Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session P6: Ballistics III: Strength and Damage Models |
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Chair: Ellen Cerreta, Los Alamos National Laboratory Room: Grand Ballroom VI |
Wednesday, June 29, 2011 2:00PM - 2:15PM |
P6.00001: Incorporation of the Deshpande-Evans Mechanism-Based Damage Model into the EPIC Code Timothy Holmquist This article presents the incorporation of a mechanism-based failure model into the EPIC code. The model was developed by Deshpande and Evans (DE) and is based on micromechanics and wing-crack theory. The model includes the effects of flaw size, flaw density, fracture toughness, friction, crack shape, and crack growth rate. It is also fully 3-dimensional and covers both compression and tension. This work incorporates the DE model into the Johnson-Holmquist-Beissel (JHB) ceramic model and provides an optional, micromechanical, approach for computing damage. A discussion of the DE damage model including the theory and its incorporation into the JHB model is provided. Computations are also presented for several ballistic impact experiments into 99.5 alumina ceramic including some parametric effects. [Preview Abstract] |
Wednesday, June 29, 2011 2:15PM - 2:30PM |
P6.00002: Anisotropic Effects on Constitutive Model Parameters of Aluminum Alloys Nachhatter Brar, Vasant Joshi Simulation of low velocity impact on structures or high velocity penetration in armor materials heavily rely on constitutive material models. The model constants are required input to computer codes (LS-DYNA, DYNA3D or SPH) to accurately simulate fragment impact on structural components made of high strength 7075-T651 aluminum alloys. Johnson-Cook model constants determined for Al7075-T651 alloy bar material failed to simulate correctly the penetration into 1'' thick Al-7075-T651plates. When simulations go well beyond minor parameter tweaking and experimental results are drastically different it is important to determine constitutive parameters from the actual material used in impact/penetration experiments. To investigate anisotropic effects on the yield/flow stress of this alloy we performed quasi-static and high strain rate tensile tests on specimens fabricated in the longitudinal, transverse, and thickness directions of 1'' thick Al7075-T651 plate. Flow stresses at a strain rate of $\sim $1100/s in the longitudinal and transverse direction are similar around 670MPa and decreases to 620 MPa in the thickness direction. These data are lower than the flow stress of 760 MPa measured in Al7075-T651 bar stock. [Preview Abstract] |
Wednesday, June 29, 2011 2:30PM - 2:45PM |
P6.00003: Modeling Interface defeat and Dwell in Long Rod Penetration into Ceramic Targets Yehuda Partom When a long rod projectile hits a ceramic target, the projectile may sometimes \underline {dwell} at the target boundary and flow radially. This dwell or interface defeat phenomenon has to do with the dynamic failure process of the ceramic target material. As ceramics are brittle materials, what is probably missing, is a realistic model for dynamic failure of brittle materials. A ``standard'' model like this is the so called JH model (which has several versions). According to JH the material fails as a function of the effective plastic strain, which is a ductile response feature. Brittle materials are not supposed to accumulate plastic strain before they're fully failed. To model dwell we propose here a different failure model. We call it BSFM (= Brittle Shear Failure Model), and it is based on the \underline {Overstress }(or overload) principle. Our BSFM is rather simple, has a small number of adjustable parameters, and is readily calibrated. We implement the model into a hydro-code, and demonstrate how it works for a typical example of dwell situation. We then calibrate the model parameters to reproduce data obtained recently at SwRI in San Antonio Texas. [Preview Abstract] |
Wednesday, June 29, 2011 2:45PM - 3:00PM |
P6.00004: A Computational Study of Segmented Tungsten Rod Penetration into a Thick Steel Target Plate at High Velocities M. Presnell, A. Rajendran This paper presents results from computational simulations of tungsten alloy segmented rod projectiles (SRP) penetrating an RHA semi-infinite target plate at high velocities. For SRP with an aspect ratio (L/D) = 1/8, a loss in penetration efficiency was seen upon successive segment impacts. Numerical simulations of a configuration in which a tungsten heavy alloy SRP penetrated a thick RHA 4340 steel at 2.6 km/s were performed using the 2006 version of the EPIC – a Lagrangian code. The configuration consisted of eight collinear impacts of discs which measured 2mm thick and 16mm in diameter. The numerical simulations considered a range of parameters including element-particle conversion, spacing and number of fragments, failure criterion, and mesh resolution that influenced the Depth of Penetration (DOP). The EPIC results using the element-to-particle conversion capability in the EPIC code are also compared with open-literature DOP data from simulations using an Eulerian finite element code, AUTODYN for a similar configuration. The present results showed a unique phenomenon of back-flowing ejecta from the crater and fragmented segments penetrating the in-coming subsequent segment. The penetration efficiency seems to be influenced by the back-flowing ejecta. Further computational investigation considered additional simulations with an impact configuration designed to minimize the ejecta effects by using washer-shaped segments; however, the results showed insignificant improvement. [Preview Abstract] |
Wednesday, June 29, 2011 3:00PM - 3:15PM |
P6.00005: Penetration scaling in atomistic simulations of hypervelocity impact C.J. Ruestes, E.M. Bringa, F. Fioretti, A. Higginbotham, E.A. Taylor, G. Graham We present atomistic molecular dynamics simulations of the impact of copper nano particles at 5 km/s on copper films ranging in thickness from 0.5 to 4 times the projectile diameter. We access both penetration and cratering regimes with final cratering morphologies showing considerable similarity to experimental impacts on both micron and millimeter scales. Both craters and holes are formed from a molten region, with relatively low defect densities remaining after cooling and recrystallisation. Crater diameter and penetration limits are compared to analytical scaling models: in agreement with some models we find the onset of penetration occurs for 1.0 $<$ f/d $<$ 1.5, where f is the film thickness and d is the projectile diameter. However, our results for the hole size agree well with scaling laws based on macroscopic experiments providing enhanced strength of a nano-film that melts completely at the impact region is taken into account. Penetration in films with pre-existing nanocracks is qualitatively similar to penetration in perfect films, including the lack of back-spall. Simulations using ``peridynamics'' are also described and compared to the atomistic simulations. [Preview Abstract] |
Wednesday, June 29, 2011 3:15PM - 3:30PM |
P6.00006: Modeling Tunnel Response to Wave Propagation in Jointed Rock with the Material Point Method Elizabeth Kallman, Tyler Baker, Howard Schreyer, Deborah Sulsky, Pamela Johnson Tunnels and other structures are often embedded underground within a media of jointed rock. If the tunnel is subjected to the resulting wave of an explosive blast in proximity, it is of interest to determine the blast properties, as well as the material and geometrical factors which identify a parameter space where the integrity of the structure may be compromised. The constitutive framework within the Material Point Method (MPM) [1,2] is extended to model joints as existing cracks. Results are presented investigating the effect of gap closure, and of impulse and energy transmission around embedded structures such as tunnels.\\[4pt] [1] Schreyer, H.L., 2007, ``Modelling surface orientation and stress at failure of concrete and geological materials'', \textit{J. for Numerical and Analytical Methods in Geomechanics}, Vol 31, pp 141-171. \\[0pt] [2] Sulsky, D., Schreyer, H., Peterson, K., Kwok, R., and Coon, M., 2007, ``Using the material-point method to model sea ice dynamics'', \textit{J. Geophys. Res.}, Vol 112:CO2S90, doi:10.1029/2005JC00329 [Preview Abstract] |
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