Title: Dynamic flow stress of pure polycrystalline aluminum: Pressure-shear plate impact experiments and extension of dislocation-based modeling to large strains

Abstract

The dynamic thermo-mechanical behavior of pure aluminum has attracted renewed interest lately due to experimental observations of an anomalous increase in Hugoniot Elastic Limit (HEL) at incipient plasticity and elevated temperatures in polycrystalline pure metals. In context of current dislocation-mediated plasticity models for metals, this increase in dynamic strength is indicative of a transition in the rate controlling mechanism for dislocation glide from being thermally assisted to phonon-drag restricted due to increase in phonon viscosity at elevated temperatures. Though these studies have helped to shed light on these important mechanisms operative in FCC metals at incipient plasticity, the extent to which they contribute to flow stress, particularly at larger strains, remains unclear. Here, we address these questions through a combined experimental and modeling effort focused on investigating the evolution of dynamic flow stress in polycrystalline aluminum using experimental data gathered from a series of combined pressure-and-shear plate impact (PSPI) experiments designed to reveal the flow stress of pure aluminum at strain rates ~ 10⁵/s, plastic strains of up to 40% and temperatures ranging from room to 866 K. In all cases, the flow stress of aluminum, as inferred from the measured transverse particle velocity histories at the free surface ofmore » an elastic tungsten carbide target plate, reveals saturation with increasing plastic strains at stress levels that decrease with increasing test temperatures. Numerical simulations are performed to correlate the experimentally observed temperature and strain rate dependence of flow stress at small and large plastic strains using the Austin-McDowell dislocation-mediated plasticity model parametrized to normal plate impact experiments conducted in an earlier study by Zaretsky and Kanel (2012). Extensions to the model are made to better represent dynamic behavior of pure aluminum at larger plastic strains as observed in elevated temperature split Hopkinson Pressure bar (SPHB) experiments of Samanta (1971) and Lindholm and Yeakly (1965), and the combined pressure-and-shear plate-impact experiments conducted in the present study. The main theoretical extension to the Austin-McDowell model made in this paper is the introduction of a new rate- and temperature- dependent dynamic recovery function, which can potentially allow for an effective reduction in the rate of accumulation of dislocations at large plastic strains. The numerical predictions of the revised and re-calibrated plasticity model are brought into agreement with the experimental observations, correlating sufficiently well with dynamic yield stress at incipient plasticity and the flow stress levels at larger plastic strains, plastic strain rates in the range 10³ – 10⁶ /s, and elevated temperatures up to near melt. The model, in concert with the experimental measurements, suggests that at incipient plasticity the rate governing mechanism for plastic flow is phonon-drag restricted dislocation glide, whereas, at higher magnitudes of plastic strain, it transitions to stress-assisted thermally activated glide. The transition between these two rate governing mechanisms is controlled by the evolution of dislocations throughout the deformation process.« less

Authors:

Zuanetti, Bryan  ^[1];

• Search DOE PAGES for author "Zuanetti, Bryan"
• Search DOE PAGES for ORCID "0000-0002-5346-6993"

Luscher, Darby Jon  ^[1];

• Search DOE PAGES for author "Luscher, Darby Jon"
• Search DOE PAGES for ORCID "0000-0003-2929-6119"

Ramos, Kyle James  ^[1];

• Search DOE PAGES for author "Ramos, Kyle James"
• Search DOE PAGES for ORCID "0000-0003-3198-5124"

Bolme, Cynthia Anne  ^[1];

• Search DOE PAGES for author "Bolme, Cynthia Anne"
• Search DOE PAGES for ORCID "0000-0002-1880-271X"

Prakash, Vikas ^[2]

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+ Show Author Affiliations

1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Washington State Univ., Pullman, WA (United States)

Publication Date:

Wed Oct 13 00:00:00 EDT 2021

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE Laboratory Directed Research and Development (LDRD) Program

OSTI Identifier:

1735907

Alternate Identifier(s):

OSTI ID: 1776114

Report Number(s):

LA-UR-20-23354
Journal ID: ISSN 0022-5096

Grant/Contract Number:  

89233218CNA000001; NA0001989; NA0002919; 20190639PRD2

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the Mechanics and Physics of Solids

Additional Journal Information:

Journal Volume: 146; Journal ID: ISSN 0022-5096

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; plate impact; phonon drag; Hugoniot elastic limit; dislocations; pressure-shear; shock; high strain-rates; normal shock compression; shear loading; incipient plasticity; phonon-drag; elevated temperatures; saturation stress; thermally assisted glide