Analysis of key factors for the interpretation of small punch test results

In recent years, great advances have been made in non-destructive or quasi-nondestructive test techniques for the determination of fracture toughness. One of the most interesting of these techniques is the one known as Small Punch, in which a punch acts on a small plane specimen, deforming it until fracture. From the continuous records of force and displacement of the punch taken during the test, it is possible to quantify the energy absorbed and then to determine the classic parameters of fracture mechanics such as ductile-to-brittle transition temperature or even the fracture toughness of the material. In this paper, fundamental aspects of the interpretation of the results of this kind of test have been studied. The effect of specimen thickness has been analysed. Moreover, a study has been carried out with the aim of clarifying the relation between the orientations in which it is possible to machine Small Punch specimens and the orientations of traditional specimens used in the determination of fracture toughness.