Ballistic panel

A substantially rigid ballistic panel made of a composite material consisting of fibers embedded in a resin, characterized in that, with regard to mechanical properties across the surface of the panel, the panel is inhomogeneous.

The present invention relates to ballistic panels made composite material 
and exhibiting enhanced protective qualities in comparison to known 
ballistic panels made of similar materials and of similar weight. 
Regardless of the material of which prior art flexible or rigid panels were 
made, they all had a common property: they were homogeneous, i.e., the 
mechanical properties of such a panel were substantially uniform 
throughout and over all points of the panel. While conventional wisdom 
would assume such panels to have optimum protective properties, it was 
surprisingly found that panels with "built-in" inhomogeneities concerning 
hardness, elongation and mechanical strength offered better protection in 
that impacting projectiles tend to be deflected towards the weaker or 
softer structural elements, thus turning a perpendicular impact into a far 
less damaging, slanting one. 
It is thus the object of the present invention to provide a ballistic panel 
of an inhomogeneous structure that will substantially enhance the 
protective capabilities of such panels and reduce the trauma effect. 
According to the invention, this object is achieved by providing a 
substantially rigid ballistic panel made of a composite material 
consisting of fibers embedded in at least one type of resin, characterized 
in that, with regard to mechanical properties across at least the surface 
of the panel, said panel is inhomogeneous. 
The invention further provides a substantially flexible, multilayer 
ballistic panel made of woven textile threads, characterized in that, with 
regard to mechanical properties, said panel is inhomogeneous. 
The invention will now be described in connection with certain preferred 
embodiments with reference to the following illustrative figures so that 
it may be more fully understood. 
With specific reference now to the figures in detail, it is stressed that 
the particulars shown are by way of example and for purposes of 
illustrative discussion of the preferred embodiments of the present 
invention only, and are presented in the cause of providing what is 
believed to be the most useful and readily understood description of the 
principles and conceptual aspects of the invention. In this regard, no 
attempt is made to show structural details of the invention in more detail 
than is necessary for a fundamental understanding of the invention, the 
description taken with the drawings making apparent to those skilled in 
the art how the several forms of the invention may be embodied in 
practice.

Referring now to the drawings, there are seen in FIGS. 1-4 several 
configurations of the above-mentioned structural elements rendering 
ballistic panels inhomogeneous, a quality that, as explained, was found to 
enhance the protective properties of these panels by deflecting an 
impacting projectile towards the weaker or softer structural elements and 
thus turning even a perpendicular impact into a far less damaging, 
slanting one. 
The panels 2 are made of a plurality of layers of a composite consisting of 
a resin matrix (phenols, polyester, epoxy, polymethane, etc.) in which, in 
a per se known manner, are embedded synthetic fibers (KEVLAR, Nylon, 
polyester, etc.), not shown. 
In one of the embodiments of the panel 2, inhomogeneity, irrespective of 
the particular shapes as represented by way of example only in FIGS. 1-4, 
is achieved by using two separate resins having different mechanical 
properties such as hardness and elongation. Thus, the rectangular matrix 
regions in FIG. 1, the square regions in FIGS. 2 and 3, and the circular 
regions in FIG. 4 consist of, e.g., a high-strength resin 4, and the 
matrix regions surrounding these shapes consist of a resin 6 of lower 
mechanical properties, or vice-versa. An example of the dimensions and 
relative positions of these regions is given in FIG. 4, with A and B being 
of an order of magnitude of 15 mm and C, of 8 mm. 
FIG. 5 is a schematic cross-section of the panel 2 along plane V--V in FIG. 
4, in which the vertical lines indicate the boundaries of the layers 8 and 
the horizontal lines denote the boundaries of the different resins 4 and 
6. For reasons of clarity, the fibers are not shown and the shading for 
each particular resin is unidirectional. The number of layers 8 depends on 
the type of projectile the panel is meant to stop. 
While in the panels of FIGS. 1-4 the above-discussed deflection effect was 
obtained by producing inhomogeneities resulting from the use in adjacent 
regions of resins of different mechanical properties, a similar effect is 
also obtainable by the use of a single resin only, and varying in adjacent 
regions the weight percentage (wt. %) of that resin, weight percentage 
being, in this case, the percentage of resin in the total weight of the 
composite panel (including resin and fibers). 
To achieve this type of inhomogeneity, the panel 2 of, say, FIG. 4, is 
subjected in its precured state to pressure by a plate 10 having a 
plurality of perforations 12 of a diameter, e.g., C and mutual distances, 
e.g., A and B, as in FIG. 4. As a result of such pressure, the regions 6 
of the layered panel 2 are compressed, with some of the material flowing 
into the perforations and producing the knobbly, "blistered" surface of 
the cross-sectional view of FIG. 6, with the surface projections 14 having 
a height of about 0.8 mm. Clearly, the panel "columns" produced by the 
stack of "nested" projections of the plurality of panel layers and aligned 
with the perforations 12, have a higher wt. % than the regions 6 that were 
subjected to pressure, being about 18%, while the wt. % of the projection 
14 is about 22%. It is also seen that the "blister"-raising effect of the 
pressure decreases with increasing depth, which reduces the brittleness of 
the lower layers, a desirable situation that enhances the protective 
properties of the panel. As an additional "bonus," the fibers inside the 
projections 14 are less prestressed in tension and are thus capable of 
absorbing larger amounts of energy before failing. 
FIG. 7 schematically represents a panel in which the inhomogeneities are 
the result of a pattern of dimples 16 embossed in the panel by means of a 
pressure plate 18 with projections 19. In this case, the panel "columns" 
defined by the diameter of the surface dimples 16 have a lower wt. % than 
the regions 6, which were not subjected to pressure. In analogy to the 
panel of FIG. 6, the effect of the embossing decreases with increasing 
depth. The fibers in the dimpled regions, on the other hand, are more 
stressed in tension than the fibers in the raised resions of FIG. 6. 
Panels with "blistered" or "dimpled" surfaces can, of course, be produced 
also with other configurations of surface patterns. 
Also known are multi-layer, flexible ballistic panels made of woven 
textiles. In analogy to the above-discussed panels made of composites, the 
protective properties of these textile panels can equally be improved by 
rendering their structure inhomogeneous. 
In the panel layer detail of FIG. 8, for instance, the number of warp 
threads 20 per unit length is much larger than that of the weft threads 
22. 
In FIG. 9, the denier number of adjacent warp and/or weft threads 24 
gradually decreases in a periodically recurrent pattern or sequence, while 
in FIG. 10 the adjacent warp and/or weft threads 26 to 34, although of the 
same denier, are of a mechanical strength that gradually decreases in a 
periodically recurrent pattern or sequence, thread 36 restarting the 
pattern, being of the same strength as thread 26. 
Obviously, these panels can all be turned into composites by impregnating 
their basic layers or basic warp or weft configurations with one of the 
resins. 
Also, the invention can just as well be realized utilizing mono-directional 
threads or fibers. 
It will be evident to those skilled in the art that the invention is not 
limited to the details of the foregoing illustrated embodiments and that 
the present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof. The present 
embodiments are therefore to be considered in all respects as illustrative 
and not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description, and all changes 
which come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.