Structural Health Monitoring (SHM) aims at ‘safe life’ rather than ‘fail safe’ structures
A paradigm change is happening to ensure the structural integrity of aerospace structures, in particular civil and military aircraft, according to Prof. C.R.L. Murthy, Professor of Aerospace Engineering, who has recently retired from the Indian Institute of Science (IISc), Bangalore.
Prof. Murthy was delivering the Prof. A.K. Rao Memorial Lecture at the National Non-Destructive Evaluation Seminar (NDE-2012), which got under way at Sahibabad near Delhi. The talk was titled ‘Non-Destructive Evaluation for Aerospace Structures: Past, Present and Future.’ Prof. Murthy was Prof. Rao’s student at the IISc. NDE or Non-Destructive Testing (NDT), as the term implies, refers to the techniques of analysis used in science and industry to evaluate the properties of a material, component or a system without causing damage to the object being analysed. The techniques include ultrasonic testing, acoustic emission, magnetic-particle and liquid penetrant testing, eddy-current testing and nuclear techniques, including radiography and neutron scattering methods.
Prof. A. K. Rao was an expert in the use of the acoustic emission technique to study the structural integrity of aircraft. Interestingly, his services were also used by the Department of Atomic Energy during the end-shield damage in RAPP-1 at Rawatbhata and pressure tube in MAPS at Kalpakkam years ago. From the early days of mere detection of defects, the NDE technology in the past included material characterisation and analysis and the present is moving towards Structural Health Monitoring (SHM), Prof. Murthy said. Much like a treadmill for cardiac function, SHM refers to monitoring the structure when it is working — and not only when it is on the ground — detect and interpret the “adverse changes” in the structure and provide intelligent estimates of the remaining useful life. Since failures are unavoidable, the philosophy in structural integrity through SHM methods has been to ensure ‘safe life’ rather than ‘fail safe’ structures.
The future will be towards making the probability of failure very small or high-damage tolerance. SHM includes the following five essential components: sensor technology, which is revolutionising NDE; diagnostic signal generation; signal processing; damage detection/identification and analysis; and, system integration. According to him, the concept of SHM is still evolving for aerospace structures, which are very complex and have complicated geometries.
“Even today,” he said, “no operational aircraft system, civil or military, is being monitored for health with sensors.” While advances in the techniques of signal processing have enabled reduction of the uncertainty of failures, the idea of total system integration is on the horizon, Prof. Murthy said. Boeing will very soon be bringing to the market a commercial aircraft that incorporates SHM in the design, he said.
Future will be towards making the probability of failure very small or high-damage tolerance Boeing will very soon be bringing to the market a commercial aircraft that incorporates SHM
Future will be towards making the probability of failure very small or high-damage tolerance
Boeing will very soon be bringing to the market a commercial aircraft that incorporates SHM