Research Activity - Complete


Project No. 29 
Determination of Fatigue Properties of Ductile Iron
Monotonic Tensile, Cyclic and Fatigue Properties of Several 
SAE Grades of Ductile Iron

Data on the low and high cycle fatigue response as well as monotonic (non-cyclic) and cyclic flow properties are required by design engineers for the proper design of many components. Although these properties data are available in SAE standard J1099, June 1998, "Technical Report on Fatigue Properties" for many competing materials, no readily available source exists for such information on ductile/nodular cast iron. Typical tensile and compression properties of ductile iron are well known, but the (1) monotonic and cyclic strength coefficients, (2) strain and stress versus fatigue life (reversal) constants, and (3) the variation in elastic modulus after repetitive cycling have not been published in the open literature or handbooks.

The Ductile Iron Society embarked on a study to develop all of the important constants used by engineers in the design of structural components. Items (1) and (3) above, were determined for eight materials that are representative of the hardness range, nodularity, and nodule sizes typical for ferrite-pearlite SAE grade D5506 nodular iron. Four of the eight materials were selected for strain-life fatigue testing with fully-reversed axial loading. The selected materials represent the full range expected for this grade of ductile iron. 

Uni-axial, strain-controlled fatigue testing was chosen due to the uniformity of the stress state between the surface and the interior of the specimen; this allows the ability to monitor the stress and strain simultaneously; the ability to measure the tensile and compression data independently (as these values can differ for ductile iron); the ability to easily and precisely relate stress-to-strain mathematically; and to be consistent with the manner in which other investigators obtain fatigue data for designers. Traditional bending fatigue testing methods (such as rotational bending or plate bending) and S-N testing (wherein the load is controlled, but the strain is not monitored), violate these necessary conditions. 

All the constants in SAE standard J1099, June 1998, were determined for four of the materials. These four materials represent three hardness levels covering the range in hardness for grade D5506. Data on other grades of ductile iron were supplied by ArvinMeritor and are also presented in the attached table. 

For more information please refer to a paper written on this subject titled "Monotonic and Cyclic Property Design Data for Ductile Iron Castings", written by John M. Tartaglia, Paige E. Ritter and Richard B. Gundlach, Climax Research Services and published by SAE, paper #2000-01-0758. This paper is available free of charge from the Ductile Iron Marketing Group c/o Ductile Iron Society at www.ductile.org/. 

Material 

Symbol

1a

2a

A

B

C

D

3a

4a

SAE Ductile Iron Grade D4018 D4512

D5506

D7003

Brinell Hardness, HBS3000

 

na

na

189

228

250

270

na

na

Pearlite Content, %

 

na

na

49

75

99

100

na

na

Monotonic Tensile Properties

Ultimate Tensile Strength (Engineering), MPa

Su

513

590

612

725

775

863

743

829

0.2% Offset Yield Strength (Engineering), MPa

Sys

321

368

368

439

437

474

447

512

Percent Elongation

%El

15.7

11.2

13.7

10.4

4.4

6.3

12.7

11.5

Percent Reduction in Area

%RA

14

9

12.1

8.2

3.9

5.7

9.4

9.5

Modulus of Elasticity, GPa

E

na

na

170

168

174

176

na

na

Monotonic Strength Coefficient, MPa

K

na

na

887

1100

1590

1760

na

na

Monotonic Strain Hardening Exponent

n

na

na

0.17

0.18

0.25

0.25

na

na

Cyclic Stress-strain Properties

0.2% Offset Yield Strength (Engineering-Tension), MPa

Sys¢

na

na

434

486

488

500

na

na

0.2% Offset Yield Strength (Engineering-Compression)

Sys¢

na

na

444

488

487

505

na

na

Cyclic Strength Coefficient (Tension), MPa

K¢

na

na

754

922

1120

1230

na

na

Cyclic Strength Coefficient (Compression), MPa

K¢

na

na

1140

1450

1640

1820

na

na

Cyclic Strain Hardening Exponent (Tension)

n¢

na

na

0.09

0.10

0.13

0.15

na

na

Cyclic Strain Hardening Exponent (Compression)

n¢

na

na

0.15

0.18

0.20

0.21

na

na

Fatigue Properties

Fatigue Strength Coefficient, MPa

sf¢

774

818

723

895

983

1030

1019

978

Fatigue Strength Exponent

b

-.071

-.089

-.062

-.074

-.087

-.083

-.082

-.070

Fatigue Ductility Coefficient

ef¢

.125

.226

.506

.494

.573

.813

.263

.124

Fatigue Ductility Exponent

c

-.626

-.672

-.683

-.686

-.728

-.722

-.648

-.660

aData supplied by Ray Sieber of ArvinMeritor

na: Not Available

Additional information in Data Book, Chapter 10, Page 6.