2.4 Fragment morphology

Macro images of compressed fragments were taken by an optical camera (EOS 70D, Canon, Japan). Micro images of compressed fragments were taken using scanning electron microscopy (SEM, Sigma300, Zeiss, German). The SEM images were used to examine the fracture surfaces, and to explain the effects of structural deformation and failure in both fracture toughness and bending tests. A matter of concern in dynamic compression tests compared with fracture toughness tests is that the cracks may initiate and connect before propagating a long distance, which is closer to fracture accrued by a suddenly applied load on most occasions. Thus, it was essential to focus on the morphology of the fragments of tested samples.