This work presents a novel characterisation method for determination of the strength and fracture toughness of high performance polymer fibres. Single fibres were extracted from the yarn, mounted onto aluminium stubs with a carbon tape and notched using the focus ion beam (FIB) milling technique. Different specimen configurations (single-edge notched (SEN), double-edge notched (DEN) and centre notched (CN)) were investigated. Tensile tests were performed using a micro stage positioned within the chamber of a scanning electron microscope (SEM) in order to observe the crack propagation and failure mode. Experimental results revealed a similar strength of notched single fibres with respect to the pristine one, however, with a reduction in the strain to failure. It was also noted that SEN liquid crystal polymer (LCP) and ultra high molecular weight polyethylene (UHMwPE) fibres failed in a different fashion, with shear planes developing at the crack tip for the former and crack propagation perpendicular to the fibre axis for the latter. The effect of different specimen configurations was examined in the determination of the fracture toughness of the fibres.
The finite element method was employed to replicate the investigated specimen configurations and test conditions. Numerical results showed good correlation with the experimental findings. Refined models will be able to correctly capture the different failure modes experimentally observed for different materials.