摘要：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.
