Study On Crack Damage Strength Damage And Acoustic Emission Characteristics Of Red Sandstone Under Uniaxial Loading

Brittle rock failure is a progressive process,rock crack damage strength is an important stress threshold in rock failure process,it is the boundary point of different failure stages in the process of rock compression,it is the distinction of different stress stages in the process of rock uniaxial compression.It is also the starting of the unstable crack growth.In order to fully understand the damage strength damage and acoustic emission characteristics of red sandstone under uniaxial loading,in this paper,based on the laboratory experiments acoustic emission test of red sandstone under uniaxial loading,analyze the accumulative acoustic emission ringing counts and main frequency regulation,exploring the acoustic emission method,crack volume strain model method,damage constitutive model method and dissipated energy method to characterize the suitability and differences of red sandstone damage;combined with the crack damage strength to study the acoustic emission regularity and damage characteristics at crack damage strength.According to the above research,the main conclusions of this paper are as follows:(1)Red sandstone under uniaxial loading,the crack damage strength and the peak strength ratio is in the rang of 0.69~0.85.(2)The rock internal microcrack is re-expanded before the crack damage strength,the accumulative acoustic emission ringing counts increase stability,the stress over crack damage strength,the crack in rock begin unstable propagation,acoustic emission has increased sharply,the acoustic emission ringing counts increased sharply points is behind the crack damage strength,The value between peak strength of the acoustic emission increased sharply strength ratio and the peak strength of the stress crack damage strength ratio is 0.15~0.3.(3)In the crack compaction stage and the elastic stage,the acoustic emission main frequency is 100~350 kHz;Stress over crack damage strength,there is a large number of 0~50 kHz and 400~500 kHz acoustic emission signal appears,the acoustic emission frequency band width,the range of frequency is 0~500 kHz.Before the crack damage strength,the rock crack compression and re-expansion,the full loading the main frequency 0~160 kHz of acoustic emission signal is not more than 20%,the main frequency 300~500 kHz high frequency of acoustic emission signal is not more than 16%.(4)Acoustic emission method,crack volumetric strain model method and damage constitutive model and energy dissipated method can characterize the damage evolution process.the damage is small in crack damage strength,the damage value based on acoustic emission method is no more than 0.2,the damage value is no more than 0.35 according to the crack volume strain model,the damage value is less than 0.18 based on the damage constitutive model,the damage value based on dissipation energy method is no more than 0.15,and the damage increases sharply after the crack damage strength.The damage by the crack volume strain model is larger than that of acoustic emission method,damage constitutive model and dissipation energy method.The rock damage is low before crack damage strength,over the crack damage strength,the damage increases rapidly lead to rock failure,the rock damage is mainly concentrated in the crack unstable stage.(5)Stress over the crack damage strength the energy dissipated is mainly concentrated in the plastic stage.A part of the rock energy dissipated is received by the acoustic emission,and the acoustic emission increases rapidly.The rapid propagation of the crack in the rock penetrates through another large amount of energy,which eventually leads to the loss of rock strength.