Fracture mechanics. Application to pressure vessels

Fracture Mechanics introduces in the mechanics of solids surfaces along which displacements are discontinuous, or cracks, which result in singular solutions. The conditions for fast fracture, or crack instability, is expressed by writing that the strain energy released by a virtual extension of the crack is at least equal to the energy necessary to that extension. If calculations are limited to the first term, singular, of the stress field near the crack tip, the instability condition is written in terms of a unique parameter, the stress intensity factor, which depends on the load and geometry data. The conditions of validity of this theory are examined, with the introduction of a plastic strain zone near the crack tip, and the practical possibilities of fracture prediction. A particular application to pressure vessels is given, in plane strain for heavy walls, in plane stress for thin vessels