2021. Vol.24. No. 1, pp. 36-40
Automated Ultrasonic Inspection of Adhesive Joints and Three-Layer Structures Made of Polymer Composite Materials
Method. These samples were analyzed using two types of automated through-transmission ultrasonic techniques. The first type is transmission of ultrasound through a layer of air, the second type is through a jet of water. Two automated systems were used:, a Technische Beratung Schittko GmbH machine for the first case, and Tecnatom robotic system for the second case. Pseudocolor C-scan is a diagnostic testing document for both systems. C-scan analysis is based on the thresholding method.
1. The inspection of stringer samples demonstrated that they can be inspected with a non-contact technique using an air inlet at frequencies of 40 and 500 kHz with a sensitivity of at least 1 cm2. The water jet inspection of adhesive joints at frequencies of 1 MHz and 5 MHz can provide a sensitivity of 0.3 cm2.
2. All samples of three-layer structures, including honeycomb cores of various thicknesses, turned out to be uninspectable when tested with an air inlet at a frequency of 500 kHz.
3. Three-layer structures with a honeycomb core height of up to 8 mm can be inspected with the non-contact through-transmission ultrasonic technique at a frequency of 40 KHz with a sensitivity of 5 cm2. Such structures can also be inspected with the jet method at a frequency of 1 MHz with a sensitivity of 1 cm2.
4. Three-layer structures with a honeycomb core height of 80 mm and more cannot be inspected with the through-transmission ultrasonic technique using an air inlet due to the significant ultrasonic attenuation. They can be inspected with the jet method at a frequency of 1 MHz with a sensitivity of 1.8 cm2.
Conclusion. Automated through-transmission ultrasonic testing of three-layer structures and adhesive joints ensures reliable detection of defects with a diameter of 15 mm for adhesive joints of monolithic parts and detection of defects with a diameter of 15–25 mm for three-layer structures, depending on the thickness of the skin and core.
Keywords: polymer compounds, UT, transducer, mode, adaptive quantization, probability distribution, ultrasonic signal thresholding.