Effect of loading rate on energy evolution of coal confined passively by CFRP sheets

In order to study the influence law of energy evolution characteristics of coal confined passively by CFRP sheets. A series of uniaxial compression tests of coal confined passively by CFRP sheets were carried out under different loading rates by the SAM–2000 rock mechanics test systems. The research results show that with the increase axial deformation, the total energy of coal confined passively by CFRP sheets first increase gradually with a “fovea inferior”, and then reaching a stable slope. The stable slope in the single-sheet condition is smaller than that in the double-sheet one, and the increase of the slope is larger than that of the latter one, but the stable slope at the maximum loading rate is cliff-like steep increase. With the increase of CFRP layers, the total energy of coal at peak and its growth ratio also increases. The effect of CFRP layers on the total energy of coal at peak and its growth rate is significantly better than that of the loading rate. The function evolution law of the total energy growth rate at peak under different rates is obtained and established a response surface considering rate and CFRP layers. When the loading rate is at its minimum or maximum, the dissipated energy rate growth ratio at peak decreases with the increase of CFRP layers, and the value at the maximum loading rate is about 6.03−8.87 times more than the value at the minimum rate. In the loading rate ranges from 1.67×10⁻³ mm/s to 1.67×10⁻² mm/s, the peak dissipation energy rate and its growth ratio also increase with the increase of the CFRP layers. The function evolution law of the dissipated energy rate growth ratio at peak under different loading rates is obtained, and the response surface considering both loading rate and CFRP layers is also established. With the increase of axial deformation, the elastic energy consumption ratio of CFRP passively confined coal has a transition from rapid steep drop to steady inflection point and then from slow increase to rapid steep increase, which is like a “fishhook” shape. The elastic energy consumption ratio near the peak shows a continuous step mutation, indicating that cracks are developing rapidly.