Study On Feature Strength Points Acoustic Emission Characteristics Of Red Sandstone

In the deep high stress conditions,rock mass is mainly characterized by brittle failure,the destruction of the brittle rock is closely related to the internal cracks of rock evolution,crack initiation strength and damage strength are two very important in the process of crack formation cut-off point.This thesis takes the red sandstone as a characteristic strengths research object,studies the characteristic strengths through uniaxial acoustic emission experiment of red sandstone,discusses and compares three kinds of methods to determine the characteristic strength,analyzes the features of acoustic emission events,ringing counts and energy at the point of characteristic strengths and acoustic emission signal peak frequency before break based on the K-means clustering analysis method,and character of acoustic emission ?N/?E and damage model.The main conclusions of this paper are as follows:(1)The crack initiation strength of red sandstone equals 0.24-0.47 times peak strength,and the crack damage strength approximately equal 0.7-0.87 times peak strength;(2)In acoustic emission method,gauging the crack initiation strength point by the first mutation of ringing counts is more simple and reliable than other acoustic emission parameters,energy should be preferentially chosen when gauging the crack damage strength point;According to the characteristics of acoustic emission,red sandstone be divided into two categories: the first category is that acoustic emission appears quiet period after damage point,the second is that acoustic emission still continue after damage point;(3)With the load increasing,the quantity of peak frequency is gradually increasing and distribution range becomes wider,peak frequency mainly concentrates in about 120 KHz and280 KHz at the beginning of the load,and near destruction,its concentrated band range becomes wider,at the same time,appears most more than 400 KHz peak frequency;(4)When the stress is less than initiation strength,the ratio of low frequency quantity and total frequency quantity is volatile,and decrease on the whole,but quantity of two types frequency increase,while the stress is more than initiation strength,the ratio remains stable until the stress reach 90% of peak strength,following the proportion of high frequency increase;(5)At the point of crack initiation,curve of the ratio of first type frequency quantity and total quantity appears inflection point,namely excessive inflection point of decreasing trends to smooth,the ratio at damage point keeps smooth,it is difficult to determine thedamage strength based on acoustic emission frequency;(6)The r value(?N/?E)curve before the destruction of red sandstone presents "ladder" shape,r value near the damage is the smallest in the whole process.So r value can be used to predict the destruction of rocks;(7)The change of r value at the point of initiation and damage is large differences in each sample,there is no regularity.So it isn't feasible to gauge the rock initiation strength and damage strength point through the change of r value.(8)X conjugate shear failure is the main failure mode of red sandstone,through microscope scanning test,the internal structure of rock after test is more compact than it before test;...