2014 regional conference - axel...
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1 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
2014 Regional Conference
Experiments and Fitting of Advanced Polymer Models in ANSYS
Kurt Miller, Axel Products, Inc.
www.axelproducts.com
2 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
axelproducts.com
3 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Structural Properties
4 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Structural Properties
5 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Structural Properties (small deformation plasticity)
6 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Plastic
7 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Plastic
8 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Plastic
9 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Plastic
10 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Thermoplastic Elastomers
11 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Teflon
12 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Crushable Foam
13 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
A General Strategy
1. Understand the loading conditions of the part
2. Understand the general behavior of the materials involved
3. Select the significant material behaviors
4. Use existing or develop material models to describe the behavior
5. Verify the performance of the material model
14 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
15 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Long Term Creep
16 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Plastic
Long Term Creep Experiments
Often Required for Metal Replacement Applications
Structural Applications May Require a Range of
Stress Levels and Temperatures
17 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Time
18 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Compression
19 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Compression
20 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Rubber
1. High strain applications
2. No distinct modulus or yield
3. Bulk >>> Shear
21 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
A Spring and a Dashpot?
22 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
What does Incompressible Mean?
23 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Volumetric Compression
K/G Relationship to Poisson's Ratio
0
20
40
60
80
100
0.3 0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 0.48 0.5
Poisson's Ratio
K/G
K/G
21
1
3
2
G
K
Poisson’s ratio approaching 0.5 means infinite bulk modulus, K
For elastomer materials Poisson’s ratio is difficult or impossible to measure
accurately. For plastic materials, it is hard to measure VC accurately. Measure
Pressure-Volume directly.
24 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Incompressibility
Not a spring and dashpot
25 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Hyperelastic Models Define a Surface
26 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Hyperelastic Models
Available Hyperelastic models:
• Arruda-Boyce Hyperelastic Material • Blatz-Ko Foam Hyperelastic Material • Extended Tube Material • Gent Hyperelastic Material • Mooney-Rivlin Hyperelastic Material • Neo-Hookean Hyperelastic Material • Ogden Compressible Foam Hyperelastic Material • Ogden Hyperelastic Material • Polynomial Form Hyperelastic Material • Response Function Hyperelastic Material • Yeoh Hyperelastic Material
Specialized Hyperelastic models:
• Anisotropic Hyperelastic Material • Bergstrom-Boyce Material • Mullins effect • User-Defined Hyperelastic Material
• Material response is isotropic, isothermal, and elastic and is assumed fully or nearly incompressible.
• There are many hyperelastic models available in ANSYS which can cover wide varieties of elastomers used in Industries.
27 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Rubber
28 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Hyperelastic Models
Curve Fitting feature
• Material curve fitting allows you to derive coefficients from experimental data that you provide for your material.
• With this capability, you compare experimental data versus program-calculated data for different nonlinear models and determine the best material model to use.
• ANSYS provides curve-fitting, based on experimental data, for all of the available hyperelastic models. Any of the hyperelasticity models in ANSYS can be used.
29 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Simple Tension
•Uniaxial loading
•Free of lateral constraint Gage Section:
Length:Width
>10:1
30 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Planar Tension
1. Uniaxial loading
2. Perfect lateral constraint
3. All thinning occurs in one direction
31 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Equal Biaxial Extension
Why?
1. Same Strain State as
Compression
2. Can Not Do Pure Compression
3. Can Do Pure Biaxial
32 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Loading Conditions
Some common Elastomers exhibit dramatic strain amplitude and cycling effects at moderate strain levels
Conclusions:
1. Test to Realistic Strain
Levels
2. Use Application
Specific Loadings to
Generate Material Data
3. Need to load and unload
to separate elastic from
plastic
33 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Loading Conditions
Some common Elastomers exhibit dramatic strain amplitude and cycling effects at moderate strain levels
Conclusions:
1. Test to Ralistic Strain
Levels
2. Use Application
Specific Loadings to
Generate Material Data
3. Need to load and unload
to separate elastic from
plastic
34 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Loading Conditions
Some common Elastomers exhibit dramatic strain amplitude and cycling effects at moderate strain levels
Conclusions:
1. Test to Realistic Strain
Levels
2. Use Application
Specific Loadings to
Generate Material Data
3. Need to load and unload
to separate elastic from
plastic
35 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Loading Conditions Some common elastomers exhibit dramatic strain amplitude and
cycling effects at moderate strain levels
Conclusions:
1. Pick one level
2. Use Mullins Model
3. Use BB Model
© 2013 ANSYS, Inc. June 4, 2014 36
The modified Ogden-Roxburgh damage function available in ANSYS has the following functional form of the damage variable
Where: r, m and are user defined material damage parameters
is the maximum virgin potential over the time
interval or the potential from which the unloading starts.
The parameters used in the Ogden-Roxburgh damage are directly available in WB-Mechanical
Note: ANSYS currently do not offer curve fitting for this material model.
m
Om
Lm
WWerf
r
11
…Mullins Effect in Elastomers
0,0 tt
)(max tWW om
© 2013 ANSYS, Inc. June 4, 2014 37
0
1
2
3
4
5
6
7
8
9
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
Engi
ne
eri
ng
Stre
ss
Stretch
Cyclic curve
Virgin Curve
…Mullins Effect in Elastomers
Unloading Points
38 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
A General Strategy
1. Understand the loading conditions of the part
2. Understand the general behavior of the materials involved
3. Select the significant material behaviors
4. Use existing or develop material models to describe the behavior
5. Verify the performance of the material model
39 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Loading Conditions Some common elastomers exhibit dramatic strain amplitude and
cycling effects at moderate strain levels
Conclusions:
1. Pick one level
2. Use Mullins Model
3. Use BB Model
40 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Bergstrom-Boyce Model
The Bergstrom-Boyce material model is a phenomenological-based, highly nonlinear material model used to model typical elastomers and biological materials.
It allows for a nonlinear stress-strain relationship, creep, and rate-dependence.
It assumes an inelastic response only for shear distortional behavior. The response for volumetric is still purely elastic
The model is based on a spring (A) in parallel with a spring and damper (B) in series.
All components (springs and damper) are highly nonlinear.
41 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
The stress state in A can be found in the tensor form of the deformation gradient tensor (F = dxi / dXj) and material parameters, as follows:
… Bergstrom-Boyce Model
42 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Commercial Fitting Tool, MCalibration
43 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Hyperelastic Models Define a Surface
44 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Simple Shear
1. Additional Strain State
2. Using DIC Strain Measuring
45 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Model Verification
Attributes of a good model verification experiment
The geometry is realistic.
All relevant constraints are measurable.
The analytical model is well understood
46 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Confinement can be Significant
47 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
Model Verification
48 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
ANSYS teams with Axel Product, Inc. (www.axelproducts.com) to offer this course that covers material testing, material modeling and finite element analysis of elastomers.
ANSYS Experimental Elastomers Training at Axel Products
49 © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential © 2013 ANSYS, Inc. June 4, 2014 ANSYS Confidential
ANSYS teams with Axel Product, Inc. (www.axelproducts.com) to offer this course that covers material testing, material modeling and finite element analysis of structural plastics such as Polyethylene (PE), Polypropylene (PP), Polyvinyl chloride (PVC) etc.
ANSYS Experimental Structural Plastic Training at Axel Products
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