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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DuPont Confidential

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

DuPont Confidential

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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100

101

102

103

104

105

106

107

30

40

50

60

70

80

90

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

100 101 102 103 104 105 106 10730

35

40

45

50

55

60

65

70

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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DuPont Confidential

� 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

0

10

20

30

40

50

60

70

80

0 20 40 60 80

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

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10

Str

ess

[MP

a]

Strain [%]

Test1

DuPont Confidential

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?

DuPont Confidential

Gerber Goodman

Ten

sio

n S

ide

Co

mp

ress

ion

Sid

e

Tension

Compression

fe-safe Fatigue Analysis Results

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����� � 300

Temperature (oC)

Coupled Fatigue Analysis Features

DuPont Confidential

� 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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