Issue 48

S. Bhowmik et alii, Frattura ed Integrità Strutturale, 48 (2019) 419-428; DOI: 10.3221/IGF-ESIS.48.40 423 coating the specimens with white paint. Continuous images are taken during the entire experimentation. The underlying principle of correlation software is to recognize and track a specific subset on the series of captured images. R ESULTS AND DISCUSSIONS he maximum static load has been recorded for small, medium and large beam specimens as 2.35 kN , 3.97 kN and 6.15 kN , respectively. Variation of recorded load values and corresponding crack mouth opening displacements (CMOD) have been plotted for three beam sizes in Fig. 5. At about 95% of the peak load, crack initiation has been observed with the final CMOD values of 0.76 mm, 0.96 mm and 1.73 mm for small, medium and large specimen respectively. During the fatigue test, crack mouth opening displacement values are recorded for every loading and unloading cycles. Typical variation of CMOD with load (Load-CMOD) for selected number of load cycles for medium beam specimen is shown in Fig. 6. Crack propagation for medium size beam has been shown in Fig. 7 in terms of horizontal strains corresponding to percentage of loads. Predictions have been made corresponding to (a) peak load (b) 90% post peak load (c) 70% post peak load (d) 50% post peak load (e) 30% post peak load and (f) 15% post peak load. Similar results have been shown in Fig. 8 for beams under fatigue loading. Load displacement variations for selected numbers of load cycles have been presented in Fig. 9. Based on the experimental results critical energy dissipation has been calculated for small, medium and large size beam specimens. The results of critical energy dissipation has been presented in Fig. 10. Estimation of tip of effective crack A method has been proposed in the present study to estimate the tip of effective crack under monotonic and repetitive loading conditions. In this method, the tip of effective crack has been located corresponding to the negligible horizontal displacement jump on either side of crack. During DIC analysis origin is marked at the tip of initial notch. Horizontal displacements fields are obtained corresponding to various reference lines through DIC analysis. Typical variation of horizontal displacement values against distance (X) corresponding to the reference lines, Y =4.9, 17.17, 41.68 and 49.31 mm are presented in Fig. 11. In this case, the displacement jump/opening has been calculated corresponding to the peak load with respect to different horizontal cross- sections. From Fig. 11, it can be observed that, the tip of the effective crack is located at 49.31 mm from the notch tip in the case of medium size beam when loaded statically. Further, the size of effective crack length has been estimated to be 26.2 mm and 98.1 mm respectively for small and large beams respectively. Similar procedure has been adopted in order to locate the tip of effective crack in medium size concrete beam under fatigue loading. Analysis has been done for 1180 th load cycle for medium size beam and the tip has been located at 47.55 mm beyond the initial notch. For small size beam, an effective crack length of 25.4 mm has been observed at 200 th load cycle. Further, for large size beam the tip of effective crack has been found to be loacated at 102.8 mm from the initial notch length corresponding to 1395 th load cycle. Figure 6: Load-CMOD variation for medium size beam specimen under fatigue loading. T