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Document Sample
Multi-Physics Numerical Modeling
and
Experimental Characterization of Materials
Vincent Y. Blouin
Assistant Professor
Materials Science and Engineering
Clemson University
MILMI Bordeaux
June 15, 2010
Background
Post-doc (Mech. Eng.)
Diplome d’ingenieur PhD Research Assistant Professor
(Hydrodynamic naval) (Marine Engineering) Assistant Professor
2/36
Research Activities
Multi-Physics Numerical Modeling
Characterization of
Calibration Material Properties
Validation Mechanical
Thermal Fluids
3/36
Hunley Submarine
1/25
Corrosion-Erosion
5/25
Thermal Behavior of Buildings
CFD FEA
Steady state fluid flow analysis Transient thermal analysis
Input: Wall temperatures Input: Heat fluxes
Output: Heat fluxes Output: Wall temperatures
Coupling between CFD and FEA.
6/36
Cooling of Precision Glass Molding
Glass lens
Cooling
channels
(N2 flow)
7/36
3D heat transfer model of assembly
8/36
Coupled 3D fluid flow / thermal analysis
Surface temperatures
N2 flow rates
Fluid flow analysis (CFD) Thermal analysis (FEA)
Required parameters: Required parameters:
Material properties Material properties
Surface conductance values
Surface heat
fluxes Boundary conditions
9/36
Temperature profile
• Gradient of 10oC through the lens
• This validates the axisymmetric assumption
10/36
Heat fluxes
• Can visualize heat fluxes
• Heat is drawn to the center of the assembly (inlet of cooling
channels)
1/25
Modeling Precision Glass Molding
• Precision glass molding requires full
understanding of
– Thermal properties
– Interaction properties
• Friction coefficient
• Heat exchange
– Viscosity as function of temperature
– Structural relaxation
– Stress relaxation
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Creep test
Constant force
Glass
sample
13/25
Experimental Characterization of Stress
Relaxation Properties
Three issues
• Separate shear and hydrostatic behavior
• Manufacture samples
• Numerical treatment to extract stress relaxation properties
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A considerable experimental effort is required
to define visco-elastic behavior of glass
1
Separate stress into shear and hydrostatic parts
ij sij ij
3
t
eij (t )
Shear constitutive law sij (t ) G1 (t t ) dt
0
t
(t )
t
Hydrostatic constitutive law (t ) G2 (t t ) dt
0
t
G1( t ) 2 G0 1( t ) G2 (t ) 3K 3( K K 0 ) 2 (t )
n
i (t ) wij e
t / ij
Relaxation functions: (Prony Series)
j 1
Stress Relaxation Basics
Strain produced by
viscous flow. The
viscosity is related Instantaneous
to the slope. Elastic Strain
Delayed
Elastic Strain
Delayed
Elastic Strain
Strain due to
viscous flow
CREEP RECOVERY
Instantaneous
Elastic Strain
16/36
Shear and Hydrostatic Deformations
Shear or deviatoric Hydrostatic or dilatation
Shape change Volume change
Comparatively easy to conduct Experiments involving pure
experiments involving pure shear hydrostatic component is complicated
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Shear and Uni-axial Tests
Shear test Uni-axial test
Shear deformation only
(pure shear) Shear deformation + Hydrostatic deformation
Literature
Rekhson S.M. (1980)
Extension of theory of linearity to complex glasses and temperature dependent
viscosity values of Pyrex® glass
Scherer. G (1986)
Fundamentals of viscoelasticity
Gy R. et al. (1994)
Retardation to Relaxation conversions
Gy R. et al. (1996)
Concept of viscoelastic moments and constants
Duffrène et al. (1997)
Overview of creep testing, methodology and experimental requirements
Pascual M.J. et al. (2001)
Temperature dependent viscosity data for Pyrex® glass
Spinner S. (2006)
Temperature dependent mechanical properties of Pyrex® glass 19/36
Overview of Characterization Process
Viscoelastic Characterization
Shear Creep-Recovery experiments Uni-axial creep-recovery experiments
Displacement-Time curve Displacement-Time curve
Shear strain-Time curve Strain-Time curve
Shear / Uni-axial
relaxation moments & constants
Isolate delayed part Isolate delayed part
Retardation function-Time curve Retardation function-Time curve
Shear / Uni-axial
retardation moments & constants
Normalized Retardation function-Time(log) Normalized Retardation function-Time(log)
Curve fit
Hydrostatic relaxation/retardation
moments & constants
Shear retardation parameters Curve fit for hydrostatic retardation parameters
Shear retardation to relaxation conversion Hydrostatic retardation to relaxation conversion
Creep tests on Helical Spring sample
(At different loads and temperatures)
2.5
2
Series1
Series2
1.5 Series3
Displacement(mm)
Series4
Series6
Series7
1 Series8
Series9
Series10
0.5
0
0 50 100 150 200 250 300 350 400 450
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Time (sec)
Curve Fitting
1
0.9
0.8
0.7
Retardation Function
0.6
0.5
0.4
0.3
0.2
0.1
0
0 1 2 3 4
10 10 10 10 10
Time (sec)
Stress Relaxation Module
Create dog-bone specimen Create spring specimen
Conduct creep relaxation test Conduct creep relaxation
at various temperatures test at diff. temperatures
Strain vs time data Displacement vs time data n
i (t ) wij e
t / ij
Data processing based on j 1
Mathematical formulations
563oC 588oC
w1j τ 1j w1j τ 1j
3.06E-03 5.96 2.91E-02 5.05
0.970 97.4 0.918 23.92
0.0260 253.2 0.051 75.3
Alternative Geometries
Helical spring
(pure shear)
Tension/compression
uniaxial test
(shear + hydrostatic)
3-point bending
(shear + hydrostatic)
Shaft under torsion
(pure shear)
24/36
Equipment
Creep frame Parallel-plates viscometer (PPV)
25
Manufacturing Samples
Pyrex BK7 LBAL35
Glass Manufacturing
27/36
Manufacturing Samples of Low Tg Glass
Manufacturing process
Short thick rod
Wrap long rod
Create ball Stretch into
around metal rod
long rod
to create spring
• Heat treatment and large deformations may alter optical
and thermo-mechanical properties
• BK7 was successful with some defects
L-BAL35 was not successful
BK7
Glass Manufacturing
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Glass Manufacturing
30/36
Glass Manufacturing
Glass Manufacturing
Glass Manufacturing
Glass Manufacturing
Optical Glasses (Low Tg)
• Sensitive to thermal shocks
• Impossible to fix once broken
• Optical glasses usually come as short rods (<20cm x 1cm)
• Prone to formation of bubbles when melted and extended
• Sand-blasted finish is harder to work with than smooth finish
Current and future work:
• Use simpler geometries (not as accurate, requires more numerical treatment)
• Develop setup to manufacture samples at controlled temperature
35/36
Current and Future Work
• Use simpler geometries (not as accurate, requires more
numerical treatment)
• Develop setup to manufacture samples at controlled
temperature
• Experimental validation of numerical simulation
• Development of automatic numerical treatment of experimental
data for extracting properties
• Use PPV for better temperature control (small samples)
36/36
