Applications of Digital Image Correlation (DIC) and the Strain Gage Method for Measuring Dynamic Mode I Fracture Parameters of the White Marble Specimen

Digital image correlation (DIC) and the strain gage method are both widely used in characterizing the fracture mechanisms of materials. However, the quantitative comparisons of rock fracture parameters between the two methods have been studied insufficiently. In this paper, dynamic three-point bending impact tests were performed on white marble specimens using DIC and the strain gage method simultaneously. The complete cracking process was recorded by two high-speed cameras situated on either side of the specimen. The crack propagation velocities were obtained and the dynamic stress intensity factors (DSIFs) were calculated by both methods for analysis and comparison. The experimental results show that the crack propagation velocities almost remain constant during the cracking process, and the evolutions of strain values recorded by gages are consistent with the modified strain variations obtained theoretically. DSIFs calculated by DIC show good agreement with the results obtained from strain gages #1 to #4, while the size effect and the multiple stress waves interfere with the strain signals sensed in strain gage #5, causing a relatively larger deviation in the DSIF. In addition, the complete fracture process (including the variations in successive displacement and strain fields) can be obtained by the DIC method, while a rough changing trend in the DSIF can be given by the strain gage method with a limited number of strain gages.