Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session Y6: Inelastic Deformations, Fracture and Spall X: New Models, Techniques, and Targets |
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Chair: Michael Greenfield, Army Research Laboratory, Nathan Barton, Lawrence Livermore National Laboratory Room: 8/9/10 |
Friday, June 19, 2015 9:15AM - 9:30AM |
Y6.00001: A simple model for dislocation emission mediated dynamic nanovoid growth Justin Wilkerson, K.T. Ramesh Failure of ductile metals has long been attributed to the microscopic processes of void nucleation, growth, and finally coalescence leading to fracture. Our traditional view of void nucleation is associated with interface debonding at second-phase particles. However, much of this understanding has been gleaned from observations of quasi-static fracture surfaces. Under more extreme dynamic loading conditions second-phase particles may not necessarily be the dominant source of void nucleating material defects, and a few key experimental observations of laser spall surfaces seem to support this assertion. Here, we motivate an alternative mechanism to the traditional view, namely shock-induced vacancy generation and clustering followed by nanovoid growth mediated by dislocation emission. This mechanism only becomes active at very large stresses, and thus it is desirable to establish a closed-form criterion for the macroscopic stress required to activate dislocation emission in porous materials. Following an approach similar to Lubarda and co-workers, we make use of stability arguments applied to the analytic solutions of the elastic interactions of dislocations and voids to derive the desired criterion. We then propose a dynamic nanovoid growth law that is motivated by the kinetics of dislocation emission. The resulting failure model is validated against a number of molecular dynamics simulations with favorable agreement. Lastly, we make use of our simple model to predict some interesting anomalous behaviors associated with high surface energies and nonlinear elasticity. [Preview Abstract] |
Friday, June 19, 2015 9:30AM - 9:45AM |
Y6.00002: Results from a new Cocks-Ashby style porosity model Nathan Barton A new porosity evolution model will be described, along with preliminary results. The formulation makes use of a Cocks-Ashby style treatment of porosity kinetics that includes rate dependent flow in the mechanics of porosity growth. The porosity model is implemented in a framework that allows for a variety of strength models to be used for the matrix material, including ones with significant changes in rate sensitivity as a function of strain rate. Results of the effect of changing strain rate sensitivity on porosity evolution will be shown. The overall constitutive model update involves the coupled solution of a system of nonlinear equations -- efficiency and robustness of the numerical implementation are significant issues. [Preview Abstract] |
Friday, June 19, 2015 9:45AM - 10:00AM |
Y6.00003: A New Technique for Monitoring Inhomogeneous Deformation during Flyer Plate Impact James Walker, Donald Grosch, Sidney Chocron, Kathryn Dannemann, Rory Bigger, Thomas Moore, Trenton Kirchdoerfer A new and unique experimental configuration was developed and demonstrated to measure the inhomogeneous deformation of heterogeneous materials during flyer plate impact tests. Flyer plate experiments were performed on a granite material with a small scale structure; strain rates ranged from $10^5$ to $10^7$ s$^{-1}$. A cross section of an impacted target was monitored and photographed during, and immediately following, passage of the shock wave through the material. Eight to sixteen images were taken during passage of the shock wave. This was accomplished using an ultra-high speed Imacon camera with very short exposure times; for example, in one experiment the exposure time was 5 nanoseconds with a framing rate of 5 million frames per second. Continuous wave lasers were used as the illumination source. Edge and notch filters were used to lessen the intensity of the impact flash in the image. The photographic data was analyzed using a digital image correlation (DIC) system. These experiments examined deformation on a cut plane within the target. [Preview Abstract] |
Friday, June 19, 2015 10:00AM - 10:15AM |
Y6.00004: Experimental and numerical study of thin fragments protection for radiographic detectors Olivier Bozier, Denis Counilh, Fabrice Gillot, Lise-Marie Adolf, Pascale Silvin, Nicolas Rambert, David Hebert, Isabelle Bertron To perform a non-intrusive measurement on a pyrotechnic setup, we usually use radiography. But due to blast and fragments, the X-ray generator head and the detectors of the radiographic chain must be protected. Since the detector holds the data we want to collect, he cannot be sacrificed. The constitution of detector shielding is therefore an essential part of a radiographic chain. The choice of shielding should take into account two conflicting needs. On one hand, shielding must be sufficiently resistant to protect the detector from the blast and fragments generated. On the other hand, it should be thin enough in order to attenuate as little as possible the radiographic signal. We carried out an experimental campaign to test the performances of various shieldings. Cylindrical projectiles of various masses (from 20g to 40g) and aspect ratios (length to diameter ratio from 0.1 to 1) that are representative fragments, have been launched with a gas gun with different initial velocities (from 1500m/s up to 2000m/s). Multiple shielding configurations have been tested. They were assemblies of successive steel, aluminum and B4C plates. Combined with a numerical study, we optimize disposition and thicknesses of the plates which fulfils our requirements in terms of detector protection and radiographic measurement. [Preview Abstract] |
Friday, June 19, 2015 10:15AM - 10:30AM |
Y6.00005: Comparative Shock Response of Additively Manufactured Versus Conventionally Wrought 304L Stainless Steel* J.L. Wise, D.P. Adams, E.E. Nishida, B. Song, M.C. Maguire, J. Carroll, B. Reedlunn, J.E. Bishop Gas-gun experiments have probed the compression and release behavior of impact-loaded 304L stainless steel specimens machined from additively manufactured (AM) blocks as well as baseline ingot-derived bar stock. The AM technology allows direct fabrication of metal parts. For the present study, a velocity interferometer (VISAR) measured the time-resolved motion of samples subjected to one-dimensional (i.e., uniaxial strain) shock compression to peak stresses ranging from 0.2 to 7.5 GPa. The acquired wave-profile data have been analyzed to determine the comparative Hugoniot Elastic Limit (HEL), Hugoniot equation of state, spall strength, and high-pressure yield strength of the AM and conventional materials. Observed differences in shock loading and unloading characteristics for the two 304L source variants have been correlated to complementary Kolsky bar results for compressive and tensile testing at lower strain rates. The effects of composition, porosity, microstructure (e.g., grain size and morphology), residual stress, and sample axis orientation relative to the additive manufacturing deposition trajectory have been assessed to explain differences between the AM and baseline 304L dynamic mechanical properties. *Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. [Preview Abstract] |
Friday, June 19, 2015 10:30AM - 10:45AM |
Y6.00006: The fracture and fragmentation behaviour of additively manufactured stainless steel 316L Russell Amott, Ernest Harris, Ron Winter, Stewart Stirk, David Chapman, Daniel Eakins Expanding cylinder experiments using a gas gun technique allow investigations into the ductility of metals and the fracture and fragmentation mechanisms that occur during rapid tensile failure. These experiments allow the radial strain-rate of the expansion to be varied in the range 102 to 104 s-1. Presented here is a comparative study of the fracture and fragmentation behaviour of rapidly expanded stainless steel 316L cylinders manufactured from either wrought bar or by additive manufacturing techniques. The results show that in the strain-rate regime studied, an additively manufactured cylinder failed at a higher strain and produced larger fragment widths compared to cylinders manufactured from wrought bar. In addition, an investigation into the role of deliberate equispaced macroscopic voids introduced into a cylinder wall has been undertaken. Using the unique properties of additive manufacture, elongated voids were introduced to the cylinder wall at an angle of 45$^{\circ}$ to the cylinder radius, and the resulting fragment patterns will be discussed. A comparison of the expanding cylinder profiles with simulations using CTH will also be presented. [Preview Abstract] |
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