Using Non-Linear Material Models in ANSYS Mechanical … · Using Non-Linear Material Models in...

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


• 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


• 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


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!


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)


Uniaxial Calibration Experiments

Split Hopkinson Pressure bar tests

Uniaxial compression Uniaxial tension

Uniaxial experiments performed for material model calibration


Experimental Test Results

Uniaxial Tension Uniaxial Compression


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?


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.


Calibration Results – MISO Plasticity

• Predicted R2=0.185


Calibration Results – Chaboche Plasticity with Rate-Dependence



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



Three Network (TN) Model

The Three Network (TN) model is a micromechanism inspired modeling framework that is commercially available from Veryst Engineering


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.



Multi-Axial Validation Testing

Small punch testing (ASTM F2183)

Spherical Indentation Testing


Validation: Small Punch Testing


Validation: Small Punch Testing

Axisymmetric FE model


Validation: Indentation


Validation: Indentation

Axisymmetric FE model


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


• 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

Using Non-Linear Material Models in ANSYS Mechanical … · Using Non-Linear Material Models in...

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