ABSTRACT

To study crack coalescence mechanism is very important on understanding the basic failure mechanics of brittle solids containing pores under uniaxial compression. In this paper, a series of physical tests of uniaxial compression on samples containing pores with varied distribution mode are carried out to investigate the coalescence mechanism of pores including crack growth patterns, and pore coalescence modes. The experimental results shown that: The crack growth pattern is different with sample containing varied original distribution; Although the failure process of the brittle medium containing multiple pores is very complex, the behavior of crack initiation, propagation and coalescence follows some basic principles, most of which are related to the interaction between two or three pores. Based on the tension mode; the shear mode; the mixed tension/shear mode and a new coalescence type, the traction mode formed by the stress interaction in zones of pore bridge was found.

INTRODUCTION

Under uniaxial compression, brittle solids containing pores are frequently observed to fail by splitting, shear- II1gand mixed mode. These failure modes are often involving with coalescence mode of pores. Since twenties century, many extensive research have been done to understand and elucidate the mechanism of coalescence mode based on crack initiation, propagation, Interaction and coalescence by using different materials and methods, such as Horri and Nemat-Nasser (1986) studied the axial spitting and the behavior of crack growth and coalescence mode by using CR39 material; Reyes, Einstein (1991) and Shen (1995) ct al also performed some uniaxial compressive tests on gypsum samples and numerical simulations containing two opened or closed flaws for discussing the different coalescence mode including the tensile, shear and mixed coalescence mode; Wong (200 J), Chau and Lin (2002,2003) conducted a serials of experiment on rock-like material and granite with varied the values of inclination of pre-existing two, three and multiple flaws, the bridge angle, and the frictional coefficient on the surfaces of the pre-existing flaws for investigating the different coalescence mechanism under uniaxial and biaxial compression.

In this paper, the work is motivated by the fact that fractures in brittle solids often form from the pore-like flaws or microcavities (1986). At least for 'rocks subjected to compressive stress, the fracture is not simply a result of a single "Griffith" crack (1979). As well known, besides cracks, bedding planes, fissures, fracture and joints, rock masses also contain some poreor cavity-like flaws, such as low-aspect ratio grain boundary cavity or biotite in granite or a slip band or lamella in a plastically deformed grain of marble. Until now there are few systematically studies regarding the propagation and coalescence of cracks initiated from pore-like flaws or soft inclusions in brittle solids. The major reason for this lacking of studies may be: it involves a more complicated mechanism of pore-pore interaction than cracks (1979). This paper presents a series of physical test results of uniaxial compression on samples containing multi-pore with varied distribution mode to investigate the coalescence mechanism of pores including crack growth from pore, and pore coalescence modes.

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