Abstract
Abstract Gray cast iron has been used as a component in various mechanical parts, such as the blocks and heads of automobile and marine engines, cylinder liners for internal combustion engines, and machine tool bases. It is desirable because of its good castability and machinability, damping characteristics, and high performance-to-cost ratio. On the other hand, weak graphite flakes present in gray cast iron serve as stress concentrators and adversely affect the material strength. Therefore, it is crucial to examine the relationship between the distribution of graphite flakes and the strength or fracture of gray cast iron. In this study, tensile tests on gray cast iron were carried out using a plate specimen and observed by scanning electron microscopy, and the microscopic deformation was observed on the specimen surface. Particularly, the change in the size of graphite flakes during the tensile tests was examined, and the observed trend was discussed. The experimental results reveal that the dimensional changes in the graphite flakes vary in the observed area and that the final fracture occurs in an area where a large dimensional change is observed, suggesting that the fracture location or critical parts of gray cast iron can be predicted from the dimensional changes of the graphite flakes at an early stage of deformation.
Highlights
Gray cast iron has been used in various mechanical parts because of its costeffectiveness, good castability and machinability, low thermal expansion coefficient, high thermal conductivity, and good damping characteristics
We summarize from the above investigations on the strength of gray cast iron that graphite flakes cause the stress concentration and considerably affect the tensile strength
The specimens were taken from the runner of diesel engine cylinder block by wire cut electrical discharge machining
Summary
Gray cast iron has been used in various mechanical parts because of its costeffectiveness, good castability and machinability, low thermal expansion coefficient, high thermal conductivity, and good damping characteristics. As casting is a manufacturing process that renders a high freedom of shape, fundamental experimental studies of gray cast iron, as well as the design and failure analyses of its components have been typically performed in combination with numerical analyses by using the finite element method (FEM). Wang et al have proposed a method for predicting the fatigue failure for camshafts in vehicles composed of gray cast iron [1]. They used the crack modeling approach in which the stress–distance relationship is approximated by a function of the remote stress and crack length, and it is best fitted to the actual stress distribution in a particular area analyzed by the FEM. The effect of the tightening of the cylinder head bolt on the lifetime of cylinder block was investigated, and some practical methods to decrease the static strain along the fillet on the upper deck of the cylinder block, such as change in the depth of the thread engagement and modification of the bead shape, were proposed to extend its lifetime under severe combustion conditions
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