and composites

Local defect resonance (LDR) makes use of high frequency vibrations to get a localized resonant activation of the defect. In this study, it is shown for various samples and damage features that the classical out-of-plane local defect resonance can be equally extended towards in-plane local defect resonance. It is found that the in-plane LDR typically occurs at higher frequencies, which is linked to the specific geometry of common defects. This increased frequency allows for a reduction in measurement time. More importantly, the results indicate that the in-plane LDR has an increased sensitivity for defects with dominant out-of-plane defect interfaces (e.g. surface breaking crack). Knowledge of both the out-of-plane and in-plane LDR provides further insight on the internal structure of a defective area. This is explicitly demonstrated on a carbon composite which was subjected to low velocity impact, inducing barely visible impact damage.