Determination of critical length and width of cracks in elements of structure by methods of destruction mechanics

Abstract

Prolonged operation of machines and structures often leads to a significant reduction in their load-bearing capacity. This is due to the appearance in the cross and longitudinal sections for various reasons of a large number of small cracks that can turn into trunk cracks. This can lead to the destruction of the structure itself.

Various methods are used to determine the ultimate state of metal or reinforced concrete structures that may be subjected to loads that cause eccentric tensile or compressive deformation and the associated formation of cracks. Such loads are especially dangerous and require more detailed calculations by methods of fracture mechanics. Different strength theories for brittle materials or fracture mechanics criteria can be used for such studies. The most common are the force criterion of J. Irwin, the deformation criterion of local destruction of M. Leonov, V. Panasyuk and D. Dagdale.

An important problem today is the assessment of the residual strength of structures damaged by defects such as cracks. An overview of the achievements on this problem can be found in the works of many famous scientists.

There are a large number of developed analytical and numerical methods for solving problems of crack theory, the solutions of which can investigate the crack resistance of materials and structures under different load conditions.

Criteria for linear fracture mechanics do not take into account a number of factors, ranging from the shape of the crack and ending with the history of formation of the material itself, its physical and mechanical characteristics and properties. For materials such as concrete and cast iron, it is necessary to use the criteria of nonlinear fracture mechanics, which take into account the nonlinearity of deformation and the heterogeneity of the material itself.

It is investigated that the accuracy of calculations of concrete and cast iron elements by methods of fracture mechanics depends on the knowledge of the real characteristics of crack resistance, obtained on the basis of modern methods.