Monitoring crack propagation at the rock-concrete interface under different strain rates using digital image correlation technology

In traditional linear elastic fracture mechanics, it is assumed that the stress at the crack tip is infinite.However, in real engineering materials, the ultimate tensile stress is finite, which leads to the formation of a nonlinear micro-cracking zone at the crack tip under applied load.In the context of concrete fracture mechanics, this region is known as the fracture process zone, which plays a crucial role in controlling crack propagation.This study employs Digital Image Correlation technology to measure the full-field displacement and strain throughout the loading process under both natural and saturated humidity conditions.By comparing the load-crack mouth opening displacement obtained from Digital Image Correlation with results from clip-on extensometers, the accuracy of Digital Image Correlation in capturing crack opening displacement at different strain rates is validated.The results indicate that the fracture process zone size and crack opening displacement evolve continuously as loading progresses, with the fracture process zone length and crack opening displacement increasing gradually.Additionally, a more pronounced linear distribution is observed at higher loads.The fracture process zone initially expands with increasing load but begins to shrink as the load diminishes.Furthermore, higher strain rates lead to a shorter fracture process zone length and correspondingly higher loads, while under saturated humidity conditions, the fracture process zone forms earlier than under natural humidity.