- Fatigue Analysis

8/13/2019 - Fatigue Analysis

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DEVELOPMENT OF LABORATORY TESTING

APPARATUS AND FATIGUE ANALYSIS FORTRACKED VEHICLE RUBBER BACKER PADS

Daniel Kujawski*, Daren DiStefano*, William Bradford***Western Michigan University, Kalamazoo, MI

**US Army RDE Command (RDECOM), Warren, MI

UNCLASSIFIED: Distribution Statement A. Approved for public release


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DISCLAIMER: Reference herein to any specific commercial company,product, process, or service by trade name, trademark, manufacturer, orotherwise, does not necessarily constitute or imply its endorsement,

recommendation, or favoring by the United States Government or theDepartment of the Army (DoA). The opinions of the authors expressedherein do not necessarily state or reflect those of the United StatesGovernment or the DoA, and shall not be used for advertising or productendorsement purposes.

UNCLASSIFIED: Distribution Statement A. Approved for public release 2


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WD 24 Road Pad

Elastomer Research

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Summary of WD: This research is aimed to develop anexperimental methodology to characterize thedegradation of tank rubber pads under service loadingcondition. The methodology is based on full scale testingof tank rubber pads under controlled loading condition inlaboratory setting. The laboratory test results would becompared with pads run at the Yuma Proving Ground.

Deliverables:

Laboratory test methodology for screening rubber compounds toincrease fatigue life and mileage

Backer pad damage prediction model of load and heat interaction onrubber fatigue degradation

Impact

This work supports the efforts of TARDEC to improve the reliability andfatigue performance of tank rubber pads (backers).

Reduce cost of testing; $1 million for 2000 proving ground miles



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Introduction

(Problem Definition)

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Large stresses imposed onelastomeric components cause themto be the life limiting factor of the tracksystem

Improvements of these componentshas a significant impact on life cyclecosts, logistics, field support andVehicle/War Fighter effectiveness

Typical field test costs over $1,000,000.00


Ground pad

Backer pads


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Motivation

TARDECs Elastomer Improvement Program (EIP)develops components with a three phase process

1) Identify

Understand failure modes2) Optimize

Computer simulation (FEA)

Customized test which mimics failure modes

Optimize component (Material selection/design)3) Validate

Full scale testing

Modify Requirements and Specifications

5UNCLASSIFIED: Distribution Statement A. Approved for public release


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Solution

The Fatigue and Fracture Lab of WesternMichigan University has partnered withTARDECs EIP lab to develop a customized test

for an Abrams T-158LL RWBP

PART I:The conception of testing apparatus alongwith its implementation will be outlined

PART II:A new methodology used to correlate thedependence of crack growth rate for straincrystallizing natural rubber in terms of tearing energywill be discussed



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Part 1: Testing Apparatus



8/23 UNCLASSIFIED: Distribution Statement A. Approved for public release

Assembly Components

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LabVIEW Interface



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Testing Procedures

Backer pad positioned under wheel

Statically loaded

Engage motor

Initiate LabVIEW interface

Remove rubber from carriage andinspect every 100 miles or as desired

14-16 AUG 2012 UNCLASSIFIED: Distribution Statement A. Approved for public release 10


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Effects of Heating

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Without heat addition With heat addition



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Summary

Cost and time efficient means of screeningelastomer components are essential

The testing apparatus described here will be able tocomplete accurate tests of the rubber components ina fraction of the time and cost of field testing

Currently over 1,000 miles of testing have been

performed



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Future Works

In order to more accurately simulate field conditions, andin order to accelerate testing time, several modificationsare being considered for the testing apparatus

In the field the elastomer components are in contact with

abrasive substrates such as dirt or gravel

For this reason the rubber tank wheel may be replaced with a

rough metal wheel in order to simulate the abrasiveness of field

operation

Also, elastomer components heat up during field testingusually around 250 F

In order to simulate this flexible heater systems are being

considered that could heat the rubber to a temperature likely

experienced in the field



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Part 2: Fatigue Analysis

Using Tearing Energy



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Lindley Approach


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Traditional Approachfor Correlating R-ratio Effects

Determine the power lawregion and obtain thematerial constants (rc ,Tc, andF) from the R=0 curve

For the other curvesdetermine the power lawslope F from the power law

region



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(Mars-Fatemi Method)

Equivalent Tearing

Energy Method



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Fatigue Crack GrowthDetermination of Threshold Region


1.E-08

1.E-07

1.E-06

0.01 0.1 1 10

da/dN(mm/cycle)

Max Tearing Energy (kJ/m^2)18


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Equivalent Tearing

Energy

Mars Fatemi Method

Without Threshold

Modified Method WithThreshold



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Collapsing Data

Without Threshold With Threshold



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Error of da/dN Prediction


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Summary

It is essential to have a means of quickly screeningmaterial properties

A deeper understanding of material behavior at slow

crack growth rates is desirable because this areaaccounts for the majority of the life of the component

The newly proposed model for approximating the crackgrowth rate vs. tearing energy relationship could providea means for quickly comparing fatigue properties ofrubber formulas



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Questions

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Documents

- Fatigue Analysis