The damage and failure of a rock mass is the inevitable consequence of the initiation

propagation

and coalescence of internal cracks within it. This process can be characterized by changes in acoustic emission and infrared radiation signals

highlighting the importance of studying the acoustic-thermal response characteristics of the damage evolution in fissured rock masses. To investigate the acoustic-thermal response characteristics of crack extension and its precursor law during the cyclic loading and unloading of fissured sandstone

tests were conducted on prefabricated fissured sandstone with varying crack inclination angles. The study analyzed the acoustic-thermal response characteristics of crack propagation

identified precursor laws of various acoustic and thermal signals

and proposed a coefficient of variation index to quantify crack evolution. The main conclusions are as follows: 1) As fissure dip angles increases

the shear-induced damage effect on the specimen becomes more pronounced

with infrared and acoustic emission signals exhibiting distinct stage characteristics during loading and unloading. 2) With increasing cyclic loading and unloading cycles

precursor laws of acoustic and thermal signals became evident

characterized by prefabricated cracks forming around high-energy acoustic emission localization points

accompanied by infrared thermal image temperature anomalies; a sudden change in acoustic emission counts

RA(the ratio of acoustic emission rise time to amplitude)

and AF(the ratio of ring counts to duration time) values during unloading

with these parameters maintaining higher values and more concentrated distributions. 3) Infrared temperature and acoustic emission RA

AF anomalies appear earliest

followed by acoustic emission localization. Acoustic emission counts show changes later

with infrared thermal images being the latest indicators. Acoustic emission localization and thermal image anomalies can provide spatial early warnings of crack formation. 4) A novel acoustic-thermal coefficient of variation (CV) index is proposed to quantify crack evolution. This index integrates crack evolution characteristics

optimizes weighting ratios

and reflects fluctuations in acoustic and thermal parameters over time

thereby characterizing crack evolution intensity. It overcomes the limitations of single acoustic or infrared signals

such as hysteresis and spatial constraints. This research provides valuable references for understanding rock disaster mechanisms

rock control strategies

and geological disaster prevention and mitigation.