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Title: MATERIAL FAILURE AND PATTERN GROWTH IN SHOCK-DRIVEN ALUMINUM CYLINDERS AT THE PEGASUS FACILITY

Abstract

No abstract prepared.

Authors:
; ;
Publication Date:
Research Org.:
Los Alamos National Lab., NM (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
784679
Report Number(s):
LA-UR-99-4137
TRN: US0302415
DOE Contract Number:
W-7405-ENG-36
Resource Type:
Conference
Resource Relation:
Conference: Conference title not supplied, Conference location not supplied, Conference dates not supplied; Other Information: PBD: 1 Aug 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM; FAILURES; IMPACT SHOCK; TEST FACILITIES; CAPACITIVE ENERGY STORAGE EQUIPMENT

Citation Formats

J. STOKES, R. FULTON, and ET AL. MATERIAL FAILURE AND PATTERN GROWTH IN SHOCK-DRIVEN ALUMINUM CYLINDERS AT THE PEGASUS FACILITY. United States: N. p., 1999. Web.
J. STOKES, R. FULTON, & ET AL. MATERIAL FAILURE AND PATTERN GROWTH IN SHOCK-DRIVEN ALUMINUM CYLINDERS AT THE PEGASUS FACILITY. United States.
J. STOKES, R. FULTON, and ET AL. 1999. "MATERIAL FAILURE AND PATTERN GROWTH IN SHOCK-DRIVEN ALUMINUM CYLINDERS AT THE PEGASUS FACILITY". United States. doi:. https://www.osti.gov/servlets/purl/784679.
@article{osti_784679,
title = {MATERIAL FAILURE AND PATTERN GROWTH IN SHOCK-DRIVEN ALUMINUM CYLINDERS AT THE PEGASUS FACILITY},
author = {J. STOKES and R. FULTON and ET AL},
abstractNote = {No abstract prepared.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1999,
month = 8
}

Conference:
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  • Understanding the surface stability of metals undergoing dynamic fracture at shock breakout is important to several applications in metals processing. The advantages of using the Pegasus II facility to investigate the phenomena occurring at shock break out are described. As an example of the data collected, we concentrate on brief descriptions of two experiments that compared the tensile failure, i.e. ''spall'', patterns in the presence of sinusoidal perturbations seeded on the free inner surface of cylindrical samples made of structural grade Al 6061.T6. These samples were subjected to ramped waves with shock pressures of 14 GPa and 50 GPa tomore » observe the effect of pressure on the production of a type of volumetric failure that is mentioned here ''microspall.'' This failed region behind the exiting surface of the shock wave is comprised of a significant volume of low-density, probably granular, material. The failure mechanism, combined with the forces that cause inertial instability, leads to rapid pattern growth in the failed material, observable as density variations, as well as to pattern growth on the surface. Pattern growth was observed to vary with perturbation amplitude, wavelength, and shock pressure. Both increased pressure and increased amplitude were shown to destabilize a stable perturbation. Increasing the wavelength by a factor of 3 was shown to result in significantly slower growth of the pattern within the failed volume. The mechanisms leading to the formation of the spall volume and to the patterns are discussed briefly.« less
  • Cracking or voiding of passivated aluminum conductor lines in integrated circuits has been observed by many workers since 1984. This problem has been brought on by the trend in the microelectronics industry to miniaturize circuitry. Most reports on the subject attribute the cause to diffusion creep. This report points out certain difficulties with this conclusion and presents the essential features of a related failure mechanism. A numerical stress analysis is presented to illustrate stress gradients in conductor lines. These stress gradients are known to drive mass transport which leads to void formation. Equations are presented which describes the growth ratesmore » of two void morphologies. A definition of failure is made and the time to failure is calculated and the relationship with line width and temperature is given. With properties of aluminum taken from the literature, it will be shown that the calculated failure time is in very good agreement with experimental data. 37 refs., 10 figs.« less
  • The authors have used the LANL Pegasus Z-pinch facility to drive a thin cylindrically-convergent Al liner to {approximately}3 km/s to launch {approximately}30 GPa shocks in a 3-mm thick 10-mm-i.d. aluminum cylinder whose interior is filled with 1 atm Xe gas. The subsequent material motion of the metal and gas is diagnosed with both radial and axial flash x-rays and with optical framing cameras. Instabilities are seeded by implanting wires of assorted higher density metal parallel to the cylinder axis. The authors have done two shots, varying the target from Al 1100-O to Al 6061-T6 to explore the effect of changingmore » material strength. The images show the spallation failure of the metal-gas interface on shock release and the effect of the seeded instabilities.« less
  • The Gurson constitutive equation and variations of it have been used extensively to model ductile damage as represented by the growth in porosity. The model has been widely used in large numerical simulations of dynamic impact and penetration. Because the growth of porosity causes softening there is always a possibility that a discontinuous bifurcation will exist at a critical value of porosity. The criterion for a discontinuous bifurcation is identical to that of loss of ellipticity and, consequently, a well-posed problem becomes ill posed once a discontinuous bifurcation exists. Since the Gurson model has been, and is continuing to be,more » used extensively in numerical solutions for a wide range of technically complex problems, it is often considered to be not feasible to confirm well-posedness by demonstrating convergence with mesh refinement. Therefore, an analytical criterion for loss of ellipticity is of considerable value for computational purposes. The analysis demonstrates that for a particular form of the Gurson model loss of ellipticity may occur at small strains and values of porosity. The inherent implication is that numerical solutions that do not include a check for loss of ellipticity, or that do not include a convergence study, may not be valid solutions.« less
  • Implicit large eddy simulation proposes to effectively rely on the use of subgrid modeling and filtering provided implicitly by physics capturing numerics. Extensive work has demonstrated that predictive simulations of turbulent velocity fields are possible using a class of high resolution, non-oscillatory finite-volume (NFV) numerical algorithms. Truncation terms associated with NFV methods implicitly provide subgrid models capable of emulating the physical dynamics of the unresolved turbulent velocity fluctuations by themselves. The extension of the approach to the substantially more difficult problem of under-resolved material mixing by an under-resolved velocity field has not yet been investigated numerically, nor are there anymore » theories as to when the methodology may be expected to be successful. Progress in addressing these issues in studies of shock-driven scalar mixing driven by Ritchmyer-Meshkov instabilities will be reported in the context of ongoing simulations of shock-tube laboratory experiments.« less