Wool fibre microdamage caused by opening processes. part III: In-situ Studies on the Tensile Failure of Damage-induced Fibres

An opening process can damage fibres in various ways and to different extents, from subtle microdamage to catastrophic fibre failure. Fibres with microdamage inflicted by one opening process may be subsequently extended to break in the same or subsequent processes or during the end-use of the fibrous products. This paper reveals how microdamage leads to failure upon further stretching of the fibre. With the help of a purpose-built ‘damage initiator’, Lincoln-wool fibres were inflicted with microdamage by a sawtooth wire, a needle pin, and a sharp blade. A dynamic tensile stage was then used to stretch the damaged fibre inside a scanning electron microscope (SEM), so that the instances of microdamage could be observed in situ as they developed. The observations showed that microdamage induced on the fibre surfaces could develop and manifest itself in various forms before leading to catastrophic fibre failure. For comparison, undamaged wool fibres were also examined similarly. The likely mechanisms of the tensile failure of damage-induced fibres are suggested, and a ‘volcano effect’ is reported as one of the remarkable features of microdamage.