Study On The Infrared Thermal Effect And Failure Precursor In The Unstable Evolution Process Of Fractured Sandstone

Infrared radiation temperature(IRT)is a geophysical method monitoring coal rock dynamic disaster.The infrared temperature and infrared thermal image have the advantage of reflecting the compression time and spatial evolution characteristics of coal rock.In order to further study the infrared thermal effect and its precursory rule of fractured sandstone.In this paper,the experimental system of infrared thermal effect of fractured sandstone is established,and the infrared radiation under different angles is tested.According to the determination results of different indexes under the infrared radiation temperature of fractured sandstone under uniaxial compression are analyzed,and the sandstone of different pre crack angle of the sample under stress field and acoustic emission dynamic distribution and variation of axial displacement field simulation experiment.The evolution characteristics of the temperature field at the critical moment before the failure of the sample were compared by using the infrared radiation contour cloud.The results show that:(1)In the process of sandstone under load damage,the infrared radiation temperature has a good response to burst,MIRT abnormal signal showed instantaneous sudden increase,sudden drop,AIRT showed the overall rise or fall.The results show that the increase range of the highest infrared temperature increases with the crack angle of the first and then decreases,and the change is 0.14~1.36~0.11?,in which the turning point is 60°or 75°.(2)The characteristics of infrared temperature change in different regions during the loading process of sandstone were studied.The area at both ends of the prefabricated crack showed a rising state,and the temperature rise of 0.08~0.17?.In the region of the middle part of the prefabricated crack,the infrared temperature decreases when the prefabricated crack is 0° and 45°,and the temperature drop of 0.03~0.09?.When the prefabricated fracture is 75 °,the temperature curve of the upper part of the prefabricated crack shows a cooling state,and the temperature rise of 0.05?,and the temperature curve in the lower part of the middle part shows a rising state,and the temperature rise of 0.08?.(3)The normal law of the MIRT curve is mainly as follows: Low temperature precursors,IRT range of 0.05~0.2?;high temperature precursors,IRT range of 0.1~0.3?.The average infrared radiation temperature curve is mainly characterized by the acceleration of temperature,the decrease of the rise and the decrease of the rise and fall.For the MIRT curve precursor,the sample prefabricated crack of 0°~60°,the load falls in the range of 73~88%;the sample prefabricated crack of 75°,90°,the load falls in about 90%.(4)With the increase of the prefabricated crack angle,the area of the low stress area in the upper and lower regions decreases gradually.At the same time,the crack initiation intensity is getting higher and higher,the specimen breaking strength is also growing,the sample carrying capacity is increasing.With the increase of the prefabricated crack angle,the acoustic emission is more and more dispersed.(5)The dynamic change of the IRT isoline cloud reflects the change of the stress field of the sample well.The local high/low temperature region exhibited by the infrared radiation temperature profile before the main rupture of the sample can be well predicted where the damage will occur and the main failure mode.And before the sample failure,the area of the MIRT area on the surface of the sample showed a sharp decrease.