Issue 50

I. Dakanali et alii, Frattura ed Integrità Strutturale, 50 (2019) 370-382; DOI: 10.3221/IGF-ESIS.50.31 378 Figure 11: Average frequency versus RA parameter for two typical ‘2 nd Class’ tests. accumulation. The signals with low RA parameter are attributed to tensile cracks and this is because of the paste’s cracks and the connection’s failure. After the maximum load, the signals present an increased RA parameter. It is evident that in this time most of the signals are due to shear or mix mode fracture (the prevailing bar’s sliding). In Fig.12, the time variation of the duration and energy of the AEs, the load and the data gathered from the LVDT of a characteristic 3 rd class test are plotted. Significant number of AEs is recorded from the very beginning. This is also clear from the AE location through the anchoring length in Fig.12b. When the bar is under compression, the paste around ex- periences more cracks due to bar’s expansion. From the diagram of the average frequency versus the RA parameter for the two characteristic time periods before the maximum load of two push-in experiments (Fig.13), it is evident that the cracks increase as the parameter RA decreases from A to B time range. Figure 12: ‘3 rd Class’ test: (a) Time variation of the load and the LVDT indications with the duration and energy (contour plot) of the AEs; (b) Time variation of the LVDT indications, the load and the y position of the AEs (along the anchoring length). Figure 13: Average frequency versus RA parameter for two typical ‘3 rd Class’ tests. (a) (b)