Improvement of Time Reversal Processing in Titanium Inspections

We have explained in previous papers [1,2] a completely different NDE technique applied to the titanium alloy billet, the time reversal process, which allows conversion of a divergent wave issuing from a defect into a convergent wave focusing on it. The time reversal method is a self adaptive technique which produces a focussed beam matched to the defect shape and generates an unfocussed wave in the case of a speckle noise source. The results have showed the ability of this technique to focus on defects in a scattering media through a complex interface. However, this technique is subject to the principal NDE systems problem: the false alarms. Indeed, high levels of grain noise can mask signals from smaller or lower acoustic reflectivity flaws and than a grains configuration can be confused with a small defect. In case of the inspection of large titanium parts such those found in the aircraft engine industry (thickness > 5″), the classical techniques are more sensitive to this problem in the deep zones: the grain density often increases with depth du to the forging technique and the backpropagated defect echoes are weak in account of the attenuation.