| This study focused on an experimental investigation with a two-dimensional indentation device controlled by a servo-hydraulic loading system and monitored with the nondestructive techniques of acoustic emission (AE) and electronic speckle pattern interferometry (ESPI). The goals of this research were to evaluate the indentation pressure as well as the size of damage (plastic) zone and to study the initiation of a tensile fracture at the intact rock-damaged rock boundary, that is, the elasto-plastic interface. The key factors were (1) the mechanical properties of the rock including the elastic and strength parameters, (2) the geometric features of the tool such as the wedge angle, and (3) the lateral confinement simulating the far-field stress. A good agreement with regard to indentation pressure and interfacial radius was found between the experimental and theoretical analyses. Furthermore, the intrinsic crack length, critical in establishing tensile fracture, was estimated and correlated to the grain size.; Apart from the verification of cavity expansion prior to the onset of tensile fracture, this work featured the application of AE and ESPI to the examination of the indentation process: namely, the evolution of tensile crack initiated at the interfacial boundary and consequential propagation. It was found that AE and ESPI, as useful nondestructive tools, not only can be applied to the fracture study, but also can evaluate the growth of damaged zone characterized by the cluster of AE as well as the intensity of image from ESPI. In addition, during the break through, the displacement discontinuity can be estimated using ESPI by counting the optical fringe pattern such that the singularity approach of stress intensity factor in the micro scale locally can be calculated. As a consequence of failure nature, the energy dissipation with respect to ductile/brittle failure mode can be estimated from the load-unload-reload history in the macro scale globally. Additionally, CMOD-controlled indentation was first setup to observe the evolution of indentation fracturing, crack stability and post-peak characters. Amid natural medium and high strength rocks, the effect of grain size on the failure mode was simulated by using high performance synthetic cementitious materials mixed with different uniform grain particles. |
