Due to the permanent increasing demand to enhance specific power output and fatigue life, an optimization of the local material properties of highly-stressed stationary gas engine parts is of utmost importance. In this paper, focus is laid on the fatigue strength characterization of the crankshaft including both manufacturing process and fatigue loading. Induction hardening as common heat treatment technique for crankshafts significantly affects the surface layer properties leading to a compressive residual stress condition and a local hardening of the material. This beneficial effect is basically well investigated and already implemented in industrial applicable recommendations, such as the FKM-guideline. In order to enhance this upgraded surface layer condition furthermore, the effect of a superimposed peening as mechanical post-treatment is analyzed in this investigation.
At first, special attention is drawn to the change of the local material properties in the surface layer. Due to an almost maximized hardening behavior, hardness measurements reveal that the superimposed mechanical post-treatment does not significantly affect the absolute hardness state, but an increase of the hardness depth is evaluated. X-ray residual stress measurements illustrate that the peening process heightens both the maximum compressive residual stress value and the effectiveness in depth.
At second, the effect of the induction hardening and the subsequent mechanical post-treatment on the fatigue strength is experimentally investigated. Therefore, a representative rotating bending specimen geometry featuring comparable manufacturing and loading conditions as the analyzed crankshaft is set-up. A comparison of the local hardness and residual stress state of the specimen with the component proofs the practicability of this procedure. The final fatigue test results show that the induction hardening, as first post-treatment step, already leads to a significant improvement compared to the base material. Further on, the additional peening process even increases this enhanced behavior and thus optimizing the durability and fatigue life of highly-stressed crankshafts.
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|Präsentation||Figure of surface layer condition - Appendix for abstract||The figure schematically shows the local condition in the surface layer. The figure acts as appendix to the abstract.||175 KB||Download|