OBSERVATION OF MICROCRACKS PATTERNS IN WESTERLY GRANITE SPECIMENS STRESSED IMMEDIATELY BEFORE FAILURE BY UNIAXIAL COMPRESSIVE LOADING
Westerly花岗岩试样单轴压缩破坏瞬时微裂纹观察

Microcrack development patterns in Westerly granite specimens stressed immediately before their ultimate failure by uniaxial compressive loading are observed using the fluorescent method proposed by Nishiyama and Kusuda(1994). Applying this method,the microscopic crack growth patterns,such as cleavage cracks within feldspar grains and intracrystalline cracks in quartz grains,and the wide-area distributions of these cracks are simultaneously confirmed with accuracy and ease. As a result of the observations,the elongated contiguous cracks estimated to have a direct impact on the final failure of granite are identified;and these cracks are roughly classified into three types. It is inferred that these three types of cracks do not develop at the same time;and each type has a different mechanism of generation. The mechanism of crack development under uniaxial compression is suggested to occur as follows. Firstly,many microcracks running parallel to the loading direction are induced by loading. Next,long cracks are induced by the elongation and coalescence of these microcracks located near the sides of the specimen. Then,the sides move outward due to further loading,generating the fault plane. The cracks within the relatively less damaged remaining parts are linked and propagated;and finally,these cracks induce the failure of specimen.