Wireless detection of internal delamination cracks in CFRP laminates using oscillating frequency changes

It is difficult to detect delamination of rotating composite components like helicopter and wind turbine blades while in-service with a wired system. In the present study, a wireless system using a tiny oscillation circuit for detecting delamination of carbon/epoxy composites is proposed. In this system, a tiny oscillation circuit is attached to the composite component. When delamination of the component occurs, electrical resistance changes, which causes a change in the oscillating frequency of the circuit. Since this system uses the composite structure itself as a sensor and the oscillating circuit is very small, it is applicable to rotating components. The electrical resistance change and oscillating frequency change due to delamination is experimentally measured using carbon/epoxy specimens. The effects of temperature changes are also measured. The wireless method is found to successfully detect embedded delamination, and to estimate the size of the delamination. The effect of temperature change is minimized by means of a temperature compensation circuit.