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Title: Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6

Abstract

The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT) within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiplemore » back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.« less

Authors:
; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1340510
Report Number(s):
SAND-2016-5698J
Journal ID: ISSN 0921-5093; PII: S0921509317300898; TRN: US1700908
Grant/Contract Number:
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing
Additional Journal Information:
Journal Volume: 687; Journal Issue: C; Journal ID: ISSN 0921-5093
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; aluminum; crystal plasticity; cyclic loading

Citation Formats

Hennessey, Conor, Castelluccio, Gustavo M., and McDowell, David L. Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6. United States: N. p., 2017. Web. doi:10.1016/j.msea.2017.01.070.
Hennessey, Conor, Castelluccio, Gustavo M., & McDowell, David L. Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6. United States. doi:10.1016/j.msea.2017.01.070.
Hennessey, Conor, Castelluccio, Gustavo M., and McDowell, David L. Wed . "Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6". United States. doi:10.1016/j.msea.2017.01.070. https://www.osti.gov/servlets/purl/1340510.
@article{osti_1340510,
title = {Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6},
author = {Hennessey, Conor and Castelluccio, Gustavo M. and McDowell, David L.},
abstractNote = {The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT) within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiple back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.},
doi = {10.1016/j.msea.2017.01.070},
journal = {Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing},
number = C,
volume = 687,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}

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  • The in-plane and out-of-plane displacement field around the tip of a crack (produced by Mode I fatigue precracking) loaded in pure, remote Mode II was measured as a function of K{sub IIapp} by electro-optic holographic interferometry. The effective Mode II stress intensity factor and the induced Mode I stress intensity factor were estimated from a fit to the near-tip expressions for the crack face displacement fields. The effective Mode II stress intensity factor was always less than the applied stress intensity factor demonstrating that the fracture surface asperities shield the crack tip. The induced Mode I stress intensity factor wasmore » roughly half that of the applied Mode II stress intensity factor, demonstrating that pure Mode II cracks cannot be obtained for cracks with microscopically rough surfaces. Plateaus and jumps in the dependence of the effective Mode II and induced Mode I stress intensity factor on the applied Mode II were correlated further supporting the notion that the fracture surface interference is based on asperity interactions. Analysis of the data shows that force transfer across the crack faces cannot be simply described by a frictional interaction across the asperities. It is suggested that deformation of the asperities must be considered to accurately model the shielding and induced crack face opening under remote Mode II loading.« less
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