Temperature–pressure characteristics of CO2 phase-transition blasting and the failure mechanism of fracturing tubes

CO₂ phase-transition blasting is a non-explosive technique that utilizes the energy released during the phase transition of carbon dioxide. The state transformation of CO₂ and the fracture behavior of fracturing tubes directly determine the effectiveness of the blasting process. Inside the fracturing tube, CO₂ undergoes successive stages, including pressurized filling, thermal phase transition, and jet release, during which its temperature, pressure, and phase undergo significant changes. Tubes with different structural configurations exhibit distinct failure modes under CO₂ pressure. Reusable bottom-discharge tubes control the release pressure via a constant-pressure rupture disc, whose pressure-bearing capacity is governed by its size and strength, showing a pronounced linear relationship among the main influencing factors. In contrast, disposable side-discharge tubes are influenced by groove parameters, and response surface analysis reveals that groove depth, groove length, and groove width affect the tube's ultimate internal pressure in descending order. During release, CO₂ forms high-velocity jets that attenuate while propagating through the annular space between the tube and the borehole wall, subsequently colliding with the wall to generate impact pressure and induce stress waves in the surrounding rock. These processes define both the dynamic and quasi-static pressure characteristics of CO₂ phase-transition blasting. The findings provide a scientific reference for optimizing the effectiveness of CO₂ phase-transition blasting.