Result of ductile iron produced revealed that fatigue values are higher than the tensile result values of the iron. some argued it should not be so. what are the reasons that can be responsible for fatigue values higher than tensile values?
Please allow us to know some more info. To me, it should not be so. But material properties of the ductile iron you used should be checked and if there any other properties that are responsible to have this trend. You need to do material characterization and some more with regard to fatigue analysis.
After melting the base metal for the production of ductile iron (the base metal having % C not less than 3.0 and % Si not less than 1.5), the metal was treated with magnesium ferrosilicon via sandwich process. The casting was analyzed for tensile and fatigue and found out that fatigue values are higher than the tensile values. An argument ensued as to why should we obtain that condition?. To me the number of voids as well as the degree of imperfections in the internal structure of a material have great influence on the fatigue result. For instance, if there is minimal cracks and voids in the internal structure of a material it can give opportunity for increase value of fatigue result, so that we can conclude that the ductile iron was produced with little flaws, but the question is wont that affects the tensile results as well? Is there any other conditions or parameters that have influence on the results discussed?