Aerospace applications

The aircraft industry is among the first ones to implement SHM methods primarily due to the problem of undetected damages and their uncontrolled growth leading to catastrophic failures causing loss of life and properties. Aircraft industry is also the most visible beneficiary of this new trend as it spends approximately twenty seven per cent of total life cycle cost on inspection [Kessler, 2005]. A substantial saving of approximately forty four percent of time in inspection of modern day fighter aircraft is obtained by implementation of SHM [Bartelds, 1997].

Followings are the representative works reported in the literature by various research groups. The studies presented below have been developed to a level of readiness and are at different stages of implementation.

Roy and Ganguli [2005] have used a finite element model of a helicopter rotor blade to analyze the effect of damage growth on the modal frequencies in a qualitative manner. Structural damage in materials evolves over time due to growth of fatigue cracks in homogenous materials and a complicated process of matrix cracking, delamination, fiber breakage and fiber-matrix debonding in composite materials. Using phenomenological models of material degradation for homogenous and composite materials it is shown that the damages can be detected by monitoring changes in lower as well as higher modes like flap (out of plane bending), lag (in plane bending) and torsional rotating frequencies. It is more pertinent for composite materials where the onset of the last stage of damage of fiber breakage is most critical. However, this study remains limited to numerical analysis only assuming the availability of dynamic response from any non destructive technique [NDT].

SHM for aerospace structures using smart materials are studied by many other researchers. Qing et al [2005] have developed a hybrid piezoelectric / fiber optic diagnostic system for quick non-destructive evaluation and long term health monitoring of aerospace vehicles and structures. The SHM system for the Eurofighter Typhoon has been reported by Hunt and Hebden [2001]. Tessler and Spangler [2005] have formulated a variational principle for reconstruction of three-dimensional shell deformations from experimentally measured surface strains, which could be used for real time SHM systems of aerospace vehicles. Balageas [2002] has presented a review of research and development in SHM at the European Research Establishments in Aeronautics.