片状黒鉛鋳鉄の引張強さに及ぼす試験片の形状と寸法の影響

抄録

  Variation in the measured strength of gray iron resulting from the differences in the profile and dimension of test pieces was examined. Experiments were performed on the test pieces with various fillet radii, gauge lengths and section diameters. Results were analyzed theoretically utilizing the stress distribution obtained by finite element method, and the stress-strain curves of each test piece. Fillet radius does not have any effect on the tensile strength of cast iron unless it is too small in comparison to the section diameter. This is because the stress around the fillet relaxes with the non-elastic behavior of cast iron. The length and diameter of the test section affect the strength in different ways. That is, the strength obviously decreases with increase in diameter, while it is not affected or slightly increased by increasing of diameter. Consequently, the statistical theory where the strength decreases with increasing specimen volume can not be applied to cast iron. The phenomenon in cast iron is explained by the fact that the eutectic cell structures of graphite flakes at the surface layer act as defects and results in the reduction of the net sectional area of the specimen. This effect becomes more pronounced in small specimens.