Experimental determination of the energy expended on elastic and plastic deformation during fragmentation of rocks by blasting

Abstract

The energy consumed in fragmentation of a solid body is expended on elastic and plastic deformation as well as on potential energy of deformation (i.e., on increasing the potential energy of the molecules situated on the newly-formed surface) [1]. The absolute values of the two first components of the energy expenditure are determined by the fragmented volume of the body, while the potential energy of deformation is determined by the area of the newly-formed surface due to fracture. To determine the total energy expended on these types of deformation, we can use an equation developed by P. A. Rebinder [2], A=qva V4-qs ~S, (1) where A is the total work of deformation, qv is the work done in elastic and plastic deformation per unit fragmented volume, qs is the work done to form unit area of new surface, AV is the fragmented volume, and AS is the area of the newly-formed surface. Khanukaev and Dolgov [3] and the present authors [4] give methods for determining the expenditure on potential energy of deformation qsAS, as well as the value of qs, which is known as the specific surface energy.We will give a method O f determining experimentally the energy expended on elastic and plastic deformation in the fragmentation of rocks by blasting. The apparatus consists of a calorimetric system including a bomb calorimeter which secures discharge of the gaseous explosion products to the atmosphere directly after completion of the explosive reaction of the charge. The rock specimen is placed inside the bomb. Calorimetric measurements are made to find the energy QI absorbed by the calorimetric system when the rock specimen is fragmented by the explosion of the charge, together with the energy Qz of explosion of a charge of equal weight but without fragmentation of the specimen. For this purpose the latter is placed some distance from the explosive charge. Figure 1 shows experimental temperature rise curves of the calorimetric system for various conditions of blasting diabase specimens. The temperature rise curve for explosion of the charge without fragmentation of the specimen clearly represents the energy transferred to the calorimetric system simply from the gaseous products from the moment of the explosion to their release to the atmosphere. This energy can be taken as approximately constant for a given calorimetric system and explosive charge, whether or not the rock specimen is fragmented by the explosion. This inference is based on the following assumptions: I) the time of interaction of the gaseous explosion products with the calorimetric system remains constant throughout all the experiments; II) as implied by the work of A. F. Belyaev and others, there is negligible heat exchange between the gaseous explosion products and the specimen.Transfer of heat energy of the gaseous explosion products to the calorimetric system has a different time dependence from transfer of energy expended on elastic and plastic deformation during fragmentation of the specimen and converted to heat energy. TMs is clearly seen from Fig. 1, w...