Aspects of the stress and fatigue performance of threaded connectors.

Threaded connectors have been used in a variety of engineering structures for
hundreds of years. Although stress analysis of threaded connectors has been
performed since the early 1900's, there are still areas that are not fully understood.
The way in which eccentricity affects the fatigue performance and stress
distribution is one such area, and is the main area of research described in this
thesis.
The techniques of photoelasticity and fatigue testing were used to determine the
effect of eccentricity on the stresses and fatigue performance of bolts. The results
show that eccentric loading has a significant effect on the fatigue performance, but
that this effect can be quantified if the local stress amplitude is considered. The
photoelastic analysis results show the eccentricity slightly increases the stress
intensity factors at the crack tip.
A number of two-dimensional and three-dimensional finite element models were
created to detennine the salient characteristics of the models. The models were
validated against the resuh from the photoelastic analysis and the results agreed
well. Accurate results can be obtained from a two-dimensional model, but the
information obtained is limited unless many models are created. However, if a
three-dimensional model is created more information can be obtained, but the nut
thread run-out must be accurately modelled to obtain the correct stress
distribution.
The shape of cracks occurring in cyclically loaded steel bolts and the effect of
crack shape on the stress distribution was also investigated. The photoelastic
analysis of cracked bolts failed to predict the shapes of cracks occurring in
cyclically loaded bolts. It is suggested that the inability of photoelasticity to
model plasticity is the cause of this failure and this is supported by results from an
elastic-plastic finite element model.