Abstract:A representative area of concern for fatigue crack growth in aircraft occurs in multi-layered metallic structures. Ultrasonic plate waves are currently being investigated by multiple initiatives to detect these types of flaws with a minimal number of sensors to enable Structural Health Monitoring (SHM). Previous work has focused on structures with one or two layers, coupled with modeling of the wave propagation within these representative samples. However, it is common for multi-layered structures to have more… Show more
“…Much work has been done on the theory and application of Lamb waves to structural health monitoring (see [20,7,9,10,11,16,17,27,1,2,3,5,6,12,18,19,24,13]). We make use of these methods in our work.…”
The Bayesian Computational Sensor Network methodology is applied to small-scale structural health monitoring. A mobile robot, equipped with vision and ultrasound sensors, maps smallscale structures for damage (e.g., holes, cracks) by localizing itself and the damage in the map. The combination of vision and ultrasound reduces the uncertainty in damage localization. The data storage and analysis takes place exploiting cloud computing mechanisms, and there is also an off-line computational model calibration component which returns information to the robot concerning updated on-board models as well as proposed sampling points. The approach is validated in a set of physical experiments.
“…Much work has been done on the theory and application of Lamb waves to structural health monitoring (see [20,7,9,10,11,16,17,27,1,2,3,5,6,12,18,19,24,13]). We make use of these methods in our work.…”
The Bayesian Computational Sensor Network methodology is applied to small-scale structural health monitoring. A mobile robot, equipped with vision and ultrasound sensors, maps smallscale structures for damage (e.g., holes, cracks) by localizing itself and the damage in the map. The combination of vision and ultrasound reduces the uncertainty in damage localization. The data storage and analysis takes place exploiting cloud computing mechanisms, and there is also an off-line computational model calibration component which returns information to the robot concerning updated on-board models as well as proposed sampling points. The approach is validated in a set of physical experiments.
“…Boundary conditions are especially a concern for multi-layered structures, where even localized changes in the boundary stress and variance in the coupling between layers can have a significant effect on the ability to detect damage [13]. A demonstration of this effect can be shown in a simple mock-up of a three layer sample as shown in Figure 1.…”
“…Guided ultrasonic waves have energy distributed through the thickness of the multilayered structure making it in principle possible to inspect the different layers. The possibility of fatigue crack detection at fastener holes in multi-layered structures using high frequency guided ultrasonic waves (working at 5 MHz) has been investigated by Lindgren et al [4]. Results from their work show that defect detection is possible, but that detection sensitivity depends on the interface conditions between the layers.…”
Aircraft structures contain multi-layered components connected by fasteners, where fatigue cracks and disbonds can develop due to cyclic loading conditions and stress concentration. High frequency guided waves propagating along the structure allow for the efficient non-destructive testing of components, such as aircraft wings. However, the sensitivity for the detection of small defects has to be ascertained. The type of multi-layered model structure investigated consists of two adhesively bonded aluminium plate-strips. High frequency ultrasonic wave propagation along the structure and the sensitivity to disbonds and small defects in the metallic layers was investigated and verified experimentally. Preliminary fatigue experiments were carried out and the sensitivity of the guided waves to monitor fatigue crack growth at a fastener hole during cyclic loading was investigated. The measurement setup has the potential for fatigue crack growth monitoring at critical and difficult to access fastener locations from a stand-off distance.
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