A Demonstration of Augmented Reality for Structural Health Monitoring and Damage Assessment

A concept study was carried out to investigate improvements on quality and efficiency in the maintenance of an aircraft in service. Structural health monitoring and in-situ damage assessment of composite components are embedded into a virtual assistant application for augmented reality glasses (Microsoft HoloLens). Its graphical user interface comprises menu-guided instructions and inspection documentation for an on-site inspection task. The integrated sensors of the glasses allow autonomous spatial orientation (inside-out-tracking). The system can thus be used as an interface between real and virtual twins within an inspection task.

In order to demonstrate our interface in an operational study, we maintain the air brake of the Eurofighter EF 2000T. We chose this component since both the physical air brake and its virtual 3D model are available at the German Aerospace Center (DLR). The main metal structure of the Airbrake was replaced by an optimised all composite structure to significantly reduce the number of individual parts and to minimise assembly effort. The structure consists of only two CFRP shells bonded together to provide structural integrity.

The demonstration includes a structural health monitoring system for in-service inspection based on ultrasonic guided waves (Lamb waves). These waves are emitted and received using a network of 36 piezo ceramic transducers that are permanently attached to the air brake structure. Structural damage causes additional wave interactions recorded by the sensors. By analysing the sensor signals and different signal paths different kinds of structural defects can be detected and located.

Subsequent damage assessment is achieved by evaluating a double-criterion combining maximum allowable strain with delamination growth potential. First, the strain field is obtained from the pristine structure under flight load.  Next, a nonlinear delamination growth analysis of the damaged area is performed. Finally, the severity of the detected damage is determined by using its position, reserve factor and delamination growth potential. It provides the basis for an on-site decision on the serviceability of the entire aircraft.

The Damage assessment result is shown as a projection on the surface of the real air brake. A remote collaboration session with an expert and shared information concludes with the damage classification and a decision on the aircraft’s airworthiness