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The strain energy density factor criterion is used to model the growth ofboth circumferential and semi-elliptical fatigue cracks in sugar cane mill crusher shafts.Shaft dimensions and loads are based on the mill shafts of the CAI “GuillermoMoncada” sugar mill in Cuba. About 85% of the Cuban sugar mill shaft failures occurin the shoulder of the bearing nearest to the square box coupling. In terms of failurepotential, the top shaft is the most critical. Calculations show that inspection intervalsas short as once every 43 days are needed to avoid unexpected failure. Application ofthe strain energy density criterion is slightly more complicated and gives slightlyshorter predicted fatigue lives than the equivalent stress intensity factor criterion.However, it offers more information about the expected growth direction of the crackwhich is potentially beneficial during NDE inspections. Calculated crack inclinationangles are found to be in good agreement with crack angles reported for failed shafts.