The fracture process of ultra-high strength polyethylene fibres

The fracture behaviour of ultra-high strength polyethylene fibres has been investigated in dead load tests as well as by electron microscopical observation of the fracture surfaces. It was found that the fracture process in the fibres involves an activation energy of about 60 to 75 kJ mol−1, which implies that the strength is mainly determined by the lateral bond strength between the molecules. Fracture is initiated at surface irregularities, such as kink bands, which leads to the formation of cracks with a fibrillated fracture surface. In this process the individual fibrils are cut through at topological defect regions in such fibrils, containing a relatively high concentration of trapped entanglements and chain ends. The ultimate strength of the polyethylene fibres was found to be inversely proportional to the square root of its diameter. Extrapolation to zero diameter yields a strength of 26 GPa for flawless fibres, which equals the theoretical strength of polyethylene.