STRAIN-ENERGY DENSITY APPROACH TO STABLE CRACK EXTENSION UNDER NET SECTION YIELDING OF AIRCRAFT FUSELAGE

In this paper, the incremental theory of plasticity is used in conjunc tion with the strain energy density criterion to determine the stress field in 4-in. wide test specimens containing 3 holes. These specimens , made from 0.04-in. thick sheets of 2024-T3 aluminum, also contained small collinear cracks emanating from the holes. The initial crack siz es varied from 0.15 to 0.26 in. Residual strength tests conducted with these specimens revealed that stable tearing occurred before failure. Analyses were performed to predict the stable crack extension and fai lure by plastic collapsed. Because of: the complexities involved with nonlinear stress analysis combined with subcritical crack extension, t he finite element method was used with the grid pattern adjusted for e ach increment of stable tearing. Reasonable correlation between the ex perimental data and predicted results was achieved.