Characterisation of mechanical behaviour of 3D printed rock-like material with digital image correlation

Abstract

In this study, 3D printing technology was used to prepare rock-like specimens containing different flaw configurations. In particular, 3D printed Brazilian disc specimens with pre-existing single and double flaws were compressed under quasi-static loading to investigate the loading capacity as well as the crack initiation, propagation and coalescence mechanism of pre-flawed rock-like specimens. For the first time, 3D printing technology was coupled with digital image correlation (DIC) analysis to systematically study the coalescence behaviour of double flawed specimens. In the experiments, DIC technique was first calibrated and validated via the compressive test on a cylindrical specimen and the three-point bending test on a notched semicircular specimen, and was then used for the comprehensive deformation and failure analysis of the pre-flawed Brazilian discs under loading. It was revealed that the DIC results are dependent more significantly on subset size than on subset spacing. The experiments showed that the 3D printed material not only can produce mechanical properties that are similar to natural brittle rock but also has advantages such as material homogeneity, high geometry flexibility, easy pre-flaw implementation and quickness in prototyping. It was also shown that DIC method is capable of accurately capturing the initiation of multiple cracks as well as their propagation direction and coalescence types. On the other hand, it was shown that the flaws configuration had significant effect on the type of cracks. In particular, tensile or shear movement of the flaws controls the type of new cracks to be formed as well as their propagation direction. Moreover, the tensile coalescence is the dominant behaviour of double-flawed specimens under loading, while shear coalescence is hard to appear.