pre-fracture zone, adhesive forces of a material, bonds between crack faces, crack formation, perforated strengthened slab, stringers

The mathematical description of crack formation model in a perforated isotropic medium intensified by cross-section stringers is carried out. The stringers action is simulated by the unknown equivalent concentrated forces in points of their edge junction with the medium. It is considered, that crack formation occurs in the process of increase of external load intensity in the medium. The task about equilibrium at the isotropic perforated medium with arisen cracks comes to the solution of non-linear singular integral equation with kernel of Cauchy type. We finde stress in the crack formation zone by solving the equation. The crack formation condition is formulated with taking into account the limit stretching of material relations criterion