Stochastic dynamics and fatigue analysis of large-scale mechanical models using multilevel substructuring

Abstract

An efficient methodology is presented for predicting dynamic response and fatigue life of large-scale nonlinear mechanical models, subjected to random excitation. The methodology developed is based on a combination of techniques leading to a fast and accurate determination of the dynamic response with a method related to an efficient prediction of fatigue life. Specifically, the first step involves application of an appropriate coordinate transformation, causing a drastic reduction in the degrees of freedom. This opens the way to the application of another numerical method, leading to direct determination of periodic steady-state response of nonlinear systems under periodic forcing. This approach provides a solid foundation for the subsequent application of a rainflow stress cycle counting method, leading to prediction of fatigue failure. The computational accuracy and effectiveness of the methodology is illustrated by a quite involved example model, representing a city bus subjected to road excitation. Typical results are presented for both the stochastic response and the fatigue life by considering excitation arising from selected road profiles with known statistical properties. Special attention is paid to assessing the effect of the nonlinearity, by considering profiles of different quality. Moreover, a critical comparison is performed on results referring to the expected fatigue lifetime, obtained by applying methods in both the frequency and the time domain. In this way, the applicability of classical spectral methods in nonlinear models is also investigated.

Utilization of modal stress approach in random-vibration fatigue evaluation

“…connectors, notches, fillets, cutouts, grooves, or other sudden shape changes, if all of these details are modeled using 3D FE method, the vibration fatigue analysis could be time-consuming during the design phase, especially in the case of large numbers of rivets and bolts. According to the relevant literature, good efforts have been made to enhance the computational efficiency of response prediction and strength evaluation for engineering structures in both static and dynamic cases, such as the reduced-order model method, 16 the multilevel substructure method, 17,18 the global/local stress approach, 19,20 etc., of which the focuses were fixed on the substructures and local positions of interest. Within this scenario, the selection of substructures or critical positions is of significant importance.…”