Fatigue Life Prediction Techniques for Unfilled Polymers with Application to Plastic Gear Design
Amir Kian Shojaei, and Pieter Volgers
DuPont Performance Materials
DuPont Confidential
DuPont’s Advanced CAE and Predictive Engineering
To support the customer with application development
by better prediction of the material performance and
optimal design
SegmentationShort Fiber
Polymers
Large Strain
Materials
Unfilled
Polymers
Composites
Creative
Design
DuPont Confidential
DuPont’s Advanced CAE and Predictive Engineering
To support the customer with application development
by better prediction of the material performance and
optimal design
SegmentationShort Fiber
Polymers
Large Strain
Materials
Unfilled
Polymers
Composites
Creative
Design
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Polymer Composites Application in Auto and Aerospac e Industries
Tailored integrated composite components can
lead to significant weight reduction.
Advanced CAE and Predictive Engineering
The reliance on mathematical analysis and simulations can reduce the
design cycle iterations and result in huge cost and time savings.
Replace Metals with Polymer Composites
Ref for pictures: http://www.dupont.com/products-and-services/plastics-polymers-resins/parts-shapes/articles/vespel-scp.html
DuPont Confidential
Content
• Objectives
• Coupled and Uncoupled Fatigue Analysis Approaches
• Fatigue-life prediction of a generic plastic gear
• Path forward
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Objectives
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To better understand the Fatigue Design procedure of
plastic components
To examine the performance of commercial Fatigue
Software (fe-safe) in design against fatigue for plastic
parts
Define the design scope and provide recommendations
to customers
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Coupled and Uncoupled Fatigue Analysis Approaches
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Road Map for Fatigue Analysis in Composites
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DPM Fatigue Prediction Engineering Tool
FEA + DPM Fatigue Package
Calibrated Models Verified User Defined
Sub-routines
CAD Design
Post-processing / Design Modifications
DESIGN EXCELLENCE CYCLE
Verified fe-safe Model
OR
Accurate Fatigue
Data
Fatigue analysis
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Fatigue Modeling of Unfilled Polymers - DuPont Delri n®
DPM Fatigue Prediction Engineering Tool for Unfilled Polym ers
� Continuum Damage Mechanics has been utilized to accurately predict the LCFto HCF life of polymer composites.
� Failure mechanisms and damage mechanics in LCF to HCF are linked to themacroscale failures.
� Coupling the cyclic plasticity, creep and fatigue damage computations enablesthe consideration of the cyclic loading history on the life prediction.
� To reduce the computational cost of the proposed coupled modeling approach acyclic jump approach is also introduced.
� The developed CDM and cyclic creep models are implemented into commercialFEA software, viz. Abaqus, through user-defined coding.
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Number of Cycles, N
Stres
s Le
vel,
∆∆ ∆∆σσ σσ
(MP
a)
Delrin 100 Exp. @ 23 oCFEA - CDM Model Prediction
Curve Fit:S
23oC
=(68.5-44) ××××N-0.15+44××××N-0.0001
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N, Number of Cycles
Str
ess
Leve
l, ∆∆ ∆∆
σσ σσ (M
Pa)
Delrin100 Exp. @ 60 oCFEA - CDM Model PredictionCurve Fit:S
60oC
=(55-42.6) ××××N-0.15+42.6××××N-0.0001
Coupled DPM Fatigue Tool Performance
Linear elastic – plastic material model performance
CDM Model Performance in capturing SN Date
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Effects of Cyclic Jump and Mesh Density
Cycle Jump Effect on Accuracy and Computational cost
Mesh Density Effect on Crack Shape and Orientation
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� Polymer composites may exhibit non-linear elastic-plastic responses
� Classical plasticity constitutive relations may fail in capturing true cyclic response of polymers
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Cyclic behavior of Plastics
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Str
ess
[MP
a]
Strain [%]
Delrin® 100 @ 23C
Campus/ProdPro data Delrin® 100 BK
Cyclic loading to full failure Delrin® 100NC
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� Polymer composites may exhibit non-linear elastic-plastic responses
� Classical plasticity constitutive relations may fail in capturing true cyclic response of polymers
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Cyclic behavior of Plastics
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Str
ess
[MP
a]
Strain [%]
Test1
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Gearbox
Assembly
- Poor quality Tetra Mesh
- Convergence/Accuracy issues
- Contact simulation result in higher computational costs
- Hex Mesh
- Contact is modeled through contact pressure
- Rotation is considered to see the interactions between teeth
- Lower computational cost
- Higher convergence rate
- Higher accuracy
CAD Model Description and Simplifications
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Simplified model with periodic
contact pressure application
Original CAD Model
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FEA Model for the Gear Mechanisms
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Sequential contact
mechanisms may results in
teeth interactions.
Rotation of the gear mechanisms is modeled through Periodic Contact Pressure
Teeth 1-2
Teeth 2-3
Teeth 3-4
Teeth 4-1
Effect of plasticity, damage and
temperature rise on adjacent teeth?
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Gerber Goodman
Ten
sio
n S
ide
Co
mp
ress
ion
Sid
e
Tension
Compression
fe-safe Fatigue Analysis Results
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Temperature (oC)
Coupled Fatigue Analysis Features
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� Fatigue in plastic components is complicated with viscoelastic and viscoplastic nature of polymers.
� fe-safe is designed for Metals, and in the case of Plastic components may face difficulties such as,
o fe-safe utilize R=-1 curve for life prediction. Mos tly R=-1 is not available for plastics.
o Current fe-safe for plastics is intended to predict the life for infinite life, with no significant heat generation.
o In some cases we need to use hyperelastic-plastic c onstitutive relations for plastic in order to get better predictions.
� Full gear tester device will be utilized to capture life of plastic gears.o The experimental data will be utilized to verify th e lifetime predictions of
both coupled and uncoupled approaches.
� A Hyperelastic-plastic Damage Model is needed for better predictions.
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Feature works and developments
DuPont Confidential
The information provided herein corresponds to our knowledge on the subject at the dateof its publication. This information may be subject to revision as new knowledge andexperience becomes available. The data provided fall within the normal range of productproperties and relate only to the specific material designated; these data may not be validfor such material used in combination with any other materials or additives or in anyprocess, unless expressly indicated otherwise. The data provided should not be used toestablish specification limits or used alone as the basis of design; they are not intended tosubstitute for any testing you may need to conduct to determine for yourself thesuitability of a specific material for your particular purposes. Since DuPont cannotanticipate all variations in actual end-use conditions DuPont makes no warranties andassumes no liability in connection with any use of this information. Nothing in thispublication is to be considered as a license to operate under or a recommendation toinfringe any patent rights.
Copyright © 2015 DuPont. All rights reserved. The DuPont Oval, DuPont™, The miracles ofscience™ and all products denoted with ® or ™ are registered trademarks or trademarksof E. I. du Pont de Nemours and Company or its affiliates.
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Thank you
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