Publications

Abstract not provided.

Bolted joints often risk failure due to the loss of fastener preload when subjected to dynamic, multiaxial loads. This process is a complex problem that depends on multiple attributes such as loading direction, rate, contact within the threads and the interface, material properties, and many others. Current literature suggests that oscillatory shearing loads appear to be most detrimental to the loss of preload in threaded fasteners. To investigate the effect of less idealized loading conditions, an experimental setup employing a bolted c-beam structure is used to study loss of preload from various initial preloads during harmonic excitation near specific resonant frequencies of the structure. The preload force is measured using bolts equipped with internal strain gauges and the structure is excited at specific modes via sine dwell excitation with an electrodynamic shaker. The experiments were designed to measure loss of preload as a function of excitation duration and strength. A finite element model incorporating a fully-threaded joint is developed in parallel to investigate the effectiveness of each at measuring and predicting bolt loosening.

A reduced order modeling capability has been developed to reduce the computational burden associated with time-domain solutions of structural dynamic models with linear viscoelastic materials. The discretized equations-of-motion produce convolution integrals resulting in a linear system with nonviscous damping forces. The challenge associated with the reduction of nonviscously damped, linear systems is the selection and computation of the appropriate modal basis to perform modal projection. The system produces a nonlinear eigenvalue problem that is challenging to solve and requires use of specialized algorithms not readily available in commercial finite element packages. This SAND report summarizes the LDRD discoveries of a reduction scheme developed for monolithic finite element models and provides preliminary investigations to extensions of the method using component mode synthesis. In addition, this report provides a background overview of structural dynamic modeling of structures with linear viscoelastic materials, and provides an overview of a new code capability in Sierra Structural Dynamics to output the system level matrices computed on multiple processors.

Abstract not provided.

Abstract not provided.