Opportunities in Protection Materials Science and Technology for Future Army Applications (2011) / Chapter Skim
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5 Lightweight Protective Materials: Ceramics, Polymers, and Metals
5 Lightweight Protective Materials: Ceramics, Polymers, and Metals
Pages 69-98
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From page 69... ...
McCauley, Weapons and Materials Research Directorate, minimizing manufacturing cost requires a deep scientific Army Research Laboratory (ARL) fellow, ARL, "Armor materials 101-501: and engineering understanding of the desirable structures Focus on fundamental issues associated with armor ceramics ‘kinetic energy and compositions of advanced protective materials as well passive armor,'" presentation to the committee, March 9, 2010.
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From page 70... ...
Of course the presence of defects will keep the design and performance of armor materials are described, ceramic from reaching the stress levels necessary to activate along with the challenges to be overcome. plasticity mechanisms, and simple, practical improvement in performance can be realized by employing nondestructive evaluation analysis to reveal the larger defects in the mateCERAMIC ARMOR MATERIALS rial.
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From page 71... ...
fellow, ARL, "Armor materials 101-501: UCRL-71817, July 23. Livermore, Calif.: Lawrence Radiation Laboratory, Focus on fundamental issues associated with armor ceramics ‘kinetic energy University of California.
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From page 72... ...
the diagonal chain (see the unit cell shown in Figure 5-2) .18 For the approximately stoichiometric B4C material, the icoCrystal Structure of Boron Carbide sahedra are B11C and the chains are C–B–C.
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From page 73... ...
, surpassing all of its denser competitors such as silicon carbide and alumina by a factor of 2.27,28,29 High FIGURE 5-3 The boron-carbon phase diagram over the range HEL would suggest that boron carbide could outperform 0-36 at % carbon. The cross-hatched region is commonly referred other armor materials.
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From page 74... ...
Physical Review Letters 102(7) : Article of disordered boron carbide under stress.
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From page 75... ...
armor material. Clearly, further experimental and theoreti- A number of notations have been developed; the most comcal work is required to more fully understand the structural mon notation, Ramsdell's, labels the polytypes as nL, where changes in boron carbide under impact loading.
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From page 76... ...
By ment and mechanical properties of fine-grained silicon carbide ceramics. purposefully seeding an α-SiC powder with b grains before Journal of the American Ceramic Society 84(5)
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From page 77... ...
Fragments from ballistic impact experiments do consequence, ceramic armor manufacturers and university indeed show a considerable amount of stacking faults and researchers are forced to employ powders that are almost twins,56,57 suggesting that materials with low stacking-fault certainly not optimal for armor applications. Beyond impedenergy twin readily under shock loading also, because the ing research and development generally and, particularly, the presence of large numbers of stacking faults provides loca- development of better protection materials, the precarioustions at which twins form easily.58 ness of domestic supply poses a risk for DoD should a need There are a very large number of crystal structures for arise for surge production of ceramic armor materials.
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From page 78... ...
The goal of deninvestment to provide an assured domestic supply for criti sification is to optimize bonding and eliminate porosity cal materials. The business case analysis to support a Title in the compacted powder so that full theoretical densities, III program in ceramic armor materials is beyond the scope along with homogeneous microstructures, can be achieved of this study.
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From page 79... ...
After die pressing, the part will have shrunk by 20 to 40 percent or so, and the final part dimensions are Appendix E characterizes commonly used ceramic sinachieved by machining and grinding. tering processes and discusses issues surrounding their ap Uniaxial die pressing is widely used for the low-cost plication to opaque armor materials.
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From page 80... ...
SiC Lower temperature, fine grains, low Oxide grain boundary phase porosity Reaction bonding Si/SiC, Si/B4C (MCT/RBSC, Low temperature, excellent complex Residual silicon RBBC) shape capability NOTE: MCT, M Cubed Technologies, Inc., RBBC, reaction-bonded boron carbide; RBSC, reaction-bonded SiC.
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From page 81... ...
Prototype micron Al2O3 for transparent armor applications. Journal of the European Ceramic Society 29(2)
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From page 82... ...
This section briefly reviews the history of their based on the strength of the bonds in the chain and the cross sectional area of the molecule.73,74,75 The predicted tensile development and current production technology and then discusses opportunities for technological innovations rel- strength of a perfect, fully extended polymeric fiber such as evant to protection materials. Nylon and silk fibers had been polyethylene is about 30 GPa and that of a perfectly packed, used to make armor vests for soldiers, but with very limited single-wall CNT fiber of ideal diameter should be about 150 success.
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From page 83... ...
1998. Carbon Fibers, third edition.
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From page 84... ...
Processing techniques for this new fiber class For example, the theoretical tensile strength of polyethylene are actively under investigation. fiber is predicted to be 33 GPa,83 and that of carbon fibers, including CNT fibers, is predicted to be between 100 and 150 Relating Tensile Properties to Ballistic Performance GPa.84,85 The tensile strength of polymeric fibers is limited by the presence of chain ends, chain entanglements, chain The development of a new fiber material and a process misorientation, voids, and impurities.86 Similarly, various to manufacture it typically costs several hundred million dol types of defects limit the tensile strength of carbon and lars.
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From page 85... ...
sile strength of 7 GPa has been reported in the laboratory.91 • Glass fiber. Glass fibers with a tensile strength of >10 The Need for Mechanical Tests at High Strain Rates GPa have recently been reported by Corning.92 The tensile properties of elastic fibers such as Kevlar • Novel carbon fibers.
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From page 86... ...
Most ballistic fabrics The study of ballistic impact of fabrics includes work by Shockey et al.103 on projectile impact, residual velocity, loadhave two-dimensional plain weave yarns in two orthogonal directions, although some work is being done on three- stroke response, energy absorption, and tensile properties of dimensional weaves and on nonwoven fabrics. Organic poly- yarns.
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From page 87... ...
, strain rates greater than 103 s–1 are needed. Since the mechan • Fibrillation, and ical behavior of polymers is pressure sensitive -- for example, • Effects of friction between the projectile and the UHMWPE has a relatively low melting point (140°C)
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From page 88... ...
1992. An analysis of the system effects in woven fabrics fabrics, energy absorbed is improved if the yarns are oriented under ballistic impact.
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From page 89... ...
Available online at http://www.google.com/patents/ materials and as armor materials. Because these materials about?
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From page 90... ...
The susceptibility RHA continues to be the benchmark with respect to to adiabatic shear localization is dependent primarily on the which most protection materials are judged: A typical objec rate of thermal softening of the material and the strain-rate tive is framed in relative terms -- for example, "at least the sensitivity.137 Thus the hardening and softening mechanisms performance of RHA at a lower areal density." Although the within the material must be considered in addition to the performance of an RHA-based armor system is measured mechanisms that simply raise the initial yield strength. For in terms of a specific threat, the fundamental stress-strain instance, many high-strength metals have very low rate response is a good initial benchmark for materials design.
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From page 91... ...
have some advantages. Aluminum alloys be much stronger than the metal before rolling, and indeed used as armor in Army vehicles include 2024, 2519, 5083, the largest tonnages of metallic armor materials are rolled 5059, 6061, 7039, and 7075.
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From page 92... ...
Important Issues Surrounding Adhesives for Lightweight ADHESIVES FOR ARMOR AND FOR TRANSPARENT Armor Applications ARMOR In automotive safety glass the strength of adhesion Adhesive interlayers are key components of both bal- between the adhesive interlayer and the polymer, glass, and ceramic layers has been tailored with good effect.142,143,144 listic glass and composite armor. Understanding, testing, and modeling of the adhesive interlayers in composite Interlayers with bonds that can delaminate from the sub- and armor are crucial for their future design and improvement.
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From page 93... ...
with most of the interlayers are made, typically have mechanical the thickness equal to a quarter wavelength so as to minimize properties that depend greatly on strain rate and pressure. reflection.146 Mechanical Impedance Cost Waves traveling through composite armor can be re Generally the cost of the adhesive is insignificant comflected or transmitted depending on the impedance mismatch pared to that of armor materials such as AlON and sapphire.
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From page 94... ...
, Trosifol (Kuraray armor is transmitted via the adhesive interlayers. Chapter 2 of Advances in Ceramic Armor155 provides a good overview Europe)
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From page 95... ...
. In armor systems, materials such as ceramics (for example, alumina, silicon carbide, or boron carbide)
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From page 96... ...
Different brazing process wets most armor materials (ceramics, tita- evaluation techniques are applied to garner different kinds of nium alloys, and steels) and forms a superior metallurgical information from the armor material.
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From page 97... ...
A need exists to build a production infrastrucstructure made of woven fabrics held together by a polymer ture for strategic ceramic powders within the United States resin. Fabrics are incorporated to take advantage of their high for the next generation of opaque and transparent ceramic strength and stiffness and to improve energy absorption and armor.
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From page 98... ...
A better basic understanding of the strengthening mechanisms in magnesium, especially hesives, brazes, and solders) whose elastic impedances and the development of ultra-fine-grained magnesium alloys thermal expansion coefficients match those of the materials through severe plastic deformation, could be highly benefi- to be bonded will improve the ballistic and blast performance cial.
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