Analysis on early warning of coal sample failure based on crack development law and strain evolution characteristics

In order to achieve effective early warning of coal sample failure under uniaxial compression, the digital speckle technology is used to analyze the evolution process of the crack field and strain field of the specimen from the global and local aspects, and the development laws of the crack and the characteristics of the strain evolution are clarified. And obtained the precursor information and early warning indicators of coal sample failure. The results showed that: there are often obvious strain concentration and deformation localization in the places where the cracks develop faster. When the crack opens or expands rapidly, the horizontal displacement of the specimen has obvious regional characteristics, the horizontal displacement and the maximum principal strain increase rapidly, and the direction of the displacement vector and the maximum principal strain also change significantly. Therefore, the rapid evolution period of deformation localization (69.4 % similar to 70 % of the failure frame), the loading load of the specimen (66.08 % similar to 69.51 % of the peak load), the direction of the displacement vector and the direction of the maximum principal strain can be used as important early warning indicators and effective precursor information before the specimen failure.