Evaluating the stability of a metric for determining the health of armor plates

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Evaluating the stability of a metric for determining the health of armor plates

Meitzler, Thomas J. / Reynolds, Thomas / Ebenstein, Samuel / Smith, Gregory

Various types of ceramic armor plates are in use by the U.S. military because of their relatively light weight as compared to traditional armor. Obviously, the level of protection is diminished if plate integrity is compromised. Various factors can cause damage to the armor, such as being hit by a projectile in a battlefield situation or by being damaged in a depot by running into some obstacle. In either situation, the vehicle occupants may not be aware that the armor has been compromised. A technique has been developed that uses piezoelectric lead zirconate titanate (PZT) transducers embedded in an armor plate to cause the plate to vibrate at various frequencies. The amplitudes of the natural and induced vibrations at the various frequencies can be used to generate a characteristic signature of the armor plate. A metric has been developed to detect deviations from the signature of an undamaged plate. This paper provides techniques for determining the stability of this metric. By testing an undamaged armor plate several times under various ambient conditions, a metric can be developed that can be used to differentiate between undamaged and damaged armor plates. The process uses several tests and then randomly picks a small subset of the total tests to develop the metric. The subsequent metric is then tested by comparing the value it gives for the entire set of tests. Analysis of the graph of metric values and their multiplicities can be used to determine the quality of the metric. Finally, the plate can be damaged as a final step in verifying that the metric distinguishes between undamaged and damaged plates.