Multi-domain contactless NDI approach: Data fusion of structural light scanning with thermography and shearography

Abstract

The proportion of composite materials (such as CFRP) compared to the metal used on modern aircrafts is rising, imposing different kind of failure modes. Since the composite structures are known to be sensitive to impact loading, there is need for means to assess the sub-surface damage in the structure rapidly. Royal Netherlands Aerospace Centre NLR has an extensive track record on contactless non-destructive inspection (NDI) methods based on optical sensors, such as 3D surface scanning, lock-in thermography and laser shearography. The combination of these methods (multi-domain inspection) enables us to assess the structural integrity of an aircraft outer surface in a short time, reducing inspection costs and the “down time” of the aircraft. Recently, NLR is working towards a 3D oriented mesh environment of an object, enhanced with NDI data, providing sub-surface damage information . The combination of the different NDI methods makes it easier to identify and classify different defect types. To demonstrate this procedure a small radome which suffered impact damage after an hail storm is used. The impact damage resulted in dents on the surface which can be detected using 3d Structural light scanning, however the internal structure can not be assed using this technique. Using lock-in thermography damage inside of the skin can be detected, but no skin-to-core disbonds can be detected using single sided inspection. By using shearography it is possible to detect disbonds between the glass fibre skin and the nomex honeycomb core. Using the combination of the aforementioned techniques, it is possible to assess the overall health of the radome. Additionally , in order to demonstrate this techniques on a larger part results from a 747-400 right hand inboard aft flap is also shown . All techniques are non-contact also allowing for a great deal of automatization during inspection.