Experimental Investigations of an Inclined Lap-Type Bolted Joint

Abstract

The dynamic response of critical aerospace components is often strongly dependent upon the dynamic behavior of bolted connections that attach the component to the surrounding structure. These bolted connections often provide the only structural load paths to the component. The bolted joint investigated in this report is an inclined lap-type joint with the interface inclined with respect to the line of action of the force acting on the joint. The accurate analytical modeling of these bolted connections is critical to the prediction of the response of the component to normal and high-level shock environmental loadings. In particular, it is necessary to understand and correctly model the energy dissipation (damping) of the bolted joint that is a nonlinear function of the forces acting on the joint. Experiments were designed and performed to isolate the dynamics of a single bolted connection of the component. Steady state sinusoidal and transient experiments were used to derive energy dissipation curves as a function of input force. Multiple assemblies of the bolted connection were also observed to evaluate the variability of the energy dissipation of the connection. These experiments provide insight into the complex behavior of this bolted joint to assist in the postulation and development of reduced order joint models to capture the important physics of the joint including stiffness and damping. The experiments are described and results presented that provide a basis for candidate joint model calibration and comparison.4

Handbook on dynamics of jointed structures.

“…A similar load history effect has been observed in the past on single-leg joint experiments in an SDOF experiment under steady state, sinusoidal loading [47,49]. During those experiments, the equivalent damping ratio also decreased in an asymptotic fashion with increasing vibration cycles.…”

“…Plotting energy dissipation per cycle as a function of the force across the joint on a log-log plot ( Figure 5.98) shows curve slopes between 2.3 and 2.5 indicating a nonlinear damping mechanism consistent with the results by Gregory and Resor [49]. While the procedures described herein are complex, it does eliminate distortions caused by temporal filters and uncertainty associated with wavelet transforms.…”

“…Any loads applied to the exterior of the system must be transferred across this bolted interface to excite the LOS. Based upon previous research done at Sandia/NM [49], it was conjectured that the primary energy dissipation mechanism would be slippage in the joint -both microslip and macroslip. Consequently, the experimental test bed was developed to facilitate the sliding of the facing surfaces past one another, exciting the mechanism of interest.…”

“…At first, ana-lytical models were simulations of very basic, jointed interfaces. Soon after began the application of the techniques to very specific hardware configurations, such as System A-0 and System A-1 Axially Oriented Subsystem (AOS) bolted joints [49]. The need for more experimental data to support various levels of model validation efforts also led to the development of additional experimental configurations.…”

“…Two separate experimental studies analyze these joints. The first [49] presents scoping experiments for evaluating the joint with the BMD and the sinusoidal techniques developed in the previous sections. These experiments establish the experimental approach for the second project, which is the first step (calibration) in an integrated model calibration and validation demonstration for a whole-joint model (Chapter 12) for System A, AOS bolted joint.…”