Abstract
An analysis focused on capturing the phenomenon of quasibrittle 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.
Highlights
Fracture 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
A method of separation of the energy amounts released for the propagation of the 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 value of fracture energy determined by this method is strongly dependent on the specimen size and geometry [9,10,12] This phenomenon is caused by the change in the size and shape of the fracture process zone (FPZ) during crack propagation, from which the change of energy dissipated in this area results
Summary
Fracture 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. To identify the properties of FPZ, a combination of adaptation of linear elastic fracture mechanics (LEFM) (which is used to express the amount of energy released for creation of the new surface of an effective crack without considering the existence of FPZ) and cohesive-crack-based fracture models for concrete and other quasi-brittle materials [19,20] (which enable the modelling of the FPZ extent) was proposed This method models the FPZ in detail during the whole fracture process along the specimen ligament. TModelling of energy dissipation during quasi-brittle fracture process through the specimen ligament he nonlinear fracture is treated in this work via a division of the energy released for the fracture propagation into two parts This separation is performed on the level of processing of the recorded P–d diagram, where P is the applied load and d is the load-point displacement.
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