Modeling of the dynamics of jointed beam structures

Mechanical joints can have significant effects on the dynamics of assembled structures. The goal of our work is to develop physics based, reduced-order, finite element models that are capable of replicating the effects of joints on vibrating structures. Various studies have shown that micro- and macroslip along the joint interface cause the interface stiffness to change and introduce energy dissipation, leading to the observed hysteresis. The authors recently developed the so-called adjusted Iwan beam element (AIBE) for finite element analysis of jointed beam structures. The element consists of two adjusted Iwan models that are arranged to give two-dimensional beam behavior. The adjusted Iwan model is a combination of springs and factional sliders that exhibits hysteretic behavior due to the stick-slip behavior of the sliders. In this paper, the sensitivity of the performance of an adjusted Iwan model, particularly its capacity to dissipate energy, to variations in its parameters is studied. Parametric analysis is also carried out on the adjusted Iwan beam element to investigate the effects of joint parameters on dynamic responses of jointed beams. Hammer tests are conducted on a jointed beam and its monolithic counterpart. The decay envelopes of impulsive responses for the two systems exhibit distinctly different dynamic properties. To verify that the adjusted Iwan beam element is capable of actually modeling the effects of joints on a vibrating structure, numerical simulations are performed of two hammer tests with different forcing levels. The joint parameters of the jointed beam are identified from the experimentally-obtained acceleration response from one hammer test by using a multi-layer feed-forward neural network (MLFF). Then, using the identified joint parameters, acceleration responses of the jointed beam in the other hammer test are predicted. The capability of the AIBE to capture the effects of bolted joints on the dynamic responses of beam structures is demonstrated through good agreement between simulated and experimental results.