Matthew A. McClelland

Surface tension and density measurements for indium and uranium using a sessile-drop apparatus with glow discharge cleaning

Abstract The sessile-drop method is used to measure the surface tension and density of liquid indium and uranium under high vacuum. Measurements are made over the temperature range 156–500°C for In and at the melting point for U. Surface oxides are efficiently removed with a glow discharge system. Drop profiles are captured by photograph and processed using nonlinear regression to yield the surface tension and density. In this regression procedure, normal distances from calculated profiles to data points are minimized. For indium, the density and surface tension measurements yield ϱ mp = 7.05 × 10 3 kg/m 3 , dϱ/d T = −0.776kg/m 3 ·°C, and γ mp = 0.568N/m, dγ/d T = −9.45 × 10 −5 N/m·°C. The results for uranium at the melting point are ϱ mp = 17.47 × 10 3 kg/m 3 and γ mp = 1.653N/m.

Simulating thermal explosion of cyclotrimethylenetrinitramine-based explosives: Model comparison with experiment

We compare two-dimensional model results with measurements for the thermal, chemical, and mechanical behavior in a thermal explosion experiment. Confined high explosives (HEs) are heated at a rate of 1°C∕h until an explosion is observed. The heating, ignition, and deflagration phases are modeled using an Arbitrarily Lagrangian-Eulerian code (ALE3D) that can handle a wide range of time scales that vary from a structural to a dynamic hydrotime scale. During the preignition phase, quasistatic mechanics and diffusive thermal transfer from a heat source to the HE are coupled with the finite chemical reactions that include both endothermic and exothermic processes. Once the HE ignites, a hydrodynamic calculation is performed as a burn front propagates through the HE. Two cyclotrimethylenetrinitramine-based explosives, C-4 and PBXN-109, are considered, whose chemical-thermal-mechanical models are constructed based on measurements of thermal and mechanical properties along with small scale thermal explosion measu...

Simulating thermal explosion of octahydrotetranitrotetrazine-based explosives: Model comparison with experiment

A model comparison with measurements for the thermal, chemical, and mechanical behaviors in a thermal explosion experiment is presented. Confined high explosives (HEs) are heated at a rate of 1°C∕h until an explosion is observed. The heating, ignition, and deflagration phases are modeled using an arbitrarily Lagrangian-Eulerian (ALE3D) code that can handle a wide range of time scales that vary from a structural to a hydrodynamic time scale. During the preignition phase, quasistatic mechanics and diffusive thermal transfer from a heat source to the HE are coupled with the finite chemical reactions that include both endothermic and exothermic processes. Once the HE ignites, a hydrodynamic calculation is performed as a burn front propagates through the HE. Two octahydrotetranitrotetrazine (HMX)-based explosives, LX-04 and LX-10, are considered, whose chemical-thermal-mechanical models are constructed based on measurements of thermal and mechanical properties along with small-scale thermal explosion measureme...

Finite element analysis of flow, heat transfer, and free interfaces in an electron‐beam vaporization system for metals

A numerical analysis is made of the liquid flow and energy transport in a system to evaporate metals. The energy from an electron-beam heats an axisymmetric metal disk supported by a water-cooled platform. Metal evaporates from the surface of a hot pool of liquid which is surrounded by a shell of its own solid. Flow in the pool is strongly driven by temperature-induced buoyancy and capillary forces, and is located in the transition region between laminar and turbulent flow. The evaporation rate is strongly influenced by the locations of the free boundaries. A modified finite element method is used to calculate the steady state flow and temperature fields coupled with the interface locations. The mesh is structured with spines that stretch and pivot as the interfaces move. The discretized equations are arranged in an ‘arrow’ matrix and are solved using the Newton–Raphson method. The electron-beam power and platform contact resistance are varied for cases involving the evaporation of aluminum. The results reveal the interaction of liquid flow, heat transfer and free interfaces.

Simulating the Thermal Response of High Explosives on Time Scales of Days to Microseconds

We present an overview of computational techniques for simulating the thermal cookoff of high explosives using a multi‐physics hydrodynamics code, ALE3D. Recent improvements to the code have aided our computational capability in modeling the response of energetic materials systems exposed to extreme thermal environments, such as fires. We consider an idealized model process for a confined explosive involving the transition from slow heating to rapid deflagration in which the time scale changes from days to hundreds of microseconds. The heating stage involves thermal expansion and decomposition according to an Arrhenius kinetics model while a pressure‐dependent burn model is employed during the explosive phase. We describe and demonstrate the numerical strategies employed to make the transition from slow to fast dynamics.

Uranium AVLIS vaporizer development

A uranium vaporization system has been developed to efficiently produce the large quantities of atomic uranium vapor that are required for an economic A VLIS process. The vapor produced is well collimated and electronically cold. Vapor is produced by high energy electrons which are magnetically steered to the melt surface. Contouring of magnetic fields helps to optimally format the primary electrons and to contain backscattered electrons. A highly compact electron beam system has been developed to facilitate modular packaging of vaporizer components. Electron beam system power will be provided by high power switching power supplies. These power supplies, which are nearing completion at LLNL, have high electrical efficiency and offer excellent protection against high-voltage arcdowns. Vapor density, composition, and quality are monitored by laser absorption spectroscopy. All laser and optical components are mounted outside the process chamber. The monitoring system is nonintrusive and is designed to survive long duration operation at high vaporization rates.

ONE-DIMENSIONAL TIME TO EXPLOSION (THERMAL SENSITIVITY) TESTS ON PETN, PBX-9407, LX-10, AND LX-17

Incidents caused by fire and combat operations can heat energetic materials that may lead to thermal explosion and result in structural damage and casualty. Some explosives may thermally explode at fairly low temperatures ( PBX-9407 > LX-10 > LX-17.