Solution (Problem 5)
This question should take about 10 minutes to complete. It is a simple application of the Griffith equation.
A Class 20 grey cast iron has an average graphite flake size about nine times as long as Class 60 type. The fracture strength of the latter is about 140 MPa. Using arguments that follow the Griffith analysis, what would you predict to be the fracture strength of the Class 20 iron?
Answer: 46.7 MPa
This is very similar to problem 2, and all that is required is to set up the two equations and eliminate the material properties, which are unknown. Recalling Griffith's equation:
we can write:
Hence the Class 20 iron has a fracture strength of some 46.7 MPa.
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