Using MTS815.03 testing system, the stress-strain complete procedures of sandstones were studied in the paper. Based on the complete procedure tests and AE investigation. the post-peak failure properties under different loading rates, as well as the relationship of rock strength and Acoustic Emission (AE) frequency were discussed. The results showed the pulses amplitude occurred only when the stress reached the yield strength. At the same time, the amplitude quickly increased to a very high value and there wasn' t abrupt increment until the specimen failed. It was also shown the frequency was 240Hz when the specimen yield. In order to study the relationship between post-peak failure properties and specimen damage, a series of results were obtained according to the damage theory.
The study of the failure mechanism and fracture of rocks isone of the most important problems in rock mechanics. The ultimate macro-fracture of rock was closely related to its microstructure and micro-flaw. In order to study the fracture and failure mechanismof rock, the process of damage and fracture should be analyzed in macro and micro scopes. Thefailure of rock under applied loads was mainly related To the initiation. growth and fracture of micro cracks. For example, Stressesrelaxation occurred with the initiation and growth of cracks. During stress relaxation, energy stored during loading emitted in stress waves and the phenomenon of Acoustic Emission (A E) engendered. The discontinuity of AE signals was correlated with the frequency of micro cracks initiation in specimens, and the pulse intensity was correlated with theenergy emitted with cracks growth,whichwas endangered onaccount of theinteraction of grains in rocks (Kaiser, 1950). two main parameters of AE in the process of rockfailure were frequency andamplitude.The frequency of AE reflected the number of micro cracks engendered in the process of rock failure, the amplitude of AE reported the intensity of micro cracks. In the present paper. the main topic was the study of post-peak failure properties of sandstone.
For this investigation, cylinder sandstone samples ofdiameter 50mm and height 100mm were produced. Experiments equipment was MTS815.03 Rock and Concrete Stiff Servo-controlled Testing System, deformation of samples was measured by longitude and transverse tensor. AE signals were received and recorded by Type AE-400B AE Instrument. The characteristic indices of samples and testing conditions were showed in table I.
As anexample, sandstone A07was analyzed. Its stress-strain complete procedure could be divided into five stages. (I) The linear elastic stage (Fig.1: a, b: OA). When the load was lower than the yield stress, rock damagewasn't engendered. Almost all micro cracks deformed in elasticity and didn't extend. There were no AE signals observed. (2) The elastic-plastic stage (Fig. I: a, b: AB). Some of the old cracks deformed in plasticity and a few micro cracks was engendered. They extended slowly.
