Northrop development will allow maintenance schedules to be based on stress analysis
After demonstrating that it can predict in real time when airframe components will develop cracks, Northrop Grumman has received a follow-on contract to continue development of its Structural Integrity Prognosis System (SIPS). The system uses analytical models, sensors and reasoning software to predict crack formation and growth.
The demonstration was conducted in August under the two-year, $14.2 million first phase of the US Defense Advanced research Projects Agency (DARPA) programme. Different sections of EA-6B structure were fatigue tested in a laboratory to see if SIPS could predict when they would fail. “In general, the predictions were pretty close on time to failure,” says John Papazian, principal investigator.
SIPS will allow operators to schedule maintenance according to usage, says Northrop, and DARPA’s goal is to provide military commanders with quantitative performance predictions so that they can operate each individual aircraft to the limit of its capability.
SIPS uses microstructural models to understand how fatigue cracks develop and predict when the material will fail. Sensors then monitor crack formation and growth in real time, feeding data to a reasoning module that updates the failure prediction. Three sensor types were tested – eddy current, electrochemical and ultrasonic. “Sensor data was very accurate,” says Papazian. “If it said a crack was 150 microns, that’s what we had.”
Under the two-year, $17.8 million second phase of the DARPA programme, Northrop will evaluate SIPS in actual full-scale aircraft fatigue tests, with the goal of having a deliverable structural prognosis system available by the end of the contract in January 2008. The system is being used in an A-10 fuselage/wing centre-section residual life test now under way, and an EA-6B outer wing-panel fatigue life test.
GRAHAM WARWICK / LONDON
Source: Flight International
