Estimation of plane strain fracture toughness from circumferentially bluntly notched round-bar specimens

Abstract

A technique is presented which allows the use of small bluntly notched round-bar specimens without fatigue pre-cracking for the determination of the plane strain fracture toughness of metallic materials. The technique is based on fracture mechanics analysis and the principle of stress concentration factors at the tip of the notch. The error inherent in the fracture toughness calculations, i.e. due to the absence of a sharp crack, can be corrected by introducing a correction factor which is a function of the normalized notch-tip radius. The technique is applied to two metallic alloys for which the plane strain fracture toughness is estimated. Small round-bar specimens having V-notches with different tip-radii have been tested in tension. A comparison of the K IC values calculated using the present technique with those obtained from sharp notches using three standard equations show reasonable agreement between the two values. It is also observed that the standard equations for calculating fracture toughness may be directly used, without any correction, for specimens having a bluntness ratio less than 0.033. The present technique is a quick and economical method with a level of accuracy adequate for many practical design purposes.