1 ICF100240PR DYNAMIC FRACTURE AND FRAGMENTATION OF BRITTLE SPHERES SUBJECT TO DOUBLE IMPACT TEST K.T. Chau , S.Z.Wu and X.X. Wei Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China ABSTRACT This paper presents a new model for dynamic fracturing of a brittle sphere subject to the "double impact test", in which the sphere is crushed dynamically between two flat rigid platens. The dynamic tensile stress field in the specimen is calculated analytically using a superposition approach by Valanis [1]. The calculated local tensile field is imposed on vertical microcracks. The crack growth velocity is established in terms of the static stress intensity factor, the dynamic fracture toughness, and the Rayleigh wave speed. The dynamic strength corresponds to the crack growth velocity becoming unbounded. Double impact tests done on plaster spheres were used to verify the present model. Experimental results show that the impact energy required for fracturing in double impact test is about 150% of that required by the static counterpart (i.e. the diametral compression test). KEYWORDS Dynamic crack growth, Impact loads, Compression and fragmentation, Spheres INTRODUCTION The dynamic fragmentation of brittle spheres under impact loads has a wide range of engineering applications. It is also one of the most fundamental problems in applied mechanics. It relates to phenomena covering a wide range of length scales, from a large length scale of the collisional evolution of asteriods to shorter length scale of the degradation of materials in process industries, such as pharmaceuticals, chemical, fertilizers and detergents. In civil engineering and rock mechanics, its application has been in the mining industry, involving grinding, crushing, and impact comminution (Chau et al. [2]). Fragmentation of boulders during the impact phase of rockfall can also be modeled by dynamic impact of spheres (Chau et al. [3-5]).
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