MULTIAXIAL HIGH CYCLE FATIGUE CRITERION IN MECHANICAL COMPONENTS SUBJECTED TO IMPACT LOAD

FEDERICO J. CAVALIERI; ALBERTO CARDONA; JOSÉ RISSO

Universidad Nacional del Litoral INTEC

Congreso; ENIEF Congreso Sobre Métodos Numéricos y sus Aplicaciones; 2006

Asociación Argentina de Mecánica Computacional

In several industries, the required design lifetime of many components often exceeds 10e8 cycles. This requirements is applicable to aircraft (gas turbine disks 10e10 cycles), automobiles (car engine 10e8cycles), and railways (high speed train 10e9cycles). Although a large amount of fatigue data has been published in the form of S-N curves, the data in the literature have been usually limited to fatigue lives up to 10e7 cycles. Using traditional fatigue criterions, a near-hyperbolic relationship between stress and fatigue life is assumed. Experimental results in steels show that, the fatigue fracture can occur beyond 10e7 cycles. This means that in very high cycles number endurance limit has not asymptotic behaviour and the concept of infinite fatigue life is not correct. For this reason, to assert the expected life time of steel components is necessary to carry out very prolonged tests. The simulation by FEM is good way to solve this problem in short times. In this paper, we present results from numerical models analyzing mechanical components subjected to high number of impact cycles using commercial software. Formulations are applied to solve the problem: Crossland, Dan Vang-Papadopoulos criterions. As the loads on the system appear from the impact of flexible elements, algorithms based on Lagrange multipliers were used. With such a method, contact conditions are infinitely rigid and induce numerical troubles. To avoid this problem relaxation contact conditions were used by adding a penalty function. The time integration algorithm used for solving this structural dynamics problem was Hilber-Hughes-Taylor (HHT) but it showed a poor high-frequency dissipation. Finally, the integration method used to solve the dynamic problem was the Generalized alpha Method, (J.Chung and Gregory Hulbert, (313)747-3170) because it achieves high frequency dissipation while minimizing unwanted low-frequency-dissipation.