Simulating scatter in fragmentation of metal rings and tubes

Understanding the break up of a metal component under high strain rate deformation by natural fragmentation is important in a range of industrial and military applications. In this work, natural fragmentation of metal rings and tubes has been simulated in a finite element model by assigning initial damage sampled from an empirical damage function. Different random sampling of this function leads to differences in behaviour, enabling both the average and scatter in fragmentation to be predicted. Once calibrated for one condition, the model provides a good prediction of the mean and scatter in the number of fragments from ring expansion experiments reported in the literature. The model has been extended to consider damage in aligned bands, replicating the spatially correlated defects expected from manufacturing processes such as extrusion or additive manufacture. Fragment formation is strongly affected by damage bands, which can lead to a much greater maximum fragment size and more consistent behaviour. However, not all high damage bands will lead to fracture, and a simple criterion for assessing this is presented.