Structural integrity assessments regarding Fatigue Crack Growth (FCG) and fracture phenomena are based on fracture mechanics theoretical background and rely upon the notion that a single parameter (usually K or J, respectively for linear elastic and elastic-plastic fracture mechanics) characterizes the crack-tip stress fields and controls local damage. However, the validity of K/J as crack-tip driving forces representative of local stress fields is only achieved if SSY (Small Scale Yielding) conditions prevail. It means that plasticity ahead of the crack must be small. Current standards (e.g.: ASTM E399, E1820, E647, ISO 12135) impose severe geometrical restrictions for the specimens (minimum thicknesses and crack depths) looking for plane strain (high constraint) conditions and therefore K and J-dominance. The main challenge is that thicknesses and/or planar dimensions of current real structures made of high toughness structural steels are in several cases not enough for the extraction of “valid” C(T), SE(B) or SE(T) specimens. In this context, subsized specimens are of great interest. As an example, Charpy geometries have been investigated during the last decades. This work is concerned about testing high structural steels and investigates the applicability of fatigue-precracked Charpy specimens for determining FCG (da/dN vs. ΔK) and J-R curves. The main issues are: i) verify the feasibility of the experiments in a servohydraulic machine in terms of scatter, control and repeatability; ii) quantify the validity limits of K and J for such reduced geometries. Samples had notches machined by EDM and were precracked reaching a/W=0.25 and a/W=0.45. FCG and J-R tests were successfully conducted with repeatability and refined 3D non-linear FE models were developed to provide compliance solutions and verify K and J dominance. Consequently, mechanical properties from subsized samples could be obtained and compared to data obtained from standardized C(T) specimens made of the same steel. The applicability of precracked Charpy geometry could be investigated, motivating further investigations in the field.

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