University of Tabriz
The fracture and crack growth of mechanical structures is a usual phenomenon which is due to the application of tensile, cyclic loading or thermal stresses on the structure. So introducing of methods to prevent the crack growth is useful. Afterward, one of the repairing methods of crack growth, consisting to make a hole in the crack tip to elimi-nate the sharp corners, was explained. This method is frequently used in air and space industry. The drilling can be done in various locations. Three locations in the crack tip for the hole were considered. In the first, the hole was situated in the left of the crack tip (Location A). In the second one, it sited in the center of the crack tip (Location B) and in the last one; it sited in the right site of the crack tip (Location C). The study of resistance against crack growth was based on the comparison of these three systems. We have analyzed the influence of theses stopping holes, their diameters and their lo-cations on the fracture toughness. The specimens were made of Al 7075-T6 alloy and they had the shape of the Compact Tension specimen. The solicitation was a mono-tonic tensile loading in the Mode I of fracture. The stress intensity factor and the criti-cal load versus to the crack length of the test bars were computed. Numerical method was carried out by finite element method using Ansys software. Following this nu-merical analysis, fracture experimentation was carried out on the tensile machine to evaluate the influence of the stopping hole on the critical load of initiation of the crack growth. In result the best location of the hole increased 54% the critical load and the location which gived the weakest result showed 11% of increasing of the load. Thus in result of this research the best location of the stopping hole and its diameter were ob-tained to increase the life of the mechanical pieces.