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FIGURE 1-2 Up-armored high-mobility multipurpose wheeled vehicle (HMMWV, or Humvee). SOURCE: Available at http://www.militaryfactory.com/armor/imgs/hmmwv-m1114uah.jpg. Courtesy of U.S. DoD.

which is not currently possible with the extensive, costly, and time-consuming practice that is perhaps best described as “build it, shoot it, and then look at it.” This problem, including specific recommendations for areas of investigation, will be addressed further at the end of Chapter 3.

This seeming technological inability to keep up with evolving needs is not exclusive to protection materials. A recent National Research Council (NRC) study, Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security,3 describes how, like advances in armor, the “vast majority of disruptive technologies since the start of the industrial revolution” have been due to materials innovations, but that “the insertion of new materials technologies has become much more difficult and less frequent” as materials development fails to keep pace with the rapid design process. This describes exactly the problems experienced with development of the new protection materials that are the focus of this study. The Integrated Computational Materials Engineering (ICME) report cites many advances and several examples of successful implementation. It advocates pushing the large body of existing computational materials science to the next step. Unfortunately, while “the optimization of the materials, manufacturing processes, and component design” is well described in the ICME report, the path forward for protection materials is far more complicated, since designs must deal with highly nonlinear and large deformations typically not encountered in commercial products, where applied stresses are kept well below the elastic limit in the linear regime. Simply put, the key materials properties—for example, tensile strength and toughness—that inform the design of commercial structures and devices are well established and extensively measured. Such is not the case for armor.

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FIGURE 1-3 Areal density of armor versus time, demonstrating that new lightweight materials such as titanium, aluminum, and ceramics have provided increased protection at a lower weight per unit area over time. The flattening curve illustrates that the challenge for the future is to be able to continue to decrease the areal density of the armor despite increased threats. SOURCE: Adapted from Fink, B.K. 2000. Performance Metrics for Composite Integral Armor. ARL-RP-8. Aberdeen Proving Ground, Md.: Army Research Laboratory.

The armor that protects U.S. fighting forces is seldom a single, homogeneous material. More often than not, what is called “armor” is actually a complex system constructed of several, often quite different, materials arranged in a very specific configuration designed to protect against a particular threat. As will be discussed extensively in this study, the properties and behavior of a protection material must be considered in the specific context of how it will be used in the construction of a particular armor system. Further, there is often little understanding of how to link specific material properties to the actual behavior of the materials and armor systems during the many types of ballistic and blast events. It is often the case that new protection materials have not been well characterized with respect to strain rates, pressures, and the like under appropriate conditions, either alone or as part of an armor system, and databases for materials’ performance and constitutive relationships are often not available. This is especially true at the high strains and very high strain rates relevant to ballistic and blast threats. This gap in knowledge greatly limits the ability of simulation codes to play a significant role in guiding the development of new materials. Moreover, the design philosophy is completely dependent on how the armor system is to be used.

In this study, the committee was guided by military applications that necessitate lightweight armor, with particular emphasis on (1) personnel protection, which includes body armor and helmets, (2) vehicle armor, and (3) transparent

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3NRC. 2008. Integrated computational systems engineering: A transformational discipline for improved competitiveness and national security. Washington, D.C.: The National Academies Press.



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