Opportunities in Protection Materials Science and Technology for Future Army Applications (2011) / Chapter Skim
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4 Integrated Computational and Experimental Methods for the Design of Protection Materials and Protection Systems: Current Status and Future Opportunities
4 Integrated Computational and Experimental Methods for the Design of Protection Materials and Protection Systems: Current Status and Future Opportunities
Pages 35-68
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From page 35... ...
tiscale, multiphysics computations could take the form of The following tools are needed for accurate simulation separate computations on the micro and macro levels or they for most applications of structural materials: could be integrated and performed in a single computation. Finally, the computational capabilities for complex material • Knowledge of material response described by sound systems must be improved as well, such that system designs constitutive models characterizing both the deforcan be optimized quickly, accurately, and confidently with mation and failure over a wide range of strain rates, uncertainties quantified.
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To calibrate the constitutive laws for a given and characterizing the basic mechanisms of deformation and material, an extensive suite of tests must be performed, from fracture in advancing protection materials. The committee tensile and compressive stress-strain tests up to tests at large goes on to address opportunities and challenges in experi- strains in differing material orientations and temperatures, with strain rates as high as 104 s–1.
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International Journal of Impact Engineering 37(5)
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As a result, the calculations give rise aluminum nitride (including phase change) to large strains, high strain rates, to a shear zone whose thickness is the width of one element.
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The relationship is shown for intact material full impact of the hit is felt by the target immediately. The and failed material, each at two different strain rates, denoted by bilayer begins to bend almost at once, and the ceramic plate ε *
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International Journal of Impact Engineering 35(8)
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To do so would require subjectMechanical response of metallic honeycomb sandwich panel structures to high-intensity dynamic loading. International Journal of Impact Engineering 35(9)
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International Journal of Impact Engineering 35(9)
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International Journal of Impact Engineering waves, projectiles, or failure processes generate associated 35(9)
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structure; they may also develop high strain rates, First, however, a broad comment is in order. One approach but the high-rate deformations vary as a function of to understanding the interaction between threat and material space and time; is to perform a highly instrumented version of the actual 3.
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is not, however, well understood, particularly at high strains and high temperatures. Some experimental techniques have been developed to measure material properties at high strain rates.
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Most of these are listed in Table I of a review36 by range of responses, it is not used as much as the Kolsky bar Field et al., which includes an exhaustive literature set. Very high strain rates (up to 5 × 104 s–1)
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In contrast to the experiments in the preceding section, the experiments in this section all generate strain rates and stress states that vary in both space and time, and the wave propagation is 40Yadev, S
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In the at very high velocities, pressures, and strain rates can also timescales associated with ultrahigh-strain-rate experiments, be accomplished using a "laser shock" apparatus, where the uniaxial strain conditions are sampled. Such results are dif - interaction of a metal film with a high-power laser pulse generates the wave.47 Such experiments are of very short ficult to compare with results obtained at high and very high strain rates (typically obtained with uniaxial stress experi- duration (typically only a few nanoseconds)
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this material. Identical experiments on the coated material Upon release, however, the material again experiences high showed only the dynamic progressive failure on the specimen strain rates, but now starting at high pressures.
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Such experiments are highly instrumented and experimental data can be a powerful tool in armor develophighly controlled versions of the real impact and are valuable ment, but this should not be the primary approach to armor for determining the sometimes unexpected couplings that development. can occur between material properties, failure processes, and Several recent developments in experimental methods system behavior.
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Currently available experimental protection materials technology, where, as discussed in this techniques are generally most sensitive to material behavior chapter, significant effort has been devoted in the last 50 under either high pressure or high strain rate, but they rarely years to developing the basic science, algorithms, simulaprovide accurate information under combined high pressure tion software, and hardware infrastructure to meet this goal. and ultrahigh strain rate.
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that encodes the fundamental mathematical formula The foregoing suggests that details of the mechanical tions and algorithms for solving the initial boundary response of the material system such as wave propagation, value problem governing the dynamics of the physilocalized plastic deformation and fracture, crack propaga- cal event. tion, and others play an important role in determining armor • Constitutive models.
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Computer Methods in Applied Mechanics and Engineering nucleation in a peridynamic solid. International Journal of Fracture 162(199(2-3)
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International Journal of Impact Engineering 5(1-4) : 61Wilkins, M.L., C.A.
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This ments into meshless particles during dynamic deformation. International is illustrated in Figure 4-17, where five different computaJournal of Impact Engineering 28(9)
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A critical missing component in the protective material simulation tools in use today is the ability to represent mate rial damage and failure explicitly. The conventional approach is to make use of so-called continuum damage models (see the section "Constitutive Models" below)
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Cohesive-element calculations ods of the extended finite-element type in existing codes: LS-DYNA89 and Abaqus.90 have proven highly predictive and have been extensively validated in a number of areas of application by, for example, Finding 4-3. A critical missing component of protective maBjerke and Lambros80 and Chalivendra et al.81 A full three-dimensional description of crack patterns terial simulation tools in use today is the ability to represent in ceramic plate impact has recently been enabled by a new material damage and failure explicitly.
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1983. A constitutive model and data for helpful and meaningful results, such as those illustrated in metals subjected to large strains, high strain rates and high temperatures.
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1985. Fracture characteristics of three that limits the localization process and introduces a characmetals subjected to various strains, strain rates, temperatures and pressures.
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This numerical manifestation of the to consistently incorporate the effect of micromechanical ill-posedness of the mathematical problem is what is usually features on material response would enable rational microreferred to as "damage-induced mesh dependency." A com structure design. mon approach to circumvent this problem in existing codes There is therefore a critical need to develop descriptions is to calibrate the material model parameters for a given of material behavior directly rooted in the first principles of mesh size.
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The great breadth behavior of the material, including well-established scaling of the field and its current state of development mean that relations such as those of Hall-Petch and Taylor.115 Finally, multiscale modeling generally cannot be easily formalized the direct simulation of polycrystalline behavior, in which as a self-contained, unified theory and therefore remains as the polycrystalline structure is resolved by the mesh, is much art as a science. As a result, there is a tendency to base within the reach of present petascale computing power.116,117 multiscale modeling on purely numerical schemes such as Large-scale simulations and a detailed experimental valida- molecular dynamics, kinetic Monte Carlo, quasicontinuum, tion process showed that this multiscale approach not only and direct numerical simulation of polycrystals.
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Research Laboratory to apply this paradigm to protection An appealing alternative to computational multiscale materials. schemes is to derive models of effective behavior across length scales analytically.
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Computer Methods in Applied Mechanics and D Klein, R
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This variability in turn provides a measure for the rigorously quantified uncertainties in the predictions as a uncertainty in the response of the protection system -- that measure of the confidence that decision makers can place in is, a measure of how well the response of the system can be such predictions; by injecting probability and statistics into pinned down under operating conditions given the randomthe calculations; by insisting on a global view of the response ness of the system. Such global optimization calculations of the system over its entire operating range, thus breaking are inordinately intensive, hence the need for extreme-scale away from the "hero calculation" mode; and by the very computing.
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Nor are the constitutive laws and property materials using observation and the experimental and cominputs available that are needed to characterize these fibers putational methods of mechanics. These methods can be in the range of strains and strain rates relevant to ballistic or used to evaluate new materials, and they are essential for blast simulations.
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2008. Integrated Computational Materials potential for aiding the architectural design of composite Engineering: A Transformational Discipline for Improved Competitiveness and National Security.
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2008. Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security.
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enable im should be established with primary focus on code validation proved understanding of fundamental material deformation and verification; multiscale, multiphysics material models; and fracture mechanisms governing protection materials integrated simulation/experimental protocols; prediction performance and (2) provide guidance for changes in mate with quantified uncertainties; and simulation-based qualirial processing.
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