Combined stress tests on pearlitic nodular iron show this material possesses a constant valued modulus of elasticity and Poisson’s ratio. The maximum shear criterion for yielding is conservative, but is sufficiently accurate for design purposes. In addition, it appears to yield in accordance with the distortion-energy theory, providing stress concentrations at the graphite nodules are taken into account. There is a density change with plastic deformation due to separation of the matrix from the graphite. Stress and strain variables may be reasonably correlated by plotting plastic work against octahedral shear stress. A smooth fracture envelope has been obtained, and fracture occurs in a direction normal to the greatest applied tensile stress. A considerable internal crack network may be opened up before fracture. Brittle cleavage facets in pearlitic nodular iron are revealed by the fractographic technique. Cleavage fracture is not obtained in ferritic nodular iron in tension, but may be obtained in the presence of notches or by low temperature of test.

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