Strain and Fatigue Strength of Rack Tooth Fillet for Leg Fixing Device of Jackup Rigs

The rack teeth of a leg fixing device, which is indispensable for jackup rig to operate in harsh environment, take cyclic load caused by waves and winds. Accordingly, it is very important to know the fatigue strength of rack teeth.In this paper, fatigue tests of rack tooth models and small bar specimens whose material is HT 80 are performed, and the analysis of the rack tooth models by finite element method is performed as elasto-plastic contact problem with friction.Comparing the calculated results with experimental ones, following results are obained.(1) The effect of frictional force on the strain at rack tooth fillet is not negligible.(2) Manson-Coffin type equation proposed by Iida is useful to predict the fatigue crack initiation life for HT 80.