Fracture Behaviors of Surface-Notched Plate Subjected to Tension or Plate Bending

Abstract

Tensile and bending tests have been carried out of surface-notched plates with particular reference to an applicability of fracture toughness parameters. Using the surface-notched specimens made from mild steels, observations are conducted of global and microscopic deformation of notched plate; in particular, crack opening displacement along notch front are paid attention. Fracture tests of specimens with a notch of which size is different have been also carried out under tension or bending.
In both tests, at first measurement procedure is settled of global strain which corresponds to global deformation. Fracture performance of surface-notched plates is affected by notch size; a considerable effect of notch depth under tention and notch length under bending on fracture strength can be observed. The distribution of COD along notch front is qualitatively consistent with it of stress intensity factor calculated by Newman et al. The point of crack front at which COD becomes maximum depends upon notch geometry and loading mode. In the specimens with deep notch under bending, in particular, that point is turned into the corner part of a surface notch.
In the specimens with part-through surface-notch, K_c-concept according to linear elastic fracture mechanics can be also applied for small scale yielding fracture. For general yielding fracture, δ_c-criterion according to the definition of the present paper can be effective.