Determination of fracture parameters in center cracked circular discs of concrete under diametral loading: A numerical analysis and experimental results

In this paper, a unified approach combining the interaction integral method with the extended finite element method is proposed to evaluate the mixed-mode stress intensity factors (SIFs) and T-stress for center cracked circular discs (CCCD) of concrete. In order to predict the crack initiation angles and fracture resistances, the generalized maximum tangential stress (GMTS) criterion is employed, which simultaneously involves the effects of the mixed-mode SIFs, the T-stress and a physical length scale rc (the size of the fracture process zone, FPZ). Moreover, a series of mixed-mode fracture experiments are conducted in the full range from pure mode I to pure mode II using the concrete CCCD specimens. The dimensionless SIFs and T-stress, calculated by the numerical method, are firstly compared with the available results in the literature to verify its accuracy and practicability. By incorporating the above dimensionless fracture parameters, a simple strength based hypothesis, the GMTS criterion and the mode I fracture resistance obtained by the diametral compression tests, the mixed-mode crack initiation angles and fracture resistances are predicted. Finally, the predicted results are compared with the experimental results. It is shown that both the fracture resistances and the crack initiation angles predicted by the GMTS criterion are more close to the experimental results than those predicted by the traditional maximum tangential stress (MTS) criterion.