The An Approach to Damage Detection in Metal Sandwich Structures with Composite-Metal Patch Bonded Repair

The work concerns the selection of measurement parameters for selected non-destructive testing methods of Mi helicopter rotor blades after repair. Considered repair cases involve metal cracks in the sandwich skin and repair damage of honeycomb structure (puncture, dent). In the event of a crack, repair is performed by applying a composite-metal repair package. In case of damage of the core, its broken piece is replaced by a new one and then applied the same metal-composite package as in the case of crack repair. The present work focuses on detecting disbond between skin and core below repair patch and cracks under the repair package. Detecting cracks and assessing their length is important because the repair technology provides the repair package without removing of cracked part of skin. Authors have used laser shearography and C-scan methods for MIA and ET. In the methods of eddy currents and mechanical impedance, analysis of the signals collected during the tests was used to determine the optimum parameters. In the laser shearography method, the physical model of the phenomenon occurring during measurement is used to determine the measurement parameters. The research was conducted on equivalent structures. The presented work is part of a program to develop the technology of repairing the rotor blades of the Mi family helicopters.