Issue 41

H. Šimonová et alii, Frattura ed Integrità Strutturale, 41 (2017) 211-219; DOI: 10.3221/IGF-ESIS.41.29 215 N UMERICAL MODEL simplified model of the cracked specimen was created in ANSYS software to determine clearly the impact of the ITZ. Note that the configuration assumed is based on the three-point bending fracture test of a beam with central edge notch, see Fig. 3 (left). In the process of model creating the effects of the vertical position of inclusion, size of the aggregate and its circular shape were ignored. The crack was modelled by introduction of appropriate boundary conditions with its tip at the interface between MTX and ITZ, see the scheme in Fig. 3. Materials were modelled as linear, elastic and isotropic, which are represented by their elastic constants, i.e. Poisson's ratio  and Young's modulus E . Thickness of ITZ for both composites was considered as the mean value of distance of individual grains of aggregate obtained from SEM micrographs, see Fig. 2. Modulus of elasticity value of cement paste ( E MTX ) was taken from above mentioned results of fracture tests (see Tab. 2) and was statistically processed – the value of 5 % quantile ( E MTX, 0.05 ), mean value ( E MTX, mean ) and 95 % quantile ( E MTX, 0.95 ) were taken into consideration. This simplification was chosen because of absence of nanoindentation tests and because of the same ratio of components (aggregate:cement) in both composites. The last information means that the elasticity modulus value of E MTX is approximately k -multiple of elasticity modulus of the composite mentioned in Tab. 2. The elasticity modulus values of ITZ ( E ITZ ) were considered as 50 % values of E MTX according to the procedure called generalized self-consistent scheme [5]. The elasticity modulus value of aggregate (quartz sand) was taken from [19] as the mean value. The complex overview is introduced in Tab. 3. Figure 3 : Scheme of the three-point bending fracture tests with central edge notch in the middle of span length (left), scheme of simplified 2D model of the cracked specimen created in software ANSYS. Composite ID Parameter Units 04042016 09052016 Thickness of ITZ [μm] 55 40 E MTX [GPa] 32.1±1.6 34.2±2.6  MTX [ ‒ ] 0.21 [20] 0.21 [20] E ITZ [GPa] 0.5 E MTX [5] 0.5 E MTX [5]  ITZ [ ‒ ] 0.21 [20] 0.21 [20] E AGG [GPa] 73±1.6 [19] 73±1.6 [19]  AGG [ ‒ ] 0.20 [20] 0.20 [20] Table 3 : Overview of the elastic constants used in the numerical model. R ESULTS or quantitative description of the influence of ITZ on the stress state in the crack tip vicinity the opening stress  yy is observed and evaluated. The mean stress  yy and the stress range   yy are calculated: A F