Opportunities in Protection Materials Science
and Technology for Future Army Applications

Committee on Opportunities in Protection Materials Science
and Technology for Future Army Applications

National Materials Advisory Board
and
Board on Army Science and Technology

Division on Engineering and Physical Sciences

NATIONAL RESEARCH COUNCIL
            OF THE NATIONAL ACADEMIES









THE NATIONAL ACADEMIES PRESS
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Opportunities in Protection Materials Science and Technology for Future Army Applications Committee on Opportunities in Protection Materials Science and Technology for Future Army Applications National Materials Advisory Board and Board on Army Science and Technology Division on Engineering and Physical Sciences

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THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This study was supported by Contract No. W911NF-09-C-0164 between the National Academy of Sciences and the Department of Defense. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the organizations or agencies that provided support for the project. International Standard Book Number-13: 978-0-309-21285-4 International Standard Book Number-10: 0-309-21285-5 This report is available in limited quantities from National Materials and Manufacturing Board 500 Fifth Street, N.W. Washington, DC 20001 nmab@nas.edu http://www.nationalacademies.edu/nmab Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet: http://www.nap.edu. Cover: A soldier wearing protective equipment (left); up-armored high-mobility multipurpose wheeled vehicle (HMMWV) (center); drawing showing penetration of target (right, upper) and interface defeat—the goal of protective material (right, lower). The lower border serves as a reminder of the continued increase in threat that drives the need for advances in protective materials. Copyright 2011 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advis - ing the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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COMMITTEE ON OPPORTUNITIES IN PROTECTION MATERIALS SCIENCE AND TECHNOLOGY FOR FUTURE ARMY APPLICATIONS EDWIN L. THOMAS, Chair, Massachusetts Institute of Technology MICHAEL F. McGRATH, Vice Chair, Analytic Services Inc. (ANSER) RELVA C. BUCHANAN, University of Cincinnati BHANUMATHI CHELLURI, IAP Research, Inc. RICHARD A. HABER, Rutgers University JOHN WOODSIDE HUTCHINSON, Harvard University GORDON R. JOHNSON, Southwest Research Institute SATISH KUMAR, Georgia Institute of Technology ROBERT M. McMEEKING, University of California, Santa Barbara NINA A. ORLOVSKAYA, University of Central Florida MICHAEL ORTIZ, California Institute of Technology RAÚL A. RADOVITZKY, Massachusetts Institute of Technology KALIAT T. RAMESH, Johns Hopkins University DONALD A. SHOCKEY, SRI International SAMUEL ROBERT SKAGGS, Los Alamos National Laboratory (retired), Consultant STEVEN G. WAX, Defense Applied Research Projects Agency (retired), Consultant Staff ERIK SVEDBERG, NMAB Senior Program Officer ROBERT LOVE, BAST Senior Program Officer NANCY T. SCHULTE, BAST Senior Program Officer HARRISON T. PANNELLA, BAST Senior Program Officer JAMES C. MYSKA, BAST Senior Research Associate NIA D. JOHNSON, BAST Senior Research Associate LAURA TOTH, NMAB Senior Program Assistant RICKY D. WASHINGTON, NMAB Administrative Coordinator ANN F. LARROW, BAST Research Assistant v

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NATIONAL MATERIALS ADVISORY BOARD ROBERT H. LATIFF, Chair, R. Latiff Associates LYLE H. SCHWARTZ, Vice Chair, University of Maryland PETER R. BRIDENBAUGH, Alcoa, Inc. (retired) L. CATHERINE BRINSON, Northwestern University VALERIE BROWNING, ValTech Solutions, LLC YET MING CHIANG, Massachusetts Institute of Technology GEORGE T. GRAY III, Los Alamos National Laboratory SOSSINA M. HAILE, California Institute of Technology CAROL A. HANDWERKER, Purdue University ELIZABETH HOLM, Sandia National Laboratories DAVID W. JOHNSON, JR., Stevens Institute of Technology TOM KING, Oak Ridge National Laboratory KENNETH H. SANDHAGE, Georgia Institute of Technology ROBERT E. SCHAFRIK, GE Aircraft Engines STEVEN G. WAX, Strategic Analysis, Inc. Staff DENNIS CHAMOT, Acting Director ERIK SVEDBERG, Senior Program Officer RICKY D. WASHINGTON, Administrative Coordinator HEATHER LOZOWSKI, Financial Associate LAURA TOTH, Senior Program Assistant NOTE: In January 2011 the National Materials Advisory Board (NMAB) and the Board on Manufacturing and Engineering Design combined to form the National Materials and Manufacturing Board. Listed here are the members of the NMAB who were involved in this study. vi

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BOARD ON ARMY SCIENCE AND TECHNOLOGY ALAN H. EPSTEIN, Chair, Pratt & Whitney, East Hartford, Connecticut DAVID M. MADDOX, Vice Chair, Independent Consultant, Arlington, Virginia DUANE ADAMS, Carnegie Mellon University (retired), Arlington, Virginia ILESANMI ADESIDA, University of Illinois at Urbana-Champaign RAJ AGGARWAL, University of Iowa, Coralville EDWARD C. BRADY, Strategic Perspectives, Inc., Fort Lauderdale, Florida L. REGINALD BROTHERS, BAE Systems, Arlington, Virginia JAMES CARAFANO, The Heritage Foundation, Washington, D.C. W. PETER CHERRY, Independent Consultant, Ann Arbor, Michigan EARL H. DOWELL, Duke University, Durham, North Carolina RONALD P. FUCHS, Independent Consultant, Seattle, Washington W. HARVEY GRAY, Independent Consultant, Oak Ridge, Tennessee CARL GUERRERI, Electronic Warfare Associates, Inc., Herndon, Virginia JOHN J. HAMMOND, Lockheed Martin Corporation (retired), Fairfax, Virginia RANDALL W. HILL, JR., University of Southern California Institute for Creative Technologies, Marina del Rey MARY JANE IRWIN, Pennsylvania State University, University Park ROBIN L. KEESEE, Independent Consultant, Fairfax, Virginia ELLIOT D. KIEFF, Channing Laboratory, Harvard University, Boston, Massachusetts LARRY LEHOWICZ, Quantum Research International, Arlington, Virginia WILLIAM L. MELVIN, Georgia Tech Research Institute, Smyrna ROBIN MURPHY, Texas A&M University, College Station SCOTT PARAZYNSKI, The Methodist Hospital Research Institute, Houston, Texas RICHARD R. PAUL, Independent Consultant, Bellevue, Washington JEAN D. REED, Independent Consultant, Arlington, Virginia LEON E. SALOMON, Independent Consultant, Gulfport, Florida JONATHAN M. SMITH, University of Pennsylvania, Philadelphia MARK J.T. SMITH, Purdue University, West Lafayette, Indiana MICHAEL A. STROSCIO, University of Illinois, Chicago JOSEPH YAKOVAC, President, JVM LLC, Hampton, Virginia Staff BRUCE A. BRAUN, Director CHRIS JONES, Financial Manager DEANNA P. SPARGER, Program Administrative Coordinator vii

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Preface Armor materials are remarkable: Able to stop multiple Coincidentally, six weeks after the final committee hits and save lives, they are essential to our military capa- meeting, the Army announced a draft program calling for bility in the current conflicts. But as threats have increased, establishment of a collaborative research alliance for materi- als in extreme dynamic environments.2 Since the committee armor systems have become heavier, creating a huge burden for the warfighter and even for combat vehicles. This study did not review the Army’s preliminary request for proposal, of lightweight protection materials is the product of a com- it is not discussed in the study. mittee created jointly by two boards of the National Research The committee was composed of a wide range of experts Council, the National Materials Advisory Board (NMAB)1 whose backgrounds in processing and characterization of ce- and the Board on Army Science and Technology (BAST), ramics, metals, polymers, and composites, as well as theory in response to a joint request from the Assistant Secretary and modeling and high-rate testing of protection materials, of the Army for Acquisition, Logistics, and Technology and combined wonderfully to make this report possible. I want the Army Research Laboratory. The committee examined to thank each and every one of the committee members for the fundamental nature of material deformation behavior at their hard work, camaraderie, and dedicated efforts over the the very high rates characteristic of ballistic and blast events. past year and in particular, Mike McGrath, the vice chair, Our goal was to uncover opportunities for development of and chapter leads Richard Haber, John Hutchinson, Nina advanced materials that are custom designed for use in armor Orlovskaya, Don Shockey, Bob Skaggs, Raúl Radovitzky, systems, which in turn are designed to make optimal use of and Steve Wax. Staff of the NMAB and the BAST did a great the new materials. Such advances could shorten the time job supporting the study and in bringing the report to fruition. for material development and qualification, greatly speed engineering implementation, drive down the areal density Edwin L. Thomas, NAE, Chair of armor, and thereby offer significant advantages for the Committee on Opportunities in U.S. military. We hope this report will have a revolutionary Protection Materials effect on the materials and armor systems of the future—an Science and Technology for effect that will meet mission needs and save even more lives. Future Army Applications 2U.S. Army. 2010. A Collaborative Research Alliance (CRA) for Ma - 1In January 2011 the National Materials Advisory Board (NMAB) and terials in Extreme Dynamic Environments (MEDE), Solicitation Number the Board on Manufacturing and Engineering Design combined to form W911NF-11-R-0001, October 28. Available online at https://www.fbo.gov/ the National Materials and Manufacturing Board. The move underscored index?s=opportunity&mode=form&id=48a13a80653b1fabe3f83ede9ddc64 the importance of materials science to innovations in engineering and 1b&tab=core&tabmode=list&=. Last accessed March 31, 2011. manufacturing. ix

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Acknowledgment of Reviewers This report has been reviewed in draft form by indi- Wayne E. Marsh, DuPont Central Research and viduals chosen for their diverse perspectives and technical Development, expertise, in accordance with procedures approved by the R. Byron Pipes, Purdue University, National Research Council’s (NRC’s) Report Review Com- Bhakta B. Rath, Naval Research Laboratory, mittee. The purpose of this independent review is to provide Susan Sinnott, University of Florida, and candid and critical comments that will assist the institution Edgar Arlin Starke, Jr., University of Virginia in making its published report as sound as possible and to ensure that the report meets institutional standards for objec- Although the reviewers listed above have provided tivity, evidence, and responsiveness to the study charge. The many constructive comments and suggestions, they were not review comments and draft manuscript remain confidential asked to endorse the conclusions or recommendations nor to protect the integrity of the deliberative process. We wish to did they see the final draft of the report before its release. The thank the following individuals for their review of this report: review of this report was overseen by Elisabeth M. Drake, NAE, Massachusetts Institute of Technology Laboratory of Charles E. Anderson, Jr., Southwest Research Energy and the Environment. Appointed by the National Re- Institute, search Council, she was responsible for making certain that Diran Apelian, Worcester Polytechnic Institute, an independent examination of this report was carried out in Morris E. Fine, Technological Institute Professor accordance with institutional procedures and that all review Emeritus, Northwestern University comments were carefully considered. Responsibility for the Peter F. Green, University of Michigan, final content of this report rests entirely with the authoring Julia R. Greer, California Institute of Technology, committee and the institution. x

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Contents SUMMARY 1 1 OVERVIEW 7 Introduction, 7 The Challenge, 7 Scope of the Study, 9 Statement of Task, 9 Study Methodology, 9 Report Organization, 9 Other Issues, 10 Overarching Recommendation, 10 2 FUNDAMENTALS OF LIGHTWEIGHT ARMOR SYSTEMS 12 Armor System Performance and Testing in General, 12 Definition of Armor Performance, 12 Testing of Armor Systems, 13 Exemplary Threats and Armor Designs, 14 Personnel Protection, 14 Threat, 14 Design Considerations for Fielded Systems, 15 Vehicle Armor, 18 Threat, 18 Design Considerations for Fielded Systems, 18 Transparent Armor, 20 Threat, 20 Design Considerations for Fielded Systems, 21 From Armor Systems to Protection Materials, 21 Existing Paradigm, 21 Security and Export Controls, 23 3 MECHANISMS OF PENETRATION IN PROTECTIVE MATERIALS 24 Penetration Mechanisms in Metals and Alloys, 25 Penetration Mechanisms in Ceramics and Glasses, 26 Penetration Mechanisms in Polymeric Materials, 28 Failure Mechanisms in Cellular-Sandwich Materials Due to Blasts, 29 Conclusions, 32 xi

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xii CONTENTS 4 INTEGRATED COMPUTATIONAL AND EXPERIMENTAL METHODS FOR THE 35 DESIGN OF PROTECTION MATERIAL AND PROTECTION SYSTEMS: CURRENT STATUS AND FUTURE OPPORTUNITIES Three Examples of Current Capabilities for Modeling and Testing, 36 Projectile Penetration of High-Strength Aluminum Plates, 36 Projectile Penetration of Bilayer Ceramic-Metal Plates, 38 All-Steel Sandwich Plates for Enhanced Blast Protection: Design, Simulation, and Testing, 40 The State of the Art in Experimental Methods, 43 Definition of the Length Scales and Timescales of Interest, 43 Evaluating Material Behavior at High Strain Rates, 45 Investigating Shock Physics, 47 Investigating Dynamic Failure Processes, 49 Investigating Impact Phenomenology, 50 Modeling and Simulation Tools, 51 Background and State of the Art, 52 New Protection Materials and Material Systems: Opportunities and Challenges, 65 Computational Materials Methods, 65 Overall Recommendations, 68 5 LIGHTWEIGHT PROTECTIVE MATERIALS: CERAMICS, 69 POLYMERS, AND METALS Overview and Introduction, 69 Ceramic Armor Materials, 70 Crystalline Ceramics: Phase Behavior, Grain Size or Morphology, and Grain Boundary Phases, 72 Crystalline Structure of Silicon Carbide, 75 Availability of Ceramic Powders, 77 Processing and Fabrication Techniques for Armor Ceramics, 78 “Green” Compaction, 78 Sintering, 79 Transparent Armor, 80 Transparent Crystalline Ceramics, 81 Fibers, 82 Effect of Fiber Diameter on Strength in High-Performance Fibers, 84 Relating Tensile Properties to Ballistic Performance, 84 Approaching the Theoretical Tensile Strength and Theoretical Tensile Modulus, 84 The Need for Mechanical Tests at High Strain Rates, 85 Ballistic Fabrics, 86 Ballistic Testing and Experimental Work on Fabrics, 86 Failure Mechanisms of Fabrics, 87 Important Issues for Ballistic Performance of Fabrics, 87 Metals and Metal-Matrix Composites, 89 Desirable Attributes of Metals as Protective Materials, 90 Nonferrous Metal Alternatives, 91 Adhesives for Armor and for Transparent Armor, 92 General Considerations for the Selection of an Adhesive Interlayer, 92 Important Issues Surrounding Adhesives for Lightweight Armor Applications, 92 Types of Adhesive Interlayers, 94 Testing, Simulation, and Modeling of Adhesives, 94 Joining, 95 Other Issues in Lightweight Materials, 96 Nondestructive Evaluation Techniques, 96 Fiber-Reinforced Polymer Matrix Composites, 97 Overall Findings, 97

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xiii CONTENTS 6 THE PATH FORWARD 99 A New Paradigm, 99 Recommendations for Protection Materials by Design, 102 Element 1—Fundamental Understanding of Mechanisms of Deformation and Failure Due to Ballistic and Blast Threats, 102 Element 2—Advanced Computational and Experimental Methods, 102 Element 3—Development of New Materials and Material Systems, 103 Element 4—Organizational Approach, 104 Critical Success Factors for the Recommended New Organizations, 105 DoD Center for the PMD Initiative, 105 Open PMD Collaboration Center, 106 Time Frame for Anticipated Advances, 107 APPENDIXES A Background and Statement of Task 111 B Biographical Sketches of Committee Members 113 C Committee Meetings 119 D Improving Powder Production 121 E Processing Techniques and Available Classes of Armor Ceramics 125 F High-Performance Fibers 136 G Failure Mechanisms of Ballistic Fabrics and Concepts for Improvement 139 H Metals as Lightweight Protection Materials 142 I Nondestructive Evaluation for Armor 148 J Fiber-Reinforced Polymer Matrix Composites 150

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Tables, Figures, and Boxes TABLES 2-1 National Institute of Justice (NIJ) Ballistic Threat Standards, 14 2-2 Metallic Armor Materials, 19 4-1 Mode or Method, Required Input, Expected Output, and Typical Software Used in Materials Science and Engineering, 67 5-1 Manufacturing Processes for Opaque Ceramic Armor Materials, 80 5-2 Typical Properties of Selected Fibers, 83 E-1 Summary of Properties of Various Ceramics for Personnel Armor Application, 126 E-2 Tensile Mechanical Properties of Spider Silks and Other Materials, 132 FIGURES S-1 New paradigm for armor development, 3 S-2 PMD initiative organizational structure involving academic researchers, government laboratories, and industry, 5 1-1 A soldier wearing protective equipment, 7 1-2 Up-armored high-mobility multipurpose wheeled vehicle (HMMWV, or Humvee), 8 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, 8 2-1 Partial and complete ballistic penetration, 13 2-2 Indoor firing ranges, 15 2-3 Examples of 7.62 mm (.30 cal) small arms projectiles, 15 2-4 Increase in ballistic performance as a function of improved fibers, 16 2-5 Interceptor body armor, 17 2-6 Effect of a ballistic threat on performance, 17 2-7 Examples of Army combat vehicles, 19 2-8 Examples of vehicle protection, 20 2-9 Schematic of vehicle armor protection system, 21 2-10 Example of transparent armor for a vehicle window, 22 2-11 Current paradigm for armor design, 22 xv

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xvi TABLES, FIGURES, AND BOXES 3-1 Impact on steel plate, 25 3-2 Polished and etched cross section through the crater in a steel plate that was impacted at 6 km/s by a 12.7-mm-diameter polycarbonate sphere, 26 3-3 Polished cross sections through the shot line of a SiC and a TiB2 target, showing typical microdamage immediately below the impact site after a no-penetration experiment with a long rod tungsten projectile, 26 3-4 Damage mechanisms observed in several ceramics, 27 A 200 × 200 × 75 mm3 monolithic soda lime glass target (confined on all sides with 3-5 polymethyl methacrylate plates) partially penetrated by a 31.75 × 6.35-mm-diameter heminosed steel rod impacting at 300 m/s and a surface of section through the shot line showing damage around the projectile cavity, 28 3-6 Three material processing zones and three stress states experienced by a material element in the path of an advancing penetrator, 29 3-7 Post-test observation of fabric damage from a platelike projectile showing yarn breakage characteristics; projectile size is shown with the fabric flap in its original position, 30 3-8 SEM micrograph revealing fibrillar microstructure in an as-spun PBZT fiber, 30 3-9 SEM side views and end-on views of matching fracture ends of a tensile-fractured PBZT fiber, 31 3-10 Sequence of computerized axial tomography scan images showing macro deformation bands in quasi-static compression-loaded ductile aluminum foam, 32 3-11 Sequential mechanisms responsible for cell collapse in ductile aluminum foam under quasi-static load, 32 3-12 Stress-strain curve for a brittle aluminum foam subjected to quasi-static compression; bands of fractured cells after imposed quasi-static engineering compressive strains of 0, 5.6 percent, 11.7 percent, 33.3 percent, and 60 percent, respectively, 32 3-13 SEM images of failed cells in brittle aluminum foam showing failure modes under compression, tension and shear, face cracking, and friction and shear between fractured cells, 33 4-1 Blunt-nosed and ogive-nosed projectiles exiting a 20-mm-thick aluminum plate, 37 4-2 Experimental results for final exit (residual) velocity as a function of initial velocity for blunt-nosed and ogive-nosed projectiles, 37 4-3 Numerical finite-element simulations of the ballistic behavior shown in Figure 4.2 depicting effects of mesh refinement and the contrast between three-dimensional and two- dimensional (axisymmetric) meshing, 37 4-4 Simulations of penetration of a plate of AA7057-T651 showing finite-element mesh for a blunt-nosed and an ogive-nosed hard steel projectile, 38 4-5 Ceramic strength versus applied pressure for the JHB constitutive model, 39 4-6 Schematic depicting the response of a clamped sandwich plate to blast loading, 43 4-7 Half-sectional square honeycomb core test panels, 43 4-8 Comparison of experimental test specimens deformed at the three levels of air blast, with simulations carried out for the same plates and level of blasts, 43 4-9 Length scales and timescales associated with typical threats to Army fielded materials and structures, 44 4-10 Experimental techniques used for the development of controlled high-strain-rate deformations in materials, 45 4-11 High-strain-rate behavior of 6061-T6 aluminum determined through servohydraulic testing, compression and torsional Kolsky bars, and high-strain-rate, pressure-shear plate impact, 46 4-12 Schematic of the high-strain-rate, pressure-shear plate impact experiment, 47 4-13 Photographs taken by a high-speed camera (interframe times of 1 μs and exposure times of 100 ns) of the dynamic failure process in uncoated transparent AlON, 50

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xvii TABLES, FIGURES, AND BOXES 4-14 Line VISAR figure showing spallation in polycrystalline tantalum, 51 4-15 Optimal transportation mesh-free simulation of a steel plate perforated by a steel projectile striking at various angles, 55 4-16 Example of a Lagrangian finite-element simulation that uses adaptive re-meshing and refinement to eliminate element distortion and to optimize the mesh, 56 4-17 A comparison of results from five computational approaches for a tungsten projectile impacting a steel target at 1,615 m/s, 56 4-18 Prediction of conical, radial, and lateral crack patterns in ceramic plate impact by the recent cohesive zone/discontinuous Galerkin method, 58 4-19 Multiscale hierarchy for metal plasticity, 61 4-20 V&V process, 63 4-21 Growth in supercomputer powers as a function of year, 64 5-1 Schematic presentation of the cross section of an armor tile typically used for armored vehicles showing the complexity of the armor architecture, 69 5-2 Rhombohedral unit cell structure of B4C showing B11C icosahedra and the diagonal chain of C-B-C atoms, 72 5-3 The boron-carbon phase diagram over the range 0-36 at % carbon, 73 5-4 A boron carbide ballistic target that comminuted during impact and a high-resolution TEM image of a fragment produced by a ballistic test at impact pressure of 23.3 GPa, 74 5-5 Schematics of the stacking sequence of layers of Si–C tetrahedra in various SiC polytypes, 76 5-6 Scanning TEM micrograph of the microstructure of spinel glass ceramic, 80 5-7 Photo showing the transparency and multi-hit performance of spinel, 82 5-8 Strength and stiffness of the strongest fiber sample and of fibers typical of the high- strength and low-strength peaks in the 1-mm gauge length distribution versus the properties of other commercially available, high-performance fibers, 83 5-9 Schematic of transverse sections of fibers, 84 5-10 Stress-strain curve for RHA steel deformed in compression at a high strain rate, 90 5-11 Composite stack of transparent layers: a ceramic strike face, adhesive interlayers, glass, polyurethane, and polycarbonate, 93 6-1 Current paradigm for armor design, 99 6-2 New paradigm for armor development, 100 6-3 PMD initiative organizational structure involving academic researchers, government laboratories, and industry, 104 E-1 Silicon carbide sample microstructures showing grains in hot-pressing, dynamic magnetic compaction followed by pressureless sintering, and uniaxial pressing followed by pressureless sintering, 128 H-1 Specific stiffness versus specific strength of various materials, including metals and ceramics, 143 H-2 High-strain-rate compressive response of a trimodal aluminum alloy, in comparison with that of rolled homogeneous armor at similar strain rates (103 s–1), 144 H-3 Optical micrograph of Al-SiC cermet, 145 J-1 Cone formation during ballistic impact on the back face of the composite target, 151 J-2 Schematic shape of delaminated regions observed in impact experiments, 152 J-3 Schematic showing plug formation, 152

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xviii TABLES, FIGURES, AND BOXES BOXES 2-1 Composition of Rolled Homogeneous Armor [L] (MIL-DTL-12560), 12 2-2 Construction of the Advanced Combat Helmet, 18 2-3 Shaped Charge Characteristics, 19 3-1 Microstructural Options for Influencing Failure Mechanisms in Metals, Ceramics, and Polymers, 24 5-1 Processing of Ceramic Powders, 78

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Acronyms and Abbreviations AlON aluminum oxynitride ICME Integrated Computational Materials ARL Army Research Laboratory Engineering (an NRC report) ARO Army Research Office ITAR International Traffic in Arms Regulations ATC Aberdeen Test Center (Maryland) ATH aluminum trihydroxide JHB Johnson, Holmquist, and Beissel ATPD Army Tank Purchase Description M&S modeling and simulation BAST Board on Army Science and Technology MMC metal matrix composites MPa megapascal CIP cold isostatic pressing MZ Mescall zone CNT carbon nanotubes CTE coefficient of thermal expansion NDE nondestructive evaluation CZM cohesive zone models NIJ National Institute of Justice NMAB National Materials Advisory Board DARPA Defense Advanced Projects Research NRC National Research Council Agency NSF National Science Foundation DMC dynamic magnetic compaction NVI normal velocity interferometer DoD Department of Defense DoE Department of Energy OHPC Omnipresent High-Performance Computing program ERDC Engineer Research and Development Center (U.S. Army) PAN polyacrylonitrile ESAPI enhanced small arms protective insert PBO polybenzoxazole PBZT poly(benzobisthiazole) FGAC functionally graded armor composites PC polycarbonate FGM functionally gradient material PE polyethylene FSP fragment simulating projectiles PMC polymer matrix composite PMD protection materials-by-design GHz gigahertz PMMA polymethyl methacrylate GPa gigapascals PPTA polyparaphenylene terephthalamide PU polyurethane HEL Hugoniot elastic limit PVB polyvinyl butyral HMMWV high-mobility multipurpose wheeled vehicle (Humvee) QMU quantification of margins and uncertainties HP hot pressing RHA rolled homogeneous armor IBA Interceptor body armor xix

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xx ACRONYMS AND ABBREVIATIONS SAN poly(styrene-co-acrylonitrile) TPU thermoplastic polyurethanes SAPI small arms protective insert SCS shear compression (test) UHMWPE ultrahigh molecular weight polyethylene SEM scanning electron microscope UQ uncertainty quantification SiC silicon carbide UV ultraviolet SiSiC siliconized silicon carbide SPS spark plasma sintering VISAR velocity interferometry system for any reflector V&V verification and validation TDI transverse displacement interferometer TEM transmission electron microscopy XCT x-ray computed tomography