Issue 41

J. Klon et alii, Frattura ed Integrità Strutturale, 41 (2017) 183-190; DOI: 10.3221/IGF-ESIS.41.25 187 to the lowest value of specific fracture energy used, middle value represents the quasi-brittle behavior and the highest value of G f indicates ductile behavior. Figure 6 : Numerical model of the test specimen D 500 with the initial relative crack length   = 0.15; fracture failure at stage  = 0.7 considering the specific fracture energy G f = 70 N/m. Figure 7 : Numerical model of the test specimen D 500 with the initial relative crack length   = 0.15; fracture failure at stage  = 0.7 considering the specific fracture energy G f = 700 N/m. Figure 8 : Scale illustration of the progress of the loading diagram (peak-deflection curve) for all variants of the specific fracture energy used. Figure 9 : Scale illustration of the progress of the R -curve for all variants of the specific fracture energy used. D ISCUSSION OF RESULTS s can be seen from Fig. 10, 11 and 12 the quantity of the dissipated energy is different for various specimen sizes and for various initial notch lengths. As expected, the amount of the dissipated energy is also changing according to the selected level of the specific fracture energy. The amount of the dissipated energy is dependent on the specimen size due to increasing ligament area. When the specimen size is larger, the amount of the dissipated energy increases. As was already mentioned – the amount of the energy dissipated during crack growth from the initial notch to the relative length a / W = 0.7 was considered. Ligament area grows approximately 2.3 times for two consecutive specimen sizes. The dissipated energy obtained by means of theoretical calculations G F(theor) corresponds to this expectation. This ratio was achieved for all three selected values of the specific fracture energy via the theoretical calculation: for the dissipated energy determined from the FEM analysis, this proportion was reached (with a deviance of 20 %) for the middle value of the specific fracture energy. The middle level of the specific fracture energy was chosen according to available loading diagrams for the actual cement composite used for preparation of the test specimens published in [12]. Its real value of specific fracture energy was G f = 70 N/m. If the higher order value of the specific fracture energy G f = 700 N/m is used the current ratio does not apply. It can be seen in Fig. 12. At this level, the amount of the energy A