Patent Grant
8267003
The present invention generally relates to vehicle armor, and more particularly relates to system for attaching an armor plate to the exterior surface of a vehicle hull.
Blast protection appliqués are used on tactical and combat ground vehicles as a method of deflecting or mitigating the effects of anti-vehicular mine blasts or attack by Improvised Explosive Devices (IEDs). The appliqués essentially comprise armor plating attached to the outer surfaces of the bottom and sides of the vehicle. The armor plating may be made of various high strength and blast resistant materials such as steel, titanium, or various composite materials including ceramic composites.
A critical and limiting element of these appliqués is the fastener joints. Currently, industrial bolts are commonly used for attaching blast protection appliqués to vehicles due to their simplicity and availability. The fasteners used are typically selected for strength and ability to transmit externally applied loads. The vast majority of commercially available high strength fasteners are made of carbon steel. Examples include ASTM A325 high-strength carbon steel bolts, ASTM A490 alloy steel bolts, and SAE J429 graded bolts, such as Grade 5 and Grade 8. However, under blast conditions these bolts often fail, resulting in secondary fragments and projectiles which may inflict additional damage and injury to the vehicle personnel. In addition the performance of vehicle armor attachment joints under blast threat or ballistic impact is poorly understood, in part because the blast and ballistic loadings are wide range dynamic events.
Accordingly a need exists for innovative methodology and/or material with which blast protection appliqués could be attached so as to withstand blast forces and pressures of an anti-vehicular mine blast.
Various exemplary embodiments of the present invention are described below. Use of the term “exemplary” means illustrative or by way of example only, and any reference herein to “the invention” is not intended to restrict or limit the invention to exact features or steps of any one or more of the exemplary embodiments disclosed in the present specification. References to “exemplary embodiment,” “one embodiment,” “an embodiment,” “various embodiments,” and the like, may indicate that the embodiment(s) of the invention so described may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase “in one embodiment,” or “in an exemplary embodiment” does not necessarily refer to the same embodiment, although it may.
It is also noted that terms like “preferably”, “commonly”, and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention.
According to one exemplary embodiment, the present disclosure comprises an apparatus for attaching a rigid armor plate to the exterior of a vehicle hull. The apparatus comprises an armor attachment point on the vehicle hull, an oversized hole through the armor plate in alignment with the armor attachment point, and a fastener extending through the oversized hole and attaching the armor plate to the armor attachment point, such that the fastener and oversized hole cooperatively define a substantial gap there-between.
According to another exemplary embodiment, the fastener is a threaded bolt with a head, and the armor attachment point comprises a clear hole in the vehicle hull and an internally threaded nut.
According to another exemplary embodiment, the internally threaded nut is a threaded weld bushing.
According to another exemplary embodiment, the apparatus further comprises a washer under the head of the bolt that overlaps a portion of the armor plate around the oversized hole.
According to another exemplary embodiment, the apparatus further comprises an elastic insert bushing disposed about the fastener, substantially filling the gap between the fastener and oversized hole.
According to another exemplary embodiment, the elastic insert bushing material is selected from the group comprising rubber, and polyurethane.
According to another exemplary embodiment, the apparatus further comprises an elastic spacer around the bolt between the armor plate and the vehicle hull.
According to another exemplary embodiment, the fastener material has an energy absorption capability in excess of 2000 ksi, and more preferably an energy absorption capability in excess of 5000 ksi.
According to another exemplary embodiment, the fastener is a threaded bolt made of 304 Stainless Steel.
According to another exemplary embodiment, the apparatus comprises a washer-shaped pivot cup residing in a countersink in the exterior end of the oversized hole in the armor plate, a spherical countersink in the inner diameter of the exterior side of the pivot cup, and a pivot washer trapped between an end of the fastener and the pivot cup, where the pivot washer has a spherical surface configured for pivoting engagement with the spherical countersink in the pivot cup.
According to another exemplary embodiment, the inner diameter of the pivot cup is substantially greater than the diameter of the fastener.
In another exemplary embodiment, the disclosure comprises a system for attaching a rigid armor plate to the exterior of a vehicle hull. The system comprises an armor attachment point on the vehicle hull, a hole through the armor plate in alignment with the armor attachment point, and a fastener extending through the hole and attaching the armor plate to the armor attachment point, wherein the fastener material has an energy absorption capability in excess of 2000 ksi., and more preferably an energy absorption capability in excess of 5000 ksi.
According to another exemplary embodiment, the fastener is a threaded bolt made of 304 Stainless Steel.
According to another exemplary embodiment, the diameter of the fastener is less than the diameter of the hole through the armor plate, defining a substantial gap there-between.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The present invention is described more fully hereinafter with reference to the accompanying drawings and/or photographs, in which one or more exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be operative, enabling, and complete. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention. Moreover, many embodiments, such as adaptations, variations, modifications, and equivalent arrangements, will be implicitly disclosed by the embodiments described herein and fall within the scope of the present invention.
Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Unless otherwise expressly defined herein, such terms are intended to be given their broad ordinary and customary meaning not inconsistent with that applicable in the relevant industry and without restriction to any specific embodiment hereinafter described. As used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one”, “single”, or similar language is used. When used herein to join a list of items, the term “or” denotes at least one of the items, but does not exclude a plurality of items of the list.
For exemplary methods or processes of the invention, the sequence and/or arrangement of steps described herein are illustrative and not restrictive. Accordingly, it should be understood that, although steps of various processes or methods may be shown and described as being in a sequence or temporal arrangement, the steps of any such processes or methods are not limited to being carried out in any particular sequence or arrangement, absent an indication otherwise. Indeed, the steps in such processes or methods generally may be carried out in various different sequences and arrangements while still falling within the scope of the present invention.
Additionally, any references to advantages, benefits, unexpected results, or operability of the present invention are not intended as an affirmation that the invention has been previously reduced to practice or that any testing has been performed. Likewise, unless stated otherwise, use of verbs in the past tense (present perfect or preterit) is not intended to indicate or imply that the invention has been previously reduced to practice or that any testing has been performed.
Floating Armor Joint Design
Referring now to
As seen in
One typical failure mode of prior art joints occurs as a result of in-plane movement of the armor plate relative to the vehicle hull, causing the bolt to be effectively sheared off by the armor. Advantageously the oversized hole 20 of the present embodiment allows armor plate 12 to shift, or float relative to the vehicle hull to a certain extent without coming into direct contact with fastener 16. The centering effect provided by the elastic insert 26 helps to ensure a symmetric circumferential gap between the fastener 16 and armor plate 12 at each joint. As a result, shear loads applied to the fastener during a blast event are greatly reduced or eliminated, substantially improving fastener survivability.
Pivoting Joint Design
As in the previously described floating armor joint design of
In addition, the spherical interface between the pivot washer 138 and pivot cup 132 allows the pivot washer, and consequently the fastener 116, to tilt in response to armor plate movement.
Fastener Material
The inventors of the present invention have discovered that a particularly significant property affecting survivability of the fastener during blast events is the material's energy absorption capability (hereinafter “EAC”). In particular the inventors have discovered that fastener survivability under impact or blast loading conditions is dependent not just on the strength of the material, but also on the amount the fastener can deform or extend prior to failure. Higher survivability relates to higher strength combined with greater total deformation leading up to failure. A good indicator of a fastener's total deformation prior to failure is the measured percent elongation of the material used for the fastener. Thus materials that exhibit both relatively high strength values and high percent elongation are preferable candidates for fastener materials.
The EAC is generally understood to mean the area under the stress strain curve for any particular material. The inventors further recognized that fastener survivability is closely linked to an approximation of the EAC obtained by taking the average of material yield strength and tensile strength (in ksi) multiplied by the elongation (in percentage times 100).
Table 1 lists selected relevant material properties for a variety of commercial metallic fasteners. Included in the table are values for Yield and Tensile (Ultimate) strengths, percent Elongation, and a calculated value for the EAC based on the foregoing property values. The strength properties range from the lowest yield stress of 25 ksi for a NICU-A-HF bolt made of Nickel-copper alloy A, to the highest yield stress of 135 ksi for a 410-HT bolt made of Martensitic stainless steel. As previously mentioned, fasteners used for attaching armor appliqué to vehicles are typically selected based upon strength. For example, typical common high strength steel fasteners currently used for armor attachment include ASTM A354 Grade BD, and SAE J429 Grade 8 bolts, among many others.
Table 2 lists properties of rods, bars, and forgings for a wide range of potentially suitable fastener materials. The materials are grouped into categories beginning with Steel, followed by Stainless Steel, and so on. Included in the table are calculated EAC values. As can be seen, EAC values range from as low as 230 for 1100H18 Aluminum, to 6464 for Haynes 25. Notably, the EAC values in Table 1 for the high strength steel fastener examples cited above are around 1700, or toward the low end of the range of EAC values in Table 2. In contrast, 304 stainless steel for example, with a calculated EAC of 5550, falls relatively near the high end of the range of Table 2. Significantly, the inventors have determined that the fastener materials in Table 2 with an EAC greater than 2000 are more likely to survive a blast load event, and thus preferred over materials with an EAC below 2000, such as the high strength alloy steel fasteners. The inventors have further determined that materials such as 304 stainless steel for example, with a calculated EAC greater than 5000, are able to survive substantially greater blast loads than most other potential fastener materials, and thus are particularly preferred choices.
Small Scale Field Blast Test
The relationship of the armor attachment joint design and fastener EAC to fastener survivability under blast loading conditions was experimentally verified with a small scale field blast test. Referring to
Three armor attachment joint designs for the bolted joints 214 were tested, namely a typical prior art design referred to as the “Baseline” Concept; the floating armor design of
Results of the small scale blast test are summarized in Table 3. The column labeled “Pass(P)/FAIL” indicates the condition of the bolts after the test, with P signifying that all of the bolts were intact after the test, and FAIL signifying that at least one bolt broke. The Baseline (Grade 8 bolt) concept was tested by incrementally increasing the weight of TNT charge from 0.1 to 1.0 lbs. One fastener in the Baseline concept failed with a TNT charge of 0.75 lbs, and all four fasteners failed when tested with 1.0 lbs. of TNT. None of the fasteners failed in any of the tests of the Concept #1 and Concept #5 joint designs using the 304 Stainless Steel bolts, up to and including tests with 1.0 lbs. of TNT.
Full Scale Blast Simulation
Further testing was performed to simulate a full scale blast event.
The results of the full scale blast simulation tests are summarized in Table 2. All tests were performed using 13.6 lbs. of UNIGEL brand TNT explosive. Of the 52 total Baseline Grade 8 bolts tested at bolted joints 311, only 17, or 33%, remained intact (not destroyed) after the blast event. In contrast, 44, or 85% of the Stainless Steel Concept #1 bolts, and 100% of the Stainless Steel Concept #5 bolts were intact after the blast event and prior to disassembly of the test sample.
For the purposes of describing and defining the present invention it is noted that the use of relative terms, such as “substantially”, “generally”, “approximately”, and the like, are utilized herein to represent an inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
Exemplary embodiments of the present invention are described above. No element, act, or instruction used in this description should be construed as important, necessary, critical, or essential to the invention unless explicitly described as such. Although only a few of the exemplary embodiments have been described in detail herein, those skilled in the art will readily appreciate that many modifications are possible in these exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the appended claims.
This invention was made with government support under contract number W56 HZV-07-C-0512 awarded by the US Army TACOM LCMC. The government has certain rights in the invention.
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