Numerical Analysis of the Influence of Stopping Holes in the Crack Growth

Fracture and crack growth of mechanical structures is a usual phenomenon caused by application of tensile, cyclic loading or thermal stresses on the structure. Therefore, introducing methods for preventing the crack growth is useful. One method for repairing crack growth, consisting of making a hole in the crack tip to eliminate the sharp corners is explained. This method is frequently used in air and space industry. Drilling can be done in various locations; however, for our study three locations in the crack tip for the hole are considered. In the first, the hole is situated in the left of the crack tip (Location A). In the second, it is sited in the center of the crack tip (Location B) and in the last it is located in the right side of the crack tip (Location C). The study of resistance against crack growth is based on the comparison of these three systems. We have analyzed the influence of these stopping holes, their diameters and their locations on the fracture toughness. The specimens were made of Al 7075-T6 alloy, and had the shape of the Compact Tension specimen. The solicitation was a monotonic tensile loading in the Mode I fracture. The stress intensity factor and the critical load versus the crack length of the test bars were computed. Numerical analysis was carried out with a finite element method using Ansys software. Following this numerical analysis, fracture experimentation was carried out on the tensile machine to evaluate the influence of the stopping hole on the critical load for initiation of the crack growth. Results show that the best location of the hole could increase the critical load by 54% and the location which gave the weakest result showed 11% of increase in the load. Thus, based on this research, the best location of the stopping hole and its diameter were found to increase the life span of mechanical pieces.