Structural Health Monitoring of Composite Fan Outlet Guide Vane: Detecting damages and impacts using piezoelectric wafer active sensors and Lamb waves
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
The use of composite materials within the aerospace industry has increased in the last decades and is still on the rise. Most composite applications are in the aircraft body parts but engine components such as fan blades and fan outlet guide vanes (FOGV) are now also to be found. Metals are well studied and both their fatigue and cracking behavior are well known but for composites this is not the case. Composites also have problems such as micro-cracking, delamination and porosity, which all can be difficult to detect but yet result in significant decreas in load carrying capacity. The ability to monitor a structure in real time would increase safety, lead to a reduction of maintenance costs, both in terms of reduced downtime and easier repairs, and allow for reduced requirements in design loads. One of the most promising techniques for a structural health monitoring system is using Lamb waves since they have a great ability to propagate over large area and have good sensitivity and resolution. A number of carbon fiber FOGV, equipped with piezoelectric transducers, has been manufactured at GKN Aerospace Sweden AB. By using the piezoelectric transducers to send a wave pulses through the structures and compare the pulse response for a damaged and an undamaged case, it has been investigated if it is possible to detect damages, what the main limitations of the system are and if there are any possible improvements to be made. The piezoelectric elements ability to detect impacts has also been investigated. Most of the testing has been performed on a carbon fiber sandwich plate, to then apply the same principles for a FOGV. Lamb waves do indeed seem to have a great potential for detecting damages and a difference between the undamaged plate and the damaged plate could be observed both in the root mean square value, the peak-to-peak alue, the time of flight and the frequency content of the pulse response. The piezoelectric sensors are very sensitive and have a great ability to detect impacts. The greatest limitations encountered during the project have been problems with the hardware, both with the amplifiers used and restrictions in data acquisition unit. Other limitations of the system are the sensitivity due to changes of boundary conditions and disturbances form external sources.
Place, publisher, year, edition, pages
2016. , 86 p.
TRITA-AVE, ISSN 1651-7660 ; 2016:73
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-203807OAI: oai:DiVA.org:kth-203807DiVA: diva2:1082644
GKN Aerospace Sweden