Engineering topics

Kaul, Ann M

Publications and source records attributed to Kaul, Ann M.

4 records

DOE OSTI2011

Task order #24 update: exploration of damage mechanisms in cylindrical geometry

A typical method of failure for ductile materials is spallation damage, which is caused by the nucleation, growth and coalescence of voids due to the presence of high tensile stress in the material. Spallation damage models, such as TEPLA, are currently implemented in hydrodynamic computer codes used at Los Alamos National Laboratory (LANL). Parameters for such constitutive models are derived from data sets obtained primarily from gas gun and shock-driven experiments, which are designed to allow one-dimensional analysis of the evolution of the failure characteristics. However, in a non-planar geometry, advanced failure models predict failure to be a multi-dimensional process. Additionally, a limited amount of data exists for the process of void nucleation, growth and coalescence. Another lightly researched area is the state of the material in the event that the spallation layer is recollected and voids are closed. The experiments described here are being conducted as part of a Campaign-l effort to provide data addressing these issues. The Russian Damage Experimental Series is designed to provide fundamental non-planar (cylindrical) spallation damage data, including early time processes (void nucleation, growth and coalescence) and late time processes (recollection of the spallation layer). Previous experiments produced data addressing some of the early time processes. This presentation will be provided to LANL and VNIIEF colleagues as a means of assessing the status of Task Order No.24 at the current time.

36 MATERIALS SCIENCE↗

DOE OSTI2010

Mesh size and code option effects of strength calculations

Modern Lagrangian hydrodynamics codes include numerical methods which allow calculations to proceed past the point obtainable by a purely Lagrangian scheme. These options can be employed as the user deems necessary to 'complete' a calculation. While one could argue that any calculation is better than none, to truly understand the calculated results and their relationship to physical reality, the user needs to understand how their runtime choices affect the calculated results. One step toward this goal is to understand the effect of each runtime choice on particular pieces of the code physics. This paper will present simulation results for some experiments typically used for strength model validation. Topics to be covered include effect of mesh size, use of various ALE schemes for mesh detangling, and use of anti-hour-glassing schemes. Experiments to be modeled include the lower strain rate ({approx} 10{sup 4} s{sup -1}) gas gun driven Taylor impact experiments and the higher strain rate ({approx} 10{sup 5}-10{sup 6} s{sup -1}) HE products driven perturbed plate experiments. The necessary mesh resolution and the effect of the code runtime options are highly dependent on the amount of localization of strain and stress in each experiment. In turn, this localization is dependent on the geometry of the experimental setup and the drive conditions.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2010

Damage experiments in a cylindrical geometry

Studying spallation damage with a cylindrical configuration allows for a natural recollection of the damaged material under proper driving conditions. Additionally, the damaged material can come to a complete rest without the application of further stopping forces. Specific areas of research include the damage initiation regime in convergent geometry, behavior of material recollected after damage, and effects of convergent geometry on the material response. Such experiments produce unique strain and shear stress states, motivating improvements in existing computational material models and increasing the predictive capabilities of codes. A LANL/VNIIEF joint experimental series has produced cylindrical aluminum failure initiation data and studied the behavior of material recollected after damage initiation and after complete failure. In addition to post-shot collection of the damaged target material for subsequent metallographic analysis, dynamic in-situ experimental diagnostics include velocimetry and transverse radial radiography. This paper will discuss the current experimental status.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2010

Modeling Solid Rayleigh-Taylor Growth

Intense impulses applied to solid materials result in high strain rates, strong plastic strains and significant temperature increments. Data in such regimes would allow confidence in extending material strength models to strain rates of 10{sup 6}-10{sup 7} s{sup -1}. High explosives can be used to accelerate a plate with a perturbation on the side facing the HE, resulting in a Rayleigh-Taylor-like perturbation growth that depends on amplitude and wavelength of the initial surface perturbation, strength of the material, time dependence of the driving pressure force, and temperature of the material. Such experiments have been conducted on perturbed copper plates at LANL, using the LANSCE proton radiography beam to obtain multiple frames of data for each experiment. The results of numerical simulations of these experiments using a 2-D ALE code are presented.

36 MATERIALS SCIENCE↗