Gradient residual stress and fatigue life prediction of induction hardened carbon steel S38C axles: Experiment and simulation

Gradient residual stress with several millimeters is retained in middle carbon S38C axles after induction hardening, which has become a critical concern for fatigue structural integrity. To address this, the axial, hoop, and radial gradient residual stress inside the axles are measured by neutron diffraction. The SIGINI Fortran subroutine was then adopted to reconstruct the global initial residual stress field in terms of measured data. Experiment and simulation results show that approximately −515 MPa (axial), −710 MPa (hoop), and −43 MPa (radial) residual stress was retained underneath the surface. Subsequently, the fatigue crack propagation behavior of S38C axles was numerically investigated in the framework of fracture mechanics. The calculated results clearly show that the compressive residual stresses at a depth of 0–3 mm from the surface could lead to the lower crack growth driving force, and fatigue cracks would not propagate as long as the crack depth is smaller than 3.7 mm for hollow S38C axles. Such results further indicates that the maximum defect size during routine examination can be permitted from the viewpoint of safety and economy. Accurate measurement and characterization of global gradient residual stress field in terms of experiment and simulation can provide an important reference for optimizing the nondestructive detection milage interval of surface-strengthened railway axles.