Cracks in a component lead to a strong elevation of the stress near the crack front. Theoretically, this according to the concept of linear elastic fracture mechanics [LEFM] (English: linear elastic fracture mechanics) at the crack tip even infinite. This would, however, according to the rules of classical strength of materials that would cause even the smallest cracks in a failure of the complete component. For this reason, a different size loads, the stress intensity factor is introduced. This is then compared with material values​​, as compared, say, the fracture toughness in order to make a statement can, whether it comes at a fraction of the component, the crack grows or there is a crack arrest.