Ceramic-metal armour systems, compared to traditional armour systems, offer enhanced ballistic performance to the operational demands of modern warfare. Such performance depends on the material properties of the constituent parts and the quality of bonding between them. Consequently, there is a need to be able to quantify the quality of the bonding to assure the performance of armour and to accelerate development of armour.

An acoustic characterisation technique has been developed to evaluate the quality of the metal-ceramic interface and dispersion of impact energy within the armour. A semi-analytical model was constructed to explain the acoustic responses and to predict the effects of material and interface changes. Bespoke piezoelectric sensors were mounted on both the front ceramic strike face and rear metallic backing. Sensor response signals were recorded from projectile impacts of 5.5, 220 and 700m/s, on alumina ceramic plates adhered using epoxy resin to metallic substrates, of either aluminium or steel.

The semi-analytical model was able to explain and predict key behaviours of the armour:

• A greater acoustic impedance mismatch between layers, resulted in less stress transmitting into the metal backing.
• Sensor response signals exhibited an increased amplitude and decreased wavelength with increasing impact velocity, due to a shorter impact duration.
• The presence of heterogenous interfaces results in an amplitude increase in later arriving peaks and the emergence of secondary peaks within the sensor response signal, such that the relative quality of the interface can be evaluated.

Increasing impact-sensor distance caused a decrease in signal amplitude. At a critical distance the signal inverted due to the angle of incidence of the acoustic wave to the sensor causing the Poisson contraction to excite the sensor. The relative arrival time of acoustic signals at 3 substrate mounted sensors triangulated strike locations on the ceramic strike face to within 5.5mm.