Redundant constraints in MBS models severely deteriorate the computational performance and accuracy of any numerical MBS dynamics simulation method. Classically this problem has been addressed by means of numerical decompositions of the constraint Jacobian within numerical integration steps. Such decompositions are computationally expensive. In this paper an elimination method is discussed that only requires a single numerical decomposition within the model preprocessing step rather than during the time integration. It is based on the determination of motion spaces making use of Lie group concepts. The method is able to reduce the set of loop constraints for a large class of technical systems. In any case it always retains a sufficient number of constraints. It is derived for single kinematic loops.

The paper contains the tatigue tests results for specimens made of three cast irons under proportional and non-proportional variable amplitude tension with torsion. The experimental data for long fatigue life have been compared with those calculated according to the algorithm with use of the modified criterion of the maximum normal stress in the critical plane. In the considered algorithm the Palmgren-Miner hypothesis of damage cumulation seems to he useless whereas the Serensen-Kcgaycv hypothesis gives satisfactory results. Applying the method of fatigue damage cumulation we obtain the critical plane direction which agrees with the experimental fracture plane very well.