Issue34

J. Saliba et alii, Frattura ed Integrità Strutturale, 34 (2015) 300-308; DOI: 10.3221/IGF-ESIS.34.32 302 200 mm 500 mm 75 mm 120 mm 700 mm 50 mm 250 mm 350 mm 60 mm 120 mm 105 mm 120 mm 110 mm 120 mm Figure 1: Specimen geometry and AE transducers position for LN200, UN100, SN200 and UN200beams. E FFECT OF RELATIVE NOTCH DEPTH ON AE CHARACTERISTIC he load-CMOD curves of notched and unnotched concrete beams are shown in Fig. 2 (a). Damage quantification was calculated based on the AE activity represented by the cumulative number of AE hits (Fig.2 (b)). For the beams with a depth of 200 mm, the results show that as the notch depth decreases, the total number of AE hits increases requiring higher energy for overcoming interfacial bond along the ligament length. For UN100, the rate of AE hits is similar to that of UN200 beams at the beginning and reaches later values between the total number of AE hits for LN200 (presenting the same ligament length) and the total number of AE hits for UN200 which could be related to the additional energy required for the crack initiation in unnotched beams and to different crack lengths. The cumulated AE energy followed the same trend and gives information on the cracks initiation that progress until the failure and thus could be related to the fracture energy measured on a global scale. 0 3 6 9 12 15 18 0 0,1 0,2 0,3 0,4 0,5 Load (kN) CMOD (mm) LN200 SN200 UN100 UN200 0 5000 10000 15000 20000 25000 30000 35000 0 0,1 0,2 0,3 0,4 0,5 Cumulative AE hits CMOD (mm) LN200 LN200 LN200 SN200 SN200 UN100 UN100 UN200 UN200 Figure 2: a) Load-CMOD curves and b) cumulative AE hits in function of CMOD for UN200, UN100, SN200 and LN200 beams. Fig. 3 presents the correlation between the load-CMOD curves and the AE characteristics during the entire loading process for the beams. The AE activity is in good correlation with the load CMOD curves. The rate of AE hits is low at the beginning and then increases after the load reached the peak indicating the propagation of the crack. The results show that the relative notch depth had a great effect on AE characteristics. In the ascending branch of load CMOD curve, the AE hits distribution increases slowly for notched beams. As the load reached about 80% of the maximal strength the rate of AE hits increases and then decreases in the post peak region at 50% of the maximal strength in the post peak region T