A method for determining crack tip location during the tuff crack propagation based on ultra-fast time resolution method and immune algorithm

Abstract

Rock is a typical brittle material, and the crack propagation rate of rock is approximately 300–700 m/s, and some even reach over 1000 m/s. This brought many challenges for accurately determining the crack tip location during the rock crack propagation by traditional high-speed photography. Because the crack propagated continuously within the shooting interval of high-speed photography, systematic errors emerged in the tracking of the crack − tip location and the determination of the crack propagation rates. Moreover, because the stress intensity factor (SIF) is a singularity parameter, determining the SIF first requires tracking the location of the crack tip in rock mechanics experiments. Thus, a new method combining the ultra-fast time resolution method, immune algorithm and DIC technology was proposed for quantitatively describing the crack propagation behavior of tuff samples. Its time resolution can reach 15 picoseconds. During this time interval, the crack propagation process can be considered frozen. Then continuous tracking of the crack tip location during the fracture process is realized by using the immune algorithm and digital image correlation (DIC) technology. Then, a series of three-point bending tests were conducted, and the fracture trajectory was obtained via this method. In addition, the SIF at the real-time crack tip was determined based on linear elastic fracture mechanics (LEFM) with the Williams stress function. The experimental results showed that the whole-field strain distribution at the picosecond scale can be obtained with this method, and the key mechanical parameters of rock fracture were determined more accurately.