Criteria of Crack Resistance of Nonlinear Fracture Mechanics of Structural Elements

Abstract

The practice of operating critical structures under extreme conditions shows that their bearing elements are destroyed as a result of the formation and gradual development of main cracks. Such failure occurs at nominal stresses below the yield strength of the material, and therefore can not be fully estimated only on the basis of classical strength theories. In this regard, to assess the crack resistance of materials and structural elements, a number of criteria are proposed: power (the stress intensity factor of G. Irwin, the cohesion coefficient of G. I. Berenblatt); deformation (the size of the plastic region on the extension of crack of G. Neuber, the opening of the shores of the fracture by M. Ya. Leonov and V. V. Panasyuk, D. Dugdale), which are obtained under the assumption of linear deformation mechanics. The energy criteria (the energy density of the tension of the shores of the A. Griffith crack, the integrals of G. P. Cherepanov and J. Rice, independent of the contour of elastoplastic deformation) are difficult to realize, and therefore have not received wide practical use. In this connection, as a result of the development of solutions previously obtained by the author for calculating local stresses, elastoplastic deformations and specific energies near the crack tip, energy (energy-form-factor) and strength (deviator stress intensity factors) criteria for fracture of nonlinear deformation mechanics for cracks of normal detachment and asymmetric shear. Under the assumption of local elastic deformation, the results of the work are consistent with the above energy criteria. A new physically grounded result was obtained with local elastoplastic deformation. The validity of the proposed criteria is confirmed by the use of the most experimentally grounded physical strength criterion - the specific energy of the change in shape, taking into account the material's plasticity and the energy state at the extreme plastic deformation. The results of this work are used for an experimental evaluation of the fracture toughness of a shaft during bending with rotation.