Fatigue Strength and Residual Stress Analysis of Deep Rolled Crankshafts 2005-01-0988
The endurance life of an engine crankshaft is closely related to its fatigue strength, in addition to other material properties and shape parameters. Deep rolling, moreover, enhances the fatigue limit by applying compressive residual stress within the fillet radius area as a major surface hardening technique. The objective of this research is to maximize engine fatigue life through crankshaft design optimization by quantifying fatigue strength for microalloyed steels versus a Cr-Mo alloy steel, and to examine the effects of deep rolling load and rolled fillet geometry.
Fatigue tests have been made with standard rotary bending test samples from both bar and forged blanks. Rig tests for actual crankshafts have been made to show how the fatigue strength correlates with different sample types. A correlation of stress distribution with bending moment was demonstrated by applying a strain gauging technique on crankshaft specimens. Therefore, an analysis of combined stresses could be made by considering the effect of static residual stress in addition to the applied dynamic bending stress.
A correlation of rolling load, surface hardness as well as residual stress distribution was observed by using an X-ray diffraction technique. Optimum conditions for rolling load, fillet geometry and material were identified. Consequently, these results were adapted to CAE analysis database to enable an optimization of safety factors.