Analysis of Kinetics and Directions of Elastoplastic Deformation and Fracture

Abstract

Safety and survivability of equipment are regulated by the strength characteristics of its individual units and elements with possible initial or operational defects such as surface differently oriented semielliptical cracks. Numerical methods of calculation allow obtaining more information about the stress-strain state (SSS) of these elements using the specified calculation algorithms of the corresponding fracture models. A change in the SSS form near the crack contour during the transition from deeper points to surface points depends on the constraint of deformations along their front, i.e., on the 3D character of the SSS. The shape change of defects such as differently oriented surface semielliptical low-cycle cracks is diagnosed on the basis of the experimental results and numerical solutions. The finite element modeling data are implemented on the basis of macros of the ANSYS software package. In this paper, we study the development pattern of elastoplastic fracture under low-cycle loading. The proposed methodology is confirmed by the parametric equations of the shape change kinetics of the considered cracks using a fractographic surface analysis of their development. The surface morphological parameters of the developed defects are analyzed on the basis of the results of testing samples with semielliptical cracks under low-cycle loading. The results of measurements of the intensity fields of elastoplastic deformations at the crack tip and the geometric characteristics of the fracture surface development are presented. An analysis of the dynamics of the local stress-strain state near the contour of differently oriented defects in parts and structural units of equipment shows good agreement between the experimental parameters of the geometry of developing cracks and the parameters obtained by numerical methods. The presented parametric equations clarify the characteristics of nonlinear destruction mechanics that allow evaluating and predicting the survivability and safety performance of critical equipment. The deformation criteria of nonlinear destruction mechanics show the dependence of the fracture development on the 3D character of the stress-strain state that indicates the direction of the geometric development of the fracture surface shape.

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Funding

This work was supported by the Russian Foundation for Basic Research, project no. 18-08-00572-a.

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Correspondence to I. V. Makarenko.

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The authors declare that they have no conflicts of interest.

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Translated by A. Ivanov

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Makhutov, N.A., Makarenko, I.V. & Makarenko, L.V. Analysis of Kinetics and Directions of Elastoplastic Deformation and Fracture. Inorg Mater 56, 1506–1510 (2020). https://doi.org/10.1134/S002016852015011X

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Keywords:

  • surface inclined semielliptical cracks
  • elastoplastic deformations and stresses
  • low-cycle fracture
  • 3D character of the stress-strain state