Strain Rate Effect of AE Characteristics in the Whole Process of Uniaxial Tensile of Mortar

We completed the uniaxial tensile test of mortar in the range of strain rate from 10 −6 to 10 −4 s −1 in the section containing softening, and carried out acoustic emission monitoring (AE) simultaneously. A series of AE parameters and spectrum analysis methods were used to identify the damage evolution process and cracking mechanism of mortar at different strain rates. The results show that, with the increase of strain rate, the peak stress and tensile elastic modulus of mortar increase obviously, and the stress level corresponding to the starting point of AE activity increases significantly as well, which indicates that the mechanical properties and AE characteristics of mortar have obvious strain rate effect. With the increase of strain rate, the cumulative AE hit decreases gradually, while the average AE hit rate increases significantly, indicating that the increase of strain rate reduces the damage degree of internal microstructure of the specimen, but the crack propagation speed increases. In the pre-peak stress stage, the average of AE ringing count and signal energy decreases with the increase of strain rate, while the average of duration increases; in the post-peak stress stage( f t − 30% f t ), the average of the three AE parameters all increase with the increase of strain rate, indicating that the strain rate effect on the damage process of mortar is different before and after peak stress, and the damage mechanism represented by different parameters is also different. In the whole process of uniaxial tensile of mortar, with the increase of strain rate, the scatter distribution of AE frequency-amplitude becomes more discrete, and the b -value shows a decreasing trend. In addition, the average level of AE peak frequency decreases with the increase of strain rate, while that of ca8 band wavelet energy spectrum coefficient increases. It is indicated that the increase of strain rate enables the crack propagation state of mortar specimen to become unstable, and the width of macrocrack increases but the proportion decreases.