Abstract
A method to estimate dynamic fracture toughness is proposed and demonstrated for a notched, carbon steel specimen. Fracture toughness is evaluated from the size of the near crack-tip plastic zone and the yield stress. The near crack-tip plastic zone is identified with Electronic Speckle-Pattern Interferometry (ESPI), and the yield stress is obtained from a uni-axial tensile experiment. Being capable of evaluating the plastic zone, this method allows us to use the Irwin's plastic correction, and thereby especially useful for estimation of dynamic fracture toughness. The experimental result has been verified at a low pulling rate via comparison with static fracture toughness evaluated by a conventional formula. The ESPI enables us to observe the temporal variation of the plastic zone, and thereby to reveal the internal crack growth and the type of fracture.
