Molten composition B-3 yield stress model

Abstract

A complete model of Composition B-3 (Comp B-3; 60/40 wt% RDX/TNT) response to abnormal thermal conditions may include effects such as plastic yield stress, non-Newtonian viscosity, thixotropy, particle settling and dissolution, and thermal decomposition. In this work yield stress is modeled as a function of RDX particle volume fraction, which is a function of temperature at dissolution equilibrium. This Comp B-3 yield stress model was determined experimentally using an initially quiescent, non-isothermal falling sphere viscometer. The notion of critical particle volume fraction is employed and defined as a point below which yield stress is zero. Yield stress is derived from percolation theory and takes the form τy = B(ϕ - ϕc)N, where ϕc is critical particle volume fraction, and B and N are fitted constants. Results show that ϕc ∼0.336, at an equilibrium mixture temperature of 158°C. Yield stress for the quiescently melted material at the RDX/TNT eutectic temperature (78.3°C) is calculated to be 146 Pa.