Ordnance – Shields – Shape or composition
Reexamination Certificate
1999-07-15
2001-11-13
Johnson, Stephen M. (Department: 3641)
Ordnance
Shields
Shape or composition
C264S640000, C089S036080, C089S036050, C002S002500
Reexamination Certificate
active
06314858
ABSTRACT:
BACKGROUND
1. Technical Field
This invention relates to armor for structures, machines and personnel, and more particularly, to an integrated, layered armor incorporating fiber reinforced ceramic matrix composite (FRCMC) material layers and methods for making it.
2. Background Art
Certain types of armor for protecting various structures and machines, as well as body armor for the protection of human beings, has been constructed from monolithic ceramic materials. These materials offer advantages in that they can be extremely hard and light weight. The extreme hardness of ceramic armor has advantages in that incoming projectiles can be shattered on impact. For example, armor made of monolithic ceramic materials is used on tanks to protect against high energy ignition (HEI) rounds. These types of projectiles are designed to penetrate into the interior of the tank before exploding. The monolithic ceramic armor is used to detonate these rounds on impact before they can penetrate the skin of the tank. This ability to detonate the HEI rounds derives from the extreme hardness exhibited by ceramic armor.
Typically, ceramic armor is made up of numerous, flat monolithic ceramic plates or tiles. These plates are sometimes arranged end to end and attached to the surface which is to be protected, such as for example, on the bottom of an airplane or helicopter to protect these aircraft from ground fire. The ceramic plates are also sometimes incorporated into a garment, such as a so called “bullet proof” vest, or other body armor.
Although, armor constructed of monolithic ceramic plates has advantages as described above, it tends to be brittle. Typically, the impact of just one round (i.e. projectile) will shatter an entire plate of the monolithic ceramic armor, even those un-impacted areas of the plate adjacent the impact site. Thus, the entire plate is rendered ineffective against subsequent rounds. In addition, the nature of monolithic ceramic materials and their associated forming methods precludes forming complex shapes or large pieces. Essentially, ceramic armor must be constructed from the aforementioned flat ceramic plates. In the case where ceramic armor is employed on an aircraft, ground vehicle, etc., there can be installation problems associated with attaching numerous flat ceramic plates to a surface that may be curved. In addition, having these numerous small plates attached to an aircraft can increase the aerodynamic drag. Additionally, constructing body armor from flat monolithic ceramic armor plates results in a cumbersome unit which tends to restrict the wearer's movements.
Accordingly, there is a need for armor which exhibits the extreme hardness of monolithic ceramic armor, but which is less brittle, capable of withstanding multiple projectile impacts, and can be formed in large, conformal shapes.
Wherefore, it is an object of the present invention to provide armor which exhibits a degree of hardness which causes projectiles to shatter upon impact, but at the same time exhibits an overall increased ductility so as to facilitate stopping the resulting pieces of the projectile from passing completely through the armor and prevents the shattering of adjacent un-impacted portions of the armor.
Wherefore, it is another object of the present invention to provide armor which can be formed into practically any shape and size desired, so as to be made to conform to the shape of the structure, machine, or even person it is meant to protect.
SUMMARY
The above-described objectives are realized with embodiments of the present invention directed to an integrated, layered armor structure having multiple layers which alternate in their exhibited characteristics between extremely hard and ductile. The extremely hard layers of the armor structure are designed to shatter an impacting projectile, or pieces thereof, and to fracture in such a way as to dissipate at least a portion of the kinetic energy associated with the projectile pieces, and to disperse the projectile pieces and hard layer fragments (and so their kinetic energy) over a wide area. The ductile layers of the armor structure are designed to yield under the force of impinging projectile pieces and hard layer fragments. This yielding dissipates at least a portion of the remaining kinetic energy of these pieces and fragments. Pieces and fragments not possessing sufficient kinetic energy to tear through the ductile layer become trapped therein, and so are stopped. Preferably, there is at least one hard layer and one ductile layer, although there can be additional layers as well, alternating between hard and ductile. The innermost layer which forms the back side of the armor can be either a hard or ductile layer. Likewise, the outermost layer of the armor can be either a hard or ductile layer depending on the application. For example, in some armor applications, particularly where the threat of multiple impacts is high, it is desirable that the outermost layer be a ductile one to increase the retention of fragmented hard layer material shattered by a previous impact. Without the overlying ductile layer, the fractured pieces of the hard layer would simply fall to the ground. However, if retained by the overlying ductile layer, these fragmented pieces of the hard layer will provide some protection, albeit to a lesser degree than a “virgin” layer, against subsequent projectile impacts in the same general area.
Preferably, the degree of hardness of each hard layer is maximized to ensure a substantial shattering of an impacting projectile. In addition, the ductility of each ductile layer is preferably maximized so as to ensure as much of the kinetic energy of the projectile pieces and hard layer fragments as possible is dissipated. It is also noted that each layer is responsible for dissipating some portion of the kinetic energy associated with the impacting projectile, and that the thickness of a layer determines at least in part how much energy is dissipated. The greater the thickness, the greater a layer's kinetic energy-dissipating ability. Given this, it is also preferred that the number of layers and thickness for each layer be selected so as to ensure any impacting projectile is stopped. Further, because the number of layers and their thicknesses will determine the weight of the armor and its overall thickness, and because this weight and overall thickness must be minimized in many applications (e.g. aircraft, body armor), it is preferred that the aforementioned selection be made so as to minimize the number of layers and the thickness of each layer to just that which will ensure the armor is capable of stopping the impacting projectile. In this regard, it is noted that the kinetic energy associated with the projectile pieces will be progressively lower for each hard layer employed in the armor. Accordingly, the thicknesses of these layers can also be progressively reduced to reduce the weight and overall thickness of the armor.
In some cases, it may be advantageous to forego a certain amount of hardness in a hard layer in deference to a higher ductility. This variation would be useful, for example, where the weight and overall thickness of the armor must be limited to a point where certain potentially encounterable projectiles could not be completely stopped from passing through the armor. In such a case, a modified hard layer having a lower hardness would not tend to shatter an impacting projectile, or piece thereof, to the same extent, but the increased ductility would increase the layer's kinetic energy-dissipating ability, thereby increasing the range of projectiles that can be stopped by the armor. Incorporating such a modified hard layer as the innermost layer of the armor would be one example where this feature would be advantageous. In such a case, the projectile would have already been substantially broken into pieces by the preceding hard layers, thereby dispersing the energy over a wider area. Thus, further shattering of the projectile pieces may not be as effective in stopping them, as would increasing
Atmur Steven Donald
Strasser Thomas Edward
Anderson Terry J.
Hoch, Jr. Karl J.
Johnson Stephen M.
Northrop Grumman Corporation
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