Congreso SAM/CONAMET 2007 San Nicolás, 4 al 7 Septiembre de 2007 MULTIAXIAL FATIGUE CRITERIONS APPLIED TO MECHANICAL COMPONENTS F. J. Cavalieri, A. Cardona, J. M. Risso Centro Internacional de Métodos Numéricos en Ingeniería (CIMEC-INTEC). CONICET- Universidad Nacional del Litoral Güemes 3450, (3000) Santa Fe, Argentina. E-mail: fcavalieri@ceride.gov.ar ABSTRACT In many practical situations, mechanical components are subjected to multiaxial loading and the required design lifetime often exceeds 10 8 cycles. For example, the expected lifetime of engine components, railroad wheels, crankshafts, turbine blades, etc. is more than 10 9 cycles. The traditional fatigue criterions assumed a hyperbolic relationship between stress and fatigue life, but experimental results in steels show that the fatigue fracture can occur beyond 10 7 cycles. This means that for very high number of cycles the fatigue limit does not an asymptotic behaviour and the concept of infinite fatigue life is not correct. So, the fatigue in metal components with design lifetimes greater than 10 7 cycles is an interesting topic for the development of advanced technologies. Taking into account that experimental fatigue tests are very expensive and time-consuming, the development of numerical fatigue models capable of predicting the durability of components, is a key task to carry out mechanical components design in shorter times. Multiaxial fatigue criterions can be classified in the following way: 1) Empirical, 2) Stress Invariants, 3) Critical Plane, 4) Strain Energy, 5) Combined Energy/Critical Plane and 6) Mesoscopic. In this paper, we present results from numerical models using the finite element method (FEM) analyzing mechanical components subjected to high number of impact cycles with an invariant criterion. Keywords: Fatigue, Multiaxial high–cycle fatigue, impact, contact. 1. INTRODUCTON Few materials have an endurance limit for a number of cycles higher than 10 6 . In general, materials do not exhibit this response, and have a continuously decreasing stress-life relationship, even in the range of 10 6 - 10 10 cycles. For this reason, to assert the expected life time of steel components, it is necessary to carry out very prolonged tests. Numerical models are a good way to solve this problem in a short time. The finite element method (FEM) is a general technique for numerical analysis, suitable to be used in fatigue simulation. Using FEM, we developed computational models to predict the fatigue life of mechanical components. Many formulations were studied, but the most recognized criterions are those developed by Crossland and Dang Van. Both criterions are able to predict the reliability of an element subjected to very high cycles fatigue (VHCF) in a shorter and less expensive way than by experimental testing. Our model links the physical criterions with numerical analysis. The objectives of this work are: 1. Presentation of a fatigue criterion. 2. Generation and validation of computational models for VHCF analysis. 3. Presentation of VHCF analysis for real mechanical systems. 2. MULTISCALE ANALYSIS OF FATIGUE MECHANISM The fatigue behavior of metals can be explored from different scales. It can be explored from the microscopic scale, which is the scale of dislocations (this is merely the scale of physicists). It can be also explored from an intermediate scale between the macroscopic and microscopic levels, this is the mesoscopic scale, which is the scale of metal grains of a metallic aggregate. The mesoscopic approach 1795