On the Modal Surrogacy of Joint Parameter Estimates in Bolted Joints

Abstract

The Surrogate system hypothesis for jointed mechanics proposes that the influence of a jointed interface on an otherwise linear system is identical irrespective of the structural features of the so-called far-field linear structure. The implication, if the hypothesis finds support, is that the characterization of a joint in a single structural context can be used for developing predictive models of completely different structures, albeit with identical joint configurations. In critical applications such as aerospace, this can potentially lead to a more cost-effective design flow enabling tighter design optimization. In order to evaluate the hypothesis, the major influences on the nonlinear behavior of a jointed structure has to be delineated and studied individually as well as in combinations. Proceeding in the spirit of previous investigations where the effect of far-field structures and joint interface modeling approaches have been tackled, the current investigation studies the so-called “modal surrogacy” of a structural system. The investigation serves to understand the sufficiency of modeling the nonlinear behavior in lower modes to make high-modal nonlinear predictions. The Brake-Reuß Beam (BRB), which is an assembly of two monolithic beams connected together using a bolted lap joint with three bolts, is used as a test specimen for the current investigations. Due to the presence of regions with zero static pre-stress in the interface, considerable separation combined with stick & slip has been numerically as well as experimentally observed. This leads to significant nonlinear effects in the response of the system and thus serves as a convenient benchmark for the current work.