Effects of small defects, matrix structures and loading conditions on the fatigue strength of ductile cast irons

• Published in: Theoretical and applied fracture mechanics Vol. 69; pp. 34 - 43
• Main Authors: Endo, Masahiro, Yanase, Keiji
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2014
• Subjects: Cast iron; Casting defects; Ductile cast irons; Fatigue strength; Fatigue strength estimation; Fatigue tests; Inhomogeneities; Lower bounds; Matrix hardness; Microstructure; Multiaxial loading; Nodular iron; Small fatigue cracks; Multiaxial loading; Ductile cast irons; Small fatigue cracks; Fatigue strength estimation; Casting defects; Matrix hardness
• ISSN: 0167-8442; 1872-7638
• DOI: 10.1016/j.tafmec.2013.12.005

•The interferential effect of graphite on fatigue limit of ductile cast iron is negligibly small.•A method to predict the lower bound fatigue limit is presented.•Effects of microstructural inhomogeneities and multiaxial loading condition are considered.•The method is convenient for practical engineers since no fatigue test is necessary.•Fatigue tests are performed for cast irons with ferritic, pearlitic and bulls-eye microstructures. The fatigue strength of ductile cast iron is influenced by microstructural inhomogeneities (i.e., graphite, casting defects and matrix structures composed of different phases). In particular, the presence of small casting defects such as micro-shrinkage cavity can frequently cause not only significant deterioration but also large scatter in fatigue strength. Therefore, the laboratory fatigue tests with a limited number of small-sized specimens could result in a non-conservative estimation. For such a material, the prediction for the lower bound of the scatter in fatigue strength is essential from a practical perspective. In this study, a novel method is presented to predict the lower bound based upon the information of microstructural inhomogeneities and loading conditions. This method offers such an advantage that the lower bound can be reasonably predicted without conducting time-consuming fatigue tests. The predictive capability of the method was verified by comparing to the experimental results obtained in rotating-bending, torsion and combined tension–torsion fatigue tests of ductile cast irons with ferritic, pearlitic and bulls-eye structures.