Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session C4: Inelastic Deformations, Fracture and Spall II |
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Chair: Bill Reinhart, Sandia National Laboratories Room: Regency Ballroom A |
Monday, July 10, 2017 11:15AM - 11:30AM |
C4.00001: On the dynamic tensile strength of an FCC metal Neil Bourne, David Jones, Saryu Fensin, Carl Trujillo, Daniel Martinez, George T. Gray III The tensile response of polycrystalline metals is often accompanied by the formation of pores within the structure of the material. This large deformation process is broadly identified as progressive with nucleation, growth, coalescence, and failure the physical path taken over very short periods of time. These are well known to be complex processes strongly influenced by microstructure, loading path, and the loading profile, which remains a significant challenge to represent and predict numerically. In a previous study, the influence of loading path on the damage evolution in high-purity tantalum has been presented; in this paper we present complimentary measurement on a pure FCC copper. Samples were shock loaded to three different peak shock stresses using both symmetric impact, and two different composite flyer plate configurations such that upon unloading the three samples displayed nearly identical ``pull-back'' signals as measured via rear-surface velocimetry. The damage evolution in the ``soft'' recovered copper samples was quantified using optical metallography, electron-back-scatter diffraction, and tomography. We shall compare metallurgical observations, velocimetry histories and one dimensional simulations to discuss dynamic failure mechanisms in this metal. [Preview Abstract] |
Monday, July 10, 2017 11:30AM - 11:45AM |
C4.00002: On the anomalous grain size dependence of spall strength Justin Wilkerson, KT Ramesh Experimental studies have identified an anomalous grain size dependence of spall strength in a few face-centered cubic metals. Here we derive the first quantitative theory capable of explaining this phenomena. The theory agrees well with experimental measurements and atomistic calculations over a very wide range of conditions. Utilizing this theory, we are able to map out three distinct regimes in which spall strength (i) increases with decreasing grain size in accordance with conventional wisdom, (ii) non-intuitively decreases with decreasing grain size, and (iii) is independent of grain size. The theory also predicts microscopic characteristics of the spall fracture surface, which agree with available data. [Preview Abstract] |
Monday, July 10, 2017 11:45AM - 12:15PM |
C4.00003: Examination of ductile spall failure through direct numerical simulation Invited Speaker: Richard Becker Direct numerical simulation is used to examine the growth and coalescence of a random population of voids leading to spall failure. Void nucleating particles are explicitly represented in the initial geometry, and the arbitrary Lagrange-Eulerian finite element code tracks the void evolution to create the spall surface. The flow fields capture strain localization associated with void interaction at low porosities and ligament necking at final coalescence. Simulations are run to assess the influence of material strain hardening and strain rate sensitivity on void growth and coalescence. These analyses also provide the evolution of longitudinal stress and the energy dissipated, and they reveal a length scale associated with the spall. Additional calculations are performed to examine the influence of loading pulse shape on spall behavior for triangular shaped pressure loading. A dependence of spall scab thickness on pulse shape is determined. These results show localization delayed until porosities reach a few percent and they demonstrate a consistent stress versus porosity relation. The simulations also provide a direct correlation between the spall stress history and the free surface velocity, which can aid in understanding stress corrections applied to experimental data. [Preview Abstract] |
Monday, July 10, 2017 12:15PM - 12:30PM |
C4.00004: Spall Response of Additive Manufactured Ti-6Al-4V Andrew Brown, Adam Gregg, JP Escobedo, Paul Hazell, Daniel East, Zakaria Quadir Additive manufactured (AM) Ti-6Al-4V was produced via electron beam melting (EBM) and laser melting deposition (LMD) techniques. The dynamic response of AM varieties of common aerospace and infrastructure metals are yet to be fully characterized and compared to their traditionally processed counterparts. Spall damage is one of the primary failure modes in metals subjected to shock loading from high velocity impact. Both EBM and LMD Ti-6Al-4V were shock loaded via flyer-target plate impact using a single-stage light gas gun. Target plates were subjected to pressures just above the spall strength of the material (3-5 GPa) to investigate the early onset of damage nucleation as a function of processing technique and shock orientation with respect to the AM-build direction. Post-mortem characterization of the spall damage and surrounding microstructure was performed using a combination of optical microscopy, scanning electron microscopy, and electron backscatter diffraction. [Preview Abstract] |
Monday, July 10, 2017 12:30PM - 12:45PM |
C4.00005: A physics-based framework for spall failure of single crystals Thao Nguyen, D.J. Luscher, Justin Wilkerson A framework for dislocation-based viscoplasticity and dynamic ductile failure has been developed to model high strain rate deformation and damage in single crystals. The rate-dependence of the crystal plasticity formulation is based on the physics of relativistic dislocation kinetics suited for extremely high strain rates. The damage evolution is based on the dynamics of void growth, which are governed by both micro-inertia as well as dislocation kinetics and dislocation substructure evolution. The resulting homogenized framework has been implemented into a commercially available finite element package, and a fairly extensive validation study against a suite of direct numerical simulations was carried out. The utility of the homogenized framework is further demonstrated through the mesoscale simulation of a polycrystal subject to dynamic loading. The simulations capture some key experimentally-observed features of damage localization along grain boundaries of particular misorientation. [Preview Abstract] |
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