Multiaxial Highcycle Fatigue Criterion in Mechanical Components Subjected to Impact Load

FEDERICO CAVALIERI; ALBERTO CARDONA; JOSÉ RISSO

Santa Fe

Congreso; 15 Congreso sobre Métodos Numéricos y sus Aplicaciones, ENIEF 2006; 2006

Asociación Argentina de Mecánica Computacional

In several industries, the required design lifetime of many components often exceeds 108 cycles. This requirement is applicable to aircraft (gas turbine disks 1010 cycles), automobiles (car engine 108 cycles), and railways (high speed train 109 cycles). Although a large amount of fatigue data has been published in the form of S-N (where S is stress and N cycles numbers) curves, the data in the literature has been usually limited to fatigue lives up to 107 cycles. Using traditional fatigue criterions, a nearhyperbolic relationship between stress and fatigue life is assumed. Experimental results in steels show that the fatigue fracture can occur beyond 107 cycles. This means that in very high cycles number the endurance limit has not asymptotic behavior and the concept of infinite fatigue life is not correct. For this reason, to assert the expected life time of steel components it is necessary to carry out very prolonged tests. FEM (Finite Element Method)simulation is a 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. Two formulations are applied to solve the problem: Crossland, Dang Van criterions. As the loads on the system appear from the impact of flexible elements, contact algorithms were used. With methods based on Lagrange multipliers, contact conditions are infinitely rigid and induce numerical perturbation. To avoid this problem relaxed contact conditions were used by adding a penalty function. In the first trials, the time integration algorithm used for solving this structural dynamics problem was Hilber-Hughes-Taylor (HHT) but it showed poor high-frequency dissipation. Finally, the integration method used to solve the dynamic problem was the generalized-method, because it achieves high frequency dissipation while minimizing unwanted low-frequency dissipation.108 cycles. This requirement is applicable to aircraft (gas turbine disks 1010 cycles), automobiles (car engine 108 cycles), and railways (high speed train 109 cycles). Although a large amount of fatigue data has been published in the form of S-N (where S is stress and N cycles numbers) curves, the data in the literature has been usually limited to fatigue lives up to 107 cycles. Using traditional fatigue criterions, a nearhyperbolic relationship between stress and fatigue life is assumed. Experimental results in steels show that the fatigue fracture can occur beyond 107 cycles. This means that in very high cycles number the endurance limit has not asymptotic behavior and the concept of infinite fatigue life is not correct. For this reason, to assert the expected life time of steel components it is necessary to carry out very prolonged tests. FEM (Finite Element Method)simulation is a 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. Two formulations are applied to solve the problem: Crossland, Dang Van criterions. As the loads on the system appear from the impact of flexible elements, contact algorithms were used. With methods based on Lagrange multipliers, contact conditions are infinitely rigid and induce numerical perturbation. To avoid this problem relaxed contact conditions were used by adding a penalty function. In the first trials, the time integration algorithm used for solving this structural dynamics problem was Hilber-Hughes-Taylor (HHT) but it showed poor high-frequency dissipation. Finally, the integration method used to solve the dynamic problem was the generalized-method, because it achieves high frequency dissipation while minimizing unwanted low-frequency dissipation.method, because it achieves high frequency dissipation while minimizing unwanted low-frequency dissipation.