SIMULATION OF DELAMINATION OF STEEL PIPES UNDER COMPLEX LOADING

The formation of a mixed-type (fracture modes I and II) internal crack in a pipe wall that is made of an ideal elastoplastic material under the action of combined tensile (compression) and bending loads is described. The fracture of such materials is illustrated using a modified Leonov–Panasyuk–Dugdale model, which additionally uses the parameter of fracture process zone diameter. Another case under consideration is complex loading during which the crack path becomes curved, so its bend angle is determined using a force integral criterion based on the stress field asymptotics in the vicinity of the crack tip. Critical fracture parameters are obtained using a two-parameter (dual) strength criterion in the case of a complex stress state. The parameters included in the resulting analytical model are analyzed. The dimensionless geometric parameters of the structure are obtained numerically using the finite element method. Quasibrittle fracture diagrams are constructed.