Rate effects on the estimation of fracture toughness by small punch tests in hydrogen embrittlement

In this article, different techniques to test notched small punch test samples in fracture conditions in aggressive environments are studied, based on the comparison of the micromechanisms at different rates. Pre-embrittled samples subsequently tested in air at rates conventionally employed (0.01 and 0.002 mm/s) are compared to embrittled ones tested in environment at the same rates (0.01 and 0.002 mm/s) and at a very slow rate (5E–5 mm/s). A set of samples tested in environment under a set of constant loads that produce very slow rates completes the experimental results. As a conclusion, it is recommended to test small punch test notched specimens in environment at very slow rates, of around E–6 mm/s, when characterizing in hydrogen embrittlement scenarios, in order to allow the material–environment interaction to govern the process.