PSI - Issue 30

S.V. Suknev et al. / Procedia Structural Integrity 30 (2020) 179–185 S.V. Suknev / Structural Integrity Procedia 00 (2020) 000–000

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Fig. 4. Dimensionless critical stress versus the loading biaxiality ratio.

Figure 4 shows experimental data (dots) on the critical stress at the instance of the initiation of tensile cracks at the hole as a function on the biaxiality ratio and the results of calculating the critical stress using Eq. (2). The calculations are carried out using 0 d and  , determined in the first series of tests. The dashed curve is calculated according to the traditional approach for 1   . It is indicated by the results obtained that the modified nonlocal criterion properly describes the effect of both the hole size and the boundary conditions on the fracture of quasi-brittle material. 5. Conclusions The field of application of the prevalent nonlocal fracture criteria based on the theory of critical distances, whose distinguishing feature is the introduction of an additional material length scale parameter that characterizes the material microstructure, is limited to brittle or quasi-brittle fracture with a small prefracture zone. It is proposed to extend the scope of the criteria to quasi-brittle fracture with a developed prefracture zone which size is not a material constant related only to its microstructure, and depends also on the plastic properties of the material, the geometry of the specimen, and boundary conditions. The proposed approach was used in the development of modified average stress criterion. An extensive set of experimental studies related to the processes of deformation and fracture of quasi-brittle geomaterial with a circular hole under non-uniformly distributed compression has been carried out, and the criterion developed has been verified. Based on these studies, the patterns of the formation of tensile cracks at the hole are established, and there is good agreement between the calculation of the critical load at the instance of fracture initiation according to modified average stress criterion and the experimental data obtained. Acknowledgements The research was supported by the Russian Foundation for Basic Research under grant number 18-05-00323. References Fuentes, J.D., Cicero, S., Procopio I., 2017. Some default values to estimate the critical distance and their effect on structural integrity assessments. Theoretical and Applied Fracture Mechanics 90, 204–212. Justo, J., Castro, J., Cicero, S., 2020. Notch effect and fracture load predictions of rock beams at different temperatures using the Theory of Critical Distances. International Journal of Rock Mechanics and Mining Sciences 125, 104161. Li, W., Susmel, L., Askes, H., Liao, F., Zhou, T., 2016. Assessing the integrity of steel structural components with stress raisers using the Theory of Critical Distances. Engineering Failure Analysis 70, 73–89.