AN EXPERIMENTAL INVESTIGATION OF DYNAMIC CRACK-PROPAGATION

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(1) 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 v/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.