High strain rate mechanisms and shear localization of ...€¦ · Rate dependent flow and failure...
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Enterprise for Multi - scale Research of Materials High strain rate mechanisms and shear localization of magnesium and its alloys V. Kannan 1 , M. Zhao 1 , N. M. Krywopusk 2,3 , L. J. Kecskes 3 , C. L. Williams 4 , T. P. Weihs 1,2,3 and K. T. Ramesh 1,2,3 1 Department of Mechanical Engineering, Johns Hopkins University; 2 Department of Materials Science & Engineering, Johns Hopkins University; 3 Hopkins Extreme Materials Institute; 4 US Army Research Laboratory, Aberdeen Proving Grounds How We Fit Technical Approach Key Goals Major Results Impact Materials-by-Design Process Transitions to ARL, within CMRG and to other CMRGs Mechanism-based Approach UNCLASSIFIED UNCLASSIFIED • Build a mechanism-based understanding of the effect of strain rate and stress state on plastic deformation and failure of magnesium and its alloys. • Focus on two magnesium alloys: Rolled and Equal Channel Angular Extruded (ECAE) AZ31B. • Characterization of rate dependent stress-strain response, deformation and failure mechanisms activated using in-situ and post-mortem microscopy. • High strain rate experiments (conventional and desktop kolsky bars, pressure- shear plate impact). • In-situ and post-mortem microscopy. Continuum framework to capture twin growth dynamics • Twin boundary (TB) modeled as a discontinuity [1] . • Anisotropic elastic-plastic continuum. • Dislocation densities allowed to evolve in twin and matrix. • Jump in elastic-plastic free energy functions (ψ) drives the TB. Driving traction [2] , , = +< >. • Incorporate high strain rate dislocation-based plastic flow laws in existing crystal plasticity codes (in collaboration with the Joshi group, U. Houston). Rate dependent flow and failure of AZ31B alloys ECAE AZ31B Rate dependence of plastic flow stress under uniaxial compression (TD compression) Mis-orientation angle distribution as a function of strain rate (TD compression) Pole figure evolution during high strain rate compression along the TD. Profuse extension twinning observed. Grain size ~ 2.5 Strain localization and failure during high strain rate compression ( ሶ ~7500 −1 ) along the TD Rolled AZ31B Strain rate dependence of plastic flow stress under uniaxial compression (TD and RD) Shear stress-shear strain response under pressure shear plate impact of rolled AZ31B Profuse extension twinning after PSPI on rolled AZ31B. Compression direction: ND; Shear direction: TD Formation of dimpled fracture surfaces under ND compression (scale bar=1) Key Accomplishments • Completed a full dataset for uniaxial compression across eight decades of strain rate for two textured AZ31B alloys (rolled and ECAE). • Performed pressure shear plate impact experiments on the rolled alloy. • Publications this year: 2 (published), 1 (under review) • All experimental data made available to the CMRG. • Collaborations with the materials processing group at JHU and ARL for material and initial characterization. • Provided validation data to modeling groups (Lloyd, Becker, Kochmann). • Established collaborations with the Joshi group at U. Houston (CP modeling). • We would appreciate help from small scale MD and DDD groups to better inform twin kinetics models in the continuum framework proposed for twin dynamics. • First direct measurements of twin nucleation and growth rates in single crystal magnesium under high strain rate loading. • Identified dominant deformation and failure mechanisms contributing to rate dependent plastic flow in two types of polycrystalline magnesium alloys. • Modeling efforts driven towards improved predictive capabilities for macroscopic material response at high loading rates and complex stress states. • Publications: ➢ V. Kannan et al., Journal of the Mechanics and Physics of Solids (2018) ➢ M. Zhao et al., Acta Materialia (2018) ➢ V. Kannan et al., (under review) The miniature Kolsky bar setup in the Ramesh lab at JHU (Strain rates ~ 10 4 −1 ) Wedge Flyer Projectile Specimen Target Incident Laser TDI NVI/NDI TDI TDI: transverse displacement interferometer NVI/NDI: normal velocity/displacement interferometer A schematic of the pressure shear plate impact experiment (Strain rates ~ 10 5 −1 ) [1] Hungyu Tsai, PhD Thesis (1994) [2] Abeyaratne and Knowles, JMPS (1990)
Transcript of High strain rate mechanisms and shear localization of ...€¦ · Rate dependent flow and failure...
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Enterprise for Multi-scale Research of Materials
High strain rate mechanisms and shear localization of magnesium and its alloys
V. Kannan1, M. Zhao1, N. M. Krywopusk2,3, L. J. Kecskes3, C. L. Williams4, T. P. Weihs1,2,3 and K. T. Ramesh1,2,3
1Department of Mechanical Engineering, Johns Hopkins University; 2Department of Materials Science & Engineering, Johns Hopkins University; 3Hopkins Extreme
Materials Institute; 4US Army Research Laboratory, Aberdeen Proving Grounds
How We Fit
Technical Approach
Key Goals
Major Results
Impact
Materials-by-Design Process
Transitions to ARL, within
CMRG and to other CMRGs
Mechanism-based Approach
UNCLASSIFIED
UNCLASSIFIED
• Build a mechanism-based understanding of the effect of strain rate and stress
state on plastic deformation and failure of magnesium and its alloys.
• Focus on two magnesium alloys: Rolled and Equal Channel Angular Extruded
(ECAE) AZ31B.
• Characterization of rate dependent stress-strain response, deformation and
failure mechanisms activated using in-situ and post-mortem microscopy.
• High strain rate experiments (conventional and desktop kolsky bars, pressure-
shear plate impact).
• In-situ and post-mortem microscopy.
Continuum framework to capture twin growth dynamics
• Twin boundary (TB) modeled as a
discontinuity[1].
• Anisotropic elastic-plastic continuum.
• Dislocation densities allowed to evolve in
twin and matrix.
• Jump in elastic-plastic free energy functions
(ψ) drives the TB.
Driving traction[2], 𝑓 𝒙, 𝑡 = 𝜌𝜓 +< 𝝈 >. 𝑭
• Incorporate high strain rate dislocation-based plastic flow laws in existing
crystal plasticity codes (in collaboration with the Joshi group, U. Houston).
Rate dependent flow and failure of AZ31B alloys
ECAE AZ31B
Rate dependence of plastic flow stress under
uniaxial compression (TD compression)
Mis-orientation angle distribution as a function of
strain rate (TD compression)
Pole figure evolution during high strain rate compression along the TD. Profuse
extension twinning observed. Grain size ~ 2.5 𝜇𝑚
Strain localization and failure during high strain rate compression ( ሶ𝜀~7500 𝑠−1) along the TD
Rolled AZ31BStrain rate dependence of plastic flow stress
under uniaxial compression (TD and RD)Shear stress-shear strain response under
pressure shear plate impact of rolled AZ31B
Profuse extension twinning after PSPI on rolled AZ31B.
Compression direction: ND; Shear direction: TDFormation of dimpled fracture surfaces under
ND compression (scale bar=1𝜇𝑚)
𝜎
𝜏
𝜏𝜎
Key Accomplishments• Completed a full dataset for uniaxial compression across eight decades of strain
rate for two textured AZ31B alloys (rolled and ECAE).
• Performed pressure shear plate impact experiments on the rolled alloy.
• Publications this year: 2 (published), 1 (under review)
• All experimental data made available to the CMRG.
• Collaborations with the materials processing group at JHU and ARL for material
and initial characterization.
• Provided validation data to modeling groups (Lloyd, Becker, Kochmann).
• Established collaborations with the Joshi group at U. Houston (CP modeling).
• We would appreciate help from small scale MD and DDD groups to better inform
twin kinetics models in the continuum framework proposed for twin dynamics.
• First direct measurements of twin nucleation and growth rates in single crystal magnesium
under high strain rate loading.
• Identified dominant deformation and failure mechanisms contributing to rate dependent plastic
flow in two types of polycrystalline magnesium alloys.
• Modeling efforts driven towards improved predictive capabilities for macroscopic material
response at high loading rates and complex stress states.
• Publications:
➢ V. Kannan et al., Journal of the Mechanics and Physics of Solids (2018)
➢ M. Zhao et al., Acta Materialia (2018)
➢ V. Kannan et al., (under review)
The miniature Kolsky bar setup in the Ramesh
lab at JHU (Strain rates ~ 104 𝑠−1)
WedgeFlyer
Projectile Specimen
Target
Incident Laser
TDI
NVI/NDI
TDI
TDI: transverse displacement interferometer
NVI/NDI: normal velocity/displacement interferometer
A schematic of the pressure shear plate impact
experiment (Strain rates ~ 105 𝑠−1)
[1]Hungyu Tsai, PhD Thesis (1994)
[2]Abeyaratne and Knowles, JMPS (1990)
𝜎
𝜏
𝜏𝜎
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