Fatigue Analysis Of A Fillet Rolled Nodular Cast Iron Crankshaft With Consideration Of Residual Stresses

On account of the outstanding performance in improving cast iron crankshaft's ability to resist fatigue,Fillet rolling technology has been widely applied nowadys.fillet rolling technology have been explored in depth by scholars both at home and abroad,but more efficient research studies are stilled needed to find the relationship and regularity between rolling parameters,fillet residual stress and fatigue strength of crankshaft.In this paper,FEA and experimental method are both used to study how the variable rolling force influences residual stress and fatigue failure of crankshaft.The aim is finding the most suitable rolling-force and modifying the function of rolling-force.In addition,microstructure of fillet are observed to expose it's changing regularity following variable rolling-force.X-ray diffraction residual stress techniques and explicit dynamics simulation are used to observe fillet's residual compressive stress corresponding to different rolling-force.and the maximum deviation of circumferential residual stress between simulation and test is 9.0%.Besides,the maximum deviation of fillet's Sinkage between simulation and test is 14.4%.Absolute value of residual stress goes up with the increase of rolling-force,and the growth rate slows down after 23500N.The analysis of normal residual stress perpendicularing to the plane where the most possibility for crack's initiation and propagating verified that the number of rolling circle and the Inclination angle of roller are rational.Electric resonance fatigue test is a effective method for analyzing crankshaft's fatigue strength.When rolling-force is small,fatigue strength of crankshaft increases quickly with the increase of rolling force.The increases rate slows down when rolling-force is larger than 23500N.Finally,the value of fatigue strength reaches maximum and become a constant when rolling-force reaches 25500N,and the applied torque increases 560%.Smith-Watson-Topper fatigue theory and effective stress intensity factor range of crankshaft which is based on linear fracture mechanics assumed by D.Taylor and modified by Simon Ho are usd to assess the effects on fatigue of crankshaft with inclusion of residual stresses.The maximum equivalent reversed stress amplitude of fillet surface occurs at the angle 40-60 degrees to the vertical direction which is the plane most possibility for crack's initiation and propagating.Based on this plane,the effective stress intensity factor range decreases with the increase of rolling force.rate slows down when rolling-force is larger than 25500N.Computational formula of rolling force is modified to improve the accuracy of rolling force selection.The result deviation between modified formula and optimum value is 5.5%.Fillet's optical microstructure,hardness and surface roughness were observed in this paper.There is no significant difference of optical microstructure with variation of rolling force.The hardness in subsurface increases with the increase of rolling force,in general.Surface roughness increases notably after the rolling peocess,which is very effective to improve the fatigue strength.But surface roughness will become constant when rolling-force gets to a certain value,which means that surface roughness will not be a major factor to fatigue limit.Finally,quantitative prediction method of fillet rolling strengthening is built,which is very useful for enterprises to select the value of rolling-force and predict fatigue strength of crankshaft.