The effects of axial length on the fracture and fragmentation of expanding rings

Rings of Ti-6Al-4V with aspect ratios (wall thickness:axial length) of 1 : 1, 1 : 2 and 1 : 4 have been expanded to failure at radial strain rates εr ～ 1 × 104 s 1 using 4340 (EN24T) steel and Cu-ETP cylindrical drivers containing a column of RDX. Expansion velocity was measured using VISAR enabling calculation of the stress-strain history of the ring alongside fragment recovery with up to 98% original ring mass recovered. Using the recovered samples average fragment length and mass and final strain have been measured along with analysis of the fracture sites to determine the active failure mechanisms. Perfect rings (aspect ratio 1 : 1) were found to undergo necking before failure, whereas the longer rings failed though ductile tensile cracking at 45° to the radius. This data is then compared with finite element analysis results.