Effect of Fracture Speed on Ductile Fracture Resistance: Part 1—Experimental

The effect of fracture speed on the ductile fracture resistance of line-pipe steels can have an important effect in the basic understanding of the toughness requirements for crack arrest. Over the last few decades, it has become recognized that the drop-weight tear test (DWTT) better represents the ductile fracture resistance than the Charpy test since it utilizes a specimen that has the full thickness of the pipe and has a fracture path long enough to reach steady-state fracture resistance. However, the fracture speed in the DWTT is typically 50 to 60 feet per second (15.2 to 18.3 m/s), whereas the fracture speed in the full-scale pipe test is 300 to 1,000 fps (91.4 to 305 m/s). Recently, the authors have extended the DWTT work and developed a modified back-slot DWTT specimen to obtain higher fracture speeds. One aspect of this modified specimen was to increase the width of DWTT sample from the standard 3-inch (76.2 mm) to 5-inch (127 mm). This was done to increase the ligament length in a relatively deep back-slotted specimen to capture more steady-state data. The initial experimental results demonstrated that this type of specimen can be used to obtain higher fracture speeds. Furthermore, the experimental results clearly showed the effect of fracture speed on the ductile fracture resistance. In this paper, to extend the work on modified back-slot DWTT specimens, the tup was instrumented to measure the load during dynamic impact. From this, the load-displacement curve, steady-state energy (or energy per area) was obtained for the modified back-slot DWTT specimens. These results were compared to those obtained from the standard 3-inch specimens. These results also clearly showed the effect of fracture speed on fracture resistance.