Modelling of size and shape of damage zone in quasi-brittle notched specimens – analytical approach based on fracture-mechanical evaluation of loading curves

Abstract

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.

Structural size effect: Experimental, theoretical and accurate computational assessment

“…The tests are described in reference [44] and were repeated in reference [52]. Other numerical simulations of the tests can be found in references [25,53,54,55,56]. To perform their computations, reference [25] used a phase-field model, references [53] and [54] considered nonlocal models, reference [55] employed a cohesive crack model and reference [56] compared the performance between a nonlocal model and the XFEM approach.…”

Pilot evaluation of a fracture process zone in a modified compact tension specimen by X-ray tomography

“…The pilot X-ray tomography obtained results will be numerically verified by using an advanced software tool, see e.g. [19][20][21]. T I Figure 8: Visualization of the Specimen XLA_0.4 inner structurearea of microcracks propagation highlighted.…”

Impact of specific fracture energy investigated in front of the crack tip of three-point bending specimen

“…This formula works with the area of a triangle defined by its corners in Cartesian coordinate system. In this case, triangles are formed by origin of coordinate system and two consecutive points of loading diagrams [15]. The last point corresponds to the relative crack length 0.7 (α = 0.7), see the schema in Fig.…”

“…The latter approach is the theoretical one -the value of the fracture energy is obtained from the basic formula G F(theor) = G f (a−a 0 ) B. Table 1: Nominal specimen dimensions tested in [14,15]; the estimated crack length (width of ligament) are shown in the right column.…”