Propagation of double internal cracks under uniaxial tension based on 3D-ILC

The multiple-crack interaction is an important research topic in fracture mechanics, but few studies have focused on the interaction of 3D internal cracks under uniaxial tension. 3D double internal cracks are generated based on 3D-ILC. Uniaxial tensile tests are performed on the specimens with different vertical spacings (d). The fracture process, stress moire, crack initiation, failure load and fractography are analyzed. Then the numerical simulation is carried out. The results show that: (1) The the two cracks attract eath other when d is 2 mm, while they first attract then repulse each other when d is 6 or 10 mm. (2) The fracture morphologies such as “intersection boundary” and “funnel” are observed. I-II mixed-mode fracture occurs inside the crack, and mode I fracture occurs at the outer side. (3) Through the stress moire, the petal-shaped stripe can be observed at the crack tips, and the parentheses-shaped stripe appears during the process of attraction. (4) The strength of the specimens is proportional to d. Compared with that of the intact samples, the tensile strength decreases by 63.39%, 50.79% and 41.09%, respectively. (5) The distributions of mode I and II stress intensity factors are obtained based on M-integral, and the crack propagation is simulated according to MTS, which is consistent with the tests. The results may provide experimental support for the corresponding theoretical researches.