Use of notched small punch test specimens for the determination of fracture properties in structural steels

•The SPT has been used to determine the fracture toughness parameters.•Longitudinally notched SPT samples of four different steels have been used.•Standard CTOD results were compared with the obtained from the SPT specimens.•The region where the cracks began was determined using SEM and a numerical model. Various attempts have been made to determine the fracture toughness of metallic alloys by means of miniature tests, such as the small punch test, SPT. The use of notched SPT samples is the most convenient way to explore but as yet there is no consensus regarding the best methodology to apply. In this paper, longitudinally notched SPT samples of different steels were tested and the opening of the mouth of the notch was measured in the course of the tests, using interrupted tests to observe where the first crack appears in the most strained region of the notch region. Numerical analyses of the notch SPT tests were also performed in order to confirm the experimental results. Comparing Crack Tip Opening Displacement (CTOD) results obtained using standard fracture toughness specimens with those derived from notched small punch tests, a procedure to obtain the value of the critical CTOD, δIC, is proposed using the notch mouth opening value measured at the maximum punch displacement registered in the miniature test.