Fig. 3

Axial stress versus axial strain at 5 MPa confining pressure and 2D digital image correlation analysis results of a sample MG-5a and b sample MG-5b (the green color curve of sample MG-5b is the axial strain which was recorded by an externally high-resolution disk load cell). A detailed description of the incremental compressive strain shown in the DIC images will be further discussed in this section