Aging of current commercial and military aircraft has become a major concern as many older aircraft are reaching their original design life. Service failures due to inaccurate characterization of aging responses may result in costly repair, premature component replacement, and loss of human lives. Fatigue is one common failure mechanism of engine components. High fluctuating loads, high temperature and temperature gradients, frequent starts and stops, stress concentrations resulting from complex geometrical shapes and from surface discontinuities produced by service conditions, all contribute to making the components fatigue-prone. The general degradation mechanisms that need to be considered include: microstructure and compositional changes, time-dependent deformation, environmental attack, and the accelerating effects at elevated temperatures.

The properties of aluminum alloys, titanium alloys, and nickel-based superalloys used in aircraft structures and engines may degrade with service conditions associated with the operation of the aircraft. Assessing the integrity of aging aircraft is enhanced by using the in-situ SSM system to measure the mechanical and fracture toughness properties nondestructively.

The SSM technology allows the establishment of current key mechanical properties which are needed as input for various damage prediction models (e.g. fatigue, creep, corrosion, etc.) as well as to evaluate the operational safety of aging aircraft. Periodic monitoring of aging aircraft with the SSM technology can be used to develop correlations between the SSM-measured mechanical properties and the damage accumulation as a function of aircraft service usage.

1. "Computer Controlled Indentation System," Final report for DoD SBIR Contract No. N00421-96-C-1121, 1998. (5.03 MB)

2. Appendixes A, B, and C of "Computer Controlled Indentation System," Final report for DoD SBIR Contract No. N00421-96-C-1121, 1998. (8.0 MB)

3. "Nondestructive Detection and Assessment of Damage in Aging Aircraft Using a Novel Stress-Strain Microprobe System," SPIE Proceedings on "Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware," Vol. 2945, 1996, pp. 217-228. (139k)