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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
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
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
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!
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)
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
7 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Experimental Test Results
Uniaxial Tension Uniaxial Compression
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?
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.
10 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Calibration Results – MISO Plasticity
• Predicted R2=0.185
11 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Calibration Results – Chaboche Plasticity with Rate-Dependence
• Predicted R2=0.571
12 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
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
13 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Three Network (TN) Model
The Three Network (TN) model is a micromechanism inspired modeling framework that is commercially available from Veryst Engineering
14 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
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
15 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Multi-Axial Validation Testing
Small punch testing (ASTM F2183)
Spherical Indentation Testing
16 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Validation: Small Punch Testing
17 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Validation: Small Punch Testing
Axisymmetric FE model
18 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Validation: Indentation
19 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
Validation: Indentation
Axisymmetric FE model
20 © 2014 ANSYS, Inc. April 19, 2015 ANSYS Confidential
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
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