Tech Briefs

These technologies are used to protect ground vehicles from ballistic impact.

A pyrotechnic charge (E-match) is embedded in the latch as the actuator to release the latch. The pyrotechnic latch was chosen mainly because of its quick response and ready availability. Pyrotechnic latches are also far more reliable than mechanical fasteners. Further, the displacement of the actuator is directly related to the amount of pyrotechnic charge incorporated in it. A piezoelectric sensor is embedded in a separated bar for detecting the ballistic impact. A PZT bimorph strip is embedded within the two plates along with a thin rubber strip for damping. The main function of the impact bar is to provide the same level with the reactive structure so that two ballistic objects will strike on the impact bar and reactive structure exactly at the same time. The former provides impact signal and the later simulates the penetration in the reactive structure.

An electronic control module (ECM) is housed in a box, and includes a sensor signal amplifier, a noise reduction and thresholding circuit, and a power supply for the actuator. The circuit is designed to take signals in from the two PZT sensors with one mounted on the substrate (PZT1) and the other mounted on the armor (PZT2). When the impact bar is deformed due to an impact, charges are generated in the PZT, which is sent to the signal processing unit.

A dropper mechanism is used to synchronously release two weights onto the reactive structure and the impact sensing bar. The dropper release mechanism consists of two electromagnets wired in parallel and operated by a switch located in the electronic control unit. Two droppers, made of steel shaft, are used to simulate the projectiles: one hitting the impact bar provides impact load for sensing; another one hitting on the reactive structure simulates the penetration and the deflection.

When the projectile hits the reactive armor, the piezoelectric sensor embedded in the armor detects the impact signal and an E-match installed in the pyrotechnic latch is detonated. There is a slot on the armor for the purpose of simulating the penetration of the projectile. Once the pyrotechnic latch is released by the detonation of E-match, the reactive armor moves under the propulsive force of the projectile. In the case of blast impact, the wave of blast pressure moves the reactive armor. The projectile is deflected by the movement of the armor.

This work was done by David Chiyo and Suhasa Bangalore Kodandaramaiah of MKP Structural Design Associates; Karl Grosh and Zheng-Dong Ma of the University of Michigan; and Basavaraju Raju and Farzad Rostam-Abadi of the US Army TARDEC. ARL-0126

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