Coalescence of Two Coplanar Internal Penny-Shaped Cracks in Brittle Solid under Uniaxial Tension Based on 3D-ILC

Crack coalescence is an important topic in the research of brittle fracture mechanics. Most of the previous studies have focused on surface or penetrating cracks, while few experimental studies have been performed on internal cracks coalescence. This study fills in the missing data. First, the 3D internal laser-engraved crack (3D-ILC) method was introduced to make internal cracks in glass without causing any damage to the surfaces of the glass. Next, uniaxial tensile tests were performed on the samples with two coplanar internal penny-shaped cracks. A new grid reconstruction algorithm is also proposed to simulate the coalescence and the growth path of two coplanar internal cracks. The crack coalescence process and fracture characteristics were analyzed in detail. The results indicate that the fracture in the test is static fracture, while the fracture is Mode I, based on the characteristics of the fracture morphology. In addition, the Wallner lines were observed after the coalescence of cracks, which were overall elliptical in shape. Before coalescence, the stress intensity factor I (KI) at the center was higher than that at the outside, indicating the attraction of the twin cracks. Then, after coalescence, the KI increased significantly at that coalescence site, which indicated that the new crack had rapidly become “elliptical” in shape following the coalescence. The normalized KII/|KImax| and KIII/|KImax| of the coplanar cracks were approximately equal to 0 in the simulation, and it was confirmed that the fracture in the test was Mode I.