Abstract
Many works have so far been made on the problem of notch strength in engineering materials, but little on cast iron.
The author carried out some experiments on the notch strength of FC 25 class cast iron, using plate tensile specimens with notches of various degrees of sharpness, and discussed the experimental results. The finite element method was used to analyze the stress distribution for blunt notch.
The results obtained are summarized as follows:
(1) The rupture strength of cast iron was decreased by the notch in plate specimen. The criterion that the average stress of the notch section is constant was not valid.
(2) The rupture strength decreased with increasing the sharpness of notch, but showed a tendency to become almost constant in the region of sharp notch (ρ<0.5mm).
(3) The stress analysis by the finite element method for blunt notch (ρ=10, 15mm) showed that the notched specimen ruptured when the maximum axial stress under the notch reached the tensile strength of smooth specimen. That is to say, the maximum stress criterion was valid.
(4) Though the rupture condition for the sharper notch was not analyzed by the method taken in this paper, it was suggested that the rupture strength was influenced by the stress gradient besides the maximum stress.
(5) The tendency of saturation of strength in the region of sharp notch is thought to be due to the microscopic notch effect of graphite flakes.
