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1 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Using Non-Linear Material Models in ANSYS Mechanical for Accurate Simulations
Jorgen Bergstrom, Ph.D. Danika Hayman, Ph.D.
Veryst Engineering, LLC
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2 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
• Veryst Engineering is a consulting firm focusing on solving advanced non-linear problems
• Failure Analysis
• Industrial Processes
• Component Failures
• Metals, Polymers, and Ceramics
• Materials Science
• Metallurgy
• Polymer Science
• Ceramics
• Mechanical Engineering
• Mechanical Testing
• Manufacturing Processes
• Polymer Mechanics & FE Simulations
• Commercial User-Material Subroutines for ANSYS
Veryst Engineering is a software partner with
ANSYS
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3 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
• Introduction to PEEK
• Experimental testing and results
• Material model calibrations
• Validation experiments
• FEA of validation tests
• Conclusions
Outline of Presentation
Goal of study: Examine different material models for predicting the response of a thermoplastic material
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4 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Common Polymer Behaviors
Small Strain Response Intermediate Strain Response
Large Strain Response
Initial Elastic Response
Strain-Rate Dependent
Viscoplastic Flow
Highly Non-Linear Unloading
These non-linear behaviors can be accurately represented in ANSYS if a suitable material model is selected and calibrated to the correct type of experimental data!
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5 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Polyether Ether Ketone (PEEK)
• Good mechanical properties (E ≈ 4 GPa, σut ≈ 100 MPa)
• Good wear resistance
• Inert, generally biocompatible
• Orthopedic applications: – Spinal implants/spacers – Fixation (screws, plates
etc.) – Biomedical textiles
(wovens, braids)
• Sealing applications (HPHT)
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6 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Uniaxial Calibration Experiments
Split Hopkinson Pressure bar tests
Uniaxial compression Uniaxial tension
Uniaxial experiments performed for material model calibration
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7 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Experimental Test Results
Uniaxial Tension Uniaxial Compression
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8 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Candidate Material Models
ANSYS Native Models:
• Bergstrom-Boyce (BB) Model (TB, BB)
• Multilinear isotropic hardening plasticity (TB, MISO)
• Chaboche non-linear kinematic hardening with Perzyna rate-dependece (TB, CHABOCHE; TB, RATE)
PolyUMod Models:
• Three Network (TN) Model The TN model is commercially available from Veryst Engineering
Which of these models is the most suitable for PEEK?
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9 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Material Model Calibrations
• The material models were calibrated using the MCalibration® software from Veryst Engineering
• The MCalibration software can calibrate all ANSYS material models using almost any combination of experimental data
• A basic version of MCalibration is available for FREE.
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Calibration Results – MISO Plasticity
• Predicted R2=0.185
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Calibration Results – Chaboche Plasticity with Rate-Dependence
• Predicted R2=0.571
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Calibration Results – BB Model • The Bergstrom-Boyce (BB) model
is a model that I developed as part of my Ph.D. work at MIT
• The BB model is a built-in feature of ANSYS
• Predicted R2=0.583
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Three Network (TN) Model
The Three Network (TN) model is a micromechanism inspired modeling framework that is commercially available from Veryst Engineering
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Calibration Results – TN Model • The Three Network (TN) model is
a material model specifically designed for thermoplastic materials.
• The TN model is available in the PolyUMod library.
• Predicted R2=0.903
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Multi-Axial Validation Testing
Small punch testing (ASTM F2183)
Spherical Indentation Testing
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Validation: Small Punch Testing
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Validation: Small Punch Testing
Axisymmetric FE model
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Validation: Indentation
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Validation: Indentation
Axisymmetric FE model
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Material Model Comparison
NMAD Calibration Small Punch Indentation Average Error
MISO 45.7 28.2 33.1 33.7
Chaboche, Rate Dep. 24.3 10.7 12.4 15.8
Bergstrom-Boyce 24.2 9.92 13.2 15.8
Three Network 13.2 6.86 19.6 13.2
NMAD: Average error between experimental data and model predictions in %
R2 Calibration Small Punch Indentation Average R2
MISO 0.185 0.680 0.841 0.569
Chaboche, Rate Dep. 0.571 0.958 0.972 0.834
Bergstrom-Boyce 0.583 0.963 0.968 0.838
Three Network 0.903 0.975 0.946 0.941
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21 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
• The mechanical response of thermoplastics and rubbers is very non-linear
• ANSYS can capture the experimentally observed behavior very accurately if:
• The material has been properly tested
• A suitable material model has been selected and calibrated
• The Three Network (TN) model is very accurate for most thermoplastics
• The Bergstrom-Boyce (BB) model and the Chaboche plasticity model with Perzyna rate-dependece are also accurate in many applications
• Veryst Engineering has significant expertise in this area and can help with both experimental testing and material model calibration
Conclusions