Published: Jan 1995
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Hydrotests, causing generally elastic failures of common pressurized-gas cylinders about 180–235 mm diameter, have permitted estimates of dynamic rip-resistance in heat-treated, low-alloy steels about 5–7 mm thick. Failures initiated from localized plastic instability of ligaments produced by narrow, axial, exterior-grooving of the cylinder walls. Depressurization proceeded at sonic speed from this origin, effectively unloading pressure behind the wave front, creating a modified rip-driving-force compared to that of gaseous pressurization at the same level. In these tests dynamic rip-arrest resulted since the full-thickness rip speed was slower than water's sonic speed.
Sometime after initiation, moderate bulging developed at most rips; bulges were pressed down and the rip welded shut. Different groove cuts and failures in each of several cylinders provided ranges of rip-arrest, the key to estimating quantitative results for three cylinders.
Methods for analytical modification of the effective hoop stress and the cylinder correction factor were not found, so a delta-process was devised for estimating the rip-driving-force variation. Variables were adjusted and computations iterated to find common solutions for rip-resistance and rip-speed behavior for the several different rips.
Closed tubes of similar material and dimensions could become ‘standard’ specimens for estimating dynamic rip resistance, without resort to instrumented measurements; a likely novel approach.
hydrotest, gas cylinder, dynamic fracture, low-alloy steel
Professional Engineer, WA and OR, aka William E.(Bill) Anderson, Eugene, OR