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/. 

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