8/3/2019 2002-01-0797

1/10

400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760

SAE TECHNICALPAPER SERIES 2002-01-0797

Component Testing and Materials Properties

of Ductile Iron Brake Anchors

Alan P. Druschitz, Nathan J. Sochor and Brandon ReneauIntermet Corporation

SAE 2002 World CongressDetroit, Michigan

March 4-7, 2002

8/3/2019 2002-01-0797

2/10

The appearance of this ISSN code at the bottom of this page indicates SAEs consent that copies of thepaper may be made for personal or internal use of specific clients. This consent is given on the condition,

however, that the copier pay a per article copy fee through the Copyright Clearance Center, Inc. OperationsCenter, 222 Rosewood Drive, Danvers, MA 01923 for copying beyond that permitted by Sections 107 or

108 of the U.S. Copyright Law. This consent does not extend to other kinds of copying such as copying forgeneral distribution, for advertising or promotional purposes, for creating new collective works, or forresale.

Quantity reprint rates can be obtained from the Customer Sales and Satisfaction Department.

To request permission to reprint a technical paper or permission to use copyrighted SAE publications in

other works, contact the SAE Publications Group.

No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written

permission of the publisher.

ISSN 0148-7191Copyright 2002 Society of Automotive Engineers, Inc.

Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE. The author is solely

responsible for the content of the paper. A process is available by which discussions will be printed with the paper if it is published in

SAE Transactions. For permission to publish this paper in full or in part, contact the SAE Publications Group.

Persons wishing to submit papers to be considered for presentation or publication through SAE should send the manuscript or a 300

word abstract of a proposed manuscript to: Secretary, Engineering Meetings Board, SAE.

Printed in USA

All SAE papers, standards, and selected

books are abstracted and indexed in theGlobal Mobility Database

8/3/2019 2002-01-0797

3/10

2002-01-0797

Component Testing and Materials Properties of Ductile

Iron Brake Anchors

Alan P. Druschitz, Nathan J. Sochor and Brandon Reneau

Intermet Corporation

Copyright 2002 Society of Automotive Engineers, Inc.

ABSTRACT

During product development and production, product

testing is often desirable to improve design robustness

and verify consistent product performance. However,

product testing is very complicated, requires highly

specialized and trained personnel and utilizes expensive,dedicated equipment and facilities.

This paper describes two brake anchor component tests

(pull and impact) and the use of strain gaged components

to determine the characteristics of the component during

loading. Data for two brake anchor designs are presented

and the component properties are then correlated with

material properties and design. The combined effect of

material properties and component design on performance

is demonstrated. The data also demonstrates that

apparently identical tests on different component designs

can lead to misleading conclusions.

BACKGROUND

Product testing has been and will continue to be a crucial

part of the product development cycle since current math

models cannot fully take into account variable material

properties and cannot fully account for all loading

conditions that might be encountered in service. For

example, castings cool at different rates in different

locations and therefore always have varying mechanical

properties. Also, the loading conditions in the foundry or

machining line often exceed those encountered in service.

Since a math model can only calculate the effect of the

loads input into the model and the material properties

assigned to the component, unforeseen loading conditions

and unforeseen material property variations may produce

early failures.

For this study, a relatively simple component (brake

anchor) was selected to demonstrate how design and

material properties interact. For this demonstration, a

variety of tests were performed: 1) one brake anchor

design was tested in two different loading conditions (pull

and impact) and 2) two brake anchor designs were tested

in numerous material conditions (as-cast and various heat

treatments). This type of data is needed by the design

engineer when specifying material requirements

developing new components and developing component

test specifications.

COMPONENT DESCRIPTION, TEST

METHODS AND MATERIAL PROPERTIES

Two similar brake anchors designed by differen

companies and produced at the INTERMET Havana

Foundry were selected for this study. The differences

between these brake anchors were both obvious and not

so obvious. The obvious difference was the shape of the

thin tie bar. In Figure 1a, the tie bar of brake anchor A

looks much thinner than the tie bar of brake anchor B.

However, when the brake anchors are inclined, Figure 1b

the tie bars appear nearly identical. Actually, the tie bar

of brake anchor A was thicker and had a well roundedcross section whereas the tie bar of brake anchor B had

two flat surfaces incorporated into the tie bar for fast brake

pad changes, which significantly reduced the cross

section thickness, and formed relatively sharp corners.

The cross sections of the two brake anchor designs are

shown in Figure 2. The not so obvious difference was the

microstructure and chemistry of the material. Basically,

both brake anchor castings had similar microstructures

with brake anchor A having slightly more pearlite, Figures

3a and b. However, brake anchor design B was prone to

carbide formation at the edges of the tie bar due to sharp

corners that cooled rapidly, Figure 4. Because of this

design problem, higher silicon content was used to

produce brake anchor B, which resulted in lower pearlite

content at approximately the same hardness.

8/3/2019 2002-01-0797

4/10

Figure 1a. Straight-on view of brake anchor designs A and B.

Figure 1b. Inclined view of brake anchor designs A and B.

Two tests were selected for this study: pull and impact.

The pull test simulated the component loading on the

vehicle and the impact test simulated the worst case

handling condition that might be encountered in the

foundry or machine shop.

The pull test loads the brake anchor under conditions

similar to those seen in service. Here, a rigid fixture,

which would be the steering knuckle on a vehicle, was

attached to the lower, moveable ram on a hydraulic load

frame, the brake anchor was bolted to the fixture, the load

arm swung into position (this arm was connected to the

upper, fixed ram) and the brake anchor pulled to failure,

Figures 5a and b. In this test, the load was applied off-

center and the brake anchor rotated under the attachment

bolts. This produced a bending stress. Since the brake

anchor rotated under the bolt, the measured load was a

function of bolt torque. Production bolts, a specified

torque value and a specified thread locking adhesive set

up time were used. During the pull test, the thin tie bar

broke followed by failure of the thicker section and

sometimes the upper bolt. Looking more closely at the

sample orientation, a clear difference in the location of a

reduced section or pocket on the thicker section of the

driver side and passenger side castings is evident. The

importance of this difference will be discussed later.

Figure 2. Cross sections through the tie bar of brake anchor designsA (left) and B (right). A mm scale is on the bottom of the photograph

Figure 3a. Typical microstructure in the tie bar region of brake anchordesign A showing well formed graphite nodules in a matrix of ~20%ferrite and 80% pearlite.

1 mm

8/3/2019 2002-01-0797

5/10

Figure 3b. Typical microstructure in the tie bar region of brake anchordesign B showing well formed graphite nodules in a matrix of ~30%ferrite and 70% pearlite.

Figure 4. Carbides in tie bar of brake anchor design B.

The impact test was developed to simulate the worst case

loading condition that might occur in the production

foundry or machine shop. In this test, the brake anchor

was attached to a rigid fixture and a hydraulic ram

punched the thin tie bar at a velocity of 254 mm per

second, Figure 6. The load as a function of ram

displacement was measured and recorded. From this

data, the energy required to initiate a crack (area under

the curve up to the point of maximum load) and the tota

energy absorbed (area under the entire curve) was

calculated by numerical integration. These values can be

compared to various loading events in the foundry and

machine shop to determine if damage might occur. A

typical load versus displacement curve is shown in Figure

7. The orientation of the tie bar cross section was critica

in this test and thus, an additional angled support was

necessary to allow the two different components to betested under identical loading conditions.

Figure 5a. Typical pull test set-up.

Figure 5b. Close-up of pull test set-up showing dial gages used fordisplacement measurement.

8/3/2019 2002-01-0797

6/10

Figure 6. Typical impact test set-up.

Figure 7. Typical load versus displacement curve for the impact test.

The casting microstructure and chemistry, which

determined material properties, had a significant effect on

component performance. To vary the properties in a

controlled manner, samples of both casting designs were

sub-critically annealed (softened), normalized (hardened)

or normalized and tempered. The microstructures were

characterized using a fully automated Clemex image

analyzer. All castings had better than 90% nodularity

The tensile properties where determined from 6.3 mm

diameter, 25.4 mm gage length tensile bars cut fromcastings. Five tensile bars of each condition were tested

in accordance with ASTM E8 and the results averaged.

The material properties of the as-cast and heat treated

castings are listed in Table I.

RESULTS AND DISCUSSION

PULL TEST. The orientation of the specimen in the pul

test fixture resulted in a difference in the measured load a

failure of as much as 36%. The reason for this difference

was the location of the fracture. Lower load at failure

values were measured when fracture occurred through the

thin pocket on the thicker section. Figures 8a and b and9a and b show the pull test specimens before and after

testing. This was not an unexpected result since the

amount of bending caused by rotation of the component

during loading was greater near the load application point

(upper half of the casting). An unforeseen consequence o

this loading variation was rapid deterioration of the fixture

for the orientation shown in Figures 9a and b. Due to the

significantly higher load, the bolt hole tended to elongate

with a subsequent loss of clamping ability, Figure 10. As

the amount of bolt hole deformation increased, the

measured load decreased. After 30 tests (five months)

the measured average load at failure decreased by 11%.

Since the purpose of this test was to verify that the

production process was not changing, this apparent loss

in load carrying capacity could be erroneously interpreted

as a manufacturing problem instead of fixture wear. For

the other fixture and orientation, the lower maximum load

produced no significant fixture wear and stable month-to

month average load at failure readings, which verified that

the production process was not changing significantly

from month to month. Typical average maximum load

results are shown in Table II.

Table I. Average Material Properties of Ductile Iron Brake Anchors

Design Condition Microstructure UTS, MPa YS, MPa El, % E, GPaHardness,

BHN

A As-cast 20% F, 80% P 572 366 6.0 179 183

A Normalized >99% pearlite 824 517 3.6 170 270

A Normalized and 675oC tempered spheroidized pearlite 706 453 3.4 172 240

B As-cast 30% F, 70% P 603 373 9.9 177 190

B 730oC sub-critically annealed >99% ferrite 459 311 17.7 175 157

B Normalized >99% pearlite 855 522 4.3 172 258

B Normalized and 675oC tempered spheroidized pearlite 790 459 7.2 170 242

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

1.7 1.9 2.1 2.3 2.5 2.7

Relative Displacement, mm

Load,

N

8/3/2019 2002-01-0797

7/10

Figure 8a. Brake anchor design B driver side in the pull-test fixturebefore testing.

Figure 8b. Brake anchor design B driver side in the pull-test fixtureafter testing. Note: brake anchor fractures through the reducedsection or pocket.

Figure 9a. Brake anchor design B passenger side in the pull-testfixture before testing.

Figure 9b. Brake anchor design B passenger side in the pull-testfixture after testing. Note: brake anchor fractures through the fullsection and not through the reduced section.

pocket

pocket

8/3/2019 2002-01-0797

8/10

8/3/2019 2002-01-0797

9/10

Table III. Effect of Loading Orientation on the Impact Properties of Brake Anchor Design B.

Average

Maximum

Load

(N)

Average Crack

Initiation

Energy (joules)

Average Deflection

at Crack Initiation

(mm)

Average Total

Absorbed Energy

(joules)

Average Total

Deflection

(mm)

Load Perpendicular to

Component12,827 46.15 5.08 77.23 10.74

Load Perpendicular to

Tie Bar9,196 39.53 6.97 62.73 14.00

Table IV. Impact Properties of Ductile Iron Brake Anchors Tested with the Load Applied Perpendicular to the Tie Bar.

Design Condition

Average

Maximum

Load (N)

Average Crack

Initiation Energy

(joules)

Average

Deflection at

Crack Initiation

(mm)

Average Total

Absorbed

Energy (joules)

Average

Total

Deflection

(mm)A As-cast 11,597 48.47 6.79 150.33 26.68A Normalized 14,697 69.24 7.68 173.10 26.18

A Normalized and tempered 12,878 121.87 12.73 215.85 27.40

B As-cast 9,196 39.53 6.97 62.73 14.00B Sub-critically annealed 7,744 85.59 14.30 132.03 26.13B Normalized 11,134 52.15 7.70 89.47 14.83B Normalized and tempered 10,542 95.42 12.84 146.68 24.48

Casting microstructure and chemistry, which determined

material properties, and casting design had a significant

effect on component performance. Ferrite is soft, weakand very ductile, pearlite is harder, stronger but less

ductile, and carbides are very hard, very strong and

brittle. Silicon decreases the amount of pearlite,

increases the strength of ferrite and suppresses carbides.

Therefore, the combination of material (microstructure and

chemistry) and casting design determined the ultimate

load bearing capacity and the ability to absorb impact.

When the two designs were compared using similar

loading conditions and similar microstructure, brake

anchor design A absorbed more energy initiating a crack

(22.6% for as-cast, 32.8% for normalized and 27.6% for

normalized and tempered) and more total energy (139.6%

for as-cast, 93.5% for normalized and 47.2% fornormalized and tempered) than brake anchor design B.

The impact properties as a function of heat treatment and

design are listed in Table IV.

The sub-critical annealing (softening) heat treatment

produced a slightly weaker but significantly tougher

component that was not as stiff as the as-cast

component, i.e., the load required to initiate a crack

decreased slightly, the energy absorbed during fracture

increased significantly, and the amount of deflection

during fracture increased significantly.

The normalizing (hardening) heat treatment produced a

significantly stronger and slightly tougher component tha

was approximately the same stiffness as the as-cas

component, i.e., the load required to initiate a crack

increased significantly, the energy absorbed during

fracture increased slightly, and the amount of deflection

during fracture was about the same.

The normalizing and tempering heat treatment produced a

slightly stronger and significantly tougher component tha

was not as stiff as the as-cast component, i.e., the load

required to initiate a crack increased slightly, the energyabsorbed during fracture increased significantly, and the

amount of deflection during fracture increased

significantly.

8/3/2019 2002-01-0797

10/10

CONCLUSIONS

1. In this study, a test that accurately simulated the

orientation and loading conditions on a vehicle was a

valuable proof test but was not the most appropriate

test for verifying that consistent product was being

produced month-to-month. For verifying product

consistency, a test that produced consistent resultswas critical. In this study, the loading conditions on

brake anchor design B - passenger side were such

that deformation of the test fixture could occur and

this deformation significantly affected the test data.

2. To properly compare similar components, the

orientation of the applied load must be consistent

(preferably in the worst case orientation).

3. In this study, brake anchor design A exhibited

consistently better impact properties due to a slightly

larger cross section and a more uniform cross

sectional shape that minimized stress risers and the

formation of carbides.

4. Heat treatment had a significant effect on the energyrequired to initiate a crack and the total energy

absorbed during fracture.

ACKNOWLEDGMENTS

The authors would like to acknowledge the assistance of

Dale tenPas (INTERMET Technical Center, Lynchburg,

VA), Ed Druschitz (summer intern) and Evan Shockley

(Governors School intern) for performing the pull and

impact tests, strain gage tests, metallography and tensile

tests. Melanie Folks is also acknowledged for performing

the various heat treatments on the castings evaluated in

this study.

CONTACT

Dr. Alan P. Druschitz received his PhD in Metallurgical

Engineering in 1982 from the Illinois Institute of

Technology, Chicago, IL. He is currently the Director of

Materials Research and Development for INTERMET

Corporation. He is located at the INTERMET Technical

Center, Lynchburg, VA 24502. He can be reached at

adruschitz@notes.intermet.com or (434) 237-8749.

Before joining INTERMET Corporation, he was a staffresearch engineer for General Motors Corporation for

fourteen years. He has been a member of the American

Foundry Society for thirteen years, the Society of

Automotive Engineers for twenty years and ASM

International for twenty-five years. He is currently the Vice

President of the Ductile Iron Society, a member of the

Industrial Advisory Board for the Central Virginia

Governors School and a Member of the Governors Board

of Transportation Safety for the Commonwealth of Virginia.