A Methodology for Characterizing Brittle Fracture of Solid Waste Forms in Accidental Impacts
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Stephen V. Topp, editor A METHODOLOGY FOR CHARACTERIZING BRITTLE FRACTURE OF SOLID WASTE FORMS IN ACCIDENTAL IMPACTS
WILLIAM J. MECHAM, LESLIE J. JARDINE AND MARTIN J. STEINDLER Argonne National Laboratory, 9700 South Cass Avenue, Argonne,
Illinois 60439
ABSTRACT A general method for characterizing the major practical effects of accidental impacts on waste packages and for evaluation of scale-model tests has been partially developed. Impact fracture of brittle waste forms has been shown elsewhere to produce particulates whose size distributions are described by the lognormal probability distribution. The model proposed for fragment generation involves the transformation of impact (kinetic) energy into elastic strain energy which is followed by fracture and energy dissipation into heat by the fracture particulates. The peak stresses developing during compressions are approximated as a function of time using elastic theory for a wide range of practical impact conditions for typical (glass) waste forms. The proposed methodology requires experimental validation in terms of correlation of stress and energy parameters with particulate parameters describing the results of fracture. Two kinds of preliminary correlations are presented: (1) calculations of stress parameters for a range of impact conditions; and (2) averages of particulate parameters obtained in standard impact tests.
INTRODUCTION The extent of fracture of a brittle body by mechanical impact is measured by the total fracture-surface area and by the amount of respirable fines in the particulate formed by the impact-fracture process. The characterization methodology described here combines: (1) a complete statistical description of the fracture particulate and (2) a stress-time model describing impact severity as a function of fall height or impact kinetic energy, and body size and shape. This methodology takes advantage of the convenient mathematical description of fracture particulates provided by the lognormal probability function [1]. This model uses energy balances and force balances to define the elastic deformation, as a function of time during the compression stage of impact. Computer numerical integrations of the basic force and energy equations were used to calculate the stresses that develop for particular cases of impact in the range of practical interest. The cases include axial, diametral, and corner impacts of cylindrical brittle bodies for impacts of both free-fall type (for accident) and the drop-weight type (for materials testing). It also adapts the principles of dimensional modeling [2] to define mean stress parameters by which the results of impact fracture can be correlated with impact severity for various conditions of impact. The brittle fracture
126 process itself cannot be described by classical methods of continuum mechanics [3], [4], and the scaling laws for impact fracture have not previously been reported in the literature [5]. The surface areas and particle size distributions of the fracture particulates obtained
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