Wire recovery length in a helical strand under axial-fatigue loading
Int J Fatigue, (1991)Abstract
An analytical model is presented for determining the recovery length of a fractured
wire in a multilayered helical strand experiencing axial-fatigue loading-the recovery
length being the length, measured from the fractured end of the wire, in which the
wire will be able to carry its appropriate share of the load.
The theory employs the interwire contact force data as obtained from previously
reported orthotropic sheet theory. Unlike previous studies, the model is capable of
following the no-slip to full-slip interwire slippage along the recovery length. Even for
full interwire frictional slippage, the theory suggests that the recovery length is a
function of the mean axial load experienced by the cable, which is contrary to previous
theoretical results.
Limited parametric studies on a series of cable constructions with widely different
cable (and wire) diameters and lay angles suggest that the recovery length is a function
of the cable construction. Nevertheless, a recovery length to cable pitch ratio of two
·is suggested as a reasonable conservative estimate irrespective of the type of strand
construction. ,
The model also considers the effect of external hydrostatic pressure on the recovery
length of sheathed helical strands in deep-water applications. It is shown that (within
operational limits) 'the recovery length decreases with increasing levels of external
pressure.
The present results may have significant implications in the context of formulating
realistic discard criteria for cables undergoing long-term axial-fatigue loading.
