Issue 49

H. Chbani et alii, Frattura ed Integrità Strutturale, 49 (2019) 763-774; DOI: 10.3221/IGF-ESIS.49.68 772 Figure 15: K IC values as function of notch length Fig. 16 groups the K R curves as function of Δa for the different studied notch lengths. We observe that the curves are practically confounded in the unstable propagation stage, which confirms that the R-curve is a unique curve independent of the notch length. Figure 16: Regrouped KR curves as function of Δa C ONCLUSIONS n this paper, three point bending tests were carried out on notched specimens made from C0.7 concrete in order to understand the mechanical behavior and the crack propagation mechanism of this quasi-brittle material. Therefore, many conclusions were made:  The crack propagates mechanism consists of two propagation stages: 1-stable propagation stage while the load is lower than P max , 2-unstable propagation stage. The stage of unstable propagation is more important than the stable propagation stage.  The stable propagation stage decreases disproportionately to the notch length.  The opening displacement mechanism of the critical notch lips occurs in a perpendicular direction to the applied load direction; this opening displacement is even higher than the notch length is small. I