Low frequency NDT techniques for the detection of disbonds and delaminations

The physical basis of a family of low frequency vibration methods which can be used for the detection of delaminations in composite materials, disbonds in adhesive joints and defective honeycomb constructions is reviewed. The family comprises the coin tap test (commercially available as the Tapometer) the mechanical impedance method (commercially available as the MIA), the membrane resonance method (commercially available as the Shurtronics Harmonic Bond Tester) and the velocimetric method (commercially available as the Sondicator). The sensitivity of all the methods is reduced as the defect depth is increased and some of them are unreliable close to the edges of a structure or on flexible structures. These effects are discussed and the relative advantages of the different techniques are reviewed