Fracture of V-notched beams made of H13 steel under small scale yielding

We present the results of an experimental campaign for measuring fracture loads and plastic areas in H13 steel specimens containing V-notches under quasi-static loading conditions. A series of specimens with three V-notch opening angles (30°, 60°, 90°) and three different thermal treatments (quenched, quenched and tempered at 550°C, and quenched and tempered at 650°C) were subjected to four-point bending experiments. Elasto-plastic material parameters and fracture toughness were determined by standard experimental procedures. Repetition of the experiments showed a very small deviation between measurements, increasing our confidence in the experimental results. Digital image correlation (DIC) techniques were employed to capture full-field strain distributions used to validate the finite element methods and examine whether simplified FE models can reliably estimate the small scale plastic areas at the V-notch tips. Our primary objective was to investigate the influence of notch geometry and material properties on the fracture load and its relationship with the plastic area. The secondary objective was to generate a validation set for theoretical models aimed at predicting the fracture load. The experimental results indicate: • The finite fracture mechanics coupled criterion (FFMCC) predicted fracture load largely underestimated the experimental observations for metallic alloys with high K I c and a small scale yielding. • A pronounced dependence of the fracture load on the V-notch opening angle was observed, similar to past observations on AISI 4340 specimens (Yosibash et al. 2022). • Linear elastic FEA may well approximate the small plastic area evolving at the V-notch tip (small scale yielding) when compared to experimental observations for relatively sharp V-notch tips (V-notch radius of the order of 30– 40 μ m ). The documented data will be used in a future investigation to extend the FFMCC to V-notched structures made of metallic alloys, commonly used in industrial applications. • An experimental 4PB database on V-notched H13 specimens with 30°, 60°, 90° opening angles is detailed. • It is used to investigate to which extent brittle-FFMCC can predict failure load in steel structures. • The FFMCC under-predicts the fracture load by ∼ 50%. • The extension of the FFMCC to steel structures is suggested.