Presentation and Comparison of Three Multiaxial Fatigue Criteria Based on Stress Invariants Applied to a Crankshaft 2010-36-0316

The crankshaft is one of the most important components of the internal combustion engine and its function is, with the rods, transforming the linear movement of the piston into rotation. Because it is under cyclic loads during all of his life, the main type of failure in these components is due to fatigue. However, as they are subject to complex loads, multiaxial stresses are arose resulting in a problem of multiaxial fatigue. Several approaches about this problem were developed, but until now, there is no universally accepted approach. This paper presents a comparison of some multiaxial high-cycle fatigue criteria based on stress invariants, namely Sines, Crossland and Kakuna-kawada criteria. Initially, some basic concepts about such criteria are presented. To facilitate the understanding of the multiaxial fatigue approach, the paper presents also an analysis of stress and fatigue in a steel axle under bending and torsion in phase and out of phase. Next, to a crankshaft of a four-cylinder engine with a forged steel SAE 1548, a stress analysis by the method of superposition of the unit efforts is performed, using the finite element method. The same fatigue criteria are applied. The efforts considered in this work are the efforts from the gas combustion inside the cylinder, the forces of inertia (rotating and alternating), the torsional vibration and the centrifugal force to the crankshaft for different speeds and at several critical positions of the crankshaft. The results of the fatigue show that the crankshaft doesn't fail and has an appropriate safety factor for all conditions and at all critical points analyzed.