Residual strength of stiffened panels with multiple site damage

On the basis of the boundary integral equations method the problem of residual strength definition of stiffened panels with multiple site damages is solved. Multiple site damages are characteristic of airplanes with large lifetime ("aging" airplanes). Multiple site damages are very dangerous, because the critical sizes of cracks in this case can be rather small, that makes their detection by nondestructive examination methods of monitoring rather difficult. In the present work on the basis of the boundary integral equations method the solution of problem of stress-strain state and residual strength of elements of aircraft structures is considered. The essence of the method consists in construction of general solution of problem as the sums of complex potentials, which base on Green function for anisotropic plate with elliptic hole. The substitution of obtained solution of problem in boundary conditions and reduction them to integral equations system allows to define stress-strain state of aircraft structures and stress intensity factors in crack tips. The effective algorithm of numerical solution of integral equations system is offered. The numerical results of stress intensity factors account in crack tips in stiffened panels are presented. The influence to panel residual strength of mutual disposition of main and secondary cracks, disposition of stiffeners, exit of crack on rivet hole is investigated. Defined load, under which occurs a merging of nearby cracks.