This paper presents S-N data generated on a newly designed tuning fork system. The materials tested were four different specimen groups of ductile iron. The tuning fork was designed to continuously monitor reversed bending loads applied to the specimen. The main objective of the project was to develop S-N curves for four particular groups of ductile iron materials. The basic material was an SAE-D5506 ductile iron, tested in both an as-cast condition and with a machined surface finish. This same material was tested in a quenched and tempered state, (SAE-DQ&T, MS-612 Grade, 1000S) with both as-cast and machined finishes. In order to carry out these experiments a test apparatus had to be designed, assembled, and calibrated. The end result of this procedure was a versatile tuning fork fixture for the application of the required pure bending loads and a permenent monitoring system calibrated to the loads applied to the specimen. This monitoring system, once calibrated, eliminated the need to strain gage each of the many specimens to be tested. The paper concludes with discussion of the results obtained. The material S-N data presented includes comparative points for the four log-log lines as computed by linear regression techniques.

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