It is well known that, because of the variations
in fiber strength, the breaking stress of a parallel
fiber bundle deviates from that of its constituent
fibers. However, prediction of strength of a
twisted fiber structure is also different from that
of a parallel fiber bundle because, in the latter
case, the effect of fiber interaction is negligible,
and also as fibers are all parallel to the axis of the
assembly (the loading direction) in the parallel
bundle, the fiber obliquity effect is nonexistent.
Moreover, strength prediction of a fibrous structure
is unlike its modulus; the strength of a material
is not a volume-average quantity but rather
an extremum quantity, dictated by the weakest
cross-section of the structure. This so-called
weakest link theorem was first elucidated by
Peirce53 in 1926 and has since been thoroughly
discussed by numerous authors.
Daniels54 demonstrated that, if the fiberstrength
distribution is of Weibull55 form, the
asymptotic strength distribution of a parallel fiber
bundle when the bundle size N is large enough is
of normal type. This conclusion has been accepted
by the latter studies. Harlow and Phoenix56 proposed
the concept of the chain-of-bundles model of
the strength of fibrous structure to tackle the
issue of statistical nature of strength of individual
filament, the size (length) effect on filament
strength as well as the load-sharing mechanism
during structure breakage. Phoenix57 also extended
their method to the analysis of twisted
fiber bundles by incorporating the fiber helical
paths into his model. However, exclusion of the