PhD Topic Background/Description: 

The aim of the project is to develop permanently installed sensors for monitoring structural hotspots. In this context a hotspot is a localised region of the structure that is thought to be a potential location for defect formation and growth. This project will explore approaches based on ultrasonic and eddy current arrays. The array would form images of a local region covering the hotspot. A key research aim is to ensure that these images are high resolution and that the coverage is as extensive as possible. The other key challenge is to design arrays that are low cost and reliable. Whilst the sensors will be permanently attached, the associated electronic instrumentation would be separate. Periodically the electronics would be connected to the sensors and readings taken. This could be via wired sensors of via electromagnetic coupling (i.e. near field communication).  

Location and defects of interest:  

The initial focus will be on detecting and sizing defects initiating from bolt-holes in multi-layered aircraft wing skins. Hence, the hotspot is the region around the bolt hole. The failure mechanism of particular interest here is through a combination of corrosion and cracking and so both must be detected. Clearly the earlier in the defects-growth cycles the defects can be detected the better. Once detected, it is also useful to track their growth as a function of time.  

Data fusion: 

Given that two sensing modalities will be explored, there is clear scope for data fusion to enhance detection and characterisation of damage. The question here is what sensitivity do the two modalities have to the defects of interest? This will enable us to understand the value of any data fusion.  

Thin layer concepts:  

Ultrasonic systems can be externally or internally mounted, enabling them to image the interior of the structure. Eddy currents are confined by the skin effect to material surfaces and so must be embedded. Both sensor systems can be formed as thin layers and hence positioned between the wings skins. There is potential to make these layers very thin (<0.1mm) and soft, so they can be placed in between the plates at manufacture. 

Current stage: 

Simulations are first being developed in order to test the sensitivities of various sensor layouts, and to provide an initial working point from which to consider data processing methods. Once validated, these simulations will be expanded to investigate what sensor layouts best achieve the above stated goals, before experimental work begins to study the efficacy of these designs.