Multi axial high cycle fatigue life model optimization for drilling tools

The fatigue life model was optimized in terms of the multi axial high cycle fatigue failures of drilling tools. Based on the multi axial fatigue theory, the stress state under the non-proportional loading and the cracking behaviour of the material under multi axial fatigue were analyzed, the multi axial fatigue models were summarized, and the Dang Van model was recommended for judging whether or not the drilling tool will be subjected to fatigue failure under the certain stress state. The fundamental criterion, derivation principle, application scope and fatigue limit calculation method were introduced. The Dang Van model was validated with field failures of the drive shaft of stabilizer steering stator which was used in the drilling process of oil and gas fields, and compared with the conventional mean stress model. The results show that the mean stress model predicts in a over conservative way, and the Dang Van model is more applicable for predicting multi axial high cycle fatigue life of drilling tools.