Influence of Mechanical Anisotropy on Micro-Voids and Ductile Fracture Onset and Evolution in High-Strength Low Alloyed Steels

Abstract

In this paper results of a wide and innovative mechanical assessment, that was performedon large diameter spiral line pipes for gas transportation, are reported. The anisotropic materialhardening has been characterized by tensile (smooth and notched specimens), torsion, andcompression tests. Tests were performed in the pipe of the pipe with specimens machined alongseveral orientations, taking into account the pipe through thickness direction. The influence ofdifferent triaxiality stress states on anisotropic behavior of the material have also been analyzed bymeans of tensile tests on notched specimens. After the experiments, the material was assessed bymeasuring the void distribution on the material as is, and on many deformed and fracturedspecimens, including tensile tests at different triaxiality, and torsion tests. The results showed that insuch a class of materials, the experimental void fraction is fully negligible and not related to theapplied plastic strain, even at the fracture proximity. As a consequence it can be concluded that, theplastic softening hypothesis may be dropped and damage due to void evolution hypothesis is notadequate.