Effects of residual stress on rolling contact fatigue of ductile iron

This study investigates the rolling contact fatigue (RCF) behavior of ductile iron (DI) using experimental and analytical method. The fatigue behavior of DI was assessed under both torsion fatigue and RCF. The RCF of DI was assessed by a 3 ball-on-rod test rig at a peak pressure of 3.6 GPa. Torsion fatigue tests were performed using an MTS test setup to determine the material’s stress-life (S-N) response. A Rockwell hardness tester was utilized to determine the global hardness of DI materials, while a nano indenter was employed to obtain the hardness distribution along the depth of the DI RCF rods. X-ray diffraction (XRD) was employed to measure the residual stresses prior to and after RCF testing to assess the effect of residual stresses on fatigue life. XRD results revealed a 32% increase in compressive residual stress after RCF testing, suggesting plastic induced residual stresses, which in turn enhanced fatigue resistance. In order to further validate the experimental findings; a continuum damage mechanics finite element (CDM-FE) model was employed for fatigue life prediction. The material constants used in the damage evolution equation of the CDM framework were obtained using torsion fatigue S-N data. Different residual stress profiles as a function of the depth of the material were incorporated into the model, and the corresponding RCF life predictions were evaluated. The analytical results demonstrated good corroboration with the experimental results, confirming the significance of residual stress in influencing fatigue performance. A two-parameter Weibull distribution was utilized to characterize the DI material’s probability of failure, demonstrating that its RCF performance is in par but slightly lower to that of high-strength steel.