Acoustic emission parameters and energy dissipation law of cyclic load and unload damage of dihydrate gypsum under different loading rate

In order to explore the effect of loading rate on physical and mechanical properties of dihydrate gypsum, cyclic loading and unloading mechanical tests were carried out at different loading rates. Test results were analyzed from the aspects of stress-strain curve, energy distribution mode, damage law and failure mode of specimen. The main research results obtained in the thesis are as follows: with the increase of the loading rate, the peak value of specimen damage first increases rapidly, and then in-creases slowly, and there is a damage threshold. In the early stage of loading, the dissipated energy of the specimen accounts for about 70% of the total energy, most of the total energy input is converted into dissipated energy. The elastic energy density shows an increasing trend with the increase of the loading rate. The elastic energy density is the highest when the loading rate is 400 ​N/s, and more elastic energy can be stored. The ratio of elastic energy u_e/u increases with the in-crease of loading rate and tends to be stable. The acoustic emission data show that the acoustic emission signals present a certain agglomeration phenomenon at the unloading point, and there is a “blank period” between the unloading point and the emergence of the next acoustic emission activity. In the early stage of specimen loading, friction-type acoustic emission is mainly generated. The cumulative ringing count when the load reaches the peak failure stress at low loading rate is more, indicating that low loading rate will produce more acoustic emission activities. With the increase of loading rate, the cumulative ringing number per unit time increases, indicating that the increase of loading rate accelerates the damage and failure of dihydrate gypsum near the peak value. The failure mode of gypsum specimens is shear failure, and the increase of loading rate of shear failure angle shows an increasing trend. The larger the loading rate is, the higher the strength of the specimen is. The more energy the press inputs during the loading process, the higher the energy absorbed by the unit volume specimen, which aggravates the development, expansion and penetration of the internal cracks of the specimen, resulting in the larger shear angle of the specimen. The test results provide a more comprehensive theoretical basis for the study of damage characteristics of dihydrate gypsum during cyclic loading and unloading.