Damage control materials for warship construction

A warship is provided with a plurality of interior volumes defined by an inner wall structure and an outer wall structure spaced apart from the inner wall structure. The space between the inner wall structure and the outer wall structure includes a syntactic foam-macrosphere composition between the wall structure which dissipates force applied to an outer wall structure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to damage control materials for warship 
construction and, more particularly, to a warship construction including 
an energy absorbing composition positioned to surround and protect areas 
of the ship that house critical elements and personnel required to 
accomplish the ship's mission. More particularly, the present invention 
relates to such a warship wherein the energy absorbing composition 
includes hollow microspheres and hollow macrospheres in a resin matrix. 
2. Description of Prior Art 
Warships are constructed from metal plates designed to withstand impact 
explosion and shock forces of weapons which are designed to damage or sink 
the ship. While the plates and the supporting structure for the plates, 
such as web frames or girders, improve the defense strength of the ship, 
limitations on their size are imposed, primarily due to considerations of 
ship buoyancy, ship stability and ease of ship handling during passage on 
the sea. Ships are formed of hulls having a variety of configurations. 
Some ships have double bottoms and double sides to form an inner hull and 
an outer hull, traditionally termed a double hull construction. In large 
ships, the space between the two hulls typically is at least about two 
meters. The volume defined by the inner surface of the inner hull 
comprises the volume within which the ships personnel are housed and 
within which weapons and supplies, including munitions are stored. The 
double hull design conventionally is orthogonally-stiffened by both 
transverse web frames and longitudinal girder (or longitudinal "webs") 
between the inner and outer hulls to form a stiff grid bottom structure 
beneath the main volume of the ship. While it is known that double hulls 
can effectively protect against minor impact forces, it is also known that 
they are ineffective to withstand strong impact forces such as that 
derived from weapons effects directed at the ship. Such strong impact 
forces cause both the inner and outer hulls to be breached. Areas of the 
warship, in addition to the hull, also must be protected against impact 
forces from incoming projectiles directed at the ship during times of war. 
Additional protection in specific areas of the ship may be required for 
the isolation of damage due to weapons effects or other extremely high 
energy releasing events. These areas include housing of personnel, 
munitions, offensive weapons and the ship's communication system. 
It has been proposed to provide strength enhancing and shock absorbing 
elements between the two hulls of double hull ship. It also has been 
proposed to provide a foam material between the two hull to provide 
improved hull strength. Such arrangements are shown, for example in U.S. 
Pat. Nos. 3,811,141; 3,831,212; 3,840,296; 3,887,952 and 3,911,190. It has 
also been proposed to utilized hollow beads between the two hulls, as for 
example by U.S. Pat. No. 3,124,626. While the use of foam material or 
hollow beads comprise an improvement over a hollow space between the two 
hulls to effect absorbance and diffusion of force applied to the outer 
hull and to reduce force transmission to the inner hull, their use is 
undesirable since a significant portion of the impact force is transmitted 
to the inner hull. 
It has also been proposed in U.S. Pat. No. 5,353,727 to provide a collision 
guard to the exterior hull surface of a marine vessel which is formed from 
a lightweight permanent buoyant material, such as a fire retardant foam, 
in order to improve resistance against forces applied to the exterior 
hull. Such modules are undesirable since they are subjected to the normal 
sea forces to which a vessel is subjected resulting in their detachment 
from the vessel. 
It has been proposed in U.S. Pat. No. 5,277,145 to increase the strength of 
a transom portion of a boat with syntactic foam formed from a resin 
containing hollow microspheres, usually made of glass. These microspheres 
generally have a diameter of between about 1 and about 100 microns. Such 
syntactic foam compositions are undesirable for use between hulls of 
double hull since they preferentially transmit rather than absorb forces 
applied to them. This is primarily due to the fact that the microspheres, 
when embedded within a thermosetting resin, are extremely resistant to 
impact forces and thus transmit impact force through the composition 
rather than collapsing up to the point wherein very high impact forces are 
applied to the syntactic foams. 
Modified syntactic foam are disclosed in U.S. Pat. No. 3,622,437 for use as 
buoyant materials to be positioned in sea environments, for example more 
than a thousand feet below the surface of the sea. Such modified syntactic 
foams include relatively large hollow spheres which provide a reduced 
density for the modified syntactic foam as compared to the unmodified 
syntactic foam. 
Accordingly, it would be desirable to provide a warship construction which 
includes an energy absorbing composition positioned in those areas of the 
warship requiring protection. In addition, it would be desirable to 
provide such a composition which does not significantly adversely effect 
the buoyancy of the vessel when the composition is positioned within the 
warship. Furthermore, it would be desirable to provide such a composition 
which preferentially absorbs energy when excessive energy is applied to it 
rather than transmitting energy to the ship's structural elements so that 
critical areas of the ship remain protected.

SUMMARY OF THE INVENTION 
In accordance with the present invention, a construction for a warship is 
provided which includes a force-absorbing composition positioned within 
the ship in areas that require protection from impact forces including 
impact force generated by incoming projectiles. The force-absorbing 
composition is a syntactic foam comprising a resin matrix and hollow 
microspheres and which includes hollow macrospheres. As used herein the 
term, "syntactic foam" means a hardened or hardenable resin matrix 
containing small hollow microspheres, such as glass microspheres or 
polymeric, e.g., polypropylene or polyurethane, microspheres having a 
diameter between about 1 and about 100 microns as defined by the ASTM 
Committee on Syntactic Foam. As used herein, the term, "macrospheres", 
means hollow spheres formed from a resin binder either alone or containing 
reenforcing fibers such as glass fibers, carbon fibers or the like having 
a diameter about 1/16 inch and 4 inches. The volume percent hardened 
syntactic foam to macrospheres is between about 10 to 60 volume % 
syntactic foam to about 40 to 90 volume % macrospheres, preferably between 
about 20 to 40 volume % syntactic foam to about 60 to 80 volume % 
macrospheres, The syntactic foam functions to provide strength and energy 
absorbing properties to the composition positioned between the two hulls. 
The macrospheres function to provide light weight, strength and energy 
absorbance capacity to the composition. 
The syntactic foam-macrosphere composition is positioned in spaces 
surrounding that portion of the ship containing materials or personnel to 
be protected by first introducing the macrospheres into the spaces. 
Thereafter, the syntactic foam, while the resin matrix is in a fluid 
state, is introduced into the spaces such as by being pumped. The 
macrospheres can have varying diameters or can have essentially the same 
diameter. After the syntactic composition has been pumped into the spaces, 
the resin portion thereof is allowed to harden by being thermally cured at 
a suitable temperature to effect crosslinking of the resin matrix and to 
render it thermosetting. Alternatively, projectiles. The force-absorbing 
composition is a syntactic foam comprising a resin matrix and hollow 
microspheres and which includes hollow macrospheres. As used herein the 
term, "syntactic foam" means a hardened or hardenable resin matrix 
containing small hollow microspheres, such as glass microspheres or 
polymeric, e.g., polypropylene or polyurethane, microspheres having a 
diameter between about 1 and about 100 microns as defined by the ASTM 
Committee on Syntactic Foam. As used herein, the term, "macrospheres", 
means hollow spheres formed from a resin binder either alone or containing 
reenforcing fibers such as glass fibers, carbon fibers or the like having 
a diameter about 1/16 inch and 4 inches. The volume percent hardened 
syntactic foam to macrospheres is between about 10 to 60 volume % 
syntactic foam to about 40 to 90 volume % macrospheres, preferably between 
about 20 to 40 volume % syntactic foam to about 60 to 80 volume % 
macrospheres, The syntactic foam functions to provide strength and energy 
absorbing properties to the composition positioned between the two hulls. 
The macrospheres function to provide light weight, strength and energy 
absorbance capacity to the composition. 
The syntactic foam-macrosphere composition is positioned in spaces 
surrounding that portion of the ship containing materials or personnel to 
be protected by first introducing the macrospheres into the spaces. 
Thereafter, the syntactic foam, while the resin matrix is in a fluid 
state, is introduced into the spaces such as by being pumped. The 
macrospheres can have varying diameters or can have essentially the same 
diameter. After the syntactic composition has been pumped into the spaces, 
the resin portion thereof is allowed to harden by being thermally cured at 
a suitable temperature to effect crosslinking of the resin matrix and to 
render it thermosetting. Alternatively, the macrosphere syntactic foam can 
be molded off site and mechanically installed on the ship. 
When the ship is subjected to an impact force initiated on an outside 
surface or an internally generated high energy, extreme loading event, the 
force is transmitted from the outside surface into the composition and, if 
the impact force is sufficiently high, the macrospheres in close proximity 
to the point of impact begin to fracture under the force of the impact 
thereby absorbing the impact force. When the impact force is sufficiently 
high, the macrospheres fracture sequentially; first at the most proximate 
points to the point of initial impact and thereafter sequentially 
fracturing progressively away from the point of initial impact. Due to 
macrosphere fracturing, the impact force is dissipated significantly prior 
to its being transmitted, by way of the hardened resin matrix of the 
syntactic foam, to the inner portion of the ship.. By substantially 
reducing the impact force prior to the force reaching the inner portion of 
the ship, the probability of significant ship damage is correspondingly 
reduced or eliminated. Accordingly, the syntactic foam-macrosphere 
composition utilized in the present invention provides substantial 
advantages over a hardened syntactic foam or an empty space. 
DESCRIPTION OF SPECIFIC EMBODIMENTS 
The terms, "wall structure" as used in herein is meant to include a curved 
or flat barrier such as a wall, bulkhead or hull which alone, or together 
with at least one other wall, bulkhead or hull defines an interior volume 
positioned within said "wall structure". Such interior volumes can be used 
for any conventional warship purpose, such as housing for personnel, 
storage of ammunition, storage of communication systems, storage of 
weapons, storage of projectile delivery systems, missile silos or the 
like. 
In accordance with the present invention the spaces within a warship such 
as the space between an inner hull and an outer hull of a double hull 
construction are filled with a composition comprising a hardened syntactic 
foam and macrospheres. The volume ratio of hardened syntactic foam to 
macrospheres is between about 10 and about 60 volume % syntactic foam, 
preferably between about 20 and 40 volume % syntactic foam and between 
about 40 and about 90 volume % macrospheres, preferably between about 60 
and about 80 volume % macrospheres. The macrospheres can have an 
essentially uniform diameter or can have a varying diameter between about 
1/16 inch and about 4 inches, preferably between about 1/4 inch and about 
1/2 inch. The macrospheres can be formed from thermoset or thermoplastic 
polymer such as of any synthetic resin composition which may include a 
reinforcing agent such as fibers including glass fibers, carbon fibers or 
the like. The macrospheres typically are formed of polyvinyl esters, 
polyesters, phenolic resins, epoxy resins, polyurethanes, polyamides, high 
density polyethelynes, polypropylenes, polyacrylonitriles, acrylonitrile 
butadiene styrene, or styrene acrylonitrile. The macrospheres typically 
are formed by conventional injecting molding such as molding two matched 
hemispheres and joining them or rotational molding or the like. 
The syntactic foam contains glass microspheres having a diameter between 
about 1 and 300 microns, preferably wherein 50% of the microspheres have a 
diameter between about 30 and about 70 microns. The resin carrier for the 
syntactic foam initially is a pumpable liquid which is curable over time 
at room temperature or at elevated temperature. Exemplary resin matricies 
include phenolic resins, epoxy resins, polyurethanes, polyesters, 
polyureas, polyvinyl esters, polyamides, or the like. The resin is curable 
to form a crosslinked thermoset hardened composition which is not flowable 
at ambient temperature. If desired, the resin can contain conventional 
resin modifiers including stiffening modifiers such as rubber modifiers 
including butane based rubbers or fibers such as glass fibers or carbon 
fibers or the like. 
Typically, the space between the inner and outer hull of a double hull 
vessel is segmented so that sub volumes thereof are defined by plate 
members which are positioned generally orthogonally within the volume. 
Segmentation of this volume provides strength to the double hull 
structure. When segmented volumes are provided within the space between 
the two hulls, orifices are provided through the walls of each segment to 
permit fluid communication into the segment volume from outside the 
segment volume. These volumes are filled with the syntactic 
foam-macrosphere composition by introducing the macrosphere composition 
into the volume through the orifice to fill the volume to the desired 
degree. Thereafter, the flowable syntactic foam composition is pumped into 
the volume to fill the remainder of the volume with the syntactic foam. A 
second orifice is provided to permit air in the volume to flow through the 
volume thereby to permit displacement thereof with the syntactic foam. The 
syntactic foam then is cured in place to form a thermoset composition 
either by effecting curing at ambient temperature or at elevated 
temperature, depending upon the cure resin utilized. Suitable curing 
temperatures are well known to a person skilled in the art. Liquid flow 
into the segment volumes is prevented by the cured resin. If desired, the 
orifices can be further sealed such as with metal plates. 
Referring to FIG. 1 a warship 1 includes a bridge section 2 for personnel 
to control the ship, gun turrets 3 and 4 stacks 5, a double hull 6, 
weapons storage areas 7, 8 and 9 and communications sections 10 having an 
antenna 11. The interior volume within hull 6 is segmented by walls, 
bulkheads or the like to isolate personnel living areas from work areas 
and weapons storage areas or the like. In one aspect of this invention the 
warship can be arranged to be remotely controlled so that no on-board 
personnel are needed. The walls or bulkhead can include orifices to permit 
personnel access to various areas of the ship. At least a portion of the 
walls or bulkheads are constructed as double walls or double bulkheads 
spaced apart from each other to form a space within which the energy 
absorbing composition can be positioned. 
Referring to FIGS. 2-4, double hull 6 includes a bow 12, a stern 14, an 
exterior hull, 20 and an interior hull 22. The interior section 24 which 
is generally formed by the interior surface of interior hull 22 can 
include a port section 26 and a starboard section 28 which are separated 
by longitudinal bulkhead 30. The longitudinal bulkhead 30 can include 
orifices (not shown) for personnel access and can extend the length of 
interior section 24. The port section 26 and starboard section 28 are 
divided along their lengths by transverse bulkheads 32 which are separated 
therefrom along the length of the section 24. The spaces 34 between the 
interior hull 22 and the exterior hull 20 are filled with the syntactic 
foam-macrosphere composition utilized in the present invention. 
The double hull shown in FIG. 2-4 is shown generally as having a plurality 
of compartments 26 separated by bulkhead 30. This construction is 
desirable since it provides increased strength to the hull structure. The 
modified syntactic foam which is positioned between the interior hull 22 
and exterior hull 20 is shown in FIG. 8. The syntactic foam portion 
comprises a hardened resin 30 containing microspheres 32 and macrospheres 
34 of varying sizes. The macrospheres 34 are hollow spheres which are 
distributed throughout the bulk matrix of resin 30. The density of the 
syntactic foam comprising the hardened resin 30 and the microspheres 32 
ranges between about 30 and about 40 pounds per cubic feet, preferably 
between about 32 and about 38 pounds per cubic feet. When the macrospheres 
34 are added to the syntactic foam in the proportions set forth above, the 
resultant composition comprising the hardened resin 30, the microspheres 
32 and macrospheres 34 has a density between about 14 and about 40 pounds 
per cubic feet, preferably between about 16 and about 24 pounds per cubic 
feet. 
The modified syntactic foam in FIG. 8 is introduced into the spaces desired 
such as the space between interior hull 22 and the exterior hull 20. As 
shown in FIG. 6 the space between the interior hull 22 and the exterior 
hull 20 can be subdivided into subvolumes 40 by means of longitudinal 
bulkheads 42 and transverse bulkheads 44. Each subvolume 40 is provided 
with an inlet orifice 46 and an outlet orifice 48 which permit the 
introduction of the modified syntactic foam described above into each 
subvolume. Typically, the macrospheres are introduced through inlet 46 
until the desired proportion of the subvolume 40 contains the 
macrospheres. Thereafter, the mixture of the hardenable fluid resin and 
the microspheres is pumped into the subvolume through the inlet 46 until 
excess resin appears at outlet 48. Thereafter, pumping of the resin and 
the microspheres into the subvolume 40 is stopped. After all of the 
subvolumes 40 have been filled with the syntactic foam utilized in the 
present invention, the resin portion of the syntactic foam is allowed to 
cure the form a thermoset resin, as described above. 
The modified syntactic foam also can be introduced into volumes of the ship 
which require impact force protection other than the hull, as illustrated 
in FIG. 5. A gun turret 47 is formed of an outer wall 49 and an inner wall 
51 to house a gun 53. The space between the walls 49 and 51 is filled with 
the modified syntactic foam containing macrospheres as described above. 
An alternative embodiment of this invention is shown in FIG. 7 wherein the 
subvolume 40 having an inlet 46 and an outlet 48 also includes mechanical 
means for dissipating impact forces to one an exterior surface such as 
exterior hull 20 as represented by arrow 50. The hollow space 52 within 
the subvolume 40 is filled with the syntactic foam- macrosphere 
composition described above. The force on exterior hull 20 is transmitted 
by vertical plates 54 which support horizontal plate 56. This force, in 
turn, is transmitted to the three vertical plates 58, then to horizontal 
plate 60, then to the four vertical plates 62 and lastly to inner hull 22. 
The plate system shown in FIG. 7 dissipates the initial force 50 so that 
any fmal force resulting from force 50 onto inner hull 22 is divided among 
the four vertical plates 62 rather than being concentrated within a small 
area of hull 22. Thus, the system of plate shown in FIG. 7 supplements the 
force dissipation function of the syntactic foam- macrosphere composition 
described above. In addition, the plates 58 can be designed to purposely 
fail when subjected to excessive force 50 so that the force 50 is not 
undesirably concentrated on inner hull 22. 
The failure mode of the syntactic foam-macrosphere composition described 
above, when utilized in the present invention is illustrated in the FIGS. 
9a, 9b and 9c. The intact syntactic foam-macrosphere composition 68, prior 
to the application of a force 70 to an exterior surface such as exterior 
hull 20 is in FIG. 9a. As shown in FIG. 9b, the row of macrospheres 72 
most proximate to impact force 70 is crushed to form crushed macrospheres 
76 (FIG. 9b) while the remaining two rows of macrospheres 78 and 80 remain 
generally intact. The destruction of the row of macrospheres 72 serves to 
absorb a portion of the force 70 and to dissipate the force 70 away from 
the initial point of impact 71 on the exterior hull 20. As the impact 
force 70 proceed into the syntactic foam-macrosphere composition. The 
second row of macrospheres 78 is fractured to further dissipate and absorb 
the impact force 70. The destruction of macrospheres under the impact 
force serves to minimize or prevent the force applied to an inner surface 
such as inner hull 22, thereby substantially increasing the probability of 
maintaining the inner hull intact.