Abstract
The influences of the matrix structure on the notch effect in tensile and rotating-bending fatigue characteristics were investigated by using four kinds of spheroidal graphite (SG) cast iron samples whose matrix structures are ferritic, pearlitic, upper bainitic and lower bainitic. While the stress concentration factor (α) was smaller than 2.3, the tensile strength of notched specimens was larger than that of smooth specimens regardless of the matrix structure. This is considered to be due to the plastic constraint effect caused by triaxial stress. All the samples showed that a notched specimen with a larger α resulted in a smaller in fatigue strength than a smooth specimen in all the α ranges examined. A larger decrement in the fatigue strength of a specimen with a larger α is considered mainly due to an earlier occurrence of cracks. The notch effect in the tensile and fatigue strength of SG iron is affected largely by its matrix structure.
