Carbon fibres with modulated properties and shape along the fibre length

The ability to introduce weak regions into carbon fibres at predetermined points should allow failure to occur in a controlled manner, and potentially mitigate the storing of elastic energy leading to sudden catastrophic failure associated with current high performance polymer matrix composites. Here we introduced damage - at the single carbon fibre level - to unsized fibres using a nanosecond pulsed laser source. Various laser treatment parameters were employed to create predefined weak/break points as well as local shape (fibre swelling) modification at the treatment site. The shape and morphology of all individual fibres tested was assessed before and after single fibre tensile tests using SEM to correlate the mechanical properties to fibre shape modification. The laser treatment resulted in swollen fibre regions at the treatment site. In some cases swollen fibres were observed to have a neck region in the centre of the affected region, probably due to simultaneous laser ablation. The tensile mechanical properties of the treated fibres were reduced significantly in comparison to the control fibres; with reductions in strength, strain and modulus of 62%, 55% and 17%, respectively. We demonstrate that the fibre failure occurred in the laser treated region producing two fibre ends with outwardly tapered ends.