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Rate effect on mechanical properties of hydraulic concrete flexural-tensile specimens under low loading rates using acoustic emission technique
Authors:Su Huaizhi  Hu Jiang  Tong Jianjie  Wen Zhiping
Institution:a State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China
b College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China
c National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety, Hohai University, Nanjing 210098, China
d Dept. of Computer Engineering, Nanjing Institute of Technology, Nanjing 211167, China
Abstract:Acoustic emission (AE) waveform is generated by dislocation, microcracking and other irreversible changes in a concrete material. Based on the AE technique (AET), this paper focuses on strain rate effect on physical mechanisms of hydraulic concrete specimens during the entire fracture process of three point bending (TPB) flexural tests at quasi-static levels. More emphasis is placed on the influence of strain rate on AE hit rate and AE source location around peak stress. Under low strain rates, namely 0.77 × 10−7 s−1, 1 × 10−7 s−1 to 1 × 10−6 s−1 respectively, the results show that the tensile strength increases as the strain rate increases while the peak AE hit rate decreases. Meanwhile, the specimen under a relatively higher strain rate shows a relatively wider intrinsic process zone in a more diffuser manner, lots of distributed microcracks relatively decrease stress intensity, thus delay both microcracking localization and macrocrack propagation. These phenomena can be attributed to Stéfan effect. In addition, further tests, namely the combination of AE monitoring and strain measuring systems was designed to understand the correlation between AE event activity and microfracture (i.e., microcracking and microcracking localization). The relative variation trend of cumulative AE events accords well with that of the load-deformation curve.
Keywords:Hydraulic concrete  Acoustic emission  Rate effect  Microcracking localization  Intrinsic process zone
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