Bending Fatique Strength of Gear Teeth under Random Loading : Part 2, Program test under gamma distributed 16 steps Loading

This report presents the test results about bending fatigue strength of gear tooth under two kinds of repeated 16 steps program loads which are gradually increasing or decreasing. Load frequencies are gamma distributed. Materials of test gears are normalized S38C and carburized SCM21. Each of test gears has module 4mm, pressure angle 20 degrees, number of teeth 27 and width 8mm. Miner's cumulative damage theorem is statistically tested and the following facts have become clear : (1) Factor of loading sequence and load frequency distribution are not significant. (2) Factor of material is significant. (3) Fatigue life has a trend that the longer the program load cycle period is, the longer is the fatigue life in comparison with the values calculated from Miner's theorem. (4) Frequency of stress which is higher than fatigue limit strength has little correlation to C. (5) The scatter of Miner's constant C is mainly due to the scatter of fatigue life, and C itself is rather deterministic.