Finite element simulation of mixed-mode I-II dynamic fracture of concrete based on an initial fracture toughness-based criterion

To study the mechanism of mixed-mode I -II dynamic fracture of concrete, a crack propagation analysis method that employs the initial fracture toughness as a parameter of crack extension is proposed. The method utilizes a field variable transference (FVT) technique to model the coupling action of the stress wave propagation and crack growth and cohesive elements to describe damage evolution. The applicability of the presented method is confirmed by modeling crack propagation in brittle semi-infinite plates under tensile stress wave loading and in three-point bending (TPB) concrete beams at loading rates varying from 2.2 x 10-6 m/s to 3.55 m/s. The theoretical and simulated dynamic stress intensity factors (DSIFs) coincide, and the simulated resistance, displacement, crack growth velocity, and failure pattern agree with the experimental results. Moreover, additional numerical experiments are performed to evaluate the influence of loading rates and the impact stiffness on the failure process of TPB concrete beams with different notch locations. The results reveal that the transition of the failure modes of notched TPB concrete beams, from a tension-shear mode at low loading rates to a flexural mode at high loading rates, is dominated by the increase of the structural inertia, and the kinetic energy absorbed by the notched TPB concrete beam decreases by reducing the impact stiffness.