Issue 39

J. Klon et alii, Frattura ed Integrità Strutturale, 39 (2017) 17-28; DOI: 10.3221/IGF-ESIS.39.03 17 Focussed on Modelling in Mechanics Modelling of size and shape of damage zone in quasi-brittle notched specimens – analytical approach based on fracture-mechanical evaluation of loading curves J. Klon, V. Veselý Brno University of Technology, Faculty of Civil Engineering, Institute of Structural Mechanics, Veveří 331/95, 602 00 Brno, Czech Republic klon.j@fce.vutbr.cz vesely.v1@fce.vutbr.cz, http: /orcid.org/0000-0002-7723-971X A BSTRACT . An analysis focused on capturing the phenomenon of quasi- brittle fracture is presented. Selected parameters relevant for quasi-brittle fracture are evaluated and an assessment of their dependence on the size and shape of the test specimen is studied. Determination of these fracture characteristics is based on the records of the fracture tests on notched specimens, particularly from recorded loading diagrams. A method of separation of the energy amounts released for the propagation of the (effective) crack and that dissipated within the volume of a large nonlinear zone at the crack tip – the fracture process zone – is introduced and tested on selected data from experimental campaigns published in the literature. The work is accompanied with own conducted numerical simulations using commercial finite element code with implemented cohesive crack model. Results from three-point bending tests on specimens of different sizes and relative notch lengths are taken into account in this study. The proposed model has only two parameters whose values are constant for all specimen sizes and notch lengths. K EYWORDS . Quasi-brittle Fracture; Loading Curve; Work of Fracture; Resistance Curve; Effective Crack; Fracture Process Zone. Citation: Klon, J., Veselý, V., Modelling of size and shape of damage zone in quasi-brittle notched specimens – analytical approach based on fracture-mechanical evaluation of loading curves, Frattura ed Integrità Strutturale, 39 (2017) 17-28. Received: 20.07.2016 Accepted: 21.09.2016 Published: 01.01.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION racture properties of quasi-brittle materials, corresponding to commonly used fracture models relevant to this type of fracture behaviour, appear to be dependent on the test specimen size, shape and boundary conditions. This fact has been well recognized in the last five or six decades (summarized in e.g. [1–4]). The reason for that is in the existence of a large zone of nonlinearly behaving material around the tip of the propagating crack. The major part of this zone is referred to as the fracture process zone (FPZ), in which mechanisms of material toughening take a place. These F