This paper mainly investigates three problems:
the relationship between the fracture toughness of rock and loading rates;
the meso-characteristics of dynamic rock fracture;
energy partitioning in the process of dynamic rock fracture.
Trois problèmes sont principalement abordes dans cet article:
La relation entre la resistance à la fracturation d'une roche, et le taux de charge;
les meso-caracteristiques de la fracture dynamique des roches;
la repartition de l"energie durant le processus de fracturation dynamique.
In diesem Artikel werden hauptsachlich drei Probleme untersucht:
die Kupplung zwischen Bruchzahigkeit von Gestein und die Belastungsgeschwindigkeit;
die meso-Charakteristik von dem dynamischen Gesteinbruch;
die Energieverteilung in dem Prozess yon dem dynamischen Gesteinbruch.
In most engineering practices, or natural disasters, rocks are usually fractured at high loading rates, i.e, dynamic (stress wave) loading. So far most of the research concerning the dynamic fracture and fragmentation of rock has been basically limited to the influences of the loading rate on uniaxial compressive rock strength (Grady & Kipp, 1987, Lundberg, 1976, and U, 1994). However, it is difficult to thoroughly investigate the dynamic fracture behaviour of rock through dynamic strength studies Since the rock is often broken into many fragments and even crushed into powder, and the sizes of the fragments depend on the loading rate. Therefore, it is of significance to focus studies on the investigation of the loading rate's influence on rock fracture toughness, which, is in fact a problem of single crack extension. This can form an important basis for the problem of multi-crack extension. So far many authors have measured the dynamic fracture toughness of rocks, but their; studies have mainly dealt with either low loading rates (Costin, 1981, Wu, 1986, and, Bazant, et. al., 1993) or macro-experimental Investigation under high loading rates (Tang & Xu, 1990, Zhang et al., 1992, and Zhang et al., 1993). Based on the background above, the main aim of this paper is to investigate the effects of loading rates on the fracture toughness of rock, the meso-fracture characteristics of rock; and energy partitioning in the process of dynamic rock fracture.
The tested rocks are Fangshan gabbro and Fangshan marble. All specimens of each kind of rock were drilled from one big block. The short rod (SR) specimen suggested by ISRM (Ouchterlony, 1988) is employed in this study. In this context, the experiment performed at the loading rates k<104 MPam½S−1 with an MTS testing machine is defined as a static fracture experiment (KIC stands for static fracture toughness), and the experiment carried out at k>104. MPam ½S−1 with the SHPB is considered as a dynamic fracture experiment (KID stands for dynamic fracture toughness). In order to apply dynamic loading to an SR specimen, the, specimen was altered (Zhang et al. 1992), see Fig.1b. A special loading wedge was designed to load the specimen so that it could be used in both static and dynamic.
