An experimental investigation of dynamic crack propagation

TLDR: In this paper, the authors performed burst tests on closed-ended thin wall tubes with axially aligned, external, semicircular, crack-like flaws and found that the crack surfaces exhibited a smooth mirror-like appearance near the crack initiation site, followed by a mist region and then a hackle region.

Abstract: Burst tests have been performed on closed-ended thin wall tubes with axially aligned, external, semicircular, crack-like flaws. The tubes were made of Araldite CT200 with HT907 hardener. Dynamic crack propagation rates between 0.14c 1 and 0.30c 1 were measured, c l being the velocity of longitudinal waves in the walls of the tubes. The fracture surfaces exhibited a smooth mirror-like appearance near the crack initiation site. This was followed by a mist region and then a hackle region. The roughness in the hackle region becomes progressively greater with distance from the initiation site and crack branching can eventually occur. The K ID /K IC (where K ID is the applied dynamic stress intensity factor and K IC is the plane strain fracture toughness) value at which the hackle region begins is about 3.34 and the K ID /K IC value at which branching begins is about 8.75. Previously reported work only contains results for K ID /K IC up to about 5. The present work contains results for K ID /K IC up to about 14, which correlate with previous work for K ID /K IC values less than about 4. However, previous work has indicated that a unique relationship may exist between υ/c 1 and K ID /K IC . The present work indicates that although this is a good approximation, a systematic variation with load (pressure in this case) has been detected.