Damage Detection in Civil Aircraft

A Talk by Dr Eddie O’Brien PhD, CEng, CPhys, FRAeS IIMechE, FInsP, FSEM
Wednesday 12th February 2014

Dr. O’Brian, prior to his talk, told us that before his retirement from Airbus in 2005, one of his responsibilities had been group leader of their Experimental Mechanics Group; this had given him the opportunity of being involved in research on many Airbus Aircraft from Concorde to the Airbus A350. His talk would be concerned he said, with the consequences of components ‘living’ under stress, and the degradation of material due to its repeated loading at a level below its static breaking stress; typical random stress might result from gusts of wind on take off or landing. Eddie’s talk was technical but not over so, and covered a great deal of ground, primarily as has been said in the field of stress analysis and crack propagation. The talk covered the research he had been involved in, to determine best procedures for understanding the effects of stress in component parts.

Dr O’Brian commenced by explaining that fatigue nucleation occurs when sufficient fatigue damage history is accumulated in a material that physical cracking is experienced. Post nucleation is the growth of a crack due to further loading cycles and Inspectors look for it during Aircraft Structural surveys.

An outline of objectives set for research to achieve Civil Aircraft Structural Health Monitoring (SHM) was given which included such aspects as remote crack growth detection monitoring, application of Ground Fatigue Tests and working towards Safety Certification. Dr O’Brian went on to explore associated other aims. Post nucleation fatigue detection of civil aircraft structures is he explained, achieved by looking at many techniques basically within stress groups, equipment groups and electrical groups; also covered were other production engineering aspects.

Vibration is the main driver for stress propagation; structures are full of vibration during operation, and early in its study the question was asked whether health monitoring could be helped by studying vibration; consequently the go-ahead was given for research and finding a team to investigate. Sinclair Wilson and colleagues including Dr Len Rogers from the off-shore oil industry commenced this study the focus being on letting the structures so say ‘speak for themselves’. Work then commenced on collecting vibration data by growing cracks to detect and monitor the consequent fatigue damage.

Dr Eddie O’Brien continued his talk by addressing problems, presenting many examples including the Concorde Rudder Jack Fitting and its showing signs of cracking due to fatigue brought about interestingly, by geometric concentration effects and other aspects such as the mechanism of crack propagation by striations or jumps as he put it, were addressed.

The talk concluded by an excellent question time which covered many peripheral subjects.

As is usual with Club meetings, the talk was followed by tea and biscuits during which members were afforded the opportunity to talk to Dr O’Brian.

The meeting concluded by about 4pm.

Michael Carey Clinch MBE FBIS FRSA CEng MIET