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

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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• 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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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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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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Uniaxial Calibration Experiments

Split Hopkinson Pressure bar tests

Uniaxial compression Uniaxial tension

Uniaxial experiments performed for material model calibration

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Experimental Test Results

Uniaxial Tension Uniaxial Compression

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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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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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• 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