The complex geometry of many composite components means that inspection has to be performed manually or by slow immersion tank techniques. TWI has developed an automated inspection system comprising two six axis robotic arms, capable of working independently and cooperatively.
The robotic arms deploy end-effectors carrying ultrasonic transducers (single element and phased array), mounted into water jet nozzles that couple the ultrasound into the part. Software developed in-house generates 3D imaging of the part as well as traditional A- and B-scan data.
The use of the phased array ultrasonic testing (PAUT) and full matrix capture (FMC) has previously been limited to metals due to the fibres in the material causing the acoustic velocity to vary with angle.
TWI has developed new algorithms that determine and correct for these variations. In addition, the shape of the surface interface can be detected and the refraction occurring is also taken into consideration. This means that high-speed inspection methods using large array probes can greatly increase the speed of inspection and non-zero incident angles can be used for complex shaped components.
FMC can be used where flaw orientation can vary or where high levels of material noise are present.
This non-contact method is very useful for thin-skinned components with complex internal structures, such as stiffeners, honeycomb or foam cores. The images produced look similar to an x-ray and are interpreted using advanced analysis tools and 3D visualisation.
A pair of high-power flash units rapidly heats the surface by a few degrees. A highly sensitive infrared camera monitors the surface as it cools. Features inside the component affect the way this heat dissipates resulting in surface temperature variations that can be processed to generate images.
Anther non-contact method, shearography uses laser light to detect strain on the component’s surface. Images of unloaded and lightly loaded conditions are compared and fringe patterns are generated. Analysis of the fringe patterns shows how the structure is performing under load. Excitation can be thermal, mechanical, or acoustic.