A new test method for the complete load-displacement curve of concrete under mixed mode I-II fracture

A new test method for measuring the complete load-displacement curve of concrete under mixed mode I-II fracture is presented in this paper. Three-point bending beams with a multi-segment notch in the midspan were selected for this purpose. The ratio of the stress intensity factors at the notch tip between mode II and mode I, K-II/K-I, varied with the notch-depth ratio of the first segment and the inclination angle of the last segment. Compared with the available testing methods, it was less challenging to follow the proposed procedure to obtain the entire load vs. displacement curves for the K-II/K-I ratio up to 1.23. By introducing the finite element method, the entire crack propagation process was reproduced based on the crack propagation criterion for a mixed mode I-II crack in concrete. The predicted crack trajectories, the load vs. crack mouth opening/shear displacement curves, the initial cracking loads, and the peak loads were validated against the experimental results. The results agreed remarkably well.