Jason Loiseau

The effect of particle strength on the ballistic resistance of shear thickening fluids

The response of shear thickening fluids (STFs) under ballistic impact has received considerable attention due to its field-responsive nature. While efforts have primarily focused on traditional ballistic fabrics impregnated with these fluids, the response of pure STFs to penetration has received limited attention. In the present study, the ballistic response of particle-based STFs is investigated and the effects of fluid density and particle strength on ballistic performance are isolated. It is shown that the loss of ballistic resistance in the STFs at higher impact velocities is governed by the material strength of the particles in suspension. The results illustrate the range of velocities over which these STFs may provide effective armor solutions.

Dynamics of explosively imploded pressurized tubes

The detonation of an explosive layer surrounding a pressurized thin-walled tube causes the formation of a virtual piston that drives a precursor shock wave ahead of the detonation, generating very high temperatures and pressures in the gas contained within the tube. Such a device can be used as the driver for a high energy density shock tube or hypervelocity gas gun. The dynamics of the precursor shock wave were investigated for different tube sizes and initial fill pressures. Shock velocity and standoff distance were found to decrease with increasing fill pressure, mainly due to radial expansion of the tube. Adding a tamper can reduce this effect, but may increase jetting. A simple analytical model based on acoustic wave interactions was developed to calculate pump tube expansion and the resulting effect on the shock velocity and standoff distance. Results from this model agree quite well with experimental data.

Phase velocity enhancement of linear explosive shock tubes

Strong, high-density shocks in a gas can be generated by end-initiating a hollow cylinder of explosive surrounding a pressurized thin-walled tube. Implosion of the tube results in a pinch that travels at the detonation velocity of the explosive, thereby driving a strong shock into the gas ahead of it. In the present study, the pinch velocity was increased beyond the detonation velocity of known explosives by dragging an oblique detonation wave along the surface of the tube. The gas shock and detonation trajectories were measured for a variety of phase velocities and tube fill pressures. Strong shocks with an average velocity of 13 km/s were observed for fill pressures as high as 6.9 MPa in helium while transient velocities as high as 19 km/s were observed. Shock trajectory performance degraded strongly with increasing phase velocity and for a velocity of 16 km/s the gas shock barely advanced ahead of the detonation.

The effect of detonation wave incidence angle on the acceleration of flyers by explosives heavily laden with inert additives

The incidence angle of a detonation wave in a conventional high explosive influences the acceleration and terminal velocity of a metal flyer by increasing the magnitude of the material velocity imparted by the transmitted shock wave as the detonation is tilted towards normal loading. For non-ideal explosives heavily loaded with inert additives, the detonation velocity is typically subsonic relative to the flyer sound speed, leading to shockless accelerations when the detonation is grazing. Further, in a grazing detonation the particles are initially accelerated in the direction of the detonation and only gain velocity normal to the initial orientation of the flyer at later times due to aerodynamic drag as the detonation products expand. If the detonation wave in a non-ideal explosive instead strikes the flyer at normal incidence, a shock is transmitted into the flyer and the first interaction between the particle additives and the flyer occurs due to the imparted material velocity from the passage of the ...

Reduction of ejecta from asperities on a metal surface upon shock breakout

Ejecta can be produced when a shock breaks out of a metallic surface with imperfections. The amount of material ejected depends on the wave profile and the surface finish. This work focuses on techniques to reduce the amount of ejecta produced. As a baseline, a Taylor wave loading was produced by detonating a high explosive next to an aluminum target featuring V-grooves on the free surface. The ejecta and free surface velocities were monitored with photonic doppler velocimetry (PDV). In an attempt to suppress the ejecta, the shock pressure was reduced by the addition of an air gap. The effect of a vacuum gap was also investigated. PDV spectrograms show that significant ejecta traveling at roughly three times the free surface velocity was produced when explosives were in contact with the target. The placement of an air gap or a vacuum gap between explosive and target suppressed detectable ejecta.

Development of an accelerating piston implosion-driven launcher

The ability to soft-launch projectiles to velocities exceeding 10 km/s is of interest for a number of scientific fields, including orbital debris impact testing and equation of state research. Current soft-launch technologies have reached a performance plateau below this operating range. In the implosion-driven launcher (ILD) concept, explosives are used to dynamically compress a light driver gas to significantly higher pressures and temperatures than the propellant of conventional light-gas guns. The propellant of the IDL is compressed through the linear implosion of a pressurized tube. The imploding tube behaves like a piston which travels into the light gas at the explosive detonation velocity, thus forming an increasingly long column of shock-compressed gas which can be used to propel a projectile. The McGill designed IDL has demonstrated the ability to launch a 0.1-g projectile to 9.1 km/s. This work will focus on the implementation of a novel launch cycle in which the explosively driven piston is accelerated in order to gradually increase driver gas compression, thus maintaining a relatively constant projectile driving pressure. The theoretical potential of the concept as well as the experimental development of an accelerating piston driver will be examined.

DEVELOPMENT OF A SINGLE‐STAGE IMPLOSION‐DRIVEN HYPERVELOCITY LAUNCHER

Work carried out on the development of a single‐stage implosion‐driven hypervelocity launcher is presented. Explosives surrounding a thin‐walled tube filled with helium works similar to the pump tube of a conventional light gas gun. Implosion of the tube drives a strong shock that reflects back and forth between the projectile and the implosion pinch, generating very high temperatures and pressures. Experiments to evaluate the implosion dynamics and performance of the pump tube were carried out, with attention given to the helium fill pressure, diameter of the pump tube, thickness of the explosive layer, and the presence of a tamper. Simple analytic models were used to approximate the performance of the launcher; their advantages and limitations are discussed. Experiments with an implosion‐driven launcher demonstrated muzzle velocities of 4 km/s with 5‐mm‐diameter aluminum projectiles, agreement with analytical models of performance is discussed. Projectile integrity was verified by high‐speed photography...

Detonation Velocity--Diameter Relation in Gelled Explosive with Inert Inclusions

The detonation velocity is measured in a gelled explosive that has been sensitize via the addition of glass microballoons (GMBs) and additionally diluted via large-scale inert inclusions. The explosive is nitromethane that has been gelled via the addition of poly(methyl methacrylate) (PMMA) and then sensitized via hot-spot inducing glass microballoons (GMBs, 3M K-1). Inert inclusions consisting of pellets of polyether block amide (PEBA, 2–3 mm in size) are then added to the explosive to make a heterogeneous explosive with heterogeneities that are at a scale disparate from those of the microballoons. The PEBA is density matched to the NM/PMMA/GMB mixture such that the large pellets remain in suspension. This system has the potential to be a synthetic explosive that can be tuned to have the properties of morphologically complex commercial blasting explosives. The velocity-diameter and velocity-thickness relation is measured using weakly confined (polyvinyl chloride) cylindrical and slab charges, respectively. The results are also used to further explore the phenomenon of anomalous scaling between axisymmetric and two-dimensional geometries.The detonation velocity is measured in a gelled explosive that has been sensitize via the addition of glass microballoons (GMBs) and additionally diluted via large-scale inert inclusions. The explosive is nitromethane that has been gelled via the addition of poly(methyl methacrylate) (PMMA) and then sensitized via hot-spot inducing glass microballoons (GMBs, 3M K-1). Inert inclusions consisting of pellets of polyether block amide (PEBA, 2–3 mm in size) are then added to the explosive to make a heterogeneous explosive with heterogeneities that are at a scale disparate from those of the microballoons. The PEBA is density matched to the NM/PMMA/GMB mixture such that the large pellets remain in suspension. This system has the potential to be a synthetic explosive that can be tuned to have the properties of morphologically complex commercial blasting explosives. The velocity-diameter and velocity-thickness relation is measured using weakly confined (polyvinyl chloride) cylindrical and slab charges, respectivel...

Scaling of the Propulsive Capability of Aluminized Gelled Nitromethane

Small mass fractions (< 20%) of micron-scale aluminium particles added to a high explosive can react quickly and with sufficient exothermicity to improve metal-acceleration ability (AA) relative to an equal volume of only the base explosive. In order for the aluminium to increase AA, exothermicity must more than offset losses in gas-production and from heating and accelerating the solid particles in the flow. Furthermore, particles must react promptly to deliver this energy prior to loss in driving pressure from product expansion or acoustic decoupling from the driven material. For these reasons, many aluminized formulations exhibit slight or no increase in AA. Furthermore, AA is typically studied using the cylinder test, which specifies a fixed, heavy copper wall. In the present study the authors have used symmetric sandwiches of flyer plates of widely different thicknesses to examine how charge scaling and plate acceleration time-scales influence the enhancement in AA for different sizes of aluminium particles. Nitromethane gelled with 4% Poly(methyl methacrylate) by mass was used for the explosive. 3M K1 microballoons were added at a mass fraction of 0.5% to sensitize the mixture. Aluminium with a mean particle size of 3.5 µm or 108 µm was added at 15% total mixture mass fraction. At 15% mass fraction, an enhancement in AA was observed for both particle sizes and flyer configurations. Results indicated an onset of reaction close to the sonic plane of the detonation wave.Small mass fractions (< 20%) of micron-scale aluminium particles added to a high explosive can react quickly and with sufficient exothermicity to improve metal-acceleration ability (AA) relative to an equal volume of only the base explosive. In order for the aluminium to increase AA, exothermicity must more than offset losses in gas-production and from heating and accelerating the solid particles in the flow. Furthermore, particles must react promptly to deliver this energy prior to loss in driving pressure from product expansion or acoustic decoupling from the driven material. For these reasons, many aluminized formulations exhibit slight or no increase in AA. Furthermore, AA is typically studied using the cylinder test, which specifies a fixed, heavy copper wall. In the present study the authors have used symmetric sandwiches of flyer plates of widely different thicknesses to examine how charge scaling and plate acceleration time-scales influence the enhancement in AA for different sizes of aluminium pa...

Down-bore two-laser heterodyne velocimetry of an implosion-driven hypervelocity launcher

The implosion-driven launcher uses explosives to shock-compress helium, driving well-characterized projectiles to velocities exceeding 10 km/s. The masses of projectiles range between 0.1 – 15 g, and the design shows excellent scalability, reaching similar velocities across different projectile sizes. In the past, velocity measurements have been limited to muzzle velocity obtained via a high-speed videography upon the projectile exiting the launch tube. Recently, Photon Doppler Velocimetry (PDV) has demonstrated the ability to continuously measure in-bore velocity, even in the presence of significant blow-by of high temperature helium propellant past the projectile. While a single laser system sampled at 40 GS/s with a 13 GHz detector/scope bandwidth is limited to 8 km/s, a two-laser PDV system is developed that uses two lasers operating near 1550 nm to provide velocity measurement capabilities up to 16 km/s with the same bandwidth and sampling rate. The two-laser PDV system is used to obtain a continuous...