Fracture toughness estimation by means of indentation test

Abstract

This paper presents the results of ball indentation tests carried out on specimens of pipeline steels. The load-ings of a spherical (D=5 mm) indenter in the range from 147 to 11875 N within absolute temperature range 77-293 K were applied. Then the indentation energy Uf, corre-sponding to condition HM =σf, where HM and σf are the Meyer’s hardness and the material’s critical cleavage frac-ture stress, was calculated. This energy Uf, is known as IEF (indentation energy to fracture). The comparison of frac-ture toughness KIc, and Uf values reveals linear relation-ships KIc(Uf) for all steels in all the investigated tempera-ture range. Angle coefficient φ, in these relationships de-pends on fracture stress in tension Sk, for every steel. For the purposes of non-destructive Sk estimation, the relation-ship between Sk and Misses stress σi, in the center of im-pression at the temperature 77 K was established. At last KIc values can be calculated from the single unified equa-tion for all investigated steels. Thus, the method of indirect fracture toughness KIc, estimation for pipeline and pressure vessel steels, based on the IEF (Indentation Energy to Fracture) model, is developed and discussed.