The authors have conducted fatigue tests on induction hardened V-notched specimens (ρ=0.25mm, 0.5mm, 1mm and 5mm) with C=0.13% steel. Induction-heating temperature was chosen 700°C, 800°C, 900°C, 1000°C, and 1100°C. The experimental results may be summarized as follows : (i) There is a favourable difference between σ
w1and σ
w2, when ρ is 0.25mm, 0.5mm, or 1mm; but no difference between σ
w1and σ
w2 at ρ=5mm. (ii) The absolute values of σ
w2 reach a maximum at 1100°C, and decrease as the heating temperature decrease. The value of σ
w1 at 1100°C is higher then that at the other temperatures, but the values of σ
w1 show no difference from those at other temperatures. The values of σ
w1 andσ
w2 are almost proportional to the hardness at the notched-bottom, within the range of these experiments. (iii) For discussion of the crack-development, we calculated the stress of crack-tip with simple form, and examined the simple relation between the calculated-stress and hardness.
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