The ultrasonic C-scan shows a dark zone in the impacted area which is caused by higher attenuation of the acoustic waves due to actuator damage. Only small parts of this region are delaminated at the interface of insulation fleece and CFPR layer. A last, a cross section was taken at the indicated line in the NDE images. Three micrographs are chosen showing typical damage structure. Vertical cracks in the ceramic plate are concentrated outside of the hit area.
Horizontal cracks appear below the incident bar due to tensil impuls response.
These small horizontal flaws scatter US waves and cause the display of damaged area in the C-scan. Bright spots in the insulation fleece above and below the actuator indicate voids resulting from its incomplete penetration with epoxy resin. These voids cause local stress differences leading to horizontal cracks within the piezoceramic. In contrast to prepreg system, the insulation fleece in DP-RTM system is completely filled with resin. Therefore, no horizontal cracking could be observed.