AReactive Structure Technology (RST) is a new class of smart structure that can react to external excitations (such as blast or ballistic impacts) in a carefully designed way using the energy pre-stored internally or from the external excitations to counteract the hazardous loading or perform other desired tasks. A reactive structure deflects an incoming projectile in order to protect a vehicle body. When a projectile hits the face plate (armor), the embedded sensors feed the impact signal to a control unit, and actuators are triggered to move the faceplate. The movement of the faceplate deflects the projectile and significantly reduces the possibility of penetration in the back plate.

A Reactive Structure deflects an incoming projectile in order to protect the vehicle body. When a projectile hits the faceplate (armor), the embedded sensors feed the impact signal to a control unit, and actuators are triggered to move the faceplate (a). The movement of the faceplate deflects the projectile and significantly reduces the possibility of penetration in the back plate (b).
A common form of reactive armor is Explosive Reactive Armor (ERA). ERA tiles are usually used as add-on armor to the portions of an armored fighting vehicle that are most likely to be hit. The use of ERA requires that the vehicle itself is fairly heavily armored. Another drawback to the use of ERA is the inherent danger to anybody near the vehicle.

Non-Explosive Reactive Armor (NERA or NxRA) uses passive material, such as rubber, sandwiched between two metal plates. The loads from NERA inflicted on the vehicle’s structure are much smaller than ERA, and therefore can be applied to lighter vehicles. However, NERA is not as effective as ERA for protecting Kinetic Energy threats.

The reactive structure (armor) proposed in this research combines the advantage of both ERA and conventional NERA and eliminates their disadvantages. It consists of two main integrated modules: 1) a face metal plate embedded with impact sensors that is able to react to the impact load and change the configuration using prestored potential energy or the energy from impact load; and 2) an electronic control module capable of differentiating external impact loads by blasts and ballistic objects from normal vibrations during operation.

Two prototypes of the reactive structure have been designed and fabricated for proving the concept. In order to simulate the projectile object, a dropper mechanism and a shooting device have also been developed. The reactive structure module is made of a spring-loaded four-bar linkage. It is held in configuration using a latch. In this position, the two springs are compressed and potential energy is stored in them. When the latch is unlocked, the springs uncoil, and the structure moves under the spring force. Thus, stored potential energy is used to bring out a configuration change. The substrate can be considered as the protected body, and the top plate represents the moving armor. The entry hole made in the top plate is for simulating the penetration by the ballistic object.

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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This article first appeared in the February, 2012 issue of Defense Tech Briefs Magazine.

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