Patent Publication Number: US-7913626-B1

Title: Kinetic energy absorber

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119(e) of U.S. provisional patent application No. 60/950,125 filed Jul. 17, 2007, which application is hereby incorporated by reference. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The inventions described herein may be manufactured, used and licensed by or for the U.S. Government for U.S. Government purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to kinetic energy absorbers and in particular to kinetic energy absorbers for projectiles. 
     Non-lethal and non-explosive projectiles are used with increasing frequency to facilitate a variety of emerging needs. These projectiles are often required to function after initial impact. Therefore, cargo and other internal components must not be damaged during the projectile&#39;s impact. 
     In the past, impact devices have been designed with metallic or polymer foams to provide energy absorption. The effectiveness and versatility of these types of materials are limited because foams are not easily tailored to achieve a specific response. Additionally, foam stiffness increases as compression occurs and requires large envelopes to effectively mitigate the g-levels produced during impact. Large-sized foam sections are often difficult or impractical for use on gun-launched projectiles. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a kinetic energy absorber. 
     It is another object of the invention to provide a kinetic energy absorber for a projectile. 
     One aspect of the invention is a kinetic energy absorbing apparatus comprising a body having a generally ogival exterior surface; and at least one kinetic energy absorbing structure (KEAS) extending generally rearwardly from substantially an interior surface of the body. A longitudinal axis of the body and a longitudinal axis of the at least one KEAS may be substantially parallel. The at least one KEAS may comprise a plurality of KEAS. The longitudinal axis of the body and longitudinal axes of the KEAS may be substantially coincident. The KEAS may be substantially evenly spaced, radially. Aft termini of the KEAS may lie in substantially a same transverse plane, or in more than one transverse plane. 
     The KEAS may comprise generally hollow structures, such as, for example, tubes, hollow polyhedrons, hollow conical structures, hollow prisms, or combinations of these. 
     Another aspect of the invention is a projectile comprising an ogival kinetic energy absorbing apparatus, a projectile body, and a spacer. The spacer may be disposed between the projectile body and a KEAS. The spacer may include at least one forwardly extending member that meshes with a KEAS. 
     The invention will be better understood, and further objects, features, and advantages thereof will become more apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIG. 1  is a side view of a projectile with a kinetic energy absorber. 
         FIG. 2  is a perspective view of one embodiment of a nose in accordance with the invention. 
         FIG. 3  is a side view of  FIG. 2 . 
         FIG. 4  is an end view of  FIG. 3 . 
         FIG. 5  is a sectional view along the line  5 - 5  of  FIG. 4 . 
         FIGS. 6-13  are perspective, partially cutaway, partially sectioned views of various embodiments of noses in accordance with the invention. 
         FIG. 14  is a perspective, partially cutaway, partially sectioned view of a projectile. 
         FIG. 15A  is a graph of impact acceleration vs. time for conventional foam and the embodiment of  FIG. 5   
         FIG. 15B  is a graph of reflected impact velocity vs. time for conventional foam and the embodiment of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention includes a kinetic energy absorber that mitigates the induced g-forces on a projectile, as well as the internal components of a projectile. Reducing induced g-forces on internal components increases their survivability. The invention may be designed to be sacrificial. That is, the structure may fail catastrophically, while leaving the remaining projectile and its components intact. 
     The present invention may comprise the nose of a projectile. The nose is mounted to the body of the projectile at the forward most point. Mounting methods may include threading, machine screws, or adhesives, depending on projectile size and function. Compared to a foam energy absorber, the present invention provides a more constant stiffness throughout the impact. 
     In general, a kinetic energy absorber structure (KEAS) may be a hollow structure that extends rearwardly from an interior surface of an ogive. The longitudinal axis of the KEA may be parallel to the longitudinal axis of the ogive. The diameter, size, number, wall thickness, radial spacing, and rearward extent of the KEAS may vary. The KEAS are designed to crush upon impact and mitigate g-loading on a projectile. 
     As impact begins, the KEAS begin to buckle successively, slowing the velocity of the projectile. As buckling continues, the KEAS will deform significantly and may rupture, thus continuing to absorb the projectile&#39;s kinetic energy. Material selection for the KEAS may be varied to provide a particular response or buckling mode, allowing the invention to be used in a variety of applications. 
     The KEAS may be used for commercial applications that require a single use kinetic energy absorber. Additionally, the KEAS may be used in a modular fashion to create large kinetic energy absorbing structures. The illustrated embodiments depict several exemplary variations. 
       FIG. 1  is a side view of a projectile  10  having a payload portion  12  and a nose  14 . Payload portion  12  may be explosive or non-explosive. In one embodiment, the payload portion  12  may include, for example, sensors, and be non-explosive. Nose  14  may have an ogival shape. Nose  14  may include kinetic energy absorbers. 
       FIG. 2  is a perspective view of one embodiment of a nose  16  in accordance with the invention.  FIG. 3  is a side view of  FIG. 2 .  FIG. 4  is an end view of  FIG. 3 .  FIG. 5  is a sectional view along the line  5 - 5  of  FIG. 4 . Nose  16  may include a cylindrical portion  18  and an ogival portion  20 . Ogival portion  20  may have an exterior surface in the form of an ogive. Cylindrical portion  18  may be used to fix nose  16  to a payload portion of a projectile. 
     As best seen in  FIGS. 4 and 5 , nose  16  may include KEAS in the form of hollow cylinders or tubes  22 ,  24 ,  26 . Tubes  22 ,  24 ,  26  may extend substantially from the interior of the ogival portion  20  rearwardly to the transverse plane A-A ( FIG. 5 ). In  FIGS. 4 and 5 , each of tubes  22 ,  24 ,  26  is shown extending to transverse plane A-A. However, one of more of the tubes  22 ,  24 ,  26  may extend rearwardly further than plane A-A, or may terminate forward of plane A-A. In  FIG. 5 , “forward” means to the right and “rearward” means to the left. 
     Three tubes  22 ,  24   26  are shown in  FIGS. 4 and 5 , but there may be more or fewer than three tubes. Tubes  22 ,  24 ,  26  may be substantially concentric, that is, the longitudinal axes of the tubes and the longitudinal axis of the nose  16  may be substantially coincident with line B-B. Tubes  22 ,  24 ,  26  may be evenly radially spaced or unevenly radially spaced. The thickness of tubes  22 ,  24 ,  26  may be the same or may be different. Tubes  22 ,  24   26  may comprise the same or different materials, and may be integral with ogival portion  20  or not integral with ogival portion  20 . 
       FIGS. 6-13  are perspective, partially cutaway, partially sectioned views of various embodiments of noses in accordance with the invention.  FIG. 6  shows a nose  30  comprising an ogival portion  32  and KEAS  34 ,  36 ,  38 . KEAS  34 ,  36  may be in the form of tubes and KEAS  38  may have a conical structure. KEAS  34 ,  36 ,  38  may be concentric with the longitudinal axis B-B of nose  30 . 
       FIG. 7  shows a nose  40  comprising tubular KEAS  42 ,  44 ,  46 . Wall thicknesses of the KEAS  42 ,  44 ,  46  may vary, whether the KEAS is tubular, conic, polyhedral or otherwise. For example, the wall thickness of KEAS  42  tapers rearwardly from thickness a to thickness b. The wall thickness may also increase rearwardly, if desired. KEAS  42 ,  44 ,  46  may include one or more slots  48  formed therein. Slots  48  may begin at the aft terminus of the KEAS and extend forwardly. Slots may be formed in a KEAS of any form, whether tubular, conic, polyhedral or otherwise. 
       FIG. 7  shows that the KEAS  42 ,  44 ,  46  need not terminate in a common transverse plane. For example, KEAS  44  terminates in transverse plane D-D and KEAS  46  terminates in transverse plane C-C. KEAS of any form, whether tubular, conic, polyhedral or otherwise, may terminate in the same or different transverse planes. 
     The KEAS  42 ,  44 ,  46  shown in  FIG. 7  are generally tubular, however, they may also be, for example, conic structures, polyhedrons comprising three or more sides, or combinations of these structures. KEAS  42 ,  44 ,  46  may be concentric with axis B-B of nose  40   
       FIG. 8  shows a nose  50  comprising KEAS  52 ,  54 . KEAS  52 ,  54  may be hollow polyhedrons. In  FIG. 8 , KEAS  52  may be a hollow triangular prism and KEAS  54  may be a hollow square prism. KEAS  52 ,  54  may be concentric with axis B-B of nose  50   
       FIG. 9  shows a nose  60  comprising KEAS  62 ,  64 ,  66  in the form of tubes. KEAS  62 ,  64  may have tapering wall thicknesses. KEAS  62 ,  64 ,  66  may be concentric with axis B-B of nose  60 . KEAS  64 ,  68  may have longitudinal ribs  68 ,  70  formed therein. Ribs  68  may be generally rounded and ribs  70  may be generally triangular in section. Ribs of any shape may be used. Ribs may be included with KEAS of any geometry. 
       FIG. 10  shows a nose  80  comprising KEAS  82 ,  84 ,  86 . KEAS  82 ,  84 ,  86  may comprise hollow conical structures, as shown. KEAS  82 ,  84 ,  86  may be concentric with axis B-B of nose  80 . 
       FIG. 11  shows a nose  90  comprising a plurality of tubular KEAS  92 ,  92   a . KEAS  92 ,  92   a  may not be concentric. The longitudinal axes E-E of the KEAS  92  may be substantially parallel to the longitudinal axis B-B of nose  90 . The axis of the KEAS  92   a  need not, but may be, coincident with the axis B-B of nose  90 . 
       FIG. 12  shows a nose  110  comprising a plurality of KEAS  112 . KEAS  112  may be hollow polyhedrons, such as hollow prisms with three or more sides. Longitudinal axes I-I of KEAS  112  may be substantially parallel to axis B-B of nose  110 . 
       FIG. 13  shows a nose  100  comprising a plurality of KEAS  102 ,  104 . KEAS  102  may be tubes. KEAS  104  may be polyhedrons having three or more sides, or may be cylinders. Longitudinal axes G-G of KEAS  104  and longitudinal axes H-H of KEAS  102  may be substantially parallel to axis B-B of nose  100 . KEAS  104  may be solid, rather than hollow. 
       FIG. 14  is a perspective, partially cutaway, partially sectioned view of a projectile  120 . Projectile  120  may comprise a body  124  and an ogival nose  122 . Nose  122  may include a plurality of KEAS  126 . A spacer  128  may comprise one or more forwardly extending members  130  that mesh or mate with the KEAS  126 . In general, the rear portions of the KEAS (whether tubes, polyhedrons, conical structures, or otherwise, and whether concentric or not concentric) may be used to mate with a spacer  128 . The spacer  128  may help to interlock the ogive  122  to the body  124  and thereby prevent sideways displacement that may occur with glancing or angled impacts. 
     A Finite Element Analysis (FEA) was conducted to determine the dynamic response of the invention and of conventional foam.  FIGS. 15A and 15B  show the predicted FEA results for induced G-loading ( FIG. 15A ) and reflected impact velocity ( FIG. 15B ) for the embodiment shown in  FIGS. 2-5 , and for conventional foam. The results show the invention may achieve a reduction in induced G-loading of about 50% compared to conventional foam. Additionally, the reduction in reflected velocity of about 60% shows that the invention absorbs more kinetic energy than conventional foam. 
     A prototype of the embodiment of  FIGS. 2-5  was built and tested. On board telemetry was used to collect acceleration data. Compared to conventional foam, the invention showed about a 40% reduction in peak G-load, from 40,000 Gs to 25,000 Gs. 
     While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.