Crankshafts Sections under Fillet Rolling Processes

Investigators: Kyoosil Choi, Md Yusuf Ali

Within automotive industry, accurate estimation of crankshafts fatigue strength is becoming more and more important with a growing trend for power improvement while pressing need for weight reduction and hence better fuel economy, power and packaging. Crankshaft fatigue damage always initiates at the cheek fillets under bending and a typical fillet rolling process has been used for years to introduce compressive residual stresses in that region to improve fatigue strengths. The residual stresses due to fillet rolling and the bending stresses near the fillets of crankshaft sections under bending loads are important driving forces to determine the bending fatigue limits of crankshafts.

The objectives of this research project are: (1) to assess the 3D residual stresses due to rolling with the Mroz anisotropic hardening rule and strain rate independent numerical computation for pressure-insensitive (forged steel crankshaft) and pressure-sensitive (cast iron crankshaft) materials by implementing the constitutive integration algorithm derived in the commercial FEA code via a user-material subroutine; (2) with consideration of the stresses due to the rolling process and the bending moment, investigate the fatigue failure near the fillet based on a linear elastic fracture mechanics approach.

3D model setup for crankshaft fillet rolling.

Compressive residual stresses due to rolling process.