Numerical Simulation Of Fatigue Life Of The Large Diameter Percussive Reverse Circulation Drill Bit

The large diameter percussive reverse circulation drill is widely used in the drilling process of large buildings,bridges and other projects.The structure fracture and weld cracking of the drill bit often happen because of the long suffering the effect of cyclic loading cycles.It is the primary cause for the low service life of the drill bit.In this paper,the research for YCJF-25-type large diameter percussive reverse circulation drill bit is studied.Firstly,the failure analysis of drill bit is studied in view of the damage.Several failure mode of the drill bit is summarized further.Subsequently,the modal analysis is researched for previous order modal of the drill bit.It verifies that the drill will not damage because of resonance.The impact process under different working conditions is simulated by using explicit dynamic module of ANSYS Workbench.Stress and strain distribution of drill bit is got though the drop test on the different impact height and different impact formation.The relationship between the fatigue damage of the drill bit and the various impact parameters are obtained by analysis results.Analysis shows that stress in impact process of drill bit increases gradually with the increase of impact height.The stress value will also become larger with the Strata hardened.In any case,the stress of the inner ring 3 and its impact face are always the largest.The inner ring 3 is the second.Partial load cases stress concentration where is in the end of the drill bit at the boundary of the formation.It cases that the stress is greater than that under normal working conditions.According to the analysis of rockfall impact,the impact force was calculated in the process of impact drilling.The fatigue life of drill bit is respectively predicted in the normal working and partial load by using nCode DesignLife.Fatigue life and fatigue dangerous points damage of drill bit are got those lay a solid foundation for the optimized analysis of drill bit.The fatigue life of the bit is 8.39×105 under normal working conditions.The fatigue life of drill bit is reduced by 7 times under the condition of partial load.The impact frequency influence on fatigue life of drill bit is studied further.It shows that fatigue life of drill bit reduce two orders of magnitude under the condition of the double impact frequency.The fatigue life of drill bit extremely is lowered.It verifies that the working frequency of the drilling rig is reasonable.According to the results of the analysis,the optimization analysis was carried out on the original bit from two aspects of materials and exerting the stiffened plate.The way that change the part material improve the fatigue life to 1.2 times,that change all improve the fatigue life to 2.3 times.The fatigue life of the drill bit can be increased to 3.3 times by exerting the stiffened plate.It provides guidance for further improvement of the large diameter percussive reverse circulation drill.