DYNAMIC FRACTURE AND FRAGMENTATION OF BRITTLE SPHERES SUBJECT TO DOUBLE IMPACT TEST

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)