FRACTURE BEHAVIOUR OF AXISYMMETRIC BARS UNDER HIGH TRIAXIAL STRESS AND LARGE STRAIN CYCLIC LOADING

Axisymmetric notched bars with notch roots of large and small radius were tested under large strain cyclic loading. The main attention is focused on the fracture behaviour of steels having cycles to failure within the range 1-100. Our study shows that a gradual transition from a static ductile nature to one of fatigue cleavage can be observed and characterized by the Coffin-Manson formula in a generalized form. Both the triaxial tensile stress within the central region of specimens and static damage caused by the first increasing load have effects on the final failure event. A generalized cyclic strain range parameter δε is proposed as a measure of the numerous factors affecting behaviour. Fractographs are presented to illustrate the behaviour reported in the paper.