Table of Contents ECNDT '98
Automated And Non-destructive Inspection of Composite Helicopter Rotor Blades Using Advanced ShearographyMICHEL HONLET*
ANDREAS ETTEMEYER AND THOMAS WALZ
Dr. Ettemeyer GmbH & Co., D-89231 Neu-Ulm, Germany
EUROCOPTER S.A., F-93126 La Courneuve, France
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As this helicopter blade inspection system is the first fully automatic production control system in european aerospace industry based on laser shearography, this application is an important step in bringing shearography techniques into production control. In this paper, the complete inspection system is presented.
The production of these rotor blades follows a rather complicated and complex procedure and, consequently, a 100% inspection of the blades is required after production. Now, for the first time, a fully automatic inspection system for helicopter rotor blades has been installed in the aerospace industries. The system is integrated into the manufacturing line and allows 100% inspection of each manufactured rotor blade.
Fig 1: Automatic shearography inspection system for helicopter rotorblades.
Fig 2: Shearography camera included in the rotor blade inspection system. Its small dimensions (only a few inches) and light weight allowing easy positioning.
Fig 3: View inside of the vacuum chamber and rotor blade waiting to be inspected.
Fig 4: Control panel of the helicopter system: two monitors show the measuring results of both sides of the rotor blade.
. A ventilation system facilitates fast pressure sequences during operation. The typical pressure difference is a few mbar. Despite the large dimensions of the vacuum chamber, the test pressure difference is realized within 5 seconds. Safety valves stop the evacuation system at the maximum allowable pressure difference of 50mbar.
The rotor blade is positioned on a sledge and fixed by automatic clamps in the center and the sledge is driven into the chamber. Fig. 2 shows a view of the rotor blade from inside the vacuum chamber at the test position. The internal chamber dimensions are designed for inspection of large main rotor blades. Two shearing cameras are positioned on a separate guiding system on each side of the rotor blade. They allow simultaneous inspection of both sides of the rotor blade during one pressure cycle.
Two laser shearography systems measure the deformation of the rotor blade surface at slight pressure changes of 50 mbar. Fig. 3 shows a shearography camera with laser illumination, inspecting a rotor blade.Each camera can observe an area of 600 x 800 mm2 (24" x 31") on each side of the rotor blade.
The inspection areas are illuminated by the green light of a 5 Watt, frequency doubled NdYAG laser. The complete laser system is integrated in the control rack of the system. No external cooling is required for laser operation. The laser light is coupled into two monomode glass fibre cables and guided to the shearography cameras. There, a diffuser system expands the laser beam, to provide homogenous laser illumination on the whole measuring field.
For each rotorblade inspection sequences are defined and stored in a database. These data contain all parameters for definition of the optical and mechanical properties during the inspection cycle. Using the rotor blade code, all parameters are automatically loaded and the inspection is started. If similar rotor blades have been inspected earlier, the measuring results are automatically compared with the stored master data of earlier inspections. Deviations are automatically indicated on the monitor.
The operator can decide to use these data as "good" master data, or to classify as "defect". In this way the system is being taught, learning the properties of each rotor blade by the experience of earlier measurements. Fig. 5 shows the menu, as it appears to the operator. Only limited numbers of operations are allowed. They can be started by just touching the monitor. Keyboard and mouse are not required. The expert can make use of full functionality of the system and, therefore, has a more complex menu, fig. 6.
The inspection result is printed out, indicating the defect position and defect size. The accuracy of the defect position is within 5 mm, the minimum defect size is 10x10mm2. Fig. 7 shows some delaminations , as they show up at the inspection.
Fig 5: Screen shot of the operator test screen: only limited numbers of functions are visible. Large buttons allow start and stop of tests just by touching the monitor.
Fig 7: Inspection results on both sides of a 800x600mm2 (31x24") field on the rotor blade with defects. The typical double indictations show local delaminations.