Abstract
Technological defects such as cracks can exist in the elements of metal structures, or cracks can appear during operation. Calculation of crack resistance, supplementing usual calculation of strength, is designed to protect such a structure from premature failure due to the unstable development of the crack. The crack resistance parameter can vary both due to increasing stress and due to increasing the length of the crack. These two factors are interrelated, therefore, usual strength calculation does not give a real estimate of strength, an actual safety factor is lower than that in usual calculation. Therefore, it is proposed alongside with the safety factor for strength to introduce a safety factor for the crack length. In the work, in general form there were obtained relations for reasonable selection of the safety factor for the crack length. For frequently used fracture criteria, dependences were derived for selecting the safety factor for the crack length. The dependences are also given for determining the breaking stress corresponding to the existing crack and the critical length of the crack under existing stresses for various fracture criteria. Based on the results obtained, there was obtained a method of analyzing strength of structural elements with cracks, which allowed determining the permissible crack length and the actual safety factor of structures. The results are of great importance with viscous and mixed fracture, where the criteria of nonlinear fracture mechanics are used.