Ductile Fracture Resistance Measurements in High Grade Steels

Recent developments in ductile fracture resistance measures in high grade steels in the pipeline industry include the crack tip opening angle (CTOA) and “steady state” fracture propagation energy, using 3-point bend specimens. The CTOA has been found to be a function of specimen ligament size. With the availability of instrumented hammers, it became possible to resolve propagation energy using the load-displacement curve using a single specimen. This paper focuses on refining the steady state fracture propagation energy, using back-slotted Drop Weight Tear Test (DWTT) specimens. The study included numerical simulation of the dynamic response of back-slotted specimens. The significance of the back-slot in altering the stress/strain field ahead of the propagation crack is discussed. The numerical simulation was also used to determine the strain rate in the “process zone” of the crack tip during steady state fracture propagation.