Abstract:
A blast mitigation method includes forming a body of solid material which transitions from a solid state to a non-flowing viscous fluid state when stressed which attaching it to the body of the undercarriage of a vehicle. The material of the body transitions from a solid state to a viscous fluid, state when an explosion occurs, is proximate the body and it absorbs at least some energy from the explosion mitigating impact on the vehicle. A plunger plate with blades extending outwardly therefrom is coupled to the body and oriented such that the blades are adjacent the body.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 13/507,051, filed May 31, 2012, which is incorporated herein by reference. 
     This application is also related to U.S. patent application Ser. No. 12/925,354 filed Oct. 19, 2010 which claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/281,314 filed Nov. 16, 2009 under 35 U.S.C, §§119, 120, 363, 365, and 37 C.F.R. §1.55 and §1.78 each of which is incorporated herein by this reference. This application is also related to U.S. patent application Ser. No. 13/385,486 filed Feb. 22, 2012, and incorporated herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     The subject invention relates to vehicle underbody blast effects and ballistic damage mitigation. 
     BACKGROUND OF THE INVENTION 
     Mines and improvised explosive devices (IEDs) can damage vehicles and injure or kill vehicle occupants. Some work has been carried out to detect and disable mines and IEDs. Other engineering concerns tailoring vehicles to be more resistant to the blast of a mine or IED. Examples include the V-hull of the MRAP and STRYKER vehicles designed to deflect away a part of the explosive forces originating below the vehicle. See for example, published U.S. Patent Application Nos. 2011/0169240 and 2011/0148147, incorporated herein by this reference. 
     There is a limit, though, to how much of the explosive blast can be deflected. And, some vehicles cannot be engineered to include a V-hull. Still other vehicles cannot be equipped with heavy armor. The military HMMWV vehicle, for example, is and must remain configured to quickly traverse difficult terrain. 
     SUMMARY OF THE INVENTION 
     In examples of this invention, a lightweight effective blast shield is designed for use as a vehicle (e.g., underbody) design or as an attachment kit for blast mitigation due to a land mine or IED explosion. The shield is designed to partially deflect away the pressure wave of a blast and/or absorb a significant part of the blast energy by use of mechanisms and a phase changing material. Structures herein may be used to absorb impulses, energy, and/or blasts may be protected in the same way. 
     The invention features a blast mitigation method of forming a body of solid material which transitions from a solid state to a viscous fluid state when stressed which attaches to the body of the undercarriage of a vehicle. The material of the body transitions from a solid state to a viscous fluid state when an explosion occurs proximate the body and absorbs at least some energy from the explosion mitigating its impact on the vehicle. Further included may be the step of disposing a plunger plate with blades extending outwardly therefrom adjacent the body and oriented such that the blades are adjacent the body. The method may further include adding, to the undercarriage of the vehicle, a second body and disposing a plunger plate between the bodies. 
     Further featured is a method of equipping a vehicle with a blast shield, the method including placing a body of damping material proximate a vehicle undercarriage, the body of damping material transitioning from a solid state to a viscous fluid state when stressed, positioning a plunger plate with outwardly extending blades proximate the body of damping material with the plunger plate blades adjacent said body of damping material, and securing the combination of the body of damping material and plunger plate to the vehicle undercarriage for blast protection. If the vehicle includes an installed hull plate, the body of damping material and plunger plate can be secured to the vehicle hull plate. In another method, the vehicle hull plate is removed. Then, the body of damping material is sandwiched between a blast shield hull plate and the plunger plate and this combination of the blast shield hull plate, body of damping material, and plunger plate is secured to the vehicle undercarriage in place of the vehicle hull plate. 
     The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
         FIG. 1  is a schematic three dimensional view showing the undercarriage of a military vehicle equipped or fitted with a blast shield in accordance with an example of the invention; 
         FIG. 2  is a schematic exploded front view showing the primary components associated with one example of a blast shield of the invention; 
         FIG. 3  is a schematic cross sectional view of the shield of  FIG. 1  positioned under a vehicle hull using a frame in accordance with examples of the invention; 
         FIG. 4  is a schematic exploded three dimensional front view showing another example of a blast shield in accordance with the invention; 
         FIG. 5  is a schematic three dimensional top view showing a plunger plate in accordance with examples of the invention; 
         FIG. 6  is a schematic exploded three dimensional view showing another example of a blast shield in accordance with the invention; 
         FIGS. 7-8  are schematic views of truncated V-hull blast shields; 
         FIG. 9  is a schematic three dimensional view showing the undercarriage of a particular military vehicle; 
         FIG. 10  is a schematic exploded view of an example of a blast shield in accordance with the invention which may be used with the vehicle shown in  FIG. 9  and/or other vehicles; 
         FIG. 11  is a schematic exploded view of an example of a side mount blast shield similar in construction to the blast shield of  FIG. 10 ; 
         FIG. 12  is a schematic exploded view showing another configuration of a blast shield in accordance with the invention; 
         FIG. 13  is a schematic exploded view showing the underside of the blast shield hull plate of  FIG. 12 ; 
         FIG. 14  is a schematic exploded view showing a side mounted version of the blast shield of  FIGS. 12 and 13 ; 
         FIG. 15  is a schematic exploded view showing another example of a blast shield in accordance with the invention; and 
         FIG. 16  is a schematic exploded view of an example of a V-hull blast shield. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
       FIG. 1  shows military vehicle  12  equipped with shield  14  including, in this particular example, frame  16  bolted to the undercarriage “hull” of the vehicle.  FIG. 2  shows one version (without the frame) where vehicle hull or a hull plate is depicted at  18 . First body  20  abuts hull  18  and here is a slab of ultra high molecular weight polyethylene (UHIVIW-PE) material which transitions from a solid state to a viscous fluid state when sufficiently stressed. First body  20  could, in other embodiments, include plies of UHMW-PE material and/or be divided into sections. A plunger plate  22  may be provided and is preferably made of metal with concentric blades  24   a - 24   d  abutting the bottom surface of slab  20  in this design. The concentric blades  24   a - 24   d  may be configured in square, rectangular, circular, and elliptic or any other geometric pattern on the plunger plate  22 . The blades could be adjacent: e.g., touching or closely spaced to slab  20  or even partially within body  20 . Other extruded sections may also be used. See also  FIG. 5 . Second body  25 ,  FIGS. 2-3  may be also included, in this example, abutting the bottom of plate  22 . Body  25  may be a one to three inch thick slab of UHMW-PE material which transitions from a solid state to a viscous fluid state when stressed. Or, body  25  could be a metal plate or a so-called “hard plate”. Such a kit could include blast shield hull plate  18  to replace an existing factory installed hull plate or the various layer(s) could be fastened to the existing vehicle hull plate. 
     When vehicle  12 ,  FIG. 1  equipped with such an undercarriage shield drives over a mine or IED which explodes, body  25 .  FIG. 2  primarily functions to absorb energy from the blast caused by soil impacting the body which in response transitions from a solid state to a viscous fluid state. The UHMW-PE material will blister, crack, and shred and become heavily embedded with soil. 
     The combination of plunger plate  22  and body  20  functions to absorb the blast energy as the blades  24  are driven into body  20  and it changes from a solid to a viscous fluid state locally near the blades in response due to the pressure of the blast. Plate  22  may deform slightly and the blades of plate  22  will embed in body  20  and cut or partially cut into body  20 . 
       FIG. 3  shows the completed assembly of all components shown in  FIG. 2 . When a critical stress magnitude is reached, the UHMW-PE material in bodies  20  and  25  undergoes a phase transition from a solid to a viscous fluid state. This phase transition occurs at or above a critical compressive stress magnitude. Upon impact, plunger blades  24   a - 24   d  penetrate into UHMW-PE slab  20 . With an increasing impact force magnitude, the UHMW-PE material undergoes a phase transition at or above the critical stress. As the UHMW-PE material ahead of and adjacent to the plunger blades transitions into a viscous fluid state, the resisting force on the plunger blades drops sharply to a lower value. The plunger blades then continue to move through the material with a gradual further rise in force magnitude until a significant amount of the impact energy is absorbed. 
     Considering the complete assembly of the blast/impact mitigation shield fitted to the underbody of a vehicle, schematically shown in  FIG. 3 , the physics of the blast effects mitigation my be explained as follows. 
     When a land-mine or and TED buried at certain depth in soil is detonated under a vehicle, first the mass of soil above the mine or IED strikes the bottom surface of the UHMW-PE body  25  with extremely high velocity. This extremely high momentum of soil is almost immediately reduced to a much smaller magnitude as the soil mass impinges on the UHMW-PE body  25 . The resulting normal force is of such high magnitude that in all areas of soil impingements the critical stress required for phase transition of UHMW-PE is crossed. The soil mass gets embedded into the phase transitioned viscous material of the UHMW-PE body and in this process a part of the blast energy is absorbed by the body  25 . The ejected soil and the blast pressure, whose magnitude depends on the explosive charge mass contained within the mine/IED and also the standoff, applies an extremely high impact force on the base of plunger plate  22 , which then forces most of the plunger blades to penetrate into the UHMW-PE body  20 . The resulting stress magnitudes in the UHMW-PE material in front of and surrounding the blades exceed the critical compressive stress magnitude for phase transition of UHMW-PE material. The blades of plunger plate  22  therefore penetrate into the locally transformed viscous material of UHMW-PE body  20 , which is supported against the application of normal force by the hull or the armor plate  18  of the vehicle. The work done in this process of plunger plate  22  displacement against the resistance offered to penetration of blades by the UHMW-PE body  20  is quite significant and this accounts for a large amount of blast energy absorption/dissipation. The remaining blast energy would cause the vehicle to be thrown up in the air. The height of throw depends on the remaining energy available following significant amount of energy absorbed by the blast/impact mitigation shield. 
     The blast/impact mitigation shield therefore reduces the net vertical upward force experienced by the vehicle and its occupants. This results in relatively lower magnitude of vertical acceleration, which can be designed to remain within a certain tolerance level for a specific threat of blast impulse. 
     The reduction in upward vertical acceleration of a vehicle fitted with a blast/impact mitigation shield following an underbody mine/IED blast can also be explained considering the rate of change of momentum. While a vehicle with only an armor plate used as underbody hull experiences a huge change in momentum within an extremely short time interval, the same vehicle, if fitted with a blast/impact mitigation shield, will take considerably longer time interval for the change of momentum due to the work done by the plunger plate  22  on the UHMW-PE body  20 . The force magnitude being proportional to the rate of change of momentum will be smaller for the latter case and so also the magnitude of vertical acceleration. 
     The preferred phase change material has an extremely high heat of fusion (145-195 J/g), and thus it requires significant amount of energy to transition it from a solid to a non-flowing viscous liquid state. In so doing, a significant amount of impact energy is dissipated. A material exhibiting a heat of fusion of greater than 190 J/g and a molecular weight of greater than 3.5 million is preferred. But, a heat of fusion greater than about 120 Joules per gram (J/g) may be acceptable. The percent crystallinity should preferably be greater than 10. 
     The molecular weight, specific heat of fusion and percent crystallinity of the UHMW-PE material stated above are preferred values. However, other polymer materials such as high density polyethylene (HDPE) and other polyethylene exhibiting similar phase transition behavior above a certain critical compression stress, but having smaller values of the above physical parameters can be used for this application. 
     In the example of  FIG. 4 , second body  25  of  FIG. 2  is not used. Instead, plate  22  abuts body  20  and body  20  abuts the hull or an armor plate under the vehicle  18 . Again, a frame may be used. In one test of this configuration, conducted using a blast test fixture weighing 17,500 pounds, three one inch thick plies of UHMW-PE material were placed between a one-quarter inch simulated hull plate  18  and plunger plate  22  as shown in  FIG. 5 . 7.27 lbs. of composition C4 explosive 8″ in diameter and 2¼″ tall in a 24″ diameter cylinder was buried with 4″ of soil (50% sand, 50% clay, 12% moisture content). The standoff between plate  22  and the soil was 15.25 inches. 
     Upon detonation of the C4 explosive, blades  24   a - 24   d  cut thorough the first layer of body  20  but only partially embedded in the second layer of body  20 . The third layer was unaffected. One-half inch thick metal plunger plate  22  was permanently deformed 1.3″ and hull  18  was deformed 2.9″. 
       FIG. 6  shows an option where plunger plate  22  abuts hull  18  and blades of plate  22  face the top of UHMW-PE body  20 . Another stiff plate may be used below the UHMW-PE body  20  (not shown in  FIG. 6 ). 
     In still another example, under carriage shield  14 ,  FIG. 1  is one or more plies and/or one or more sections of UHMW-PE or similar material without a plunger plate. Frame  16  is also optional. 
     Six 1″ layers were bolted to a ¾″ thick rolled homogeneous armor (RHA) steel test “hull” and tested as in the example above. At a 9.25″ standoff, the hull plate was permanently deformed by 2⅞″. The bottom most layer of UHMW-PE material was blistered, cracked, and shredded (heavily soil embedded). The second layer of UHMW-PE material was only marginally affected and was intact, somewhat discolored since it was somewhat exposed to this soil blast. The third through sixth layers of UHMW-PE material were unaffected. With a 15.25″ standoff using four layers of 1″ thick UHMW PE material, the hull plate deformed by 4″. The lowest most UHMW-PE layer was intact but imbedded with soil. The second through fourth layers were unaffected. 
     Examples of the invention provide a new type of blast or impact energy absorption that utilize a novel design and unique elastic-plastic deformation behavior of ultra high molecular weight (UHMW) polyethylene or similar materials. They unexpectedly exhibit rapid absorption of kinetic energy and reduce blast force magnitude through an energy absorption process and in causing slight delay in the rate of change of momentum during an impact or blast event. The UHMW-PE material undergoes a reverse phase transition back to solid state when the stress level drops below the critical value following the impact or blast event. It dissipates the absorbed energy by way of expansion through solidification and also in doing work by partially pushing back the plunger or plunger blades. See also U.S. application Ser. No. 13/385,486 file Feb. 22, 2012 incorporated herein by this reference. 
     Featured is a blast mitigation shield comprising damping material in a solid state and which transitions from a solid to a viscous fluid state when stressed in compression above a critical stress, for example due to a blast event. A plunger plate includes blades positioned in or adjacent to the damping material to be driven into the damping material when impacted by a blast event transitioning the damping material to a viscous fluid state absorbing the impact. In other examples, the system described herein is configured as a drop platform. The “hull” described herein is thus the primary surface of the drop platform. 
     Blast or impact shields in accordance with the examples of the invention include one or more bodies of damping material in a solid state and which transition from a solid to a viscous fluid state when stressed in compression. Examples of the material include ultra high molecular weight polyethylene, high density polyethylene (HDPE), and equivalents thereof. A constraining frame is optional. If used, the plunger plate may include extended blades which may terminate in pointed knife portions positioned at or closely adjacent to the damping material. When the plunger plate is impacted by a blast event or an impact event, the blades are driven into the damping material transitioning it locally near the blades from a solid to a viscous fluid state absorbing the energy of the blast or the impact through work done by the plunger blades. For an airdrop platform, the damping material and/or plunger blades may be secured to the bottom of a drop platform, and/or distributed as narrow strips along the perimeter of the bottom surface. 
     The blast/impact mitigation shield can be designed for a vehicle having flat bottom hull as schematically shown in  FIG. 1  and also for a vehicle having a “V-shaped” hull or a “double V-shaped hull”.  FIGS. 7 and 8  schematically show examples of a vehicle underbody truncated V-hull  18 ′ and corresponding truncated V-shaped blast/impact mitigation shield design. The blast/impact mitigation shield can be designed and configured to meet the same objective of blast effect mitigation. 
       FIG. 9  depicts a “Mine Resistant Ambush Protected” (MRAP) vehicle with existing hull plate  18 . At the factory or in the field, the blast shield may be attached to hull plate  18  or, alternatively, hull plate  18  could be removed and the blast shield, typically including a replacement blast shield hull plate, could be fastened to the vehicle undercarriage in place of the factory provided hull plate. In other designs, the blast shield extends along most of the undercarriage of the vehicle. In still other designs, the blast shield is disposed inside the vehicle, on the vehicle floor or deck for example. 
       FIG. 10  shows a truncated-V configured blast shield assembly including ⅜″ steel plunger plate  30  with blades  32  (1½″ tall and 3/16″ thick). In other designs, the blades are post-like structures, pyramid shaped, for example. In this example, UHMW-PE body  34  is divided into sections  34   a ,  34   b ,  34   c  and  34   d  1¾″ to 2″ thick to conform to the contours of both plunger plate  30  and hull plate  36 . Each section could include multiple plies. In other examples, a monolith sheet or sheets are used and they are shaped to conform to plunger plate  30 . In this particular example, hull plate  36  is also a truncated-V shaped metal plate ⅜″ thick with stiffener members  38   a  and  38   b . UHMW-PE strips  40   a  and  40   b  reside on the top of hull plate  36 . Typically, fasteners are used to secure plunger plate  30  to both UHMW-PE body  34  and hull plate  36 . Hull plate  36  then includes bolting rails  37   a  and  37   b  for mounting the sandwich assembly to the bottom of the vehicle or even to the existing factory installed hull plate, armor, or the like. Plunger plate  30  in this particular embodiment utilizes both longitudinal and transverse blades in the pattern shown which penetrate body section  34   a - 34   d . The longitudinal and transverse blades also act to stiffen blast plate  30  and transfer the blast forces over a greater effective area for larger penetration of the UHMW-PE  34   a - 34   d  to maximize the absorption of energy. 
     In other examples, hull plate  36  and plunger plate  30  have a V-shaped, or flat, or conforming shape to fit a particular vehicle undercarriage. 
       FIG. 10  shows a bottom mount configuration while  FIG. 11  shows a side mount configuration where plunger plate  30  now includes side plates  50   a  and  50   b  and hull plate  36  includes corresponding side plates  52   a  and  52   b . Hull plate side plates  52   a  and  52   b  can be fastened to the vehicle undercarriage. 
       FIGS. 12-13  show a design where plunger plate blades  32 ′ are formed of metal angle or triangle shaped members. UHMW-PE body  34 ′ has sections  34   a ′,  34   b ′,  34   c′  and  34   d′  (3 inches thick) with grooves  60  formed in the underside thereof corresponding to blades  32 ′ of plunger plate  30 ′ so the blades thereof are received in the grooves of the UHMW-PE body. This design enables a thinner overall assembly with a thicker body of blast absorbing material resulting in a greater standoff between the blast shield and the ground. 
     Hull plate  36  may also include blades  62  on its underside (like a plunger plate) and the top of body  34 ′ may now include grooves  64  receiving blades  62  therein. Blades  62  may also be triangular shaped steel members. Hull plate  36 ′ may further include stiffening member  66 . UHMW-PE strips  40   a  and  40   b  may also be provided as before. The grooves  64  on the top of body  34 ′ are offset from the grooves  60  on the bottom of body  34 ′. As before, the angled blades  32 ′ and  62  may penetrate and entrap the phase transitioned material of body  34 ′ between the hull and blast plates and partly absorb the energy released by a blast. 
       FIG. 14  shows a side mount version of the design of  FIGS. 12-13  wherein plunger plate  30 ″ includes side plates  70   a  and  70   b  and hull plate  36 ″ includes side plates  72   a  and  72   b . In some designs, plunger plate  30 ″ includes blades and/or hull plate  36 ″ includes blades. Depending on the specific design, absorbing body  34 ′ may include top and/or bottom grooves. 
       FIG. 15  shows another possible design with plunger plate  30 ″″ having blades  32 ″, UHMW-PE body sections  34   a ″- 34   d″,  0.25 inch hull plate  36 ″, and strips  40   a  and  40   b . Here, the bottom of body sections  34 ″ may be smooth. Grooves  64 ′ in the top surface of the body sections correspond to blades (e.g., blade  62 ) extending downwardly from the bottom of hull plate  36 ′″. It is also possible for body sections  34 ″ to have grooves on the bottom surface thereof receiving the blades of plunger plate  30 ″. A side mount version of this design is also possible.  FIG. 16  shows a V-hull design with plunger plate  30   iv , body section  34   a′″  and  34   b′″ , and hull plate  36   iv . 
     Thus, although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
     In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. 
     Other embodiments will occur to those skilled in the art and are within the following claims.