Abstract:

In terms of the studies of the mechanical excavation of tunnels, there are very few researches focusing on the contact mechanism of cutting process of rock. This paper investigated the effect of groupcutter on the normal wedge indentation fracture. The specimens are indented by doubleindenters and the fracture process is monitored by electronic speckle pattern interferometry (ESPI) to investigate the failure characteristics such as localization of microcracks, initiation and propagation of macrocrack.The complete loading curves, including post peak stages, of the indentation tests are acquired by using crack opening displacement (COD) control as the feedback signal in a closedloop, hydraulic loading system (MTS). This paper presents experimental results with respect to the entire loading history including prior and postpeak behaviors of the rocklike mortar specimens. By varying the space between cutters, the effect of cutter space on the indentation mechanism is examined under unconfined lateral pressure condition. With the advantages of ESPI measurements, such as high accuracy (in micron), noncontact, realtime and wholefield, it is able to monitor the growth of elastoplastic interface and its critical value corresponding to the transit of ductile (displacement continuity) to brittle fracture (displacement discontinuity) during the indentation tests prior to peak loading.

Key words: electronic speckle pattern interferometry (ESPI), doubleindenters, elastoplastic interface, brittle crack initiation