Crack monitoring is highly important to understand rock damage evolution. In order to study the characteristics of rock crack propagation and damage deformation

uniaxial compression tests were carried out on standard fine yellow sandstone samples embodied prefabricated cracks with different inclination angles (0°?90°). The 3D-DIC technology was used to obtain the strain distribution of the rock sample in the three-dimensional space coordinates

and combined with acoustic emission

the crack propagation and evolution were monitored from the perspective of optics and acoustics. Therefore

a method for calculating the principal strain of cracks was proposed

which quantitatively characterizes the damage variable D value of rock deterioration. Finally

the influencing factors of determining the characteristic strength of the rock sample by the acoustic emission method and the damage variable D value were discussed. The conclusions are as follows: (1) The principal strain of the crack reflects the time-varying rate and the spatial expansion trend of the homologous cracks during the loading process of the rock sample

which can better characterize the cracking behavior of the rock. (2) The acoustic emission method is suitable for determining the initiation stress of a rock sample

but not for determining the damage stress. The crack initiation stress of damage variable D value lags behind that of the acoustic emission method

but it is suitable for determining the characteristic value of the damage stress. (3) The normalized crack initiation stress range determined by combining acoustic emission and DIC technology is 0.63?0.94

and the normalized damage stress range is 0.83?0.99. (4) Prefabricated cracks will affect the mechanical properties of rock materials. With the dip angle increasing

the crack initiation stress

damage stress and peak stress of the rock show an increasing trend. The initiation of cracks become more difficult because it is difficult to form a local strain field accumulation. The results show that 3D-DIC technology can improve the understanding of rock cracking behavior

and is more important for rock damage monitoring and identification.