Effort is being made at the National Research Institute for Metals (NRIM) to establish reliable fatigue data for representative materials in the Japanese Industrial Standard (JIS). The present paper provides the results of statistical analysis of S-N data for three JIS carbon steels (0.35C, 0.45C, and 0.55C) and three JIS low alloy steels (0.40C-1Cr, 0.35C-1Cr-0.2Mo, and 0.40-1Cr-0.2Mo) tested for the NRIM Fatigue Data Sheets. Twelve different heats on average were examined for each steels at three quench-tempered states (550, 600, and 650°C tempered) using about twenty specimens each.
The Probit analysis method using weighting was applied to this large number of small sample S-N data by pooling them on a stress scale relative to the tensile strength of each material. The analysis revealed that the relative fatigue limit was around 0.54 with the standard deviation near 0.02 of the tensile strength. An asymmetric fatigue strength distribution tailed in the weaker side was observed for the materials with their strength higher than 900N/mm2. The cause of this skewed distribution was discussed in relation to the pronounced influence of small defects on fatigue strength of higher strength materials.
