Experimental and numerical fatigue evaluation of lightweight crankshafts

The development of lightweight components in the automotive industry is an important aspect in designing of products aiming to reducing fuel consumption, optimal use of material resources and sustainability. The optimization of internal combustion engines (ICE) components can be performed for example by mass subtraction procedure and use of different materials. Optimizing crankshafts is challenging due to the applied bending and torsion loads that increase the stress concentrations in critical regions. In this context, the objective of the present work is to propose a numerical approach for fatigue assessment of crankshafts, which must reduce the number of specimens required in experimental tests and the development costs. The stress distribution of a commercial crankshaft model was determined numerically from harmonic response analysis, and correction factors related to surface treatments and failure criterion were applied for estimating the fatigue strength. The fatigue strength estimated numerically was compared to experimental fatigue tests results, and this methodology was also applied to a lightweight model obtained by means of mass reduction. The fatigue strength estimation showed 2 % and 7 % relative error for the original and lightweight crankshaft models, respectively. In addition, both numerical and experimental results achieved about 10 % of mass reduction for the commercial crankshaft without considerable influence on the bending and torsion fatigue strength. The present work indicates that the proposed numerical approach can predict with good accuracy the fatigue strength of crankshafts during the design stage.